ALBERT

Description: ABSTRACT With the objective to understand the generation, propagation and nonlinear evolution of ion cyclotron waves (ICWs) in the corona and solar wind, we use electromagnetic hybrid (kinetic ions, fluid electrons) simulations with a non-uniform magnetic field. ICWs are generated by the temperature anisotropy of O 5+ ions as minority species in a proton-electron plasma with uniform density. A number of magnetic field models are used including radial and spiral with field strength decreasing linearly or with the square of the radial distance. O 5+ ions with perpendicular temperature larger than parallel are initially placed in the high magnetic field regions. These ions are found to expand outward along the magnetic field. Associated with this expansion, ion cyclotron waves propagating along the magnetic field are also seen to expand outward. These waves are generated at frequencies below the local gyro-frequency of O 5+ ions propagating parallel and anti-parallel to the magnetic field. Through analysis of the simulation results we demonstrate that wave generation and absorption takes place at all radial distances. Comparing the simulation results to observations of ICWs in the solar wind shows some of the observed wave characteristics may be explained by the mechanism discussed in this paper.

Description: The characteristics of nighttime medium-scale travelling ionospheric disturbance (MSTID) features observed over Yonaguni (24.5 o N, 123.0 o E; 19.3 o N dip latitude), Japan are studied using all-sky imaging of OI 630.0 nm airglow emission. The uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere. Typical low latitude limit of mid-latitude type nighttime MSTIDs possessing phase front alignments along the northwest to the southeast occurs in this region. These MSTID features are rarely sighted at dip latitudes below 15 o . We selected two year period for analysis in which one year corresponded to the solar minimum conditions and another year to the solar maximum conditions. The MSTIDs were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods. Their observed range of wavelengths, phase velocities, phase front alignment and propagation directions are similar to those observed at typical mid-latitude sites. However, on many occasions the phase fronts of the observed MSTIDs did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes. Detailed investigation suggests that the poleward propagating enhancement of airglow intensity, probably associated with the midnight pressure bulge, causes the MSTID features to disappear when they reach lower latitudes later in the night. When the MSTIDs reach lower latitudes well before midnight, they are found to be inhibited by the equatorial ionization anomaly crest region.

Description: We study a magnetosphere-ionosphere coupling at low-latitudes during a moderate (CIR/HSS-driven) geomagnetic storm on 22 July 2009. Recently, it has been shown that during major (CME-driven) storms, quasi-trapped 〉30 keV electrons largely enhance below the radiation belt in the forbidden zone and produce an additional ionization in the topside ionosphere. In this work, we examine a case of the recurrent storm when the magnetosphere-ionosphere coupling through the quasi-trapped electrons also may take place. Data from NOAA/POES and Japanese GOSAT satellites were used to identify the forbidden electron enhancement (FEE). We find a positive vertical gradient of the electron fluxes that indicates to the radiation belt as a source of FEE. Using global ionospheric maps (GIM), radiotomography reconstructions from beacon data and COSMIC/FS3 radio occultation measurements, we have observed an unusually large area in the night-time ionosphere with increased total electron content (TEC) and prominent elevation of the F-layer at low-latitudes that coincides with FEEs spatially and temporarily. Ionizing particles are considered as an addition source of ionization along with generally accepted mechanisms for storm time TEC increase (a positive ionospheric storm). We discuss relative contributions of the FEE and disturbance dynamo electric field in the TEC increases during the storm recovery phase.

Description: Bursty bulk flow (BBF) events, frequently observed in the magnetotail, carry significant energy and mass from the tail region at distances that are often greater than 20 R E into the near-Earth plasma sheet at ~10 R E where the flow is slowed and/or diverted. This region at ~10 R E is referred to as the BBF braking region. A number of possible channels are available for the transfer or dissipation of energy in BBF events including adiabatic heating of particles, the propagation of Alfvén waves out of the BBF braking region and into the auroral region, diverted flow out of the braking region, and energy dissipation within the braking region itself. This study investigates the generation of intense high-frequency electric field activity observed within the braking region. When present, these intense electric fields have power above the ion cyclotron frequency and almost always contain nonlinear structures such as electron phase space holes and double layers, which are often associated with field-aligned currents. A hypothesis in which the observed high-frequency electric field activity is generated by field-aligned currents resulting from turbulence in the BBF braking region is considered. Although linear Alfvén waves can generate field-aligned currents, based on theoretical calculations, the required currents are likely not the result of linear waves. Observations from the THEMIS satellites support the picture of a turbulent plasma leading to the generation of nonlinear kinetic structures. This work provides a possible mechanism for energy dissipation in turbulent plasmas.

Description: Dipolarization fronts (DFs) are often associated with the leading edge of Earthward bursty bulk flows in the magnetotail plasma sheet. Here multi-spacecraft THEMIS observations are used to show that a spatially limited region of counter-propagating ion beams, whose existence is not evident in either the plasma moments or the electric field, is observed on the low density side of DFs. The THEMIS magnetic field data are used to establish appropriate comparison cuts through a particle-in-cell (PIC) simulation of reconnection, and very good agreement is found between the observed and simulated ion distributions on both sides of the DF. Self-consistent back-tracing shows that the ion beams originate from the thermal component of the pre-existing high density plasma into which the DF is propagating; they do not originate from the inflow region in the traditional sense. Forward tracing shows that some of these ions can subsequently overtake the DF and pass back into the high density pre-existing plasma sheet with an order-of-magnitude increase in energy; this process is distinct from other ion reflection processes that occur directly at the DF. The interaction of the reconnection jet with the pre-existing plasma sheet therefore occurs over a macroscopic region, rather than simply being limited to the thin DF interface. A more general consequence of this study is the conclusion that reconnection jets are not simply fed by plasma inflow across the separatrices, but are also fed by plasma from the region into which the jet is propagating; the implications of this finding are discussed.

Description: Low energy (1-10 MeV) neutrons emanating from the Sun provide unique information about accelerated ions with steep energy spectra that may be produced in weak solar flares. However, observation of these solar neutrons can only be made in the inner heliosphere where measurement is difficult due to high background rates from neutrons produced by energetic ions interacting in the spacecraft. These ions can be from solar energetic particle events or produced in passing shocks associated with fast coronal mass ejections. Therefore, it is of the utmost importance that investigators rule out these secondary neutrons before making claims about detecting neutrons from the Sun. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging ( tect MESSENGER ) Neutron Spectrometer recorded an hour-long neutron transient beginning at 15:45 UTC on 2011 June 4 for which [13] claim there is “strong evidence" that the neutrons were produced by the interaction of ions in the solar atmosphere. We studied this event in detail using data from the MESSENGER neutron spectrometer, gamma-ray spectrometer, X-ray Spectrometer, and Energetic Particle Spectrometer, and from the particle spectrometers on STEREO A . We demonstrate that the transient neutrons were secondaries produced by energetic ions, probably accelerated by a passing shock, that interacted in the spacecraft. We also identify significant faults with the authors’ arguments in favor of a solar neutron origin for the transient.

Description: The response of the D-region low latitude ionosphere has been examined for extreme space weather event of 14-16 December 2006 associated with a X1.5 solar flare and an intense geomagnetic storm ( Dst  = -146 nT) using VLF signals from NWC (19.8 kHz) and NPM (21.4 kHz) transmitters monitored at Suva (Geog. 18.10 ο S, 178.40 ο E), Fiji. Modeling of flare associated amplitude and phase enhancements of NWC (3.6 dB, 223 o ) and NPM (5 dB, 153 o ) using Long Wave Propagation Capability code shows reduction in the D-region reflection height ( H ') by 11.1 km and 9.4 km, and enhancement in ionization gradients described by increases in the exponential sharpness factor ( β ) by 0.122 and 0.126 km -1 , for the NWC and NPM paths, respectively. During the storm the daytime signal strengths of the NWC and NPM signals were reduced by 3.2 dB on 15 and 16 December (for about 46 hrs) and recovered by 17 December. Modelling for the NWC path shows that storm-time values of H ' and β were reduced by 1.2 km and 0.06 km -1 , respectively. Morlet wavelet analysis of signals amplitudes shows no clearly strong signatures of gravity wave propagation to low latitudes during the main and recovery phases. The reduction in VLF signal strength is due to increased signal attenuation and absorption by the Earth-ionosphere waveguide due to storm-induced D-region ionization changes and hence changes in D-region parameters. The long duration of the storm effect results from the slow diffusion of changed composition/ionization at D-region altitudes compared with higher altitudes in the ionosphere.

Description: We study the ion density and temperature in the pre- and post-dipolarization plasma sheets in the Earth's magnetotail, using 9 years (2001–2009) of Cluster data. For our study we selected cases when Cluster observed dipolarization fronts (DFs) with an earthward plasma flow greater than 150 km/s. We perform a statistical study of the temperature and density variations during the DF crossings. Earlier studies concluded that on average the temperature increases while the densitydecreases across the DF. Our statistical results show a more diverse picture: While ~53% of the DFs follow this pattern (category A), for ~28% the temperature decreases while the density increases across the DF (category B). We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of the category B showed no clear pattern in the pressure change. Both categories are associated with earthward plasma flows, but with some difference: (1) Category A flows are faster than category B flows. (2) The observations indicate that category B flows are directed perpendicular to the current in the near-Earth current sheet while category A flows are tilted slightly duskward from this direction. (3) The background B z of category B is higher than that of category A. Based on these results we hypothesize that after reconnection takes place, a BBF emerges with category A characteristics, and as it travels earthward it further evolves into category B characteristics, which is in a more dipolarized region with slower plasma flow (closer to the flow braking region).

Description: Ice cores are archives of climate change and possibly large solar proton events (SPEs). Wolff et al . [2012] used a single event, a nitrate peak in the GISP2-H core, which McCracken et al . [2001a] time associated with the poorly quantified 1859 Carrington event, to discredit SPE-produced, impulsive nitrate deposition in polar ice. This is not the ideal test case. We critique the Wolff et al. analysis and demonstrate that the data they used cannot detect impulsive nitrate events because of resolution limitations. We suggest re-examination of the top of the Greenland ice sheet at key intervals over the last two millennia with attention to fine resolution and replicate sampling of multiple species. This will allow further insight into polar depositional processes on a sub-seasonal scale, including atmospheric sources, transport mechanisms to the ice sheet, post-depositional interactions, and a potential SPE association.

Description: Severe geomagnetic storms have a strong impact on space communication and satellite navigation systems. Forecasting the appearance of geomagnetically induced disturbances in the ionosphere is one of the urgent goals of the space weather community. The challenge is that the processes governing the distribution of the crucial ionospheric parameters has a rather poor quantitative description and the models, built using the empirical parameterisations, have limited capabilities for operational purposes. On the other hand, data assimilation techniques are becoming more and more popular for nowcasting the state of the large-scale geophysical systems. We present an example of an ionospheric data assimilation system performance assessment during a strong geomagnetic event, which took place on 26 September 2011. The first-principle model has assimilated slant total electron content measurements from a dense network of ground stations, provided by the Norwegian Mapping Authority. The results have shown satisfactory agreement with independent data and demonstrate that the assimilation model is accurate to about 2–4 TEC units, and can be used for operational purposes in high-latitude regions. The operational system performance assessment is the subject of future work.

Description: [1]  The last solar minimum period was anomalously extended and low in EUV irradiance compared with previous solar minima. It can readily be expected that the thermosphere and ionosphere must be correspondingly affected by this low solar activity. While there have been unanimous reports on the thermospheric changes, being cooler and lower in its density as expected, the ionospheric responses to low solar activity in previous studies were not consistent with each other, probably due to the limited ionospheric observations used for them. In this study, we utilized the measurements of total electron content (TEC) from TOPEX and JASON-1 satellites during the periods of 1992 to 2010, which includes both the last two solar minimum periods, in order to investigate how the ionosphere responded to the extremely low solar activity during the last solar minimum compared with previous solar minimum. Although the global daily mean TECs show negligible differences between the two solar minimum periods, the global TEC maps reveal that there are significant systematic differences ranging from about -30% to +50% depending on local time, latitude and season. The systematic variations of the ionospheric responses seem to mainly result from the relative effects of reduced solar EUV production and reduced recombination rate due to thermospheric changes during the last solar minimum period.

Description: [1]  Some of the potentially most destructive effects of severe space weather storms are caused by the Geomagnetically Induced Currents. GICs can cause failures of electric transformers and result in wide-spread blackouts. GICs are induced by the time variability of the magnetic field, and are closely related to the time derivative of the local magnetic field perturbation. Predicting dB/dt is rather challenging, since the local magnetic perturbations and their time derivatives are both highly fluctuating quantities, especially during geomagnetic storms. The currently available first-principles based and empirical models cannot predict the detailed minute-scale or even faster time variation of the local magnetic field. On the other hand, Pulkkinen et al. [2013] demonstrated recently that several models can predict with positive skill scores whether the horizontal component of dB/dt at a given magnetometer station will exceed some threshold value in a 20-minute time interval. In this paper we investigate if one can improve the efficiency of the prediction further. We find that the Space Weather Modeling Framework, the best performing among the five models compared by Pulkkinen et al. [2013], shows significantly better skill scores in predicting the magnetic perturbation than predicting its time derivative, especially for large deviations. We also find that there is a strong correlation between the magnitude of dB/dt and the magnitude of the horizontal magnetic perturbation itself. Combining these two results one can devise an algorithm that gives better skill scores for predicting dB/dt exceeding various thresholds in 20-minute time intervals than the direct approach.

Description: [1]  As a weakly magnetized planet, Mars ionosphere/atmosphere interacts directly with the shocked solar wind plasma flow. Even though many numerical studies have been successful in reproducing numerous features of the interaction process, these earlier studies focused mainly on interaction under steady solar wind conditions. Recent observations suggest that plasma escape fluxes are significantly enhanced in response to solar wind dynamic pressure pulses. In this study, we focus on the response of the ionosphere to pressure enhancements in the solar wind. Through modeling of two idealized events using a magnetohydrodynamics model, we find that the upper ionosphere of Mars responds almost instantaneously to solar wind pressure enhancements, while the collision dominated lower ionosphere (below ~150 km) does not have noticeable changes in density. We also find that ionospheric perturbations in density, magnetic field and velocity can last more than an hour after the solar wind returns to the quiet conditions. The topside ionosphere forms complicated transient shapes in response, which may explain unexpected ionospheric behaviors in recent observations. We also find that ionospheric escape fluxes do not correlate directly with simultaneous solar wind dynamic pressure. Rather, their intensities also depend on the earlier solar wind conditions. It takes a few hours for the ionospheric/atmospheric system to reach a new quasi-equilibrium state.

Description: [1]  Combining THEMIS wave and particle observations and a quantitative calculation of linear wave growth rate, we demonstrate that magnetosonic (MS) waves can be locally excited by ion ring distributions in the Earth's magnetosphere when the ion ring energy is comparable to the local Alfven energy. MS waves in association with ion ring distributions were observed by THEMIS A on 24 November 2010 in the afternoon sector, both outside the plasmapause where the wave spectrum varied with f LHR and inside the plasmapause where the wave frequency band remained nearly constant. Our plasma instability analysis in three different regions shows that higher and narrow frequency band MS waves are excited locally outside the plasmapause, and lower and broad frequency band MS waves are excited in the region where the density slightly increases. However, there is no evidence for wave excitation inside the plasmapause, and wave propagation from a distant source is needed to explain their existence. The simulation of the MS wave growth rate spectra during this event agrees reasonably well with the observed wave magnetic field power spectra. We also simulated a MS wave event on 19 October 2011 in the dusk sector, and found that the ion ring distribution with an ion ring energy slightly higher than the local Alfven energy can excite the typical broad band MS waves outside the plasmapause.

Description: [1]  The second Radio Aurora Explorer (RAX-2) satellite has completed more than 30 conjunction experiments with the AMISR chain of incoherent scatter radars in Alaska, and Resolute Bay, Canada. Coherent radar echoing occurred during four of the passes: three when E region electron drifts exceeded the ion acoustic speed threshold and one during HF heating of the ionosphere by the HAARP heater. In this paper, we present the results for the first three passes associated with backscatter from natural irregularities. We analyze, in detail, the largest drift case because the plasma turbulence was the most intense and because the corresponding ground-to-space bi-static scattering geometry was the most favorable for magnetic aspect sensitivity analysis. A set of data analysis procedures including interference removal, autocorrelation analysis, and the application of a radar beam deconvolution algorithm mapped the distribution of E region backscatter with 3 km resolution in altitude and ∼ 0.1 ∘ in magnetic aspect angle. To our knowledge, these are the highest resolution altitude-resolved magnetic aspect sensitivity measurements made at UHF frequencies in the auroral region. In this paper, we show that, despite the large electron drift speed of ∼ 1500 m/s, the magnetic aspect sensitivity of sub-meter scale irregularities is much higher than previously reported. The root-mean-square of the aspect angle distribution varied monotonically between 0.5-0.1 ∘ for the altitude range 100-110 km. Findings from this single but compelling event suggest that sub-meter scale waves propagating at larger angles from the main E  ×  B flow direction (secondary waves) have parallel electric fields that are too small to contribute to E region electron heating. It is possible anomalous electron heating in the auroral electrojet can be explained by (a) the dynamics of those sub-meter scale waves propagating in the E  ×  B direction (primary waves) or (b) the dynamics of longer wavelengths.

Description: [1]  Working toward a physical understanding of how solar-wind/magnetosphere coupling works, four arguments are presented indicating that the solar-wind electric field v sw  × B sw does not control the rate of reconnection between the solar wind and the magnetosphere. Those four arguments are (1) that the derived rate of dayside reconnection is not equal to solar-wind electric field, (2) that electric-field driver functions can be improved by a simple modification that disallows their interpretation as the solar-wind electric field, (3) that the electric field in the magnetosheath is not equal to the electric field in the solar wind, and (4) that the magnetosphere can mass load and reduce the dayside reconnection rate without regard for the solar-wind electric field. The data is more consistent with a coupling function based on local control of the reconnection rate than the Axford conjecture that reconnection is controlled by boundary conditions irrespective of local parameters. Physical arguments that the solar-wind electric field controls dayside reconnection are absent; it is speculated that it is a coincidence that the electric field does so well at correlations with geomagnetic indices.

Description: [1]  This paper presents a case study from a single, six-hour observing period to illustrate the application of techniques developed for interferometric radio telescopes to the spectral analysis of observations of ionospheric fluctuations with sparse arrays. We have adapted the deconvolution methods used for making high dynamic range images of cosmic sources with radio arrays to making comparably high dynamic range maps of spectral power of wavelike ionospheric phenomena. In the example presented here, we have used observations of the total electron content (TEC) gradient derived from Very Large Array (VLA) observations of synchrotron emission from two galaxy clusters at 330 MHz as well as GPS-based TEC measurements from a sparse array of 33 receivers located within New Mexico near the VLA. We show that these techniques provide a significant improvement in signal to noise (S/N) of detected wavelike structures by correcting for both measurement inaccuracies and wavefront distortions. This is especially true for the GPS data when combining all available satellite/receiver pairs, which probe a larger physical area and likely have a wider variety of measurement errors than in the single-satellite case. In this instance, we found the peak S/N of the detected waves was improved by more than an order of magnitude. The data products generated by the deconvolution procedure also allow for a reconstruction of the fluctuations as a two-dimensional waveform/phase screen that can be used to correct for their effects.

Description: [1]  In this paper, we test whether time periods with hot proton temperature anisotropy are associated with EMIC waves, and whether the plasma conditions during the observed waves satisfy the linear theory threshold condition. We identify 865 events observed by the Composition DIstribution Function (CODIF) instrument onboard Cluster spacecraft 4 (SC4) during 1 January 2001 – 1 January 2011 that exhibit a positive temperature anisotropy ( A hp  =  T ⊥  h / T ∥  h  − 1) in the 10-40 keV protons. The events occur over an L range from 4 to 10 in all magnetic local times and at magnetic latitudes (MLAT) within ±50°. Of these Hot Proton Temperature Anisotropy (HPTA) events, only 68 events have electromagnetic ion cyclotron (EMIC) waves. In these 68 HPTA events, for those at 3.8〈 L  ≤ 5 and |MLAT| ≤ 10 ° , the EMIC waves with powers 〉1.0 nT 2 /Hz mainly appear in the region with f EMIC / f H , eq  〈 0.8. Two stop bands are present, one near the region with f EMIC / f H , eq  ≈ 0.33, the other in the region with 0.8 〈  f EMIC / f H , eq  〈 0.9. Most of the EMIC waves in the He, H, and 〉 H bands satisfy A hp /( A hp  + 1) 〉  f EMIC / f H , lo , A hp /( A hp  + 1) 〉 0.45 *  f EMIC / f H , lo , and A hp /( A hp  + 1) 〈 0.45 *  f EMIC / f H , lo .   f EMIC , f H , eq   and f H , lo are the EMIC wave frequency, the magnetic equatorial and the local proton gyrofrequencies. We also find that the EMIC waves predominantly occur with A hp  〉 0.25. By testing a threshold equation for the EMIC instability based on linear theory, we find that for EMIC waves with |MLAT| ≤ 10 ° in the He, H and 〉 H bands the percentages that satisfy the predicted conditions for wave growth by the threshold equation are 15.2%, 24.6% and 25.6%. For the EMIC waves with |MLAT| 〉 10 ° the percentages that satisfy the wave growth predicted conditions are only 2.8%, 2.6% and 0.0%. Finally, possible reasons for the low forecast accuracies of EMIC waves are suggested.

Description: Ecological Applications, Volume 24, Issue 1, Page 3, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 23-24, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 227-228, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 71-83, January 2014. Concerns about bycatch of protected species have become a dominant factor shaping fisheries management. However, efforts to mitigate bycatch are often hindered by a lack of data on the distributions of fishing effort and protected species. One approach to overcoming this problem has been to overlay the distribution of past fishing effort with known locations of protected species, often obtained through satellite telemetry and occurrence data, to identify potential bycatch hotspots. This approach, however, generates static bycatch risk maps, calling into question their ability to forecast into the future, particularly when dealing with spatiotemporally dynamic fisheries and highly migratory bycatch species. In this study, we use boosted regression trees to model the spatiotemporal distribution of fishing effort for two distinct fisheries in the North Pacific Ocean, the albacore (Thunnus alalunga) troll fishery and the California drift gillnet fishery that targets swordfish (Xiphias gladius). Our results suggest that it is possible to accurately predict fishing effort using

Description: [1]  The simultaneous onset of the preliminary impulse (PI) of the geomagnetic sudden commencement at high latitude and dayside dip equator is explained by means of the TM 0 mode waves propagating at the speed of light in the Earth-ionosphere waveguide (EIW) [Kikuchi et al., 1978]. A couple of issues remain to be addressed in the EIW model: (1) How is the TM 0 mode wave is excited by the field-aligned currents in the polar region? (2) How are the quasi-steady ionospheric currents are achieved by the TM 0 mode waves? (3) How simultaneous or delayed are the onset and peak of the equatorial PI with respect to the high latitude PI? To address these issues, we examine the TEM (TM 0 ) mode wave propagation in the finite-length transmission lines replacing the pair of FACs (magnetosphere-ionosphere (MI) transmission line) and the Earth-ionosphere waveguide (ionosphere-ground (IG) transmission line). The issue (1) is addressed by showing that a fraction of the TEM mode wave is transmitted from the MI to IG transmission lines through the polar ionosphere. To address the issues (2) and (3), we examine the properties of the finite-length IG transmission line with finite ionospheric conductivity. It is shown that the ionospheric currents start to grow instantaneously and continue to grow gradually with time constants of 1-10 sec depending on the ionospheric conductivity. The MIG transmission line enables us to explain the instantaneous onset and delayed peak time of the equatorial PI and quick electric field response of the low latitude ionosphere and inner magnetosphere.

Description: [1]  Plasmoids and other reconnection-related signatures have been observed in Jupiter's magnetotail through analysis of magnetic field and energetic particle data. Previous studies have established the spatial distribution and recurrence period of tail reconnection events, and identified the location of a statistical x-line separating inward and outward flow. Here we present new analysis focusing specifically on 43 plasmoid signatures observed in magnetometer data in order to establish the average properties and internal structure of Jovian plasmoids. We present statistics on the observed plasmoid length scale, duration, radial position, and local time distribution. On average, the observed plasmoids have a ~3 R J radial extent and ~7 minute duration, and result in the closure of ~4-8 GWb of open flux from reconnection of open field lines in the post-plasmoid plasma sheet. We also determine the amount of mass released and the magnetic flux closed in order to understand the role of tail reconnection in the transport of mass and flux in Jupiter's magnetosphere. The observed plasmoid properties are consistent with a mass loss rate of ~0.7-120 kg/s and a flux closure rate of ~7-70 GWb/day. We conclude that tail reconnection and plasmoid release is an important method of flux transport at Jupiter but likely cannot account for the mass input from Io, suggesting that additional mass loss mechanisms may be significant. Finally, we examine the plasmoid interior structure through minimum variance analysis and find that most plasmoids lack a core field and are better described by magnetic loops rather than flux ropes.

Description: [1]  Hot flow anomalies (HFAs) represent a subset of solar wind discontinuities interacting with collisionless bow shocks. They are typically formed when the normal component of the motional (convective) electric field points toward the embedded current sheet on at least one of its sides. The core region of an HFA contains hot and highly deflected ion flows and rather low and turbulent magnetic field. In this paper, we report observations of possible HFA-like events at Mercury identified over a course of two planetary years. Using data from the orbital phase of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, we identify a representative ensemble of active current sheets magnetically connected to Mercury's bow shock. We show that some of these events exhibit magnetic and particle signatures of HFAs similar to those observed at other planets, and present their key physical characteristics. Our analysis suggests that Mercury's bow shock does not only mediate the flow of supersonic solar wind plasma but also provides conditions for local particle acceleration and heating as predicted by previous numerical simulations. Together with earlier observations of HFA activity at Earth, Venus, Mars, and Saturn, our results suggest that hot flow anomalies could be a common property of planetary bow shocks, and show that the characteristic size of these events is controlled by the bow shock standoff distance and/or local solar wind conditions.

Description: [1]  This paper investigates the influence of two solar eclipses on the ionosphere complexity measures: Tsallis entropy, Renyi entropy, Hurst exponent, beta exponent, fractal dimension. The study used GPS TEC measured at 3 locations in Japan during the solar eclipses of 22 July 2009 and 21 May 2012.This is the first effort to compare the complexity measures by comparing TEC time series of the eclipse day with those from the day before and day after the eclipse. It was found from analysis of the TEC observations that there were no abnormal variations of the complexity parameters from their expected values for either eclipse. Model calculations also show that TEC deviations during the eclipses are small.

Description: [1]  We have analyzed the data of the world neutron monitor network for the first ground level enhancement of solar cycle 24, the GLE on May 17, 2012. A newly computed neutron monitor yield function and an inverse method are applied to estimate the energy spectrum, anisotropy axis direction and pitch-angle distribution of the high-energy solar particles in interplanetary space. The method includes the determination of the asymptotic viewing cones of neutron monitor stations through computations of trajectories of cosmic rays in a model magnetosphere. The cosmic ray particle trajectories are determined with the MAGNETOCOSMICS code using Tsyganenko 1989 and IGRF models. Subsequent calculation of the neutron monitor responses with the model function is carried out, that represents an initial guess of the inverse problem. Derivation of the solar energetic particle characteristics is fulfilled by fitting the data of the global neutron monitor network using the Levenberg-Marquardt method over the nine-dimensional parameter space. The pitch-angle distribution and rigidity spectrum of high-energy protons are obtained as function of time in the course of the GLE. The angular distribution appears quite complicated. It comprises a focused beam along the interplanetary magnetic field line from the Sun and a loss-cone feature around the opposite direction, possibly indicative of the particle transport in interplanetary magnetic field structures associated with previous coronal mass ejections.

Description: [1]  Geomagnetic activity is strongly controlled by solar wind and Interplanetary Magnetic Field (IMF) conditions, especially the southward component of IMF (IMF Bs). We analyze the statistical properties of IMF Bs at 1 AU using in situ observations for more than a solar cycle (1995 - 2010). IMF Bs-events are defined as continuous IMF Bs intervals with varying thresholds of Bs magnitude and duration, and categorized by different solar wind structures, such as magnetic cloud (MC), interplanetary small-scale magnetic flux rope (ISMFR), interplanetary coronal mass ejection (ICME) without MC signature (ejecta), stream interacting region (SIR), and shock, as well as events unrelated with well-defined solar wind structures. The statistical properties of IMF Bs-events and their geoeffectiveness are investigated in detail based on satellite and ground measurements. We find that the integrated duration and number of Bs-events follow the sunspot number when Bz 〈 -5 nT. We also find that in extreme Bs-events (t 〉 6 hours, Bz 〈 -10 nT), a majority (53 %) are related to MC and 10 % are related with ejecta, but nearly a quarter are not associated with any well-defined solar wind structure. We find different geomagnetic responsesfor Bs-events with comparable duration and magnitude depending on what type of solar wind structures they are associated with. We also find that great Bs-events (t 〉 3 hours, Bz 〈 -10 nT) do not always trigger magnetic storms.

Description: [1]  This technique paper describes a novel method for quantitatively and routinely identifying auroral breakup following substorm onset using the Time History of Events and Macroscale Interactions During Substorms (THEMIS) all-sky imagers (ASIs). Substorm onset is characterised by a brightening of the aurora that is followed by auroral poleward expansion and auroral breakup. This breakup can be identified by a sharp increase in the auroral intensity i(t) and the time derivative of auroral intensity i'(t) . Utilising both i(t) and i'(t) we have developed an algorithm for identifying the time interval and spatial location of auroral breakup during the substorm expansion phase within the field of view of ASI data based solely on quantifiable characteristics of the optical auroral emissions. We compare the time interval determined by the algorithm to independently identified auroral onset times from three previously published studies. In each case the time interval determined by the algorithm is within error of the onset independently identified by the prior studies. We further show the utility of the algorithm by comparing the breakup intervals determined using the automated algorithm to an independent list of substorm onset times. We demonstrate that up to 50% of the breakup intervals characterised by the algorithm are within the uncertainty of the times identified in the independent list. The quantitative description and routine identification of an interval of auroral brightening during the substorm expansion phase provides a foundation for unbiased statistical analysis of the aurora to probe the physics of the auroral substorm as a new scientific tool for aiding the identification of the processes leading to auroral substorm onset.

Description: [1]  We applied the Grad-Shafranov (GS) reconstruction technique to Martian magnetic flux ropes observed by Mars Global Surveyor in order to estimate their spatial structures. This technique can provide a magnetic field map of their cross section from single spacecraft data, under the assumption that the structure is two-dimensional, magneto-hydrostatic, and time-independent. We succeeded in recovering the spatial structure for 70 events observed between April 1999 and November 2006. The reconstruction results indicate that the flux rope axes were mostly oriented horizontal to the Martian surface, and were randomly distributed with respect to the typical plasma streamline. A subset of events with duration longer than 240 sec was observed at solar zenith angles larger than 75 deg. These events all occur downstream from strong crustal magnetic field in the southern hemisphere, indicating an association between the crustal fields and the detected flux ropes. Using the shape and size of the flux ropes obtained from the GS reconstruction, we estimate lower limits on their volume that span 2–3 orders of magnitude, with larger flux ropes observed downstream from strong crustal magnetic fields. Estimated ion escape rates associated with flux ropes are of the order of 10 22 –10 23 ion/sec, being approximately 10% of previously estimated escape rates during solar minimum.

Description: Ecological Applications, Volume 24, Issue 1, Page 4-14, January 2014. Although market-based incentives have helped resolve many environmental challenges, conservation markets still play a relatively minor role in wildlife management. Establishing property rights for environmental goods and allowing trade between resource extractors and resource conservationists may offer a path forward in conserving charismatic species like whales, wolves, turtles, and sharks. In this paper, we provide a conceptual model for implementing a conservation market for wildlife and evaluate how such a market could be applied to three case studies for whales (minke [Balaenoptera acutorostrata], bowhead [Balaena mysticetus], and gray [Eschrictius robustus]). We show that, if designed and operated properly, such a market could ensure persistence of imperiled populations, while simultaneously improving the welfare of resource harvesters.

Description: Ecological Applications, Volume 24, Issue 1, Page 15-23, January 2014. We critique a proposal to use catch shares to manage transboundary wildlife resources with potentially high non-extractive values, and we focus on the case of whales. Because whales are impure public goods, a policy that fails to capture all nonmarket benefits (due to free riding) could lead to a suboptimal outcome. Even if free riding were overcome, whale shares would face four implementation challenges. First, a whale share could legitimize the international trade in whale meat and expand the whale meat market. Second, a legal whale trade creates monitoring and enforcement challenges similar to those of organizations that manage highly migratory species such as tuna. Third, a whale share could create a new political economy of management that changes incentives and increases costs for nongovernmental organizations (NGOs) to achieve the current level of conservation. Fourth, a whale share program creates new logistical challenges for quota definition and allocation regardless of whether the market for whale products expands or contracts. Each of these issues, if left unaddressed, could result in lower overall welfare for society than under the status quo.

Description: Ecological Applications, Volume 24, Issue 1, Page 142-157, January 2014. Global wetland biodiversity loss continues unabated, driven by increased demand for freshwater. A key strategy for conservation management of freshwater systems is to maintain the quantity and quality of the natural water regimes, including the frequency and timing of flows. Formalizing an ecological model depicting the key ecological components and the underlying processes of cause and effect is required for successful conservation management. Models linking hydrology with ecological responses can prove to be an invaluable tool for robust decision-making of environmental flows. Here, we explored alternative water management strategies and identified maximal strategies for successful long-term management of colonial waterbirds in the Macquarie Marshes, Australia. We modeled fluctuations in breeding abundances of 10 colonial waterbird species over the past quarter century (1986–2010). Clear relationships existed between flows and breeding, both in frequencies and total abundances, with a strong linear relationship for flows 〉200 GL. Thresholds emerged for triggering breeding events in all 10 species, but these varied among species. Three species displayed a sharp threshold response between 100 GL and 250 GL. These had a breeding probability of 0.5 when flows were 〉180 GL and a 0.9 probability of breeding with flows 〉350 GL. The remaining species had a probability greater than 0.5 of breeding with flows 〉400 GL. Using developed models, we examined the effects of five environmental flow management strategies on the variability of flows and subsequent likelihood of breeding. Management to different target volumes of environmental flows affected overall and specific breeding probabilities. The likelihood of breeding for all 10 colonial waterbirds increased from a regulated historical mean (±SD) of 0.36 ± 0.09 to 0.53 ± 0.14, an improvement of 47.5% ± 18.7%. Management of complex ecosystems depends on good understanding of the responses of organisms to the main drivers of change. Considerable opportunity exists for implementing similar frameworks for other ecosystem attributes, following understanding of their responses to the flow regime, achieving a more complete model of the entire ecosystem.

Description: Ecological Applications, Volume 24, Issue 1, Page 84-93, January 2014. Information on landscape-scale patterns in species distributions and community types is vital for ecological science and effective conservation assessment and planning. However, detailed maps of plant community structure at landscape scales seldom exist due to the inability of field-based inventories to map a sufficient number of individuals over large areas. The Carnegie Airborne Observatory (CAO) collected hyperspectral and lidar data over Kruger National Park, South Africa, and these data were used to remotely identify 〉500 000 tree and shrub crowns over a 144-km2 landscape using stacked support vector machines. Maps of community compositional variation were produced by ordination and clustering, and the importance of hillslope-scale topo-edaphic variation in shaping community structure was evaluated with redundancy analysis. This remote species identification approach revealed spatially complex patterns in woody plant communities throughout the landscape that could not be directly observed using field-based methods alone. We estimated that topo-edaphic variables representing catenal sequences explained 21% of species compositional variation, while we also uncovered important community patterns that were unrelated to catenas, indicating a large role for other soil-related factors in shaping the savanna community. Our results demonstrate the ability of airborne species identification techniques to map biodiversity for the evaluation of ecological controls on community composition over large landscapes.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Vegetation-type conversions between grasslands and shrublands have occurred worldwide in semi-arid regions over the last 150 years. Areas once covered by drought deciduous shrubs in Southern California (Coastal Sage Scrub) are converting to grasslands dominated by non-native species. Increasing fire frequency, drought, and nitrogen deposition have all been hypothesized as causes of this conversion, though there is little direct evidence. We constructed rain-out shelters in a Coastal Sage Scrub community following a wildfire, manipulated water and nitrogen input in a split plot design, and collected annual data on community composition for four years. While shrub cover increased through time in all plots during the post-fire succession, both drought and nitrogen significantly slowed recovery. Four years after the fire, average native shrub cover ranged from over 80% in water addition, ambient nitrogen plots to 20% in water reduction, nitrogen addition plots. European grass cover was high following the fire and remained high in the water reduction plots through the third spring after the fire before decreasing in the fourth year of the study. Adding nitrogen decreased the cover of native plants and increased the cover of Eurasian grasses, but also increased growth of crown-sprouting individuals of one shrub species. Our results suggest that extreme drought during post-fire succession may slow or alter succession, possibly facilitating vegetation-type conversion of Coastal Sage Scrub to grassland. Nitrogen addition slowed succession and, when combined with drought, significantly decreased native cover and increased grass cover. Fire, drought, and atmospheric N deposition are widespread aspects of environmental change that occur simultaneously in this system. Our results suggest these drivers of change may reinforce each other, leading to a continued decline of native shrubs and conversion to annual grassland.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Accelerating climate change and other cumulative stressors create an urgent need to understand the influence of environmental variation and landscape features on the connectivity and vulnerability of freshwater species. Here, we introduce a novel modeling framework for aquatic systems that integrates spatially-explicit, individual-based, demographic and genetic (demogenetic) assessments with environmental variables. To show its potential utility, we simulated a hypothetical network of 19 migratory riverine populations (e.g., salmonids) using a riverscape connectivity and demogenetic model (CDFISH). We assessed how stream resistance to movement -- a function of water temperature, fluvial distance, and physical barriers -- might influence demogenetic connectivity and hence population vulnerability. We present demographic metrics (abundance, immigration, and change in abundance) and also genetic metrics (diversity, differentiation, and change in differentiation), and combine them into a single vulnerability index for identifying populations at risk of extirpation. We considered four realistic scenarios that illustrate the relative sensitivity of these metrics for early detection of reduced connectivity: (1) maximum resistance due to high water temperatures throughout the network, (2) minimum resistance due to low water temperatures throughout the network, (3) increased resistance at a tributary junction caused by a partial barrier, and (4) complete isolation of a tributary, leaving resident individuals only. We then apply this demogenetic framework using empirical data for a bull trout metapopulation in the upper Flathead River system, Canada and USA, to assess how current and predicted future stream warming may influence population vulnerability. Results suggest that warmer water temperatures and associated barriers to movement (e.g., low flows, de-watering) are predicted to fragment suitable habitat for migratory salmonids, resulting in the loss of genetic diversity and reduced sizes in certain vulnerable population. This demogenetic simulation framework, which is illustrated in a web-based interactive mapping prototype (http://ptolemy.dbs.umt.edu/pvm/), should be useful for evaluating population vulnerability in a wide variety of dendritic and fragmented riverscapes, helping to guide conservation and management efforts for freshwater species.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Tree and shrub abundance has increased in many grasslands causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns of shrub proliferation, little is known about (i) how they are influenced by grazing or (ii) the extent to which they are influenced by intraspecific interactions. We addressed these questions by quantifying changes in the spatial distribution of Prosopis velutina (mesquite) shrubs over 74 years on grazed and protected grasslands. Livestock are effective agents of mesquite dispersal and mesquite plants have lateral roots extending well beyond the canopy. We therefore hypothesized that mesquite distributions would be (a) random on grazed areas mainly due to cattle dispersion and clustered on protected areas due to decreased dispersal and interspecific interference with grasses; and (b) that clustered or random distributions at early stages of encroachment would give way to regular distributions as stands matured and density-dependent interactions intensified. Assessments in 1932, 1948 and 2006 supported the first hypothesis, but we found no support for the second. In fact, clustering intensified with time on the protected area and the pattern remained random on the grazed site. Although shrub density increased on both areas between 1932 and 2006, we saw no progression toward a regular distribution indicative of density-dependent interactions. We propose that processes related to seed dispersal, grass-shrub seedling interactions, and hydrological constraints on shrub size interact to determine vegetation structure in grassland-to-shrubland state changes with implications for ecosystem function and management.

Description: [1]  From a survey of Polar plasma waves conducted over the interval 1 April, 1996 to 4 April, 1997 (during solar minimum) at and inside the plasmasphere, magnetosonic waves were detected at all local times with a slight preference of occurrence in the midnight-postmidnight sector at L = 3 to 4. The waves occurred primarily during heightened geomagnetic (AE) activity. Wave occurrence (and intensities) peaked at ~ ±5° of the magnetic equator, with half-maxima at ~ ±10°. For other wave events, magnetosonic waves were also detected as far from the equator as +20° and -60° MLAT, but at lower intensities. An extreme magnetosonic wave intensity event of amplitude B w  = ~ ± 1 nT and E w  = ~ ± 25 mV/m was detected during the survey period. The event occurred near local midnight (0022 MLT), at the magnetic equator (MLAT = -0.5°), at the plasmapause (L = 3.5), and during an intense substorm/convection event (AE = 624 nT; SYM-H = -33 nT). If more stringent requirements (| MLAT| ≤ 5° and AE 〉 300 nT) are imposed, the wave occurrence rate approaches ~50% for the 23 to 00 MLT bin at L = 3 to 4. This strong local time anisotropy in the location of magnetosonic wave occurrence rate supports the idea of generation by protons injected from the plasmasheet into the midnight sector magnetosphere by substorm electric fields. Magnetosonic waves were also detected near late morning (1031 MLT) during relative geomagnetic quiet (low AE). We mention that one possible generation mechanism is a recovering/expanding plasmasphere engulfing preexisting energetic ions, which in turn leads to an ion instability. The wave magnetic component oscillations are aligned along B 0 , the ambient magnetic field direction, and the electric component oscillations are orthogonal to B 0 , indicating linear polarization. The magnetosonic wave amplitudes decreased at locations further from the magnetic equator, while transverse whistler mode wave amplitudes increased. We argue that intense magnetosonic waves are always present somewhere in the magnetosphere during strong substorm/convection events. We thus suggest that modelers use dynamic particle tracing codes and the maximum (rather than average) wave amplitudes to simulate wave-particle interactions.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Mounting evidence now shows that fishing activity modifies both heritable life-history traits and ecological processes in harvested populations. However, ecological and evolutionary changes are intimately linked and can occur on the same time-scale, and few studies have investigated their combined effect on fish population dynamics. Here, we contrast two population subunits of a harvested fish species in the Northeast Atlantic, the European hake (Merluccius merluccius), in the light of the emerging field of evolutionary demography, which considers the interacting processes between ecology and evolution. The two subunits experienced similar age/size truncation due to size-selective fishing, but displayed differences in key ecological processes (recruitment success) and phenotypic characteristics (maturation schedule). We investigate how temporal variation in maturation and recruitment success interactively shape the population dynamics of the two subunits. We document that the two subunits of European hake displayed different responses to fishing in maturation schedules, possibly because of the different level of adaptive phenotypic plasticity. Our results also suggest that high phenotypic plasticity can dampen the effects of fisheries-induced demographic truncation on population dynamics, whereas a population subunit characterized by low phenotypic plasticity may suffer from additive effects of ecological and life-history responses. Similar fishing pressure may thus trigger contrasting interactions between life history variation and ecological processes within the same population. The presented findings improve our understanding of how fishing impacts eco-evolutionary dynamics, which is a keystone for a more comprehensive management of harvested species.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Conservation practitioners, faced with managing multiple threats to biodiversity and limited funding, must prioritize investment in different management actions. From an economic perspective, it is routine practice to invest where the highest rate of return is expected. This return-on-investment (ROI) thinking can also benefit species conservation, and researchers are developing sophisticated approaches to support decision-making for cost-effective conservation. However, applied use of these approaches is limited. Managers may be wary of 'black-box' algorithms or complex methods that are difficult to explain to funding agencies. As an alternative, we demonstrate the use of a basic ROI analysis for determining where to invest in cost-effective management to address threats to species. This method can be applied using basic geographic information system and spread sheet calculations. We illustrate the approach in a management-action prioritization for a biodiverse region of eastern Australia. We use ROI to prioritize management actions for two threats to a suite of threatened species: habitat degradation by cattle grazing and predation by invasive red foxes (Vulpes vulpes). We show how decisions based on cost-effective threat management depend upon how expected benefits to species are defined and how benefits and costs co-vary. By considering a combination of species richness, restricted habitats, species vulnerability, and costs of management actions, small investments can result in greater expected benefit compared with management decisions that consider only species richness. Furthermore, a landscape management strategy that implements multiple actions is more efficient than managing only for one threat or more traditional approaches that don't consider ROI. Our approach provides transparent and logical decision-support for prioritizing different actions intended to abate threats associated with multiple species; it is of use when managers need a justifiable and repeatable approach to investment.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Fire is becoming a pervasive driver of environmental change in Amazonia and is expected to intensify, given projected reductions in precipitation and forest cover. Understanding of the influence of post-deforestation land cover change on fires in Amazonia is limited, even though fires in cleared lands constitute a threat for ecosystems, agriculture, and human health. We used MODIS satellite data to map burned areas annually between 2001 and 2010. We then combined these maps with land cover and climate information to understand the influence of land cover change in cleared lands and dry season severity on fire occurrence and spread in a focus area in the Peruvian Amazon. Fire occurrence, quantified as the probability of burning of individual 232m spatial resolution MODIS pixels was modeled as a function of the area of land cover types within each pixel, drought severity, and distance to roads. Fire spread, quantified as the number of pixels burned in 3x3 pixel windows around each focal burned pixel, was modeled as a function of land cover configuration and area, dry season severity, and distance to roads. We found that vegetation regrowth and oil palm expansion are significantly correlated with fire occurrence but that the magnitude and sign of the correlation depend on drought severity, successional stage of regrowing vegetation and oil palm age. Burning probability increased with the area of non-degraded pastures, fallow, and young oil palm and decreased with larger extents of degraded pastures, secondary forests and adult oil palm plantations. Drought severity had the strongest influence on fire occurrence overriding the effectiveness of secondary forests but not of adult plantations to reduce fire occurrence in severely dry years. Overall, irregular and scattered land cover patches reduced fire spread but irregular and dispersed fallows and secondary forests increased fire spread during dry years. Results underscore the importance of land cover management for reducing fire proliferation in this landscape. Incentives for promoting natural regeneration and perennial crops in cleared lands might help reduce fire risk if those areas are protected against burning in early stages of development and during severely dry years.

Description: [1]  On January 9, 2002 and November 14, 2001, the São Luís 30 MHz coherent backscatter radar observed unusual day-time echoes scattered from the equatorial electrojet. The electrojet echoing layers on these days, as seen in the range time intensity (RTI) maps, exhibited quasi-periodic oscillations. Time-frequency decomposition of the magnetic field perturbations ΔH , measured simultaneously by the ground-based magnetometers, also showed evidence of short period waves. The ground-based observations were aided by measurements of the brightness temperature in the water vapor and infrared bands made by the GOES 8 satellite. The GOES 8 satellite measurements indicated evidence of deep tropospheric convection activities, which are favorable for the launch of atmospheric gravity waves (AGW) near São Luís. Our multi-technique investigation, combined with an analysis of the equatorial electric field and current density, indicates that AGW forcing could have been responsible, via coupling with E-region electric fields, for the short-period electrojet oscillations observed over São Luís.

Description: [1]  The diurnal variation of the global electric circuit is investigated using the World Wide Lightning Location Network (WWLLN), which has been shown to identify nearly all thunderstorms ( [16], using WWLLN data from 2005). To create an estimate of global electric circuit activity, a clustering algorithm is applied to the WWLLN dataset to identify global thunderstorms from 2010 – 2013. Annual, seasonal, and regional thunderstorm activity is investigated in this new WWLLN thunderstorm dataset in order to estimate the source behavior of the global electric circuit. Through the clustering algorithm, the total number of active thunderstorms are counted every 30 minutes creating a measure of the global electric circuit source function. The thunderstorm clusters are compared to precipitation radar data from the Tropical Rainfall Measurement Mission satellite and with case studies of thunderstorm evolution. [2]  The clustering algorithm reveals an average of 660 ± 70 thunderstorms active at any given time with a peak-to-peak variation of 36%. The highest number of thunderstorms occurs in November (720 ± 90) and the lowest number occurs in January (610 ± 80). Thunderstorm cluster and electrified storm cloud activity are combined with thunderstorm overflight current measurements to estimate the global electric circuit thunderstorm contribution current to be 1090 ± 70 A with a variation of 24%. By utilizing the global coverage and high time resolution of WWLLN, the total active thunderstorm count and current is shown to be less than previous estimates based on compiled climatologies.

Description: [1]  Dynamics of the dayside magnetosphere and proton radiation belt was analyzed during unusual magnetic storm on 21 January 2005. We have found that during the storm from 1712 to 2400 UT, the subsolar magnetopause was continuously located inside geosynchronous orbit due to strong compression. The compression was found to be extremely strong from 1846 to 2035 UT when the dense plasma of fast erupting filament produced the solar wind dynamic pressure Pd peaked up to 〉100 nPa and, in the first time, the upstream solar wind was observed at geosynchronous orbit during almost 2 hours. Under the extreme compression, the outer magnetosphere at L  〉 5 was pushed inward and the outer radiation belt particles with energies of several tens of keV moved earthward, became adiabatically accelerated and accumulated in the inner magnetosphere at L  〈 4 that produced the intensified ring current with an exceptionally long lifetime. The observations were compared with predictions of various empirical and first principles models. All the models failed to predict the magnetospheric dynamics under the extreme compression when the minimal magnetopause distance was estimated to be ~3 Re. The inconsistencies between the model predictions and observations might result from distortions of plasma measurements by extreme heliospheric conditions consisting in very fast solar wind streams (~1000 km/s) and intense fluxes of solar energetic particles. We speculated that anomalous dynamics of the magnetosphere could be well described by the models if the He abundance in the solar wind was assumed to be 〉20%, which is well appropriate for erupting filaments and which is in agreement with the upper 27% threshold for the He/H ratio obtained from Cluster measurements.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. There is a growing need for operational biodiversity mapping methods to quantify and to assess the impact of climate change, habitat alteration and human activity on ecosystem composition and function. Here, we present an original method for the estimation of α- and β-diversity of tropical forests based on high-fidelity imaging spectroscopy. We acquired imagery acquired over high-diversity Amazonian tropical forest landscapes in Perú with the Carnegie Airborne Observatory and developed an unsupervised method to estimate the Shannon Index (H') and variations in species composition using Bray-Curtis Dissimilarity (BC) and non-metric multidimensional scaling (NMDS). An extensive field plot network was used for the validation of remotely sensed α- and β-diversity. Airborne maps of H' were highly correlated with field α-diversity estimates (r = 0.86), and BC was estimated with demonstrable accuracy (r = 0.61-0.76). Our findings are the first direct and spatially-explicit remotely sensed estimates of α- and β-diversity of humid tropical forests, paving the way for new applications using airborne and space-based imaging spectroscopy.

Description: [1]  Type III radio bursts are produced near the local electron plasma frequency and/or near its harmonic by fast electrons ejected from the solar active regions and moving through the corona and solar wind. These bursts have dynamic spectra with frequency rapidly falling with time. This paper presents two new methods developed to detect type III bursts automatically in the data from High Frequency Receiver (HFR) of the STEREO/WAVES (S/WAVES) radio instrument onboard the STEREO spacecraft. The first technique is applicable to the low frequency band (HFR-1: 125 kHz to 1.975 MHz) only. This technique can possibly be implemented in on-board satellite software aimed at preliminary detection of bursts and identification of time intervals with relatively high solar activity. In the second technique the bursts are detected in both the low frequency band and the high frequency band (HFR-2: 2.025 MHz to 16.025 MHz), with the computational burden being higher by one order of magnitude as compared with that for the first technique. Preliminary tests of the method show that the performance of the first technique is quite high, P dL  = 72 % ± 3 %. The performance of the second technique is considerably higher, P dL  +  H  = 81 % ± 1%, while the number of false alarms does not exceed 10% for one daily spectrum.

Description: [1]  A dipolarizing flux bundle (DFB) is a small magnetotail flux tube (typically 〈 ~3 R E in X GSM and Y GSM ) with a significantly more dipolar magnetic field than its background. Dipolarizing flux bundles typically propagate earthward at a high speed from the near-Earth reconnection region. Knowledge of a DFB's flux transport properties leads to better understanding of near-Earth (X = -6 to -30 R E ) magnetotail flux transport and thus conversion of magnetic energy to kinetic and thermal plasma energy following magnetic reconnection. We explore DFB properties with a statistical study using data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. To establish the importance of DFB flux transport, we compare it with transport by bursty bulk flows (BBFs) that typically envelop DFBs. Because DFBs coexist with flow bursts inside BBFs, they contribute 〉65% of BBF flux transport, even though they last only ~30% as long as BBFs. The rate of DFB flux transport increases with proximity to Earth and to the pre-midnight sector, as well as with geomagnetic activity and distance from the neutral sheet. Under the latter two conditions the total flux transport by a typical DFB also increases. Dipolarizing flux bundles appear more often during increased geomagnetic activity. Since BBFs have been previously shown to be the major flux transporters in the tail, we conclude that DFBs are the dominant drivers of this transport. The occurrence rate of DFBs as a function of location and geomagnetic activity informs us about processes that shape global convection and energy conversion

Description: [1]  The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere towards dawn and out of the ionosphere towards dusk, linked by a westward electrojet. We use multi-spacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 Jan 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft travelled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal sub-structure on scales of 100 km at altitudes of 4,000-7,000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120-240 s after Cluster 4 at 1,300-2,000 km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction,in contrast to the expected east-west orientation of the pre-onset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs) we conclude that significant questions remain for the explanation of SCW structuring by BBF driven “wedgelets”. Our results therefore represent constraints on future modelling and theoretical frameworks on the generation of the SCW.

Description: [1]  Large horizontal winds and wind shears have been measured in the lower thermosphere by rockets, lidars, and non-specular meteor radars. This paper describes a detailed analysis of 3 multi-hour non-specular meteor radar data sets collected at the Jicamarca Radio Observatory. This provides some of the highest resolution sustained measurements in this part of the atmosphere. These show: (1) intense wind speeds, maintaining 180 m/s for half an hour and 160 m/s for another half an hour; (2) winds structured in layers that move up or, more commonly, down in the pre-dawn hours at rates of a few km/hr; (3) intense wind shears that typically persist at around 50 m/s/km but, in one instance, sustains values approaching 100 m/s/km for a few hours.

Description: [1]  We present results from an analysis of high-latitude ionosphere-thermosphere (IT) coupling to the solar wind during a moderate magnetic storm which occurred on 5-6 August 2011. During the storm, a multi-point set of observations of the ionosphere and thermosphere was available. We make use of ionospheric measurements of electromagnetic and particle energy made by the Defense Meteorological Satellite Program (DMSP), and neutral densities measured by the Gravity Recovery and Climate Experiment (GRACE) satellite to infer: (1) the energy budget and (2) timing of the energy transfer process during the storm. We conclude that the primary location for energy input to the IT system may be the extremely high latitude region. We suggest that the total energy available to the IT system is not completely captured either by observation or empirical models.

Description: [1]  The level of solar activity varies from cycle to cycle. This variability is probably caused by a combination of nonlinear and random effects. Based on surface flux transport simulations, we show that the observed inflows into active regions and towards the activity belts provide an important nonlinearity in the framework of Babcock-Leighton model for the solar dynamo. Inclusion of these inflows also leads to a reproduction of the observed proportionality between the open heliospheric flux during activity minima and the maximum sunspot number of the following cycle. A substantial component of the random variability of the cycle strength is associated with the cross-equatorial flux plumes that occur when large, highly-tilted sunspot groups emerge close to the equator. We show that the flux transported by these events is important for the amplitude of the polar fields and open flux during activity minima. The combined action of inflows and cross-equatorial flux plumes provides an explanation for the weakness of the polar fields at the end of solar cycle 23 (and hence for the relative weakness of solar cycle 24).

Description: [1]  We present the first direct measurement of neutral oxygen in the lunar exosphere, detected by the Chandrayaan-1 Energetic Neutral Analyzer (CENA). With the lunar surface consisting of about 60% of oxygen in number, the neutral oxygen detected in CENA's energy range (11 eV – 3.3 keV) is attributed to have originated from the lunar surface, where it is released through solar wind ion sputtering. We verify this proposition by comparing the measured oxygen content in two different mass spectra groups with ion sputtering theory. One group contains mass spectra that were recorded when the solar wind consisted of almost pure hydrogen and the other group contains mass spectra that were recorded when the helium content in the solar wind was very high (〉3.5%). Since helium is a much more effective sputtering agent than hydrogen (5% of alpha particles present in the solar wind typically contribute 30% of the total sputter yield), these two groups should show clear differences in the oxygen sputter yield. Fitting of CENA's mass spectra with calibration spectra from ground and in-flight data resulted in the detection of a robust oxygen signal, with a flux of 0.2 to 0.4 times the flux of backscattered hydrogen, depending, as expected, on the solar wind helium content and particle velocity. These measurements present the first in-situ detection of oxygen in the lunar exosphere. For the two solar wind types observed, we derive sub-solar surface oxygen atom densities of N 0  = (1.1 ± 0.3) ⋅ 10 7 m − 3 and (1.4 ± 0.4) ⋅ 10 7 m − 3 , respectively, which agree well with earlier model predictions and measured upper limits. From these surface densities we derive, by modeling, column densities of N C  = (1.5 ± 0.5) ⋅ 10 13 m − 2 and (1.6 ± 0.5) ⋅ 10 13 m − 2 . [2]  In addition, in the CENA mass spectra, we identified for the first time a helium component. This helium is attributed to backscattering of solar wind helium (alpha particles) from the lunar surface as neutral energetic helium atoms, which has been observed for the first time. This identification is supported by the characteristic energy of the measured helium atoms, which is roughly four times the energy of reflected solar wind hydrogen, and the correlation with solar wind helium content.

Description: [1]  The diffuse aurora is an almost permanent feature in the Earth's upper polar atmosphere, providing the major source of ionizing energy input into the high-latitude region. Previous theoretical and observational studies have demonstrated that whistler-mode chorus scattering primarily accounts for intense nightside diffuse auroral precipitation within ~ 8 R E , but what causes the dayside diffuse aurora remains poorly understood. Using conjugate satellite wave and particle observations on 13 August 2009 from the THEMIS spacecraft and ground-based all-sky imager measurements at the South Pole on the dayside, we perform a quantitative analysis of wave driven diffusion and electron precipitation. Our results demonstrate that the dayside chorus scattering was the dominant contributor to the observed dayside diffuse auroral precipitation and that the chorus wave intensity primarily controlled its brightness, indicating that dayside chorus can be the major driver of the Earth's dayside diffuse aurora. While further investigations are required to bring closure to the origin of the dayside diffuse aurora under differing solar wind conditions and geomagnetic situations, our finding is an important complement to recent work on the formation mechanism of the diffuse aurora and provides improved understanding of the roles of resonant wave-particle interactions in diffuse auroral precipitation pattern on a global scale.

Description: [1]  Ultra Low Frequency (ULF: 0.001-5 Hz) magnetic records have recently been used in the search for short term earthquake prediction methods. The separation of local and global effects in the magnetic records is the greatest challenge in this research area. Geomagnetic indices are often used to predict global ULF magnetic behavior where it is assumed that increases in a geomagnetic index correspond with an increase in ULF power. This paper examines the relationships between geomagnetic indices and ULF power, spectral polarization ratio and the relationship between the spectral polarization ratio and solar wind parameters. The power in the ULF, Pc3-5 bands (10-600 s) shows a linear correlation coefficient of  0.2 with the Kp magnetic activity index. The correlation varies with magnetic local time (MLT) and latitude. The correlation coefficient is inversely related to the integrated power in the ULF Pc3 band (10-45 s) over MLT and magnetic latitude. The ratio of spectral powers Z ( ω )/ G ( ω ) is discussed and shown to be a promising parameter in the search for earthquake precursor signals in ULF records.

Description: [1]  Recent testing of a quantitative model describing the classical (region-1-sense, referred to as the R1 current loop) substorm current wedge (SCW) revealed systematic discrepancies between the observed and predicted amplitudes, which suggested us to include additional region-2-sense currents (R2-loop) earthward of the dipolarized region (SCW2L model). In this paper we discuss alternative circuit geometries of the 3d substorm current system and interpret simultaneous observations of the magnetic field dipolarizations by NOAA Geostationary Operational Environmental Satellite (GOES) and by NASA Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, to quantitatively investigate the SCW2L model parameters. During two cases of a dipole-like magnetotail configuration, the dipolarization/injection front fortuitously stopped at r  ∼ 9 Re for the entire duration of ∼ 30 min-long SCW-related dipolarization within a unique, radially-distributed multi-spacecraft constellation, which allowed us to determine the locations and total currents of both SCW2L loops. In addition, we conducted a survey of the dipolarization amplitudes in events, simultaneously observed at 6.6 Re (GOES) and 11 Re (THEMIS) under a wide range of magnetotail conditions. We infer that the ratio I 2 / I 1 varies in the range 0.2 to 0.6 (median value 0.4) and that the equatorial part of the R2 current loop stays at the distance r  〉 6.6 Re in the case of a dipole-like field geometry ( BZ 0  〉 75 nT at 6.6 Re prior to the onset), but it is located at r  〈 6.6 Re in the case of a stretched magnetic field configuration (with BZ 0  〈 60 nT). Since the ground midlatitude perturbations are sensitive to the combined effect of the R1- and R2-sense current loops with the total current roughly equal to I 1  −  I 2 , the ratio I 2 / I 1 becomes an important issue when attempting to monitor the current disruption intensity from ground observations.

Description: Ecological Applications, Volume 24, Issue 1, Page 229-233, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 181-195, January 2014. Stable isotopes are valuable tools for partitioning the components contributing to ecological processes of interest, such as animal diets and trophic interactions, plant resource use, ecosystem gas fluxes, streamflow, and many more. Stable isotope data are often analyzed with simple linear mixing (SLM) models to partition the contributions of different sources, but SLM models cannot incorporate a mechanistic understanding of the underlying processes and do not accommodate additional data associated with these processes (e.g., environmental covariates, flux data, gut contents). Thus, SLM models lack predictive ability. We describe a process-based mixing (PBM) model approach for integrating stable isotopes, other data sources, and process models to partition different sources or process components. This is accomplished via a hierarchical Bayesian framework that quantifies multiple sources of uncertainty and enables the incorporation of process models and prior information to help constrain the source-specific proportional contributions, thereby potentially avoiding identifiability issues that plague SLM models applied to “too many” sources. We discuss the application of the PBM model framework to three diverse examples: temporal and spatial partitioning of streamflow, estimation of plant rooting profiles and water uptake profiles (or water sources) with extension to partitioning soil and ecosystem CO2 fluxes, and reconstructing animal diets. These examples illustrate the advantages of the PBM modeling approach, which facilitates incorporation of ecological theory and diverse sources of information into the mixing model framework, thus enabling one to partition key process components across time and space.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e. cyanobacteria, lichens and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte) and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently-aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: 1) species with high resistance and resilience to grazing, 2) species with high resistance but low resilience, 3) species with low resistance but high resilience, and 4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. The American pika (Ochotona princeps) has become a species of concern for its sensitivity to warm temperatures and potential vulnerability to global warming. We explored the value of radiocarbon dating of fecal pellets to address questions of population persistence and timing of site extirpation. Carbon was extracted from pellets collected at 43 locations in the western Great Basin, USA, including 3 known occupied sites and 40 sites of uncertain status at range margins or where previous studies indicated the species is vulnerable. We resolved calibrated dates with high precision (within several years), most of which fell in the period of the mid-late 20th century "bomb curve." The two-sided nature of the bomb curve renders "far-" and "near-side" dates of equal probability, which are separated by 1-4 decades. We document methods for narrowing resolution to one age range, including stratigraphic analysis of vegetation collected from pika haypiles. No evidence was found for biases in atmospheric 14C levels due to fossil-derived or industrial CO2 contamination. Radiocarbon dating indicated that pellets can persist for 〉59 years; known-occupied sites resolved contemporary dates. Using combined evidence from field observations and radiocarbon-dating, and the Bodie Mountains (Mtns) as an example, we propose a historical biogeographic scenario for pikas in minor Great Basin mountain ranges adjacent to major cordillera wherein historical climate variability led to cycles of extirpation and re-colonization during alternating cool and warm centuries. Using this model to inform future dynamics for small ranges in biogeographic settings similar to the Bodie Mtns, CA, extirpation of pikas appears highly likely under directional warming trends projected for the next century, even while populations in extensive cordillera (e.g., Sierra Nevada, Rocky Mtns, Cascade Range) are likely to remain viable due to extensive, diverse, habitat and high connectivity.

Description: We present Cluster observations of wave-particle interactions during an earthward-propagating dipolarization front (DF) and associated fast plasma bulk flows detected at the central current sheet in Earth's magnetotail. During this period, flux tubes behind the DF frequently contain more energetic or hotter ions than did the pre-existing flux tubes ahead of the DF. On the other hand, electrons within the DF flux tubes heat less, or are even colder, than were the pre-existing populations, and are often accompanied by superposed isolated beams. At the same time, electrostatic emissions are strongly enhanced over a wide range of frequencies (up to several times the electron cyclotron frequency) behind the DFs. This low-frequency electrostatic wave power is well correlated with ion energization. From linear theory, we find two wave modes: a high-frequency beam mode and a low-frequency whistler mode that are associated with the electron beam component. We attribute the generation of whistlers to electron beams that persist for a while before undergoing rapid thermalization. The existence of isolated beam components behind DFs detected during the 4-sec Cluster spin period indicates that DFs either provide a continuous source of electron beams or facilitate a physical process that maintains the beams against rapid thermalization. Our analysis suggests that the earthward motion of the DF flux tube, via Fermi acceleration as the magnetic field lines behind the DF shorten, can lead to the persistent electron beams that generate whistler mode waves, which in turn can heat ions. This scenario, by which free energy in electron beams generates waves that then heat ions, accounts for the Cluster observations of different energization behaviors between electrons and ions behind DFs.

Description: We examine a unique data set from seven Hubble Space Telescope (HST) ‘visits’ that imaged Saturn's northern dayside ultraviolet emissions exhibiting usual circumpolar ‘auroral oval’ morphologies, during which Cassini measured the interplanetary magnetic field (IMF) upstream of Saturn's bow shock over intervals of several hours. The auroras generally consist of a dawn arc extending towards noon centered near ~15º co-latitude, together with intermittent patchy forms at ~10º co-latitude and poleward thereof, located between noon and dusk. The dawn arc is a persistent feature, but exhibits variations in position, width, and intensity, which have no clear relationship with the concurrent IMF. However, the patchy post-noon auroras are found to relate to the (suitably lagged and averaged) IMF B z , being present during all four visits with positive B z and absent during all three visits with negative B z . The most continuous such forms occur in the case of strongest positive B z . These results suggest that the post-noon forms are associated with reconnection and open flux production at Saturn's magnetopause, related to the similarly-interpreted bifurcated auroral arc structures previously observed in this LT sector in Cassini UVIS data, whose details remain unresolved in these HST images. One of the intervals with negative IMF B z , however, exhibits a pre-noon patch of very high latitude emission extending poleward of the dawn arc to the magnetic/spin pole, suggestive of the occurrence of lobe reconnection. Overall, these data provide evidence of significant IMF-dependence in the morphology of Saturn's dayside auroras.

Description: A three-dimensional (3D) particle-in-cell (PIC) simulation of the whistler anisotropy instability is carried out for a collisionless, homogeneous, magnetized plasma with β e  = 0.10. This is the first 3D PIC simulation of the evolution of enchanced fluctuations from this growing mode driven by an anisotropic electron velocity distribution with T ⊥  e / T ‖ e  〉 1 where ⊥ and ∥ represent directions perpendicular and parallel to the background magnetic field B o , respectively. The early-time magnetic fluctuation spectrum grows with properties reflecting the predictions of linear theory with narrowband maxima at kc / ω e  ≃ 1 and k  ×  B o  = 0, and a wavevector anisotropy in the sense of k ⊥  〈 〈  k ∥ . Here ω e represents the electron plasma frequency. At later times the fluctuations undergo both a forward transfer to shorter wavelengths, also with k ⊥  〈 〈  k ∥ , and an inverse transfer to longer wavelengths with wavevector anisotropy k ⊥  〉 〉  k ∥ . The inverse transfer is consistent with a prediction of nonlinear three-wave coupling theory.

Description: Auroral ionospheric F-region density depletions observed by PFISR (Poker Flat Incoherent Scatter Radar) during the MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) sounding rocket campaign are critically examined alongside complementary numerical simulations. Particular processes of interest include cavity formation due to intense frictional heating and Pedersen drifts, evolution in the presence of structured precipitation, and refilling due to impact ionization and downflows. Our analysis uses an ionospheric fluid model which solves conservation of mass, momentum, and energy equations for all major ionospheric species. These fluid equations are coupled to an electrostatic current continuity equation to self-consistently describe auroral electric fields. Energetic electron precipitation inputs for the model are specified by inverting optical data, and electric field boundary conditions are obtained from direct PFISR measurements. Thus, the model is driven in as realistic a manner as possible. Both ISR data and simulations indicate that the conversion of the F-region plasma to molecular ions and subsequent recombination is the dominant process contributing to the formation of the observed cavities, all of which occur in conjuction with electric fields exceeding ∼ 90 mV/m. Furthermore, the cavities often persist several minutes past the point when the frictional heating stops. Impact ionization and field-aligned plasma flows modulate the cavity depth in a significant way, but are of secondary importance to the molecular generation process. Informal comparisons of the ISR density and temperature fits to the model verify that the simulations reproduce most of the observed cavity features to a reasonable level of detail.

Description: Energetic particle injections in the near-Earth plasma sheet are critical for supplying particles and energy to the inner magnetosphere. Recent case studies have demonstrated a good correlation between injections and transient, narrow, fast flow channels as well as earthward reconnection (dipolarization) fronts in the magnetotail, but statistical observations beyond geosynchronous orbit (GEO) to verify the findings were lacking. By surveying trans-geosynchronous injections using THEMIS, we show that their likely origin is the earthward-traveling, dipolarizing flux bundles following near-Earth reconnection. The good correlation between injections and fast flows, reconnection fronts and impulsive, dawn-dusk electric field increases is not limited to within 12 R E , but extends out to 30 R E . Like near-Earth reconnection, both ion and electron injections are most probable in the pre-midnight sector. Similar to bursty bulk flows (BBFs), injection-time flow speeds are faster with increasing distance from Earth. With faster flows, injection intensity generally increases and extends to higher energy channels. With increased geomagnetic activity, injection occurrence rate increases (akin to that of BBFs) and spectral hardening occurs (κ decreases). The occurrence rate increase within the inner magnetosphere suggests that injections populate the radiation belts more effectively under enhanced geomagnetic activity. Our results are inconsistent with the classical concept of an azimuthally wide injection boundary moving earthward from ~9-12 R E to GEO under an enhanced cross-tail electric field. Rather, particle injection and transport occur along a large range of radial distances due to effects from earthward-penetrating, azimuthally localized, transient, strong electric fields of recently reconnected, dipolarizing flux bundles.

Description: A method for estimating the vector neutral wind profiles in the mesosphere and lower thermosphere (MLT) region of the upper atmosphere from Arecibo dual-beam incoherent scatter radar data is presented. The method yields continuous estimates of both the altitude-averaged F -region plasma drifts and all three components of the altitude-resolved neutral wind profiles in the MLT using data taken while the Arecibo feed system swings in azimuth. The problem is mixed determined, and its solution is not inherently unique. Second order Tikhonov regularization is used to find solutions consistent with the available data while being minimally structured, additional structure being unsupported by the data. The solution is found using the method of conjugate gradient least squares and sparse matrix mathematics. Example data acquired during an interval of midlatitude spread F are used to illustrate the method. The estimated wind profiles exhibit characteristics broadly consistent with gravity waves but are impulsive, with features that generally persist for less than one and a half wave periods.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Studies of predator-prey demographic responses and the physical drivers of such relationships are rare, yet essential for predicting future changes in the structure and dynamics of marine ecosystems. Here, we hypothesize that predator-prey relationships vary spatially in association with underlying physical ocean conditions, leading to observable changes in demographic rates, such as reproduction. To test this hypothesis, we quantified spatio-temporal variability in hydrographic conditions, krill, and forage fish to model predator (seabird) demographic responses over 18 years (1990-2007). We used principal component analysis and spatial correlation maps to assess coherence among ocean conditions, krill, and forage fish, and generalized additive models to quantify interannual variability in seabird breeding success relative to prey abundance. The first principal component of 4 hydrographic measurements yielded an index that partitioned "weak/warm upwelling" and "strong/cool upwelling" years. Partitioning of krill and forage fish time series among shelf and oceanic regions yielded spatially-explicit indicators of prey availability. Krill abundance within the oceanic region was remarkably consistent between years, whereas krill over the shelf showed marked interannual fluctuations in relation to ocean conditions. Anchovy abundance varied on the shelf, and was greater in years of strong stratification/weak upwelling and warmer temperatures. Spatio-temporal variability of juvenile forage fish covaried strongly with each other and with krill, but was weakly correlated with hydrographic conditions. Demographic responses between seabirds and prey availability revealed spatially-variable associations indicative of the dynamic nature of habitat-prey relationships. Quantification of spatially-explicit demographic responses, and their variability through time, demonstrates the possibility of delineating specific critical areas where the implementation of protective measures could maintain functions and productivity of central place foraging predators.

Description: We report the peculiar interaction of two type III bursts observed in the solar wind. As electrons beams propagating on the same magnetic field lines cross, a spectacular depletion of the type III radio emission is observed. We combine observations from the WAVES experiment on board the STEREO mission together with kinetic plasma simulations to study the extinction of type III radio emission resulting from the interaction between two electron beams. The remote observations enable to follow the electron beams in the interplanetary medium and show that the level of radiated radio waves is recovered after the beam crossing. The in situ observations of beam-driven Langmuir waves give evidence for Langmuir decay. The density fluctuations are extracted from in situ observations. The velocity of the beams is independently evaluated from in situ observations of decaying Langmuir waves and remote radio observations. The kinetic simulations show that the level of beam-driven Langmuir waves is reduced as the two beams cross. We show that the slow beam induced a strong reduction of the quasilinear relaxation of the fast beam, limiting the amplitude of the generated Langmuir waves. Moreover, in the case of two electron beams, the lack of Langmuir waves coherence reduces the efficiency of the Langmuir parametric decay. We thus conclude that the observed depletion of the type III radio 5 is independent of the radio emission mechanism, as long as it depends on the Langmuir amplitude and coherence.

Description: The solar minimum period between solar cycles 23 and 24 was the longest since the beginning of space-based measurements, and many manifestations of solar activity were unusually low. Thermospheric neutral density was about 30% lower than during the previous solar minimum, but changes in the ionosphere between the two solar minima are more controversial. Solar radiation, geomagnetic activity, and anthropogenic increases in greenhouse gases, can all play a role in these changes. In this paper, we address the latter of these potential contributions, the degree to which secular change driven by greenhouse gases, primarily CO 2 , could be responsible for the observed changes. New 3D model simulations find a global mean density decrease at 400 km of 5.8% between the two recent solar minima, which is larger than earlier 1D model results, and in better agreement with observations. From these model simulations and from other observational work, we estimate that the contribution of secular change to global mean neutral density decrease between the two recent solar minima is less than ~6%. The contribution of secular change to the global average decrease of F-region ionosphere peak density ( N m F 2 ) and altitude ( h m F 2 ), near mid-day, is estimated to be 1.5% and 1.5 km, respectively. However, secular changes in the ionosphere exhibit large variations with local time, geographic location, and season. The mid-day change of N m F 2 seen in the model simulations ranged between +6% and -9%, and the change of h m F 2 ranged between +11 km and -11 km, depending on geographic location.

Description: In this paper we study the planetary magnetic disturbance during the magnetic storm occurring on 05 April 2010 associated with high speed solar wind stream due to a coronal hole following a CME. We separate the magnetic disturbance associated to the ionospheric disturbance dynamo (Ddyn) from the magnetic disturbance associated to the prompt penetration of magnetospheric electric field (DP2). This event exhibits different responses of ionospheric disturbance dynamo in the different longitude sectors (European-African, Asian and American). The strongest effect is observed in the European-African sector. The Ddyn disturbance reduces the amplitude of the daytime H-component at low latitudes during four consecutive days in agreement with the Blanc and Richmond's model of ionospheric disturbance dynamo. The amplitude of Ddyn decreased with time during the four days. We discuss its diverse worldwide effects. The observed signature of magnetic disturbance process in specific longitude sector is strongly dependent on which Earth's side faces the magnetic storms (i.e., there is a different response depending on which longitude sector is at noon when the SSC hits).Finally we determined an average period of 22 hours for Ddyn using wavelet analysis.

Description: Complex magnetosphere-ionosphere coupling mechanisms result in high latitude irregularities that are difficult to characterize using only Global Navigation Satellite System (GNSS) scintillation measurements. However, GNSS observations combined with physical parameters derived from modeling can be used to study the physics of these irregularities. We have developed a full three dimensional (3D) electromagnetic (EM) wave propagation model called “Satellite-beacon Ionospheric-scintillation Global Model ofthe upper Atmosphere" (SIGMA), to simulate GNSS scintillations. This model eliminates the most significant approximation made by the previous simulation approaches about the correlation length of the irregularity. Thus, for the first time, using SIGMA wecan accomplish scintillation simulations of significantly high fidelity. While the model is global, it is particularly applicable at high latitudes as it accounts for the complicated geometry of the magnetic field lines in these regions. Using SIGMA wesimulate the spatial and temporal variations in the GNSS signal phase and amplitude on the ground. In this paper, we present the model and results from a study to determine the sensitivity of the SIGMA outputs to different input parameters. We have deduced from our sensitivity study that the peak to peak (P2P) power gets most affected by the spectral index and line of sight (LOS) direction, while the P2P phase and standard deviation of the phase ( σ φ ) are more sensitive to the anisotropy of the irregularity. The sensitivity study of SIGMA narrows the parametric space to investigate when comparing the modeled results to the observations.

Description: The attenuation of VLF signals from lightning and ground-based VLF transmitters during transionospheric propagation has been the subject of recent interest, as discrepancies have been found between satellite data and model calculations. Previous modeling efforts, however, have not considered the self-absorption effect due to nonlinear heating and ionization in the lower ionosphere. A self-consistent model of ionospheric heating is presented here using a time-domain model of VLF wave propagation through the ionosphere. The model is able to estimate the attenuation of signals due to heating below ~100 km altitude. In this model, the ionospheric state is updated as the fields propagate, leading to changes in collision frequency and electron density, which in turn affect the wave propagation. We use this model for ground-based VLF transmitters at different frequencies, amplitudes, and latitudes (i.e., magnetic dip angle), and for lightning-generated sferics with different amplitudes, at different latitudes, and using a variety of ionospheric density profiles. We find that the inclusion of self-consistent heating causes a change in the transionospherically propagating wave amplitude that varies considerably with the source amplitude and other parameters. Typical values for the heating contribution to wave attenuation are 1-2 dB for VLF transmitters, but greater than 10 dB for large amplitude lightning discharges. An interesting effect is observed for VLF transmitters and low-amplitude lightning, where the signal is actually enhanced due to heating, rather than attenuated, in the direction propagating across the Earth's magnetic field.

Description: The present work has investigated the configuration of field-aligned currents (FACs) during a long period of radial interplanetary magnetic field (IMF) on 19 May 2002 by using high-resolution and precise vector magnetic field measurements of the CHAMP satellite. During the interest period IMF B y and B z are weakly positive and B x keeps pointing to the Earth for almost 10 hours. The geomagnetic indices Dst is about -40 nT and AE about 100 nT on average. The cross polar cap potential calculated from Assimilative Mapping of Ionospheric Electrodynamics and derived from DMSP observations have average values of 10-20 kV. Obvious hemispheric differences are shown in the configurations of FACs on the day and nightside. At the south pole FACs diminish in intensity to magnitudes of about 0.1  μA/m 2 , the plasma convection maintains two cell flow pattern, and the thermospheric density is quiet low. However, there are obvious activities in the northern cusp region. One pair of FACs with a downward leg toward the pole and upward leg on the equatorward side emerge in the northern cusp region, exhibiting opposite polarity to FACs typical for duskward IMF orientation. An obvious sunward plasma flow channel persists during the whole period. These ionospheric features might be manifestations of an efficient magnetic reconnection process occurring in the northern magnetospheric flanks at high latitude. The enhanced ionospheric current systems might deposit large amount of Joule heating into the thermosphere. The air densities in the cusp region get enhanced and subsequently propagate equatorward on the dayside. Although geomagnetic indices during the radial IMF indicate low level activity, the present study demonstrates that there are prevailing energy inputs from the magnetosphere to both the ionosphere and thermosphere in the northern polar cusp region.

Description: The interaction of planetary bodies with their surrounding magnetized plasma can often be described with the magneto-hydrodynamic (MHD) equations, which are commonly solved by numerical models. For these models it is necessary to define physically correctboundary conditions for the plasma mass and energy density, the plasma velocity and the magnetic field. Many planetary bodies have electrically non-conductive surfaces, which do not allow electric current to penetrate their surfaces. Magnetic boundary conditions, which consider that the associated radial electric current at the planetary surface is zero are difficult to implement because they include the curl of the magnetic field. Here we derive new boundary conditions by a decomposition of the magnetic field in poloidal and toroidal parts. We find that the toroidal part of the magnetic field needs to vanish at the surface of the insulator. For the spherical harmonics coefficients of the poloidal part we derive a Cauchy boundary condition, whichalso matches a possible intrinsic field by including its Gauss coefficients. Thus we can additionally include planetary dynamo fields as well as time-variable induction fields within electrically conductive subsurface layers. We implement the non-conducting boundary condition in the MHD simulation code ZEUS-MP using spherical geometry and provide a numerical implementation in Fortran 90 as auxiliary-material on the JGR website. We apply it to a model for Ganymede's plasma environment. Our model also includes a consistent set of boundary conditions for the other MHD variables density, velocity and energy. With this model we can describe Galileo spacecraft observations in and around Ganymede's mini-magnetosphere very well.

Description: Ecological Applications, Ahead of Print. Translocation experiments, in which researchers displace animals then monitor their movements to return home, are commonly used as tools to assess functional connectivity of fragmented landscapes. Such experiments are purported to have important advantages of being time efficient and standardizing 'motivation' to move across individuals. Yet, we lack tests of whether movement behavior of translocated birds reflects natural behavior of unmanipulated birds. We compared the routine movement behavior of a tropical hummingbird (Phaethornis guy) to that of experimentally translocated individuals. We tested for differences in site-selection patterns during movement at two spatial scales (point and path levels). We also compared movement rates between treatments. Behaviors documented during translocation experiments reflected those observed during routine movements. At the point level, both translocated and non-translocated birds showed similar levels of preference for mature tropical forest. At the path level, step selection functions showed both translocated and non-translocated hummingbirds avoiding movement across non-forested matrix and selecting streams as movement corridors. Movement rates were generally higher during translocation experiments. However, the negative influence of forest cover on movement rates was proportionately similar in translocation and routine movement treatments. We report the first evidence showing that movement behavior of birds during translocation experiments is similar to their natural movement behavior. Therefore, translocation experiments may be reliable tools to address effects of landscape structure on animal movement. We observed consistent selection of landscape elements between translocated and non-translocated birds, indicating that both routine and translocation movement studies lead to similar conclusions regarding the effect of landscape structure and forest composition on functional connectivity. Our observations that hummingbirds avoid non-forest matrix and select riparian corridors also provides a potential mechanism for pollen limitation in fragmented tropical forest.

Description: Ecological Applications, Ahead of Print. Climate change vulnerability assessments for species of conservation concern often use species distribution and ecological niche modeling to project changes in habitat. One of many assumptions of these approaches is that food web dependencies are consistent in time and environmental space. Species at higher trophic levels that rely on the availability of species at lower trophic levels as food may be sensitive to extinction cascades initiated by changes in the habitat of key food resources. Here we assess climate change vulnerability for Ursus arctos (grizzly bears) in the southern Canadian Rocky Mountains using projected changes to 17 of the most commonly consumed plant food items. We used presence-absence information from 7,088 field plots to estimate ecological niches and to project changes in future distributions of each species. Model projections indicated idiosyncratic responses among food items. Many food items persisted or even increased, although several species were found to be vulnerable based on declines or geographic shifts in suitable habitat. This included Hedysarum alpinum (alpine sweet vetch), a critical spring and autumn root-digging resource when little else is available. Potential habitat loss was also identified for three fruiting species of lower importance to bears: Empetrum nigrum (crowberry), Vaccinium scoparium (grouseberry) and Fragaria virginiana (strawberry). A general trend towards uphill migration of bear foods may result in higher vulnerability to bear populations at low elevations which are also those that are most likely to have human-bear conflict problems. Regardless, a wide diet breadth of grizzly bears, as well as wide environmental niches of most food items, make climate change a much lower threat to grizzly bears than other bear species such as polar bears and panda bears. We cannot exclude, however, future alterations in human behavior and land use resulting from climate change that may reduce survival rates.

Description: Ecological Applications, Ahead of Print. Efforts to test and improve terrestrial biosphere models (TBMs) using a variety of data sources have become increasingly common. However, geographically extensive forest inventories have been under-exploited in previous model-data fusion efforts. Inventory observations of forest growth, mortality, and biomass integrate processes across a range of time scales, including slow time-scale processes such as species turnover, that are likely to have important effects on ecosystem responses to environmental variation. However, the large number (thousands) of inventory plots precludes detailed measurements at each location, so that uncertainty in climate, soil properties, and other environmental drivers may be large. Errors in driver variables, if ignored, introduce bias into model-data fusion. We estimated errors in climate and soil drivers at U.S. Forest Inventory and Analysis (FIA) plots, and we explored the effects of these errors on model-data fusion with the Geophysical Fluid Dynamics Laboratory LM3V dynamic global vegetation model. When driver errors were ignored or assumed small at FIA plots, responses of biomass production in LM3V to precipitation and soil available water capacity appeared steeper than the corresponding responses estimated from FIA data. These differences became non-significant if driver errors at FIA plots were assumed large. Ignoring driver errors when optimizing LM3V parameter values yielded estimates for fine-root allocation that were larger than biometric estimates, which is consistent with the expected direction of bias. To explore if complications posed by driver errors could be circumvented by relying on intensive study sites where driver errors are small, we performed a power analysis. To accurately quantify the response of biomass production to spatial variation in mean annual precipitation within the eastern U.S. would require at least 40 intensive study sites, which is larger than the number of sites typically available for individual biomes in existing plot networks. Driver errors may be accommodated by several existing model-data fusion approaches, including hierarchical Bayesian methods and ensemble filtering methods; however, these methods are computationally expensive. We propose a new approach, in which the TBM functional response is fit directly to the driver-error-corrected functional response estimated from data, rather than to the raw observations.

Description: Ecological Applications, Ahead of Print. Despite intensive monitoring, temporary emigration from the sampling area can induce bias severe enough for managers to discard life-history parameter estimates toward the terminus of the times series (terminal bias). Under random temporary emigration unbiased parameters can be estimated with CJS models. However, unmodeled Markovian temporary emigration causes bias in parameter estimates and an unobservable state is required to model this type of emigration. The robust design is most flexible when modeling temporary emigration, and partial solutions to mitigate bias have been identified, nonetheless there are conditions were terminal bias prevails. Long-lived species with high adult survival and highly variable non-random temporary emigration present terminal bias in survival estimates, despite being modeled with the robust design and suggested constraints. Because this bias is due to uncertainty about the fate of individuals that are undetected toward the end of the time series, solutions should involve using additional information on survival status or location of these individuals at that time. Using simulation, we evaluated the performance of models that jointly analyze robust design data and an additional source of ancillary data (predictive covariate on temporary emigration, telemetry, dead recovery, or auxiliary resightings) in reducing terminal bias in survival estimates. The auxiliary resighting and predictive covariate models reduced terminal bias the most. Additional telemetry data was effective at reducing terminal bias only when individuals were tracked for a minimum of two years. High adult survival of long-lived species made the joint model with recovery data ineffective at reducing terminal bias because of small-sample bias. The naïve constraint model (last and penultimate temporary emigration parameters made equal), was the least efficient, though still able to reduce terminal bias when compared to an unconstrained model. Joint analysis of several sources of data improved parameter estimates and reduced terminal bias. Efforts to incorporate or acquire such data should be considered by researchers and wildlife managers, especially in the years leading up to status assessments of species of interest. Simulation modeling is a very cost effective method to explore the potential impacts of using different sources of data to produce high quality demographic data to inform management.

Description: Ecological Applications, Ahead of Print. Warmer and drier climate over the past few decades has brought larger fire sizes and increased annual area burned in forested ecosystems of western North America, and continued increases in annual area burned are expected due to climate change. As warming continues, fires may also increase in severity and produce larger contiguous patches of high severity. We use remotely sensed burn-severity data from 125 fires in the northern Cascade Range of Washington, USA, to explore relationships between fire size, severity, and the spatial pattern of severity. We examine relationships between climate and the annual area burned and the size of wildfires over a 25-year period. We test the hypothesis that increased fire size is commensurate with increased burn severity and increased spatial aggregation of high severity. We also ask how local ecological controls might modulate these relationships by comparing results over the whole study area (the northern Cascade Range) to those from four ecological subsections within it. We found significant positive relationships between climate and fire size, and between fire size and the proportion of high severity and spatial-pattern metrics that quantify the spatial aggregation of high-severity areas within fires, but the strength and significance of these relationships varied among the four subsections. In areas with more contiguous subalpine forests and less complex topography, the proportion of high severity and spatial aggregation of high severity were more strongly correlated with fire size. If fire sizes increase in a warming climate, changes in the extent, severity, and spatial pattern of fire regimes will likely be more pronounced in higher-severity fire regimes with less complex topography and more continuous fuels.

Description: Ecological Applications, Ahead of Print. Fremont cottonwood (Populus fremonti, Eckenwal.) is a foundation riparian tree species that drives community structure and ecosystem processes in southwestern U.S. ecosystems. Despite its ecological importance, little is known about the ecological and environmental processes that shape its genetic diversity, structure and landscape connectivity. Here, we combine molecular analyses of 82 populations including 1,312 individual trees dispersed over the species' geographical distribution. We reduced the dataset to 40 populations and 743 individuals to eliminate admixture with a sibling species, and used multi-variate restricted optimization and reciprocal causal modeling, to evaluate the effects of river network connectivity and climatic gradients on gene flow. Our results confirmed the following: First, gene flow of Fremont cottonwood is jointly controlled by the connectivity of the river network and gradients of seasonal precipitation. Second, gene flow is facilitated by mid-sized to large rivers, and is resisted by small streams and terrestrial uplands, with resistance to gene flow decreasing with river size. Third, genetic differentiation increases with cumulative differences in winter and spring precipitation. Our results, suggest that ongoing fragmentation of riparian habitats will lead to a loss of landscape level genetic connectivity, leading to increased inbreeding and the concomitant loss of genetic diversity in a foundation species. These genetic effects will cascade to a much larger community of organisms, some of which are threatened and endangered.

Description: Ecological Applications, Ahead of Print. Identifying determinants of the probability and intensity of infections is important for understanding the epidemiology of wildlife diseases, and for managing their impact on threatened species. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis, has decimated populations of some amphibians. However, recent studies have identified important environmental constraints on the disease, related to the pathogen's physiological tolerances. In this study, we identified several intrinsic and extrinsic determinants of the probability and intensity of chytrid infections for the threatened Growling Grass Frog (Litoria raniformis) in south-eastern Australia, and used mark-recapture to estimate the effect of chytrid infections on the probability of survival of these frogs. Water temperature and salinity had negative effects on both the probability and intensity of chytrid infections. We coupled models of the infection process with a model of the effect of chytrid infections on the probability of survival to assess variation in the impact of chytridiomycosis between wetlands with differing temperature and salinity profiles. Our results suggest that warm, saline wetlands may be refuges from chytridiomycosis for L. raniformis, and should be priorities for protection. Our results also suggest that management actions that increase water temperature (e.g. reducing canopy shading) and salinity (e.g. complementing inflows with groundwater) could be trialled to reduce the impacts of chytridiomycosis on this species. This and other recent studies highlight the value of research on environmental risk factors for chytridiomycosis.

Description: Ecological Applications, Ahead of Print. Terrestrial soil is a large reservoir of atmospherically deposited mercury (Hg). However, few studies have evaluated the accumulation of Hg in terrestrial ecosystems in the northeastern United States, a region which is sensitive to atmospheric Hg deposition. In this study, we characterize Hg and organic matter in soil profiles from 139 sampling sites for five sub-regions across the northeastern United States, and estimate atmospheric Hg deposition to these sites by combining numerical modeling with experimental data from the literature. We did not observe any significant relationships between current net atmospheric Hg deposition and soil Hg concentrations or pools, even though soils are a net sink for Hg inputs. Soil Hg appears to be preserved relative to organic carbon (OC) and/or nitrogen (N) in the soil matrix, as a significant negative relationship was observed between the ratios of Hg/OC and OC/N (r = 0.54, p 〈 0.0001) that shapes the horizonal distribution patterns. We estimated that atmospheric Hg deposition since 1850 (3.97 mg m-2) accounts for 102% of the Hg pool in the organic horizons (3.88 mg m-2) and 19% of the total soil Hg pool (21.32 mg m-2), except for the Southern New England (SNE) sub-region. The mean residence time for soil Hg was estimated to be 1,800 years, except SNE which was 800 years. These patterns suggest that in additional to atmospheric deposition, the accumulation of soil Hg is linked to the mineral diagenetic and soil development processes in the region.

Description: Ecological Applications, Ahead of Print. Predicting how climate change is likely to interact with myriad other stressors that threaten species of conservation concern is an essential challenge in aquatic ecosystems. This study provides a framework to accomplish this task in salmon-bearing streams of the northwestern United States, where land-use related reductions in riparian shading have caused changes in stream thermal regimes, and additional warming from projected climate change may result in significant losses of coldwater fish habitat over the next century. Predatory non-native smallmouth bass have also been introduced into many northwestern streams and their range is likely to expand as streams warm, presenting an additional challenge to the persistence of threatened Pacific salmon. The goal of this work was to forecast the interactive effects of climate change, riparian management, and non-native species on stream-rearing salmon, and to evaluate the capacity of restoration to mitigate these effects. We intersected downscaled global climate forecasts with a local-scale water temperature model to predict mid- and end-of-century temperatures in streams in the Columbia River basin; we compared one stream that is thermally impaired due to the loss of riparian vegetation and another that is cooler and has a largely intact riparian corridor. Using the forecasted stream temperatures in conjunction with fish-habitat models, we predicted how stream-rearing Chinook salmon and bass distributions would change as each stream warmed. In the highly modified stream, end-of-century warming may cause near total loss of Chinook salmon rearing habitat and a complete invasion of the upper watershed by bass. In the less modified stream, bass were thermally restricted from the upstream-most areas. In both systems, temperature increases resulted in higher predicted spatial overlap between stream-rearing Chinook salmon and potentially predatory bass in the early summer (2-4-fold increase) and greater abundance of bass. We found that riparian restoration could prevent the extirpation of Chinook salmon from the more altered stream, and could also restrict bass from occupying the upper 31 km of salmon rearing habitat. The proposed methodology and model predictions are critical for prioritizing climate-change adaptation strategies before salmonids are exposed to both warmer water and greater predation risk by non-native species.

Description: Ecological Applications, Volume 24, Issue 3, Page 528-538, April 2014. A unique high temporal frequency data set from an irrigated cotton–wheat rotation was used to test the agroecosystem model DayCent to simulate daily N2O emissions from subtropical vertisols under different irrigation intensities. DayCent was able to simulate the effect of different irrigation intensities on N2O fluxes and yield, although it tended to overestimate seasonal fluxes during the cotton season. DayCent accurately predicted soil moisture dynamics and the timing and magnitude of high fluxes associated with fertilizer additions and irrigation events. At the daily scale we found a good correlation of predicted vs. measured N2O fluxes (r2 = 0.52), confirming that DayCent can be used to test agricultural practices for mitigating N2O emission from irrigated cropping systems. A 25-year scenario analysis indicated that N2O losses from irrigated cotton–wheat rotations on black vertisols in Australia can be substantially reduced by an optimized fertilizer and irrigation management system (i.e., frequent irrigation, avoidance of excessive fertilizer application), while sustaining maximum yield potentials.

Description: Ecological Applications, Ahead of Print. Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e. cyanobacteria, lichens and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte) and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently-aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: 1) species with high resistance and resilience to grazing, 2) species with high resistance but low resilience, 3) species with low resistance but high resilience, and 4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Description: Ecological Applications, Ahead of Print. Post-fire predictions of forest recovery under future climate change and management actions are necessary for forest managers to make decisions about treatments. We applied the Climate-Forest Vegetation Simulator (Climate-FVS), a new version of a widely used forest management model, to compare alternative climate and management scenarios in a severely burned multi-species forest of Arizona, U.S.A. The incorporation of seven combinations of General Circulation Models (GCM) and emissions scenarios altered long-term (100 years) predictions of future forest condition compared to a No Climate Change (NCC) scenario, which forecast a gradual increase to high levels of forest density and carbon stock. In contrast, emissions scenarios that included continued high greenhouse gas releases led to near-complete deforestation by 2111. GCM-emissions scenario combinations that were less severe reduced forest structure and carbon stock relative to NCC. Fuel reduction treatments that had been applied prior to the severe wildfire did have persistent effects, especially under NCC, but were overwhelmed by increasingly severe climate change. We tested six management strategies aimed at sustaining future forests: prescribed burning at 5, 10, or 20-year intervals, thinning 40% or 60% of stand basal area, and no-treatment. Severe climate change led to deforestation under all management regimes, but important differences emerged under the moderate scenarios: treatments that included regular prescribed burning fostered low density, wildfire-resistant forests composed of the naturally dominant species, ponderosa pine. Non-fire treatments under moderate climate change were forecast to become dense and susceptible to severe wildfire, with a shift to dominance by sprouting species. Current U.S. forest management requires modeling of future scenarios but does not mandate consideration of climate change effects. However, this study showed substantial differences in model outputs depending on climate and management actions. Managers should incorporate climate change into the process of analyzing the environmental effects of alternative actions.

Description: Ecological Applications, Ahead of Print. Digital repeat photography is becoming widely used for near surface remote sensing of vegetation. Canopy greenness, which has been used extensively for phenological applications, can be readily quantified from camera images. Important questions remain, however, as to whether the observed changes in canopy greenness are directly related to changes in leaf-level traits, changes in canopy structure, or some combination thereof. We investigated relationships between canopy greenness and various metrics of canopy structure and function, using five years (2008-2012) of automated digital imagery, ground observations of phenological transitions, leaf area index (LAI) measurements, and eddy-covariance estimates of gross ecosystem photosynthesis from the Harvard Forest, a temperate deciduous forest in the northeastern USA. Additionally, we sampled canopy sunlit leaves on a weekly basis throughout the growing season of 2011. We measured physiological and morphological traits including leaf size, mass (wet/dry), nitrogen content, chlorophyll fluorescence, and spectral reflectance, and characterized individual leaf color with flatbed scanner imagery. Our results show that observed spring and autumn phenological transition dates are well captured by information extracted from digital repeat photography. However, spring development of both LAI and the measured physiological and morphological traits are shown to lag behind spring increases in canopy greenness, which rises very quickly to its maximum value before leaves are even half their final size. Based on the hypothesis that changes in canopy greenness represent the aggregate effect of changes in both leaf-level properties (specifically, leaf color) and changes in canopy structure (specifically, LAI), we developed a two end-member mixing model. With just a single free parameter, the model was able to reproduce the observed seasonal trajectory of canopy greenness. This analysis shows that canopy greenness is relatively insensitive to changes in LAI at high LAI levels, which we further demonstrate by assessing the impact of an ice-storm on both LAI and canopy greenness. Our study provides new insights into the mechanisms driving seasonal changes in canopy greenness retrieved from digital camera imagery. The nonlinear relationship between canopy greenness and canopy LAI has important implications both for phenological research applications and for assessing responses of vegetation to disturbances.

Description: In recent years we have benefitted greatly from the first in-orbit multi-wavelength images of Saturn's polar atmosphere from the Cassini spacecraft. Specifically, images obtained from the Cassini UltraViolet Imaging Spectrograph (UVIS) provide an excellent view of the planet's auroral emissions, which in turn give an account of the large-scale magnetosphere-ionosphere coupling and dynamics within the system. However, obtaining near-simultaneous views of the auroral regions with in situ measurements of magnetic field and plasma populations at high-latitudes is more difficult to routinely achieve. Here we present an unusual case, during Revolution 99 in January 2009, where UVIS observes the entire northern UV auroral oval during a two-hour interval while Cassini traverses the magnetic flux tubes connecting to the auroral regions near 21 LT, sampling the related magnetic field, particle, and radio and plasma wave signatures. The motion of the auroral oval evident from the UVIS images requires a careful interpretation of the associated latitudinally “oscillating” magnetic field and auroral field-aligned current signatures whereas previous interpretations have assumed a static current system. Concurrent observations of the auroral hiss (typically generated in regions of downward directed field-aligned current) support this revised interpretation of an oscillating current system. The nature of the motion of the auroral oval evident in the UVIS image sequence, and the simultaneous measured motion of the field-aligned currents (and related plasma boundary) in this interval, is shown to be related to the northern hemisphere magnetosphere oscillation phase. This is in agreement with previous observations of the auroral oval oscillatory motion.

Description: We have developed a technique by which to estimate the spatial distribution of plasmaspheric helium ions based on extreme ultraviolet (EUV) data obtained from the IMAGE satellite. The estimation is performed using a linear inversion method based on the Bayesian approach. The global imaging data from the IMAGE satellite enables us to estimate a global two-dimensional distribution of the helium ions in the plasmasphere. We applied this technique to a synthetic EUV image generated from a numerical model. This technique was confirmed to successfully reproduce the helium ion density that generated the synthetic EUV data. We also demonstrate how the proposed technique works for real data using two real EUV images.

Description: Ecological Applications, Ahead of Print. The degree to which recent bark beetle (Dendroctonus ponderosae) outbreaks may influence fire severity and post-fire tree regeneration is of heightened interest to resource managers throughout western North America, but empirical data on actual fire effects are lacking. Outcomes may depend on burning conditions (i.e., weather during fire), outbreak severity, or intervals between outbreaks and subsequent fire. We studied recent fires that burned through green-attack / red-stage (outbreaks 〈 3 yr before fire) and gray-stage (outbreaks 3-15 yr before fire) subalpine forests dominated by lodgepole pine (Pinus contorta var. latifolia) in Greater Yellowstone, Wyoming, USA, to determine if fire severity was linked to pre-fire beetle outbreak severity and whether these two disturbances produced compound ecological effects on post-fire tree regeneration. With field data from 143 post-fire plots that burned under different conditions, we assessed canopy and surface fire-severity, and post-fire tree seedling density against pre-fire outbreak severity. In the green-attack / red stage, several canopy fire-severity measures increased with pre-fire outbreak severity under moderate burning conditions. Under extreme conditions, few fire-severity measures were related to pre-fire outbreak severity, and effect sizes were of marginal biological significance. The percentage of tree stems and basal area killed by fire increased with more green-attack vs. red-stage trees (i.e., the earliest stages of outbreak). In the gray stage, by contrast, most fire-severity measures declined with increasing outbreak severity under moderate conditions, and fire severity was unrelated to outbreak severity under extreme burning conditions. Post-fire lodgepole pine seedling regeneration was unrelated to pre-fire outbreak severity in either post-outbreak stage, but increased with pre-fire serotiny. Results suggest bark beetle outbreaks can affect fire severity in subalpine forests under moderate burning conditions, but have little effect on fire severity under extreme burning conditions when most large wildfires occur in this system. Thus, beetle outbreak severity was moderately linked to fire severity, but the strength and direction of the linkage depended on both endogenous (outbreak stage) and exogenous (fire weather) factors. Closely-timed beetle outbreak and fire did not impart compound effects on tree regeneration, suggesting the presence of a canopy seedbank may enhance resilience to their combined effects.

Description: Ecological Applications, Ahead of Print. Ecological reserves provide important wildlife habitat in many landscapes, and the functional connectivity of reserves and other suitable habitat patches is crucial for the persistence and resilience of spatially structured populations. To maintain or increase connectivity at spatial scales larger than individual patches, conservation actions may focus on creating and maintaining reserves and/or influencing management on non-reserves. Using a graph-theoretic approach, we assessed the functional connectivity and spatial distribution of wetlands in the Rainwater Basin of Nebraska, U.S.A., an intensively cultivated agricultural matrix, at four assumed, but ecologically realistic, anuran dispersal distances. We compared connectivity in the current landscape to the historical landscape and putative future landscapes, and evaluated the importance of individual and aggregated reserve and non-reserve wetlands for maintaining connectivity. Connectivity was greatest in the historical landscape, where wetlands were also the most densely distributed. The construction of irrigation reuse pits for water storage has maintained connectivity in the current landscape by replacing destroyed wetlands, but these pits likely provide suboptimal habitat. Also, because there are fewer total wetlands (i.e., wetlands and irrigation reuse pits) in the current landscape than the historical landscape, and because the distribution of current wetlands is less clustered than that of historical wetlands, larger and longer-dispersing, sometimes non-native species may be favored over smaller, shorter-dispersing species of conservation concern. Because of their relatively low number, wetland reserves do not affect connectivity as greatly as non-reserve wetlands or irrigation reuse pits; however, they likely provide the highest-quality anuran habitat. To improve future levels of resilience in this wetland habitat network, management could focus on continuing to improve the conservation status of non-reserve wetlands, restoring wetlands at spatial scales that promote movements of shorter-dispersing species, and further scrutinizing irrigation reuse pit removal by considering effects on functional connectivity for anurans, an emblematic and threatened group of organisms. However, broader conservation plans will need to give consideration to other wetland-dependent species, incorporate invasive species management, and address additional challenges arising from global change in social-ecological systems like the Rainwater Basin.

Description: Ecological Applications, Ahead of Print. Ecosystem-based management of natural resources involves an explicit consideration of trade-offs among ecosystem services. In marine fisheries, there is the potential for a trade-off between the supporting role of small pelagic fish and cephalopods in food webs, and the provisioning service they play as a major target of fisheries. Because these species play central roles in food webs by providing a conduit of energy from small prey to upper trophic level predators, we hypothesized that trade-offs between these two ecosystem services could be predicted based on energetic properties of predator-prey linkages and food web structure. We compiled information from 27 marine food web models (Ecopath) that included either small pelagic fish or cephalopods, described predator-prey linkages involving these species, and developed a novel analytical framework to estimate how changes in yields of forage species would propagate through food webs and other fisheries. Consistent with expectations, diet overlap between predators and prey was generally low, and predator prey linkages tended to be asymmetric; contribution of these species to predator diets was, on average, larger than the contribution of individual predator stocks to prey mortality. The estimated trade-offs between yields of forage fish and predator species were highly variable when we assumed joint bottom-up and top-down control on predation. Roughly one-third of this variance was related to an interactive effect of fishing and predation intensity; strong trade-offs were predicted when fishing intensity on forage species is high and when predators account for a high proportion of total forage mortality. When trophic connections were presumed to be driven by bottom-up processes, trade-offs were more predictable but generally very small. Contrary to our expectations, trade-offs were not easily predicted from energetic properties, largely because predators of forage species exhibited a high degree of intra-guild predation and also consumed many of the same prey as forage species. Given the limited ability to a priori predict the food web implications of forage fisheries, we suggest that a precautionary risk-based approach be applied to decisions about acceptable biological removals of forage fish and biological targets used for their management.

Description: Ecological Applications, Ahead of Print. Accelerating climate change and other cumulative stressors create an urgent need to understand the influence of environmental variation and landscape features on the connectivity and vulnerability of freshwater species. Here, we introduce a novel modeling framework for aquatic systems that integrates spatially-explicit, individual-based, demographic and genetic (demogenetic) assessments with environmental variables. To show its potential utility, we simulated a hypothetical network of 19 migratory riverine populations (e.g., salmonids) using a riverscape connectivity and demogenetic model (CDFISH). We assessed how stream resistance to movement -- a function of water temperature, fluvial distance, and physical barriers -- might influence demogenetic connectivity and hence population vulnerability. We present demographic metrics (abundance, immigration, and change in abundance) and also genetic metrics (diversity, differentiation, and change in differentiation), and combine them into a single vulnerability index for identifying populations at risk of extirpation. We considered four realistic scenarios that illustrate the relative sensitivity of these metrics for early detection of reduced connectivity: (1) maximum resistance due to high water temperatures throughout the network, (2) minimum resistance due to low water temperatures throughout the network, (3) increased resistance at a tributary junction caused by a partial barrier, and (4) complete isolation of a tributary, leaving resident individuals only. We then apply this demogenetic framework using empirical data for a bull trout metapopulation in the upper Flathead River system, Canada and USA, to assess how current and predicted future stream warming may influence population vulnerability. Results suggest that warmer water temperatures and associated barriers to movement (e.g., low flows, de-watering) are predicted to fragment suitable habitat for migratory salmonids, resulting in the loss of genetic diversity and reduced sizes in certain vulnerable population. This demogenetic simulation framework, which is illustrated in a web-based interactive mapping prototype (http://ptolemy.dbs.umt.edu/pvm/), should be useful for evaluating population vulnerability in a wide variety of dendritic and fragmented riverscapes, helping to guide conservation and management efforts for freshwater species.

Description: Ecological Applications, Ahead of Print. Fire regimes of the Canadian boreal forest are driven by certain environmental factors that are highly variable from year to year (e.g., temperature, precipitation) and others that are relatively stable (e.g., land cover, topography). Studies examining the relative influence of these environmental drivers on fire activity suggest that models making explicit use of inter-annual variability appear to better capture years of climate extremes, whereas those using a temporal average of all available years highlight the importance of land-cover variables. It has been suggested that fire models built at different temporal resolutions may provide a complementary understanding of controls on fire regimes, but this claim has not been tested explicitly with parallel data and modelling approaches. We addressed this issue by building two models of area burned for the period 1980-2010 using 14 explanatory variables to describe ignitions, vegetation, climate, and topography. We built one model at an annual resolution, with climate and some land-cover variables being updated annually, and the other model using 31-year fire "climatology" based on averaged variables. Despite substantial differences in the variables' contributions to the two models, their predictions were broadly similar, which suggests coherence between the spatial patterns of annually varying climate extremes and long-term climate normals. Where the models' predictions diverged, discrepancies between the annual and averaged models could be attributed to specific explanatory variables. For instance, annually updating land cover allowed us to identify a possible negative feedback between flammable biomass and fire activity. These results show that building models at more than one temporal resolution affords a deeper understanding of controls on fire activity in boreal Canada than can be achieved by examining a single model. However, in terms of spatial predictions, the additional effort required to build annual models of fire activity may not always be warranted in this study area. From a management and policy standpoint, this key finding should boost confidence in models that incorporate climatic normals, thereby providing a stronger foundation on which to make decisions on adaptation and mitigation strategies for future fire activity.

Description: Ecological Applications, Ahead of Print. Fire is becoming a pervasive driver of environmental change in Amazonia and is expected to intensify, given projected reductions in precipitation and forest cover. Understanding of the influence of post-deforestation land cover change on fires in Amazonia is limited, even though fires in cleared lands constitute a threat for ecosystems, agriculture, and human health. We used MODIS satellite data to map burned areas annually between 2001 and 2010. We then combined these maps with land cover and climate information to understand the influence of land cover change in cleared lands and dry season severity on fire occurrence and spread in a focus area in the Peruvian Amazon. Fire occurrence, quantified as the probability of burning of individual 232m spatial resolution MODIS pixels was modeled as a function of the area of land cover types within each pixel, drought severity, and distance to roads. Fire spread, quantified as the number of pixels burned in 3x3 pixel windows around each focal burned pixel, was modeled as a function of land cover configuration and area, dry season severity, and distance to roads. We found that vegetation regrowth and oil palm expansion are significantly correlated with fire occurrence but that the magnitude and sign of the correlation depend on drought severity, successional stage of regrowing vegetation and oil palm age. Burning probability increased with the area of non-degraded pastures, fallow, and young oil palm and decreased with larger extents of degraded pastures, secondary forests and adult oil palm plantations. Drought severity had the strongest influence on fire occurrence overriding the effectiveness of secondary forests but not of adult plantations to reduce fire occurrence in severely dry years. Overall, irregular and scattered land cover patches reduced fire spread but irregular and dispersed fallows and secondary forests increased fire spread during dry years. Results underscore the importance of land cover management for reducing fire proliferation in this landscape. Incentives for promoting natural regeneration and perennial crops in cleared lands might help reduce fire risk if those areas are protected against burning in early stages of development and during severely dry years.

Description: Ecological Applications, Ahead of Print. Intraguild predators both feed on and compete with their intraguild prey. In theory, intraguild predators can therefore be very effective as biological control agents of intraguild prey species, especially in productive environments. We investigated this hypothesis using the mixotrophic chrysophyte Ochromonas as intraguild predator and the harmful cyanobacterium Microcystis aeruginosa as its prey. Ochromonas can grow photoautotrophically, but can also graze efficiently on Microcystis. Hence, it competes with its prey for inorganic resources. We developed a mathematical model and parameterized it for our experimental food web. The model predicts dominance of Microcystis at low nutrient loads, coexistence of both species at intermediate nutrient loads, and dominance of Ochromonas but a strong decrease of Microcystis with further nutrient enrichment. We tested these theoretical predictions in chemostat experiments supplied with three different nitrogen concentrations. Ochromonas initially suppressed the Microcystis abundance by 〉 97% compared to the Microcystis monocultures. Thereafter, however, Microcystis gradually recovered to ~20% of its monoculture abundance at low nitrogen loads, but to 50-60% at high nitrogen loads. Hence, Ochromonas largely lost control over the Microcystis population at high nitrogen loads. We explored several mechanisms that might explain this deviation from theoretical predictions, and found that intraspecific interference at high Ochromonas densities reduced their grazing rates on Microcystis. These results illustrate the potential of intraguild predation to control pest species, but also show that the effectiveness of their biological control can be reduced in productive environments.

Description: Ecological Applications, Ahead of Print. A novel strategy for suppressing disease transmission by Aedes aegypti, the main vector of dengue, uses releases of mosquitoes infected with the bacterium Wolbachia pipientis. Wolbachia are currently released to interfere with viral transmission, but there is also potential to use strains in mosquito suppression and elimination programs via the deleterious effects of the bacterium on the host. Mosquito suppression depends on target areas being relatively isolated to prevent reinvasion and on local climatic conditions. Here we explored the opportunity for suppression of Ae. aegypti in central Queensland, Australia, by using microsatellite data and simulations based on CIMSiM models of local weather conditions and breeding container data. Our results indicate that Wolbachia-induced extinctions in central Queensland are possible, although they may eventually be compromised by ongoing mosquito migration between towns until these sources are also suppressed. The results highlight a novel use of deleterious Wolbachia infections to achieve ecological as well as disease-related endpoints.

Description: Ecological Applications, Ahead of Print. The decreasing abundance of mature forests and their fragmentation have been identified as major threats for the preservation of biodiversity in managed landscapes. In this study, we developed a multi-level framework to coordinate forest harvestings so as to optimize the retention or restoration of large mature forest tracts in managed forests. We used mixed-integer programming for this optimization, and integrated realistic management assumptions regarding stand yields and operational harvest constraints. The model was parameterized for eastern Canadian boreal forests, where clearcutting is the main silvicultural system, and used to examine two hypotheses. First, we tested if mature forest tract targets had more negative impacts on wood supplies when implemented in landscapes that are very different from targeted conditions. Second, we tested the hypothesis that using more partial cuts can be useful to attenuate the negative impacts of mature forest targets on wood supplies. The results indicate that without the integration of an explicit mature forest tract target, forest management strategies lead to relatively high fragmentation levels. Forcing the retention or restoration of large mature forest tracts on 40% of the landscapes had negative impacts on wood supplies in all types of landscapes, but these impacts were less important in landscapes that were initially fragmented. This counter-intuitive result is explained by the presence in the models of an operational constraint that forbids diffuse patterns of harvestings, which are more costly. Once this constraint is applied, the residual impact of the mature forest tract target is low. The results also indicate that partial cuts are of very limited use to attenuate the impacts of mature forest tract targets on wood supplies in highly fragmented landscapes. Partial cuts are somewhat more useful in landscapes that are less fragmented, but they have to be well coordinated with clearcut schedules in order to contribute efficiently to conservation objectives. This modelling framework could easily be adapted and parameterized to test hypotheses or to optimize restoration schedules in landscapes where issues such as forest fragmentation and the abundance of mature or old-growth forests are a concern.

Description: Ecological Applications, Ahead of Print. Cellulose δ18O and δD can provide insights on climates and hydrological cycling in the distant past and how these factors differ spatially. However, most studies of plant cellulose have used only one isotope, most commonly δ18O, resulting in difficulties partitioning variation in δ18O of precipitation versus evaporative conditions that affect leaf water isotopic enrichment. Moreover, observations of pronounced diurnal differences from conventional steady-state model predictions of leaf water isotopic fractionation have cast some doubt on single isotope modeling approaches for separating precipitation and evaporation drivers of cellulose δ18O or δD. We explore a dual isotope approach akin to the concept of deuterium-excess (d), to establish deuterium deviations from the global meteoric water line in leaf water (Δdl) as driven by relative humidity (RH). To demonstrate this concept, we survey studies of leaf water δ18O and δD in hardwood versus conifer trees. We then apply the concept to cellulose δ18O and δD using a mechanistic model of cellulose δ18O and δD to reconstruct deuterium deviations from the global meteoric water line (Δdc) in Quercus macrocarpa, Q. robur and Pseudotsuga menziesii. For each species Δdc showed strong correlations with RH across sites. Δdc agreed well with steady state predictions for Q. macrocarpa while for Q. robur the relationship with RH was steeper than expected. The slope of Δdc versus RH of P. menziesii was also close to steady state predictions, but Δdc were more enriched than predicted. This is in agreement with our leaf water survey showing conifer Δdl was more enriched than predicted. Our data reveal that applications of this method should be appropriate for reconstructing RH from cellulose δ18O and δD after accounting for differences between hardwoods and conifers. Hence, Δdc should be useful for understanding variability in RH associated with past climatic cycles, across regional climates, or across complex terrain where climate modeling is challenging. Furthermore, Δdc and inferred RH values should help in constraining variation in source water δ18O.

Description: Ecological Applications, Ahead of Print. The size, shape, and connectivity of water bodies (lakes, ponds, and wetlands) can have important effects on ecological communities and ecosystem processes, but how these characteristics are influenced by land use and land cover change over broad spatial scales is not known. Intensive alteration of water bodies during urban development, including construction, burial, drainage, and reshaping, may select for certain morphometric characteristics and influence the types of water bodies present in cities. We used a database of over 1 million water bodies in 100 cities across the conterminous United States to compare the size distributions, connectivity (as intersection with surface flow lines), and shape (as measured by shoreline development factor) of water bodies in different land cover classes. Water bodies in all urban land covers were dominated by lakes and ponds, while reservoirs and wetlands comprised only a small fraction of the sample. In urban land covers, as compared to surrounding undeveloped land, water body size distributions converged on moderate sizes, shapes toward less tortuous shorelines, and the number and area of water bodies that intersected surface flow lines (i.e. streams and rivers). Potential mechanisms responsible for changing the characteristics of urban water bodies include: preferential removal, physical reshaping or addition of water bodies, and selection of locations for development. The relative contributions of each mechanism likely changes as cities grow. The larger size and reduced surface connectivity of urban water bodies may affect the role of internal dynamics and sensitivity to catchment processes. More broadly, these results illustrate the complex nature of urban watersheds and highlight the need to develop a conceptual framework for urban water bodies.