ALBERT

Description: Interferometry measurements of range spread meteor trail echoes (RSTEs; also known as nonspecular echoes) have provided new insights into both the irregularity structures in meteor trails and lower-thermospheric winds (LTWs). In this study, we used trail echoes observed with the newly installed Sanya (18.4°N, 109.6°E) 47.5 MHz VHF coherent radar and the Sanya all-sky meteor radar to estimate instantaneous zonal and hourly averaged meridional winds from RSTEs and hourly averaged zonal and meridional winds from large numbers of specular meteor echoes. The mean height variations in both the zonal and meridional winds estimated from the RSTEs were generally consistent with those estimated from specular meteor echoes below 96 km. This gives validity to the technique proposed recently by Oppenheim et al. (2009) and suggests that RSTE measurements made with a small radar can be used to investigate LTWs, whereas this had previously been limited to larger radars such as the Jicamarca radar. However, some observations show significant differences in wind magnitude at individual heights at times. The results of RSTE measurements show the presence of an intense westward wind with a speed near 100 ms−1. In contrast, the specular meteor zonal winds were generally less than 50 ms−1. On the other hand, the meridional drift of RSTEs derived from the meridional Doppler velocity at higher altitudes shows a very poor correlation with the specular meteor meridional wind. Potential causes for the discrepancy in wind estimates obtained from RSTE and specular meteor trail echoes are discussed.

Description: High precision observations during Solar Cycle 23 using the Wisconsin H-alpha Mapper (WHAM) Fabry-Perot quantify a factor of 1.5 ± 0.15 higher Balmer α column emission intensity during near-solar-maximum than during solar minimum conditions. An unresolved question is how does the observed solar cycle variation in the hydrogen column emission compare with that calculated from the hydrogen distribution in atmospheric models? We have compared WHAM solar minimum and near-solar-maximum column intensity observations with calculations using the thermospheric hydrogen density profile and background thermospheric conditions from the Mass Spectrometer Incoherent Scatter (NRLMSISE-00) empirical model extended to exospheric altitudes using the analytic exosphere model of Bishop (1991). Using this distribution, we apply the lyao_rt global resonance radiative transfer code of Bishop (1999) to calculate expected intensities that would be observed from the ground for the viewing conditions of the observations. The observed intensities are brighter than those calculated for the corresponding conditions, indicating that when MSIS is used as the thermospheric hydrogen distribution the derived intensities are too low. Additionally, both the observed and calculated WHAM hydrogen column emission intensities are higher for near-solar-maximum than for solar minimum conditions. There is better agreement between observations and intensities calculated using the evaporative analytic exosphere model at solar maximum, suggesting an underestimation of modeled satellite atoms at high altitudes. This result is consistent with sensitivity studies using the option for a quasi-exobase for satellite atoms to account for the creation of satellite orbits from charge exchange collisions.

Description: The main goal of this paper is to estimate the errors involved in applying a quasi-static convection model such as the Rice Convection Model (RCM) or its equilibrium version (RCM-E), which neglect inertial currents, to treat the injection of fresh particles into the inner magnetosphere in a substorm expansion phase. The approach is based on the idea that the dipolarization process involves earthward motion of a bubble that consists of flux tubes that have lower values of the entropy parameter than the surrounding medium. Our tests center on comparing MHD simulations with RCM- and RCM-E-like quasi-static approximations, for cases where the bubble is considered to be a thin ideal-MHD filament. Those quasi-static solutions miss the interchange oscillations that are often a feature of the MHD results. RCM and, to a lesser extent, RCM-E calculations tend to overestimate the westward electric field at the ionospheric footprint of the bubble and underestimate its duration. However, both get the time integral of the E × B drift velocity right as well as the net energization of the particles in the filament. The quasi-static approximation is most accurate if its computed value of the braking time of the bubble's earthward motion is long compared to the period of the relevant interchange oscillation. Comparison of MHD filament simulations of interchange instability with corresponding RCM calculations suggests a similar validity criterion. For plasma sheet conditions, the quasi-static approximation is typically best if the background medium has low β, worst if it consists of highly stretched field lines.

Description: The Geoelectrodynamics and Electro-Optical Detection of Electron and Suprathermal Ion Currents (GEODESIC) sounding rocket encountered more than 100 filamentary density cavities associated with enhanced plasma waves at ELF (

Description: This paper presents a quantitative theory of “interchange oscillations,” which occur as an earthward-moving low-entropy plasma bubble slows and eventually comes to rest. Our theoretical picture is based on an idealized situation where an ideal-MHD magnetic filament moves without friction through a stationary background that represents the plasma sheet. If the relevant region of the background plasma sheet is interchange stable, then the filament usually executes a damped oscillation about an equilibrium position, where its entropy parameter matches the local background. The oscillations are typically dramatic only if the equatorial plasma beta is greater than about one. We derive an approximate analytic formula for the oscillation period, which is not simply related to slow- or intermediate-wave travel times. For an oscillation that Panov and collaborators carefully studied using THEMIS data, our simple theory, though based on an unrealistic 2D background magnetic field, predicted an oscillation period that agrees with the observations within about 40%. The simulations suggest that the ionospheric oscillation should lag behind the magnetospheric one by between 40 and 90 degrees. Ionospheric conductance affects the damping rate, which maximizes for an auroral zone conductance ∼2 S. Adding a friction force acting between the filament and the background increases the decay rate of the oscillation.

Description: We present an improved time-domain model of the lightning electromagnetic pulse (EMP) interaction with the lower ionosphere. This improved model inherently accounts for the Earth's curvature, includes an arbitrary number of ion species, and uses a convolutional Perfectly Matched Layer (PML) boundary. We apply an improved model of electron heating due to the lightning EMP and electrostatic fields, and we include ionization, attachment, and detachment. In addition to modeling lightning, this model can be used for long-distance VLF wave propagation in the Earth-ionosphere waveguide, heating of the lower ionosphere by VLF transmitters, and heating in the F-region ionosphere by lightning. In this paper we present three initial results of this model. First, we compare results of ionospheric heating and electron density disturbances with and without electron detachment taken into account. We find that detachment is important only for the QE effects on time scales longer than 1 ms. Second, we find a simple explanation for the recently-reported “elve doublets”, which we find are an effect of the rise and fall times of the lightning waveform. In particular, we find that all elves are doublets, and the rise and fall times of the current pulse control the brightness and separation in time of the two successive halves of the elve. Third, we find a similar simple explanation for “ring” sprites, whole columns appear in a circle symmetric around the discharge axis. We find that ring sprites can be initiated for particular current waveforms, where the QE and EMP fields in the mesosphere produce a maximum reduced field away from the discharge axis.

Description: Ground based optical instruments are invaluable tools for studies of processes associated with the cusps and auroral morphology. In this work we present a method for obtaining the magnetic latitude of the open/closed field line boundary (OCB) from the cusp 6300 Å[OI] auroral red line using a meridian scanning photometer. The method which is based on a pre-defined reference cusp aurora produced by the GLOW model is examined with respect to uncertainties, and we describe how a set of equations describing the error is constructed. The method is applicable to data from optical instruments located at high latitude observation sites such as Svalbard and Antarctica. Equations describing both errors and the mapping altitude for transforming the OCB from instrument centered coordinates to magnetic latitude for instrumentation located in Svalbard (Longyearbyen) are presented. Further, by applying the GLOW model we present results illustrating the great variability in the altitude profile of the atomic oxygen 6300 Å[OI] red line emission in the cusp. A simple calculation showing how a poleward neutral wind will change the latitudinal shape of the cusp aurora is also performed.

Description: Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude side of the auroral oval. The pulsating aurora was observed by a 30-Hz sampled all-sky imager (ASI) at Gillam (56.4°N, 265.4°E), Canada, at ∼0840-0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at ∼0.1–0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian-scanning photometer. After auroral pulsation began at ∼0842 UT, both THD and THEMIS E which was near THD in the mid-tail at 11.6–11.8 RE, observed enhanced field-aligned electron fluxes at energies of 1–10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5–9 RE. We suggest that the observed field-aligned electrons, which are probably caused by Fermi-type acceleration associated with earthward plasma flow in the mid-tail plasma sheet, are modulated by some wave processes to cause pulsating auroras.

Description: We performed three-dimensional Hall magnetohydrodynamic (MHD) simulations of magnetic reconnection with finite width along the direction perpendicular to the antiparallel magnetic field (i.e., the direction of the electric current). Previous similar simulations including the Hall term have shown that the localized reconnection region itself can broaden in the anticurrent direction when the initial current is carried only by electrons. However, there is still no clear understanding of the behavior of the reconnection region in the presence of the initial ion current as in the Earth's magnetotail plasma sheet since no simulations have been carried out under such situations. In this study, we performed a systematic parametric survey considering the cases in which the initial current is carried not only by electrons but also by ions and found that the speed and direction of the current-aligned broadening of the reconnection region are almost equal to those of background ion and electron flows that carry the current. This result means that location and size of the localized reconnection region vary with time, depending on plasma conditions in the background current sheet in Hall MHD regime. The rate of the localized reconnection can reach close to the value in the two-dimensional case, even when reconnection starts in an extremely narrow region with its current-aligned width equal to an ion inertial length. The localized reconnection process also produces the asymmetry of the current-aligned structure of the reconnection jet. These results can explain various observational features related to magnetic reconnection in the near-Earth magnetotail.

Description: This first paper in a two part series summarizes the current theory and the data-driven solar wind model for simulating dynamic spectra of type II radio bursts. It also introduces performance metrics and techniques for extraction of model shock parameters from these dynamic spectra. We use an iterative downhill simplex method which compares two dynamic spectra and quantitatively assesses and improves the agreement using two figures of merit: the first is based on the correlation function and the second is based on a normalized differences over the data set. By maximizing the agreement we are able to extract the input model shock parameters to within 30% or better when using model solar winds of increasing complexity. The effects on the spectra predicted and on the figures of merit from changing the model shock parameters and solar wind model are also investigated. The iterative downhill extraction method is then applied to the type II dynamic spectrum predicted using a realistic model solar wind and a shock model estimated for an observed type II event. The shock parameters are recovered to within 10% of the correct solution.

Description: Beat-wave generation of very low frequency (VLF) waves by two HF heaters in the ionosphere is formulated theoretically and demonstrated experimentally. The heater-induced differential thermal pressure force and ponderomotive force, which dominate separately in the D and F regions of the ionosphere, drive an electron current for the VLF emission. A comparison, applying appropriate ionospheric parameters shows that the ponderomotive force dominates in beat-wave generation of VLF waves. Three experiments, one in the nighttime in the absence of D and E layers and two in the daytime in the presence of D and E layers, were performed. X mode HF heaters of slightly different frequencies were transmitted at CW full power. VLF waves at 10 frequencies ranging from 3.5 to 21.5 kHz were generated. The frequency dependencies of the daytime and nighttime radiation intensities are quite similar, but the nighttime radiation is much stronger than the daytime one at the same radiation frequency. The intensity ratio is as large as 9 dB at 11.5 kHz. An experiment directly comparing VLF waves generated by the beat-wave approach and by the amplitude modulation (AM) approach was also conducted. The results rule out the likely contribution of the AM mechanism acting on the electrojet and indicate that beat-wave in the VLF range prefers to be generated in the F region of the ionosphere through the ponderomotive nonlinearity, consistent with the theory. In the nighttime experiment, the ionosphere was underdense to the HF heaters, suggesting a likely setting for effective beat-wave generation of VLF waves by the HF heaters.

Description: Infrared radiative emissions by carbon dioxide (CO2) and nitric oxide (NO) are the major cooling mechanisms of the lower thermosphere. During geomagnetically active periods, the NO density and cooling rate in the auroral regions increase significantly as a result of particle precipitation and Joule heating. Previous studies have shown that the time for NO density to recover to quiet time levels is longer than that of the thermosphere temperature or density recovery. This study explores the implications of these different recovery rates for the post-storm thermosphere. Thermosphere densities retrieved from the CHAMP and GRACE accelerometer measurements and NO cooling rates measured by TIMED/SABER are used to examine their variations during the post-storm period of the October 2003 geomagnetic storms. It was found that thermosphere densities at both CHAMP and GRACE altitudes recovered rapidly and continuously decreased below the quiet time densities during the post-storm period, especially at middle latitudes. Compared with the quiet time values, the maximum depletion in the CHAMP and GRACE densities after the storm is about 23–36%, and the estimated decrease of thermospheric temperature is as large as 70–110 K. Our analysis suggests that the elevated NO cooling rate, resulting from the slower recovery of NO densities in the post-storm period, is a plausible cause for this apparent post-storm overcooling of the thermosphere.

Description: In this paper we present and analyze the Gadanki radar observations of an unusual event of daytime radar echoes from the E region, which spread over a range of 105–150 km and displayed a “U shape” in the range-time SNR map. The U shape echoing structure was an added feature to the commonly observed lower E region echoes with slowly descending features and 150 km echoes with range migration displaying a forenoon descent and afternoon ascent. Distinctly different Doppler velocities were observed in the two arms of the U shape structure with velocities increasing with height and surprisingly exceeding the Doppler velocities of the 150 km echoes. The Doppler spectra display features very similar to those observed below 100 km indicating turbulence as the underlying process. A collocated ionosonde observed unusually strong sporadic E (Es) activity with maximum reflected/scattered frequency (ftEs) reaching 16 MHz in close correspondence with the U shape structure. During the same duration, a collocated 250.6 MHz scintillation receiver revealed scintillation activity, not observed before from Gadanki. The unusual radar observations, strong Es activity, and daytime scintillation are first of its kind from Gadanki. Detailed analysis suggests that the U shape radar echoes extending to 150 km range were due to the sidelobe detection of the E region irregularities with special features that were also responsible for the daytime scintillation. The genesis and implication of the irregularities are discussed.

Description: The statistical characteristics of small-scale spatial and temporal electric field variability in the high-latitude regions of Earth's ionosphere are investigated using 48 months of data from the Super Dual Auroral Radar Network (SuperDARN) radars in both hemispheres. Electric field fluctuations on spatial scales between 45 km and 450 km and on temporal scales between 2 min and 20 min are considered. It is found that both the distribution shapes and scale-size dependencies of the fluctuations are consistent with the expected properties of a turbulent flow. The observed spatial and temporal variability is influenced primarily by the magnitude of the shear or gradient in the background plasma drift and by season and solar cycle, suggesting plasma instabilities and gradients in the conductance as sources of the electric field variability. The relationship between spatial and temporal variability is investigated and it is found that the fluctuations are likely to be a mixture of convecting static and time-varying structures. It is also observed that the small-scale variability has statistical characteristics that are very similar in the two hemispheres. For practical purposes, although a stretched exponential function best matches the data, the distribution of observed electric field fluctuations can be approximated using an exponential function, enabling straightforward generation of nearly realistic random fluctuations.

Description: In this paper we validate the method of Johnsen et al. (2012) for obtaining the cusp open/closed field line boundary (OCB) by the means of a single meridian scanning photometer (MSP). Three cases of conjugate measurements between the Longyearbyen MSP and the NOAA-16 satellite are presented. The satellite OCB as obtained by the energetic particle detectors carried onboard the NOAA-16 satellite is well co-located with the OCB as obtained by the ground-based MSP and well within the calculated uncertainties. We conclude that the method presented by Johnsen et al. (2012) for deriving the cusp OCB using a single MSP produces conscientious results.

Description: We extend traditional, single payload, interferometric techniques to a multiple payload sounding rocket mission, and apply these techniques to measure the parallel and perpendicular wavelength of auroral VLF hiss from 8 kHz–20 kHz. We model the wavelength distribution of auroral hiss as a cone at a fixed angle with respect to the magnetic field that is isotropically distributed in the perpendicular plane. We apply this model to calculate the interferometric observables, coherency and phase, for a sounding rocket mission whose wave electric field receivers are on payloads that are separated 2–3 km along the magnetic field and 55–200 m across the magnetic field. Using an interferometer formed by comparing the collinear sphere-to-skin electric field antennas on a single payload, we estimate a lower limit on the perpendicular wavelength of VLF hiss of ∼60 m. Analysis of coherency and phase due to this conical wave vector distribution for a multipayload interferometer reveals the existence of a spin dependent coherency pattern. From this coherency pattern we generate an upper limit perpendicular wavelength estimate for VLF hiss of ∼350 m. The inter-payload phase gives an accurate estimate of the parallel wavelength of ∼6000–8000 m. This parallel wavelength is combined with the lower (upper) limit perpendicular wavelength estimates to generate upper (lower) limits on wave-normal angle. These limits are each within one degree of the predicted electrostatic whistler wave resonance cone angle verifying that VLF hiss propagates on this resonance cone.

Description: The wave number 4 (wave 4) and wave number 3 (wave 3) longitudinal structures in the thermospheric neutral mass density are understood as tidal structures driven by diurnal eastward propagating zonal wave number 3 (DE3) and wave number 2 (DE2) tides, respectively. However, those structures have been identified using data from limited time periods, and the consistency and recurrence of those structures have not yet been examined using long-term observation data. We examine the persistence of those structures by analyzing the neutral mass density data for the years 2001–2008 taken by the Challenging Minisatellite Payload (CHAMP) satellite. During years of low solar activity the amplitude of the wave 4 structure is pronounced during August and September, and the wave 4 phase shows a consistent eastward phase progression of 90° within 24 h local time in different months and years. During years of high solar activity the wave 4 amplitude is small and does not show a distinctive annual pattern, but the tendency of the eastward phase shift at a rate of 90°/24 h exists. Thus the DE3 signature in the wave 4 structure is considered as a persistent feature. The wave 3 structure is a weak feature in most months and years. The amplitude and phase of the wave 3 structure do not show a notable solar cycle dependence. Among the contributing tidal modes to the wave 3 structure, the DE2 amplitude is most pronounced. This result may suggest that the DE2 signature, although it is a weak signature, is a perceivable persistent feature in the thermosphere.

Description: Recent observations in the inner magnetotail have shown rapid and significant flux increases (usually an order of magnitude of increase within seconds) of suprathermal electrons (tens of keV to hundreds of keV) associated with earthward moving dipolarization fronts. To explain where and how these suprathermal electrons are produced during substorm intervals, two types of acceleration models have been suggested by previous studies: acceleration that localizes near the reconnection site and acceleration that occurs during earthward transport. We perform an analytical analysis of adiabatic acceleration to show that the slope of source differential fluxes is critical for understanding adiabatic flux enhancements during earthward transport. Observationally, two earthward propagating dipolarization fronts accompanied by energetic electron flux enhancements observed by the THEMIS spacecraft have been analyzed; in each event the properties of dipolarization fronts in the inner magnetosphere (XGSM ≈ −10RE) were well correlated with those further down the tail (XGSM ≈ −15RE or XGSM ≈ −20RE). Coupled with theoretical analysis, this enables us to estimate the relative acceleration that occurred as the electrons propagated earthward between the two spacecraft. During the two events studied, the differential fluxes of supra thermal electrons had steep energy spectra with power law indices of −4 to −6.These spectra were much steeper than those at lower energy, as well as those of the supra thermal electrons observed before the fronts arrived. A compression factor of 1.5 as the electrons propagated earthward induced a flux increase of suprathermal electrons by a factor of 7 to 17. Provided these steep spectra, we demonstrate that adiabatic acceleration from the betatron and Fermi mechanisms simultaneously operating can account for these flux increases. Since both analytical analysis and data from the two events show that adiabatic acceleration during earthward transport does not significantly change the power law indices, the steep spectra were likely to be traced back to their source region, presumably near the reconnection site.

Description: Ionospheric Sq current systems during unusually strong and prolonged stratospheric sudden warming (SSW) events in January 2006 and January 2009 are examined by analyzing ground-magnetometer data for the American and Asian longitude sectors. During these SSW events, a significant decrease and increase of the Sq equivalent current intensity are observed in the Northern and Southern Hemispheres, respectively, along with a reduction in the longitudinal separation between the northern and southern current vortices. Numerical experiments using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model show that changes in the solar anti-symmetric (2,3) semidiurnal tide can bring about similar changes in the Sq current system.

Description: The extreme ultraviolet (EUV) imager on the IMAGE satellite provided the first global images of the plasmasphere leading to enhanced understanding of plasmapause structure and dynamics. However, few studies have investigated the structure and dynamics of the inner plasmasphere (regions interior to the plasmapause), which previous in situ observations have shown to often be highly structured. This study is the first to systematically analyze global images of the density structure of the inner plasmasphere by using data from the EUV imager on the IMAGE satellite. We find that the inner plasmasphere exhibits both fine and meso-scale structure characterized by rapid density fluctuations and density enhancements of varying amplitudes (factors of ∼ 2–5) and spatial scales (from 10 s of minutes to 6 hours MLT) that occur regularly in the aftermath of geomagnetic storms. The level of variability within the azimuthal structure was found to increase with increasing geomagnetic activity. The observations suggest that some meso-scale azimuthal density structure observed in the inner plasmasphere is from “fossil” plasmapause features entrained inside the expanding and refilling plasmasphere.

Description: A new empirical model of radiation-belt electrons in the low-Earth-orbit region has been developed based upon decade-long in situ observations from several low-altitude-orbiting satellites. This model—LEEM—aims to provide the electron environment conditions that a satellite would encounter in a given low Earth orbit. This model presents electron flux values for five energy ranges (0.03–2.5 MeV, 0.1–2.5 MeV, 0.3–2.5 MeV, 1.5–6 MeV, and 2.5–14 MeV) within the space below an altitude of ∼600 km. Compared to the de-facto standard empirical model of AE-8, this model not only has a better data coverage in this specific region, but also can provide statistical information on flux levels such as worst cases and occurrence percentiles instead of solely mean values. The comparison indicates that the AE-8 model not only highly overpredicts the fluxes in the inner belt region in most cases, especially for the MeV electrons, which cannot be accounted for by the widely quoted error factor of 2 for AE-8, but also is unable to reflect the observed orders of magnitude variations in electron intensities. The LEEM model is carefully validated with both in-sample and out-of-sample tests. The characteristic electron environments along the International Space Station track and other virtual orbits are given as examples and as a demonstration of the use of the model.

Description: The ionosphere response resulting from minimum solar activity during cycle 23/24 was unusual and offered unique opportunities for investigating space weather in the near-Earth environment. We report ultra low frequency electric field signatures related to the ionospheric Alfvén resonator detected by the Communications/Navigation Outage Forecasting System (C/NOFS) satellite in the equatorial region. These signatures are used to constrain ionospheric empirical models and offer a new approach for monitoring ionosphere dynamics and space weather phenomena, namely aeronomy processes, Alfvén wave propagation, and troposphere-ionosphere-magnetosphere coupling mechanisms.

Description: This paper reports the existence of plasma caves, minima in the electron density located at 5–10° to the magnetic equator, in the bottomside ionosphere based on electron densities simulations from the International Reference Ionosphere (IRI-2007) and clear evidences given by plasma density and drift measurements of the Dynamic Explorer 2 (DE 2) satellite during 1981–1983. The IRI simulations suggest plasma caves as daytime features (08:00–19:00 LT; length of 18,158 km in the longitudinal direction), that range from the E region up to about 300 km altitude with 10° (or 1100 km) width in the latitudinal direction. In situ measurements of the ion and electron densities probed by the DE 2 confirm the existence of the plasma caves at low altitudes of the EIA ionosphere. The unexpected downward and upward (or weakly and strongly upward) ion drifts at the magnetic equator and the two off equators seem to play an important role responsible for the plasma cave formation.

Description: The interaction between interplanetary shocks and the Earth's magnetosphere manifests in many important space physics phenomena including particle acceleration. We investigated the response of the inner magnetospheric hydrogen and oxygen ions to a strong interplanetary shock impinging on the Earth's magnetosphere. Both hydrogen and oxygen ions are found to be heated/accelerated significantly with their temperature enhanced by a factor of two and three immediately after ∼1 min and ∼12 min of the shock arrival respectively. Multiple energy dispersion signatures of ions were found in the parallel and anti-parallel direction to the magnetic field immediately after the interplanetary shock impact. The energy dispersions in the anti-parallel direction preceded those in the parallel direction. Multiple dispersion signatures can be explained by the flux modulations of local ions (rather than the ions from the Earth's ionosphere) by ULF waves. It is found that the energy spectrum from 10 eV to ∼40 keV are highly correlated with the cross product of observed ULF wave electric and magnetic field (V = (E × B)/B2), which indicate that both cold plasmaspheric plasma and hot thermal ions (10 eV to ∼40 keV) are accelerated and decelerated with the various phases of ULF wave electric field. We then demonstrate that ion acceleration due to the interplanetary shock compression on the Earth's magnetic field is rather limited, whereas the major contribution to acceleration comes from the electric field carried by ULF waves via drift-bounce resonance for both the hydrogen and oxygen ions. The integrated hydrogen and oxygen ion flux with the poloidal mode ULF waves are highly coherent (〉0.9) whereas the coherence with the toroidal mode ULF waves is negligible, implying that the poloidal mode ULF waves are much more efficient in accelerating hydrogen and oxygen ions in the inner magnetosphere than the toroidal mode ULF waves. The duration of high coherence for oxygen ions with the poloidal mode ULF wave is longer than that for hydrogen ions, indicating that oxygen ions can be heated/accelerated more efficiently by the poloidal mode ULF wave induced by the interplanetary shock.

Description: We present a generalized multipoint analysis of physical quantities, such as magnetic field and plasma flow, based on spatial gradient properties, where the multipoint data may be taken by irregular (distorted) configurations of any number of spacecraft. The methodology is modified from a previous, fully 3-D gradient analysis technique, designed to apply strictly to 4-point measurements and to be stable for regular spacecraft configurations. Here, we adapt the method to be tolerant against distorted configurations and to return a partial result when fewer spacecraft measurements are available. We apply the method to a variety of important physical quantities, such as the electric current density and the vorticity of plasma flows based on Cluster and THEMIS multiple-point measurements. The method may also have valuable applications on the coming Swarm mission.

Description: When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. While these periods are usually considered “quiet,” they can lead to intense localized energy deposition into the dayside ionosphere. We analyze two intervals during the geomagnetic storm on 24 August 2005: one with steady duskward IMF and one with steady dawnward IMF. Using outputs from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) and data from the Defense Meteorological Satellite Program, we show that intense Joule heating exists on fast ionospheric flow channels which lie on open field lines. In addition, the flow channels on open field lines have large components in the sunward direction and therefore resist the bulk solar wind and magnetosheath flow. We compare observed velocities with predicted reconnection jet speeds using magnetosheath and cusp parameters from an MHD simulation. Results suggest that the fast ionospheric flow corresponds to portions of the reconnection jet populated by low-density plasma. The importance of ionospheric conductance in determining the ionospheric flow is also discussed.

Description: We report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 July 2009. Sixteen and sixty-three tweek atmospherics were observed at Moshiri and Kagoshima, Japan, where the magnitudes of the solar eclipse were 0.458 and 0.966, respectively. This was the first observation of tweek atmospherics during a low-magnitude eclipse (0.458). The average and standard deviation of the reflection height were 94.9 ± 13.7 km at Moshiri and 87.2 ± 12.9 km at Kagoshima. The reflection height at Moshiri was almost the same as that for normal nighttime conditions in July (96.7 ± 12.6 km) in spite of the low magnitude of the eclipse. The reflection height at Kagoshima seems be divided into two parts: propagation across the total solar eclipse path and propagation in the partial solar eclipse path. During the eclipse, we also observed the phase variation in the LF transmitter signals. The average change in the phase delay of the LF signals was 109° for the paths that crossed the eclipse path and 27° for the paths that did not cross the eclipse path. Assuming a normal daytime height for LF waves of 65 km, a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5–6 km for the paths across the eclipse and 1–2 km for partial eclipse paths. The wide range of estimated tweek reflection heights at Kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses.

Description: We have quantitatively investigated the radiation belt dynamic variations of 1.5–6.0 MeV electrons during 54 coronal mass ejection (CME)–driven storms from 1993 to 2003 and 26 corotating interaction region (CIR)–driven recurrent storms in 1995 by utilizing case and statistical studies based on the data from the SAMPEX satellite. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore, we have constructed the radiation belt content (RBC) index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the prestorm average RBC index, we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt, although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit.

Description: In this paper, we study for the first time the daytime vertical E × B drift velocities from Gadanki and Kototabang using the Doppler shifts of the 150-km echoes observed during 2008–2010, a period of low solar activity. Drift velocities are mostly positive and confined to 35 m s−1 at both the locations, except for Gadanki where on a few occasions negative drift velocities have been observed in the afternoon hours. Drift velocities generally show a decreasing trend with local time and the largest drift is generally observed in the forenoon hours consistent with extensively reported observations and models of E × B drift. Drift velocities from Gadanki and Kototabang compared exceeding well on some days and differed remarkably on many days despite the fact that they are longitudinally separated by only 20°. The day-to-day variation in the drift velocity could be as high as 15 m s−1 at Gadanki and 7 m s−1 at Kototabang. Seasonal mean drifts over Gadanki are found to be generally larger than those of Kototabang. The observations have been compared in detail with those reported earlier based on ground- and satellite- based observations and also with the Scherliess-Fejer model. The observed differences in the drifts at the two locations, including the downward drifts, have been discussed in the light of current understanding of the longitudinal variability of E × B drift.

Description: While the outer radiation belt (3.5 〈 L 〈 8.0) is highly variable with respect to geomagnetic activity, the inner radiation belt (1.2 〈 L 〈 2.0) is relatively stable. Less attention has been paid to the inner electron belt in recent years. It has been generally accepted that the equilibrium structure of radiation belt electrons is explained by the slow inward radial diffusion from a source in the outer belt and losses by Coulomb collision and wave-particle interaction. In this study, we examine this well accepted theory using the radial profiles of the phase space density (PSD), inferred from in situ measurements made by three different satellites: S3–3, CRRES, and POLAR. Our results show that electron PSD in the inner electron belt has a clear prominent local peak and negative radial gradient in the outer portion of the inner zone, i.e., decreasing PSD with increasing L-value. A likely explanation for the peaks in PSD is acceleration due to energy diffusion produced by lightning-generated and anthropogenic whistlers. These results indicate that either additional local acceleration mechanism is responsible for the formation of the inner electron belt or inner electron belt is formed by sporadic injections of electrons into the inner zone. The currently well accepted model of slow diffusion and losses will be further examined by the upcoming Radiation Belt Storm Probes (RBSP) mission.

Description: Statistical observations by the THEMIS spacecraft show a dawn-dusk asymmetry in plasma parameters within the Earth's magnetosheath. Proton density and temperature are greater on the dawnside while the magnetic field strength and bulk flow are greater on the duskside. The asymmetry has been measured just outside the magnetopause in the dayside magnetosheath through 1114 boundary crossings from 2008 through 2010. These results are compared with modeling from the BATS-R-US global MHD code and are consistent with the expected asymmetries that would result from the interactions of the Parker spiral interplanetary magnetic field with the Earth's bow shock. Solar cycle variations are analyzed for the current and past studies to predict the influence of upstream conditions during different time periods.

Description: Statistical maps of small-scale electric field variability in the high-latitude ionosphere are derived for the Northern and Southern Hemispheres using 48 months of data from the Super Dual Auroral Radar Network (SuperDARN). Maps of variability magnitude (from scales of 45–450 km and 2–20 min) are derived for a range of interplanetary magnetic field (IMF) orientations and dipole tilt angles (the angle between the best fit dipole axis and the plane perpendicular to the Sun-Earth line). It is found that the observed spatial distribution of average variability is significantly modified as the IMF and dipole tilt conditions change. Under negative (winter-like) and neutral (equinox-like) dipole tilt angles, variability is concentrated in the auroral and dayside cusp regions, and the spatial distributions of variability appear to be correlated to those of large- and small-scale field-aligned currents (FACs). Additionally, variability on the nightside is found to be more enhanced in the downward FAC region than it is in the upward FAC region. Under positive (summer-like) dipole tilt angles, the average variability magnitudes across the high-latitude regions are smaller than those observed under negative dipole tilt angles, and the spatial distributions are more uniform. These dipole tilt effects suggest that scale-size- and conductivity-dependent field-aligned potential drops and conductivity-dependent changes in the processes that generate variability are possible factors that impact the observed small-scale electric field variability. In general, Southern Hemisphere maps appear very similar to Northern Hemisphere maps, although some minor differences are observed that may result from interhemispheric asymmetries in the geomagnetic field.

Description: The composition of ions plays a crucial role for the fundamental plasma properties in the terrestrial magnetosphere. We investigate the oxygen-to-hydrogen ratio in the near-Earth magnetosphere from −10 RE 274 keV O+ ion intensities, relative to the corresponding hydrogen intensities; (3) In contrast to ∼10 keV ions, the 〉274 keV O+ ions show the strongest acceleration during growth phase and not during the expansion phase itself. This suggests a connection between the energy input to the magnetosphere and the effective energization of energetic ions during growth phase; (4) The ratio between quiet and disturbed times for the intensities of ion ionospheric outflow is similar to those observed in the near-Earth magnetosphere at 〉274 keV. Therefore, the increase of the energetic ion intensity during disturbed time is likely due to the intensification and the effective acceleration of the ionospheric source. In conclusion, the energization process in the near-Earth magnetosphere is mass dependent and it is more effective for the heavier ions.

Description: During high-speed stream (HSS) events the solar wind speed increases, and the cross polar cap potential increases, leading to increased Joule heating at high latitudes. The heat input at high latitudes heats the polar regions, which then conducts to lower latitudes, producing global heating. The heating occurs during the risetime of the cross polar cap potential and throughout the period of high cross polar cap potential as seen in our simulation. These simulations are performed using the Utah State University global thermosphere model driven by Joule heating rates that are consistent with electric fields observed by DMSP-15 observations of HSS events. Cooling occurs as the cross polar cap potential decreases and continues for several days after the cross polar cap potential has returned to background values. Polar cap ionospheric observations are compared to model simulations of heating and cooling, providing evidence that the thermospheric model is capturing the HSS energy input and the post-HSS multiday return to pre-HSS conditions. The HSS heating can be as high as 100 K (as seen from both the model and the data) at high latitudes, with a corresponding, but lower, global increase in thermospheric temperature.

Description: Flux ropes have long been observed in the upper atmosphere of Venus and more recently at Mars. Here we present magnetic field measurements of flux ropes encountered at the southern terminator of Mars by Mars Global Surveyor and compare them to a flux rope model. This allows several parameters of each rope to be inferred. Remarkably similar flux ropes are met repeatedly at the southern terminator over a period of the Martian year, when strong crustal magnetic fields are upstream of their position, indicating that they are most likely stationary and attached to the upstream crustal fields. A mechanism is described that could produce the observed flux ropes.

Description: On 5 April 2010 a series of energetic electron injections, acceleration, and loss events appeared to induce an operational anomaly in the Galaxy 15 geosynchronous communications satellite. We describe the energetic electron precipitation conditions leading to the anomaly. A few hours prior to the anomaly electron acceleration at 〉0.6 MeV, and loss at 〉30 keV, were observed simultaneously. The acceleration took place in the region of the Galaxy 15 satellite on the nightside and the precipitation of electrons primarily on the dayside. The precipitation was confined to L-shells outside of the plasmapause and appeared to be driven by chorus waves via a weak diffusion process. An hour prior to the anomaly, a solar wind shock event generated a few minutes of 30–150 keV electron precipitation but only on the dayside, over a large L-shell range (4.8 〈 L 〈 13). The timing of the precipitation burst was consistent with electromagnetic ion cyclotron (EMIC) waves seen on the dayside, but the high geomagnetic latitude of the precipitation suggests that EMIC wave growth associated with high cold density regions in the plasmasphere is unlikely to have played a role. A substorm injection event shortly after the shock appears to have ultimately triggered the upset on Galaxy 15. However, the peak 〉30 keV electron precipitation fluxes of 1.35 × 107 el cm−2 s−1 sr−1 were roughly the same level as other large substorm events previously analyzed, indicating either a sensitivity to the energetic electron environment prior to the event or that the satellite was in a vulnerable situation.

Description: We investigate the effects of solar energetic particle (SEP) events on the Martian ionosphere using observations from the Mars Global Surveyor (MGS) Electron Reflectometer (ER) and Radio Science (RS) experiments. Although MGS/ER is not designed to measure solar storm particles, it detects SEPs as increased instrument background. Using this proxy for SEP fluxes near Mars, we compare electron density profiles obtained from the RS experiment during periods of high and low SEP activity. Six case studies show no clear evidence for an increase in the ionospheric electron density between 200 and 100 km altitudes. However, 4 of the 6 events show a small increase in electron density below 100 km altitude during SEP events, suggesting that high-energy (10–20 keV) electrons may cause ionization in the lower ionosphere. We also observe an ∼25% decrease in the ionospheric electron density between ∼100 and ∼120 km altitude for the two strongest events, suggesting that SEPs trigger a process that increases electron loss in this altitude range of the lower ionosphere. However, we cannot be confident from only two events that this effect is caused directly or indirectly by increased SEP fluxes. A statistical study confirms the case study results, but not over all solar zenith angles. Additionally, we observe depletions in the topside ionospheric electron density at some solar zenith angles, which can be explained by compression of the ionosphere by the passing CME.

Description: In this paper we compare and contrast chorus, electron cyclotron harmonics (ECH), and Z mode emissions observed at Jupiter and Saturn and relate them to recent work on electron acceleration at Earth. Intense chorus emissions are observed near the magnetic equator, the likely source region, but the strongest intensities are on either side of the magnetic equator. Chorus intensities at Jupiter are generally about an order of magnitude larger than at Saturn, and the bandwidth of chorus at Jupiter can reach 7 or 8 kHz (∼0.6 fc), while at Saturn it is typically

Description: Polarizations of Pi2 pulsations in the magnetosphere and on the ground in the auroral zone are inconsistent when field line motions in the meridian and transverse planes are both in the fundamental harmonic. To resolve these inconsistencies, we propose a third harmonic mode in the meridian planes. The excitation of the third harmonic is explained by dusk-to-dawn currents at the equatorial plane, which are driven by diamagnetic currents during substorm injections. We propose diamagnetic currents in the equatorial plane and compressional input at the outer boundary as the source of Pi2 pulsations in the magnetosphere.

Description: The relationship between monoenergetic electron acceleration and broadband electron acceleration is uncertain, although some have speculated that the latter is a temporal transient, and may evolve into the former. Here we have taken advantage of DMSP satellite coincidences to investigate the issue. We consider 1668 cases where one DMSP satellite observed an electron acceleration event covering at least 2 s, hence as many discrete accelerated spectra, and a second satellite subsequently observed an electron acceleration at the same location. The spatial coincidence required was tight, with a maximum separation of 0.1° magnetic latitude and 0.15 h magnetic local time. Time separations of 0–10 min were considered in 1 min bins, with auroral acceleration flagged as either monoenergetic, broadband, or a mixture of both. Within the first temporal bin (0–1 min), the second satellite had a high probability of observing the same type of aurora as the first, establishing consistency. When the first satellite observed monoenergetic aurora, the second satellite also observed monoenergetic aurora (about 80% of the time), and this continued to up to about 10 min of UT separation. In most of the other 20% of the cases, the second satellite also recorded monoenergetic acceleration but with an additional mixture of broadband acceleration. Thus monoenergetic aurora does not seem to typically evolve on a time scale of minutes. However, when the first satellite encounter was with broadband acceleration, the second encounter was highly time-dependent, with broadband dominating the second satellite encounter only in the 0–1 min bin. Between 1 and 5 min, the probability of observing a mixture of auroral types jumped, and after 6 min, the auroral acceleration was nearly as likely to be monoenergetic as broadband. Finally, if the first satellite encountered a mixture of acceleration, the second encounter was progressively more likely to be entirely monoenergetic aurora as time increased. These results are consistent with the idea that broadband aurora may be inherently a transient, and often progresses to monoenergetic aurora, while the latter is quasi-static.

Description: The Far-Ultraviolet Imager on the IMAGE spacecraft (IMAGE-FUV) has been used to observe O+ plasma depletions in the post-sunset equatorial ionosphere. Small-scale density irregularities associated with such depletions are believed to adversely affect trans-ionospheric radio signals such as GPS. Prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference. An automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions. Here we use this method to create a large database of the zonal drift velocities of these depletions. We present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude, which is essential to represent their behavior. A comparison of the observed drift velocities with zonal winds from both an empirical model (Horizontal Wind Model; HWM07) and a first-principles model (the TIEGCM) reveals that the plasma depletions' drift velocities have a latitudinal gradient that cannot be explained solely by the F-region dynamo in the post-sunset period, at least by these climatological models. This suggests that these plasma depletions may not simply drift with the background F-region plasma. It has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow, which may explain the previously-observed discrepancy in the drift velocities and the discrepancy in their gradients reported here.

Description: The vertical structure of the nightside ionosphere of Mars and its dependence on solar zenith angle are currently poorly determined, as is the importance of two key sources of nightside plasma, electron precipitation and transport of dayside plasma. We examined 37 electron density profiles of the ionosphere of Mars at solar zenith angles of 101°–123° obtained by the Mars Express Radio Science Experiment (MaRS) between 18 August and 1 October 2005. In general, solar activity was low during this period, although several solar energetic particle events did occur. The results show that (1) trends in peak electron density and altitude with solar zenith angle are consistent with transport of dayside plasma as an important plasma source up to 115°, but not higher; (2) peak altitudes of around 150 km observed at larger (〉115°) solar zenith angles are consistent with simulated plasma production by electron precipitation; and (3) peak altitudes observed during solar energetic particle events are at 90 km, consistent with accepted models. Solar energetic particle events can be the main source of nightside plasma. These results challenge current models of the nightside ionosphere, including their implications for plasma sources. The total electron content is correlated with peak electron density, requiring explanation. Due to the geographical distribution of this data set (latitudes poleward of 38°N), we do not explore the influence of crustal field strength and direction on the nightside ionosphere.

Description: Bright aurorae can be excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modeling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest that particle acceleration occurs throughout this region. Using multispacecraft observations from Cluster, we have examined two upward current regions on 14 December 2009. Our observations show that the potential difference below C4 and C3 changed by up to 1.7 kV between their respective crossings, which were separated by 150 s. The field-aligned current density observed by C3 was also larger than that observed by C4. The potential drop above C3 and C4 was approximately the same in both crossings. Using a novel technique of quantitively comparing the electron spectra measured by Cluster 1 and 3, which were separated in altitude, we determine when these spacecraft made effectively magnetically conjugate observations, and we use these conjugate observations to determine the instantaneous distribution of the potential drop in the AAR. Our observations show that an average of 15% of the potential drop in the AAR was located between C1 at 6235 km and C3 at 4685 km altitude, with a maximum potential drop between the spacecraft of 500 V, and that the majority of the potential drop was below C3. Assuming a spatial invariance along the length of the upward current region, we discuss these observations in terms of temporal changes and the vertical structure of the electrostatic potential drop and in the context of existing models and previous single- and multispacecraft observations.

Description: Previous investigations into Saturn's aurora have shown that they are strongly controlled by the solar wind. Here, for the first time, we use a combination of ground-based infrared observations of the aurora and in situ measurements of the magnetosphere in order to better understand this association. We show that large-scale variability in both the intensity and ion flow velocities can be directly correlated with the solar wind dynamic pressure, with, in particular, the arrival of solar wind compressions. Large compressions in the solar wind trigger the same morphological changes in the auroral structure as have previously been seen in UV images, and these are accompanied by the loss of the open field line corotation region seen in the velocity measurements. This region has been explained as an “old core” of magnetic field lines open to the solar wind, protected from reconnection due to the twisting in the magnetotail, and therefore requires that this region be removed only by major compressions in the solar wind; thus, our observations here generally agree with this model. In addition, we have observed a 〉8 h delay between the arrival of a major compression and the resulting effect upon the aurora, suggesting that reconnection must either occur well into the tail or that there are other processes in the chain of events that lead to the major dawn brightening seen in both these observations and previously studied UV images.

Description: We present a multipoint case study of solar wind and magnetospheric observations during a transient magnetospheric compression at 23:19 UT on 15 October 2008. We use high time resolution magnetic field and plasma data from the THEMIS and GOES 11/12 spacecraft to show that this transient event corresponded to an abrupt rotation in the IMF orientation, a change in the location of the foreshock, and transient outward bow shock motion. We employ results from a global hybrid code model to reconcile the observations indicating transient inward magnetopause motion with the outward bow shock motion.

Description: It is shown that the low frequency plasma wave equation can be obtained much more directly than by the previously used method of solving for the determinant of a matrix involving the three components of the electric field vector. The more direct method uses a two-dimensional current density vector space that is precisely equivalent to the previously used three-dimensional electric field vector space. Unlike the electric field, the current density is restricted by the quasi-neutrality condition to a two-dimensional vector space. Comparison with previously obtained dispersion relations is provided and a method is presented for obtaining exact analytic solutions for the three roots of the cubic dispersion relation. The commonly used kinetic Alfvén dispersion relation is shown to be valid only for near-perpendicular propagation in a low beta plasma. It is shown that at a cross-over point where the perpendicular wave phase velocity equals the ion acoustic velocity, the coupling between Alfvén and fast modes vanishes and the Alfvén mode reverts to its cold form even in situations where the Alfvén velocity is smaller than the electron thermal velocity. A method is prescribed by which measurement of wave electric current density completely eliminates the space-time ambiguity previously believed to be an unavoidable shortcoming of single-spacecraft frequency measurements.

Description: We examine the pitch angle distribution (PAD) of suprathermal electrons (〉40 keV) inside the flux pileup regions (FPRs) that are located behind the dipolarization fronts (DFs), in order to better understand the particle energization mechanisms operating therein. The 303 earthward-propagating DFs observed during 9 years (2001–2009) by Cluster 1 have been analyzed and divided into two groups according to the differential fluxes of the 〉40 keV electrons inside the FPR. One group, characterized by the low flux (F 〈 500/cm2 · s · sr · keV), consists of 153 events and corresponds to a broad distribution of IMF Bz components. The other group, characterized by the high flux (F ≥ 500/cm2 · s · sr · keV), consists of 150 events and corresponds to southward IMF Bz components. Only the high-flux group is considered to investigate the PAD of the 〉40 keV electrons as the low-flux situation may lead to large uncertainties in computing the anisotropy factor that is defined as A = F⊥/F∥ − 1 for F⊥ 〉 F∥, and A = −F∥/F⊥ + 1 for F⊥ 〈 F∥. We find that, among the 150 events, 46 events have isotropic distribution (|A| ≤ 0.5); 60 events have perpendicular distribution (A 〉 0.5), and 44 events have field-aligned distribution inside the FPR (A  〈 −0.5). The perpendicular distribution appears mainly inside the growing FPR, where the flow velocity is increasing and the local flux tube is compressed. The field-aligned distribution occurs mainly inside the decaying FPR, where the flow velocity is decreasing and the local flux tube is expanding. Inside the steady FPR, we observed primarily the isotropic distribution of suprathermal electrons. This statistical result confirms the previous case study and gives an overview of the PAD of suprathermal electrons behind DFs.

Description: We present and analyze data on auroral arcs obtained during a pass of the FAST satellite over the field-of-view of the all-sky camera at Ft. Simpson (Canada), supported by ground-based magnetometer and SuperDARN radar data, and plasma data from THEMIS-A near the source region of the auroral currents. The auroral event took place at 19:00 MLT during substorm activity further east. Active auroral arcs were present over six degrees in latitude moving equatorward with significant changes in brightness and structure. New arcs were forming continuously at the polar border of the auroral oval which was marked by an Alfvénic arc. The data analysis revealed that the equatorward drift of the arcs was in part due to convective motion of the plasma frame but was rather dominated by proper motions of the arcs. Interpretation of these findings in the framework of theoretical work by one of the authors reproduces quantitatively the observed proper motion as a consequence of the progressive erosion of magnetic shear stresses. Most important was the possibility to deduce the interaction time scale between arc and source region. On average it corresponded to about six to eight transit times of an Alfvén wave between arc and source plasma or two fundamental eigenperiods of toroidal mode or azimuthally polarized Alfvén waves. However, large variations of the interaction times and corresponding proper motions were found. They are attributed to temporal and spatial variations of the energy input from the source plasma. The more remarkable is the fact that analysis on the basis of a quasi-stationary model produces consistent results. The progressive release of shear stresses during the equatorward motion of the arcs leads to the conclusion that they are dying after having reached the maximum of the poleward Pedersen current.

Description: We summarize observations by the MESSENGER spacecraft of highly coherent waves at frequencies between 0.4 and 5 Hz in Mercury's inner magnetosphere. This survey covers the time period from 24 March to 25 September 2011, or 2.1 Mercury years. These waves typically exhibit banded harmonic structure that drifts in frequency as the spacecraft traverses the magnetic equator. The waves are seen at all magnetic local times, but their observed rate of occurrence is much less on the dayside, at least in part the result of MESSENGER's orbit. On the nightside, on average, wave power is maximum near the equator and decreases with increasing magnetic latitude, consistent with an equatorial source. When the spacecraft traverses the plasma sheet during its equatorial crossings, wave power is a factor of 2 larger than for equatorial crossings that do not cross the plasma sheet. The waves are highly transverse at large magnetic latitudes but are more compressional near the equator. However, at the equator the transverse component of these waves increases relative to the compressional component as the degree of polarization decreases. Also, there is a substantial minority of events that are transverse at all magnetic latitudes, including the equator. A few of these latter events could be interpreted as ion cyclotron waves. In general, the waves tend to be strongly linear and characterized by values of the ellipticity

Description: We present results from the numerical study of ULF waves generated by the ionospheric feedback instability in density cavities. The goal of the study is to explain several spectral features of ULF waves detected on the ground in close vicinity of intense discrete auroral arcs. These features include (1) localization of the waves packages across the ambient magnetic field, (2) variation of the wave frequency in relatively small amplitude waves, and (3) presence of several discrete harmonics in the spectrum of the relatively large amplitude waves. Time-dependent, two-dimensional simulations based on the two-fluid MHD model performed in the dipole, axisymmetrical geometry of the ambient magnetic field with realistic parameters of the plasma density in the ionosphere and the magnetosphere demonstrate that the ionospheric feedback instability inside the density cavity indeed provides a good, quantitative explanation of these features of ULF waves observed at high latitudes during substorm onsets.

Description: In this paper, presented for the first time the three-dimensional global morphology and seasonal variations of scintillation index (S4 index) measured from the signal-to-noise ratio (SNR) intensity fluctuations of L1 channel of GPS radio occultation (RO) signals using FORMOSAT-3/COSMIC (in short, F3/C) satellites for a low solar activity year 2008. The S4 index, which confined around ±30° magnetic latitudes, is found to start around post-sunset hours (1900 MLT, magnetic local time) and often persists till post-midnight hours (0300 MLT) between 150 and 350 km altitudes during equinox and northern winter seasons while no activity is observed during southern winter season. However, high latitudes are characterized with no scintillation activity beyond 150 km during any season, which implying that in the solar minimum period the drives of instabilities in the auroral, cusp and polar cap regions, namely the gradient drift and velocity shear, are absent. The S4 index at F region altitudes during magnetically quiet times is more intense and extends to higher latitudes than that observed during disturbed time consistent with earlier studies. The equatorial S4 index appears below the peak of F2 layer (hmF2) during most of the seasons although the associated intensities and the time of maximum occurrences are relatively higher and earlier during vernal equinox followed by autumn equinox. This equinoctial asymmetry could be primarily attributed to the asymmetries in eastward drift velocities, thermospheric meridional winds and plasma densities. Further, the global maps of S4 index at E region altitudes (between 75 and 125 km) show strong seasonal variations with highest activity during northern and southern summer solstice in the middle latitudes while it appears on both sides of magnetic equator with less or no activity at and around the equator during equinox seasons. The absence of S4 index along the equator can be understood in terms of the vanishing vertical component of the magnetic field lines that can inhibit the vertical movement and layered deposition of ionized particles of thin irregular electron density layers such as Es-layers. Keeping in view the importance of these valuable database, we would like to emphasize that the F3/C GPS RO technique can be used to study the ionospheric irregularities at GHz frequency globally directly from the high-rate L1 data, which reiterating its importance as a powerful tool to explore the terrestrial ionosphere on a global scale.

Description: A two-dimensional numerical model of low-altitude auroral flux tubes has been developed for simulation of coupling between the magnetosphere and the ionosphere. The model considers a realistic ionosphere with multiple ion and neutral species, collisions, cooling and heating processes, as well as the North-South electric field due to the global azimuthal plasma convection. In the paper, a detailed description of the model is given. A representative simulation where the ionosphere is perturbed by an Alfvén wave is discussed. The model demonstrates formation of intense parallel electric fields, radiation of Alfvén waves by density perturbations in the convective flow, and electron and ion heating.

Description: Toward the understanding of the effect of the magnetosphere originated disturbances on the global ionospheric electric field and current system, we developed a two-dimensional ionospheric potential solver based on the so-called “thin shell model.” The important extension from the previous studies is that our model covers the pole-to-pole ionosphere without placing any boundary at the equator. By using this solver, we investigate how the ionospheric electric field changes from undershielding condition to overshielding condition as the field aligned current (FAC) distribution changes. Calculations are performed by changing IR2/IR1 (the ratio of current intensities of region 2 (R2) and region 1 (R1) FACs) and by moving R2-FAC relative to the fixed R1-FAC. The results are summarized as follows: (1) The turning point, at which the ionosphere turns from undershielding to overshielding is IR2/IR1 = 0.7 ∼ 0.8. (2) With increasing the local time deference between the R1 and R2-FAC peaks, the efficiency of the shielding by R2-FAC increases but the associated potential skews to the nightside. (3) At the same time the shielding effect is weakened around noon, where the R1-potential intrudes to the low latitude region instead, but the R2-potential remains dominant at other local times. The result suggests that the overshielding or undershielding should be identified by observations not only in a limited local time sector but also in the overall ionosphere as much as possible. In order to accurately describe the ionospheric condition, we suggest new classification terms, “complete-overshielding” and “incomplete-overshielding.”

Description: Transpolar arcs are large-scale auroral features which are observed within the polar cap when the IMF has a northward component. One leading candidate formation mechanism proposes that they are formed by reconnection in the magnetotail some time after a period of dayside reconnection with a non-zero IMF BY component which introduces a twist into the magnetotail. As a result of the twist, the mechanism predicts that the return flows of the newly closed magnetic field lines are asymmetric about midnight; their direction should depend upon the IMF BY component in the hours beforehand and should be opposite in the northern and southern hemispheres. In this paper, we use data from the SuperDARN network of high-latitude ionospheric radars to examine whether such ionospheric flows are present before the formation of 33 transpolar arcs. We find that the flows are present and in a manner that is consistent with the reconnection mechanism for 76% of the events; in the remaining few, the discrepancy can be attributed either to an uncertainty in the formation time determined for the arc (due to previous polar cap activity in the same local time sector) or due to the geometry of the radars which observe the backscatter.

Description: The global electron content (GEC) derivation is initiated by summing up the total electron content of each cell of Global Positioning System GPS-TEC global map multiplied by the cell area. Algorithm of GEC calculation is improved in the present paper using the electron density varying with height through the total volume of a spherical layer in near-Earth space up to 20,200 km (GPS orbit) reconstructed from TEC with the International Reference Ionosphere model extended to the Plasmasphere (IRI-Plas). An analytical model is first derived for two-phase typical GEC storm profile by a common epoch analysis of 10 storms during 2001–2011 with the starting time put at the origin of the negative phase of GEC departure from the quiet reference (5 day median). It is found that GEC depletion occurs synchronously with decrease of the solar wind velocity and the outset of recovery of the magnetospheric ring current (the equatorial Dst index) and the auroral electrojet (AE index). Thus, the GEC is an indicator of the plasma injection in the ionosphere and plasmasphere with the solar wind energy inducing the positive phase of GEC storm during 24 h with electron number increased by 10–20% followed by a negative phase with GEC decrease by 10–20% during 40 h of a plasma release (ejection) into the magnetosphere tail beyond the three Earth radii (GPS orbit).

Description: The goal of this paper is to deliver a long-missing interpretation of a central issue of the NASA-MPE barium injection experiment performed in September 1971. It pertains to the interaction with the ionosphere. Observations of the cloud's motion revealed no obvious sign of such interaction. The barium vapor was released from a Scout rocket at an altitude of 31,000 km above South America during late evening hours and was observed for more than 4000 s. The barium plasma split into several field-parallel streaks which moved for a long time as if subject to constant acceleration as viewed from the inertial frame of the rocket at release. This means that no reflection of energy due to a mismatch of ionospheric conductivity and the characteristic impedance of an impinging Alfvén wave was observed. It is this finding that has never been properly interpreted. Furthermore, after a careful assessment of the barium cloud properties and environmental parameters, we find a theoretical coupling time to the ambient flow which turns out to be substantially longer than observed. Although this appears to indicate that some interaction with the ionosphere occurred, we can rule out multiple wave reflections during the observed acceleration phase. Discarding other possibilities, we interpret the observed motions as sign of perfect matching of the momentum and energy flux into the ionosphere with the rate of dissipation. This is achieved during the initial phase by scale breaking of the cloud into streaks with narrow widths which allow parallel potential drops along the Alfvén wings because of the waves' inertial nature and inside the lower ionosphere owing to the finite parallel resistivity, thereby greatly reducing the effective Pedersen conductivity. The significance of this finding goes beyond understanding the barium injection experiment. It sheds light on how magnetospheric plasma irregularities can share momentum and energy with the ionosphere in an optimized fashion.

Description: We assess whether magnetically and electrically self-consistent ring current simulations can account simultaneously for in situ magnetic field and ion flux measurements in the inner magnetosphere during the large 10 August 2000 storm (min Dst = −107 nT). We use the Rice Convection Model–Equilibrium (RCM-E) and drive it with time-dependent magnetic field, electric field, and plasma boundary conditions that are guided by empirical and assimilative models. Comparisons of the simulated and observed magnetic field from Geostationary Operational Environmental Satellites (GOES) and observed proton differential flux spectra from Los Alamos National Laboratory (LANL) satellites are made at geosynchronous orbit (GEO). Similarly, simulated and observed magnetic field and proton density and temperature are compared along the orbit of Polar (r ∼ 1.8–9 RE) for the event. The simulated and observed magnetic field components agree reasonably well at GEO and along the orbit of Polar. However, since the effects of substorm dipolarizations are not explicitly modeled, the simulation fails to reproduce observed sawtooth fluctuations in the magnetic field. Over energies from 1 to 150 keV, the RCM-E reproduced well the ion dispersion features in the LANL 1994-084 ion differential flux spectra over energies at GEO and proton densities and temperatures calculated from Polar proton flux measurements. Thus, the RCM-E simulations can account simultaneously for in situ magnetic field and ion flux measurements for the 10 August 2000 storm. This demonstrates that a self-consistent model can produce realistic features of the storm time inner magnetosphere.

Description: Compared to the dayside, dynamics on the flanks of the magnetopause are poorly understood. To help bridge this knowledge gap we analyzed Cluster plasma and field measurements acquired during a 90-min period on 20 November 2003 when Cluster crossed the magnetopause four times in the vicinity of the sash. MHD simulations provide a context for Cluster observations. Crossings were between the magnetosheath and an S-shaped plasma sheet, rather than to the open-field lobes of the magnetotail. Cluster encountered two regions of MHD-breaking differences between perpendicular ion velocities and E × B convection. Ion adiabatic expansion parameter (δi) calculations show that ion gyrotropy was not broken during an episode of strong Alfvén wave activity in the magnetosheath. However, gyrotropy was broken (δi 〉 1) during the fourth magnetopause crossing. In the magnetosheath, ion guiding-center motion was maintained but inertial effects associated with temporally varying electric fields are probable sources of velocity differences. Regarding the magnetopause crossing, the generalized Ohm's law limits possible sources for breaking ion gyrotropy to inertial forces and/or electron pressure gradients associated with a nearby reconnection event. We suggest that Cluster witnessed effects of a temporally varying and spatially limited, flow-through reconnection event between open mantle field lines from the two polar caps adding new closed flux to the LLBL at the sash. Future modeling of flank dynamics must consider inertial forces as significant drivers at the magnetopause and in the adjacent magnetosheath.

Description: It is known that the sudden injection of energy during geomagnetic storms can excite atmospheric gravity waves (AGWs) or traveling atmospheric disturbances (TADs). Together with large-scale circulation, these AGWs/TADs transport energy and momentum away from their sources. In this paper, we investigate possible involvement of AGWs/TADs during solar flares. Model simulations of an X17 flare that occurred on October 28, 2003 shows that AGWs/TADS contributed to flare energy transport from the sunlit South-Pole region to the nightside equatorial region in 3–4 h, resulting in ∼10% nightside equatorial neutral density enhancement in the upper thermosphere. These nightside AGWs/TADs have a phase speed on the order of ∼750 m/s and a horizontal wavelength on the order of 4000 km. Enhanced solar heating to the thermosphere through enhanced ionization during flares occurs on the entire dayside, with the spatial scale of the increased solar heating being too large to excite AGWs/TADs. Further analysis revealed that strong localized enhancement of Joule heating was produced during the October 28, 2003 flare. This sudden injection of the localized heating, together with preexisting AGWs/TADs excited by moderate geomagnetic activity prior to the flare, produced intensified AGWs/TADs, which propagated energy and momentum to the equatorial region. On the other hand, model simulations showed that, under assumed geomagnetically quiet conditions, strong localized enhancement of Joule heating and AGWs/TADs were not produced during the flare. This interplay between geomagnetic activity and solar flares can be a challenge to space weather monitoring, specification, and forecasting.

Description: Ionospheric origin O+ accelerated in the cusp/cleft region is one source for the O+ observed in the plasma sheet. This O+ is convected over the polar cap, flowing along open field lines to the tail lobes, and finally entering the plasma sheet. In this paper we use Cluster/CODIF data to study how the occurrence of cusp origin O+ in the polar cap and tail lobe changes over the solar cycle. Our study shows that the probability to observe cusp origin O+ decreases steeply during the declining phase of solar cycle 23 and starts to increase again at the start of the solar cycle 24. The decrease is much greater in the tail lobes than in the polar cap. A detailed analysis reveals that the O+ on the dominant transport path moves to higher latitudes in the Northern Hemisphere and more sunward in the Southern Hemisphere during the declining phase of the solar cycle (from the solar maximum to the solar minimum), so that the O+ no longer reaches the near-Earth (

Description: This paper presents our effort to assimilate FORMOSAT-3/COSMIC (F3/C) GPS Occultation Experiment (GOX) observations into the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM) by means of ensemble Kalman filtering (EnKF). The F3/C electron density profiles (EDPs) uniformly distributed around the globe which provide an excellent opportunity to monitor the ionospheric electron density structure. The NCAR TIE-GCM simulates the Earth's thermosphere and ionosphere by using self-consistent solutions for the coupled nonlinear equations of hydrodynamics, neutral and ion chemistry, and electrodynamics. The F3/C EDP are combined with the TIE-GCM simulations by EnKF algorithms implemented in the NCAR Data Assimilation Research Testbed (DART) open-source community facility to compute the expected value of electron density, which is ‘the best’ estimate of the current ionospheric state. Assimilation analyses obtained with real F3/C electron density profiles are compared with independent ground-based observations as well as the F3/C profiles themselves. The comparison shows the improvement of the primary ionospheric parameters, such as NmF2 and hmF2. Nevertheless, some unrealistic signatures appearing in the results and high rejection rates of observations due to the applied outlier threshold and quality control are found in the assimilation experiments. This paper further discusses the limitations of the model and the impact of ensemble member creation approaches on the assimilation results, and proposes possible methods to avoid these problems for future work.

Description: The characteristic time scaling of the electron flux evolution at geosynchronous orbit (GEO), resulting from the quasilinear wave-particle interaction, is investigated. The upper limit of the electron flux increase rate, due to the interaction with waves, is deduced from the energy diffusion equation (EDE). Such a time scaling allows for a comparison with experimentally measured fluxes of energetic electrons at GEO. It is shown that the analytically deduced time scaling is too slow to explain the observed increase in fluxes. It is concluded that radial diffusion plays the most significant role in the build up of the energetic electrons population at GEO. However, this conclusion is only justified if the seed population energies are very low.

Description: Radial diffusion is one of the most important acceleration mechanisms for radiation belt electrons, which can be enhanced from drift-resonant interactions with large-scale fluctuations of the magnetosphere's magnetic and electric fields (Pc5 range of ULF waves). In order to physically quantify the radial diffusion coefficient, DLL, we run the global Lyon-Fedder-Mobarry (LFM) MHD simulations to obtain the mode structure and power spectrum of the ULF waves and validate the simulation results with available satellite measurements. The calculated diffusion coefficients, directly from the MHD fields over a Corotating Interaction Region (CIR) storm in March 2008, are generally higher when solar wind dynamic pressure is enhanced or AE index is high. In contrary to the conventional understanding, our results show that inside geosynchronous orbit the total diffusion coefficient from MHD fields is dominated by the contribution from electric field perturbations, rather than the magnetic field perturbations. The calculated diffusion coefficient has a physical dependence on μ (or electron energy) and L, which is missing in the empirical diffusion coefficient, DLLKp as a function of Kp index, and DLLKp are generally greater than our calculated DLL during the storm event. Validation of the MHD ULF waves by spacecraft field data shows that for this event the LFM code reasonably well-reproduces the Bz wave power observed by GOES and THEMIS satellites, while the Eφ power observed by THEMIS probes are generally underestimated by LFM fields, on average by about a factor of ten.

Description: This paper presents a study of thermospheric and ionospheric response to the 2008 minor sudden stratospheric warming (SSW) event. This period was characterized by low solar and geomagnetic activity. The study was performed using the Global Self-consistent Model of Thermosphere, Ionosphere, and Protonosphere (GSM TIP). Model results were compared with ionosonde data from Irkutsk, Kaliningrad, Sao Jose dos Campos, and Jicamarca. The SSW event was modeled by specifying the temperature and density perturbations at the lower boundary of the GSM TIP (80 km altitude). GSM TIP simulation allowed the reproduction of the lower thermosphere temperature disturbances (the occurrence of the quasi-wave 1 structure at 80–130 km altitude with a vertical scale of ∼40 km), the negative response of F2 region electron density and the positive response of electron temperature at 300 km during the 2008 minor SSW event. The main formation mechanism of the global ionospheric response is due to the disturbances (decrease) in the n(O)/n(N2) ratio. The change in zonal electric field is another important mechanism of the ionospheric response at low latitudes.

Description: The concept of the ‘wave-turbopause layer’ is introduced and discussed in this study, which defines the wave-turbopause as a layer having a lower and upper boundary, where maximum dissipation of atmospheric waves happens. The analysis is carried out using three years of SABER temperature measurements (2004–2006) and seasonal and latitudinal variability of the wave-turbopause layer is established. On an average, it is found that there is a maximum of ∼5–20 km difference in altitude between the lower and upper boundaries of the wave-turbopause. Seasonally, the winter hemispheric high latitudes have the highest wave-turbopause which decreases toward the summer hemisphere with a secondary maximum at the summer hemisphere midlatitude. Moreover, the monthly variability of the wave-turbopause and mesopause is studied for 50°N, 0° and 50°S latitudes. On global scale, the latitude-height sections of zonal mean gravity wave potential energy of the MLT region is compared with the wave-turbopause characteristics. The wave-turbopause pattern seems to be superposed on the potential energy transition pattern which exposes an intermediate layer sandwiched between low and high magnitudes of potential energy. Thus the present study proposes the concept of the wave-turbopause layer and substantiates the same by discussing its latitudinal structure, seasonal and monthly variability, correlation with the cold point mesopause and gravity wave potential energy in the MLT region.

Description: We examine the contribution of photo-dissociation under quiet solar conditions to the global OH and O distributions in Saturn's inner magnetosphere by performing a Monte Carlo simulation. We first calculate the H2O distribution generated by H2O sources, namely Enceladus' cryo-volcanic plumes, satellite sputtering, and E ring sputtering. We calculate the OH distribution through photo-dissociation reactions using the calculated H2O distribution and then calculate the O distribution from the obtained H2O and OH distributions. We quantitatively evaluate the role of the energy increment of produced OH and O particles due to photo-dissociation by comparing the resultant distribution of OH and O particles with and without the energy increment. To quantitatively examine the effect of photo-dissociation on the spreading of OH and O clouds, we use the H2O model including charge exchange and neutral/neutral collisions based on Cassidy and Johnson (2010), as the initial distribution. For the OH (O) density in the region outside 5 Rs (6 Rs), the density with energy increment is greater than that without energy increment. The contribution of calculated OH density with energy increment to the observation is more than ∼10%. The OH ratio outside 6 Rs decreases with radial distance from Saturn. On the other hand, the contribution of calculated O density with energy increment to the observation is less than 10% except for around Enceladus.

Description: The strong westward electrojet and simultaneous upward drift of the equatorial ionospheric peak observed over South-East Asia and Indian equatorial regions during the prolonged Dst minimum phase of an intense geomagnetic storm during 14–15 December 2006 are investigated for the altitudinal variation of zonal electric field polarity using ground based and space-borne observations. The results show first observational evidence for simultaneous existence of daytime westward and eastward zonal electric fields at equatorial E and F region altitudes, respectively, in a wide longitude sector. While the westward electric fields at E region altitudes cause westward electrojet, at the same time, the eastward zonal electric fields at F region altitudes cause the upward drift of the equatorial ionospheric peak and reinforcement of the equatorial ionization anomaly (EIA) even in the topside ionosphere (∼660 km). The reversal of the electric fields is found to occur at ∼280 km height. A clear bifurcation of F region plasma at ∼280 km is evident in the iso-electron density contours due to these oppositely polarized zonal electric fields, which manifests as an unusually deep cusp between F1 and F2 layers on equatorial ionograms.

Description: There are significant uncertainties in the calculation of photometric and ionization masses of meteors, particularly those derived from meteor head echoes observed by high power, large aperture radars. Simultaneous observations of meteors with the EISCAT UHF tristatic system and narrow field two-station intensified video were conducted in October 2007; 11 hours of data produced four useful meteors observed on all three radar receivers and both cameras. The positions and speeds calculated on the two systems generally agree to within the observational uncertainty. The photometric and ionization masses for each meteor were calculated using several values of luminous efficiency and ionization probability from literature, and all of these masses were found to agree to within the estimated error in the methods. More observations are required to select among the various values of ionization coefficient and luminous efficiency.

Description: Interaction with EMIC (electromagnetic ion cyclotron) waves is thought to be a key component contributing to the very rapid loss of both ring current and radiation belt particles into the atmosphere. Estimated loss rates are heavily dependent on the assumed spatial distribution of the EMIC wave. Statistical maps of the spatial distribution have been produced using in-situ satellite data. However, with limited satellite data it is impossible to deduce the true spatial distribution. In this study, we present ground-based observations using all-sky imager and search coil magnetometer networks, which provide the large-scale distribution and motion of the EMIC wave-particle interaction regions. We observed several spots of isolated proton auroras simultaneously with Pc1/EMIC waves at subauroral latitudes during the expansion phase of a storm-time substorm on 9 March 2008. The isolated auroras were distributed over ∼4-hours MLT preceding midnight. The POES-17 satellite confirmed enhancements of 30-keV proton precipitations over the isolated auroras. The equatorward motion of the auroras and frequency drift of the wave were consistent with the plasmasphere eroding due to a polar cap potential enhancement modeled by a numerical simulation. We also found that relativistic electron precipitation was not always associated with the isolated aurora, depending strongly on the plasma density profile near the plasmapause. This study shows that the specific distribution of ring current proton precipitation can be visualized through the ground network observations. By combining with upcoming inner-magnetosphere satellite missions, these remote-sensing observations are very important for quantitative understanding of the particle loss in the inner magnetosphere.

Description: We present a rare event that was recorded over Arecibo using sodium (Na) lidar. Billow-like structures with periods of ∼60 min were seen in the Na layer above 102 km on the night of 7–8 July 2010. The absence of any high-altitude structure was noted on the following night. Spectral analysis using the Lomb-Scargle technique reveals periods with larger power on the first night as compared to the adjacent one. The keograms derived from a sequence of 557.7 nm airglow images show the passage of a large frontal wave on 7–8 July 2010. Further investigation on the occurrence of neutral instabilities was carried out using mesospheric temperature and horizontal wind obtained from the Sounding of Atmosphere using Broadband Emission Radiometry (SABER) and TIMED Doppler Interferometer (TIDI) instruments onboard the TIMED satellite. A good agreement is observed between the temperatures derived from SABER and ground-based airglow instruments. The mesospheric temperature and horizontal wind profiles allowed the determination of square of the Brunt-Väisälä frequency and Richardson number to quantitatively evaluate the possible role of different instabilities in generating this structure. The profile of the former entity reveals that the region is convectively stable during the time when the event was observed. However, the presence of strong shears in the region, where billow-like structures are observed on 7–8 July 2010, is noted along with a Richardson number of 0.22, indicating the likely occurrence of dynamical instability. Thus, the present work suggests that dynamical instability make conditions conducive for billow-like structures in the Na layer above 102 km. The possible role of plasma processes in generating these structures is also discussed.

Description: A topic of great current interest in atmospheric dynamics is the developing recognition of the influence of the diurnal eastward-propagating non-migrating tide of wave number 3 (DE3) on the thermosphere. Longitudinal variations of the equatorial F region ionospheric electron density show a zonal wave number 4 (wave-4, WN4) pattern, expected for satellite observations at a fixed local time with respect to a rotating Earth. WINDII observations of airglow O(1S) volume emission rate (VER), excited by photoelectron impact on atomic oxygen at 250 km have previously been interpreted as neutral density observations; they have shown the wave 4 to be a common density perturbation in the equatorial thermosphere. The analysis has been extended further by examining thermospheric neutral temperatures from September 1992 to April 1993 at 245 km height derived from the vertical gradient of the observed daytime O(1S) VERs at 235–255 km yielding the atomic oxygen density scale heights centered at this altitude. The thermospheric temperatures show a distinct and persistent wave-4 signature at 20°S–40°S with a pronounced increase during March equinox.

Description: Terrestrial gamma-ray flashes (TGFs) are bright, sub-millisecond bursts of gamma-rays, originating within the Earth's atmosphere. Most TGFs have been detected by spacecraft in low-Earth orbit. Only two TGFs have previously been observed from within our atmosphere: one at ground level and one from an aircraft at 14.1 km. We report on a new TGF-like gamma-ray flash observed at ground level, detected by the 19-station Thunderstorm Energetic Radiation Array (TERA) at the University of Florida/Florida Tech International Center for Lightning Research and Testing (ICLRT). The gamma-ray flash, which had a duration of 52.7 μs, occurred on June 30, 2009 during a natural negative cloud-to-ground lightning return stroke, 191 μs after the start of the stroke. This event is the first definitive association of a gamma-ray flash with natural CG lightning and is among the most direct links to a specific lightning process so far. For this event, 19 gamma-rays were recorded, with the highest energy exceeding 20 MeV. The high-energy radiation exhibited very different behavior from the typical x-ray emission from lightning. Specifically, the gamma-ray flash had a much harder energy spectrum, consistent with relativistic runaway electron avalanche (RREA) multiplication; it did not arrive in sub-microsecond bursts, typical of leader emission from lightning, and it occurred well after the start of the return stroke, which has not been previously observed for the x-ray emission from lightning. Nevertheless, we present evidence that the source region for the gamma ray flash was the same as that for the preceding leader x-ray bursts.

Description: Theoretical arguments and large-scale two-fluid simulations are used to study the spreading of reconnection X-lines localized in the direction of the current as a function of the strength of the out-of-plane (guide) magnetic field. It is found that the mechanism causing the spreading is different for weak and strong guide fields. In the weak guide field limit, spreading is due to the motion of the current carriers, as has been previously established. However, spreading for strong guide fields is bidirectional and is due to the excitation of Alfvén waves along the guide field. In general, we suggest that the X-line spreads bidirectionally with a speed governed by the faster of the two mechanisms for each direction. A prediction on the strength of the guide field at which the spreading mechanism changes is formulated and verified with three-dimensional simulations. Solar, magnetospheric, and laboratory applications are discussed.

Description: A correlative study of rotational temperatures and radiance of mesospheric hydroxyl (OH) was made using spectrographic measurements from the midlatitude site at Millstone Hill, Massachusetts (42.6°N, 71.5°W). The OH radiance and temperatures were strongly correlated, and the correlation showed a marked seasonal dependence. The dependence was also evident on smaller timescales ranging from days to months. Dynamical effects appeared to dominate the temperature-radiance relationship compared to the photochemistry responsible for the hydroxyl emission rate. The effect was illustrated clearly when the measurements were temporally averaged, hence removing the dynamical influence. A strong summer maximum in OH radiance was observed contrary to a minimum in summer Mass Spectrometer Incoherent Scatter (MSIS) [O] volume mixing ratio values. An increase in mesospheric gravity wave activity during the summer, a feature not observed by the MSIS model, was the likely cause of the summer OH maximum.

Description: Observed phases and amplitudes of VLF radio signals propagating on (near) tropical all-sea paths, both short, ∼300 km, and long, ∼10 Mm, are used to find daytime parameter changes for the lowest edge of the (D-region of the) Earth's ionosphere as the solar cycle advanced from a very low sunspot number of ∼5 up to ∼60, in the period 2009–2011. The VLF phases, relative to GPS 1-s pulses, and amplitudes were measured ∼100 km from the transmitter, where the direct ground wave is very dominant, ∼300 km from the transmitter, near where the ionospherically reflected waves form a (modal) minimum with the ground wave, and ∼10 Mm away where the lowest order waveguide mode is fully dominant. Most of the signals came from the 19.8 kHz, 1-MW transmitter, NWC, North West Cape, Australia, propagating ENE, mainly over the sea, to the vicinity of Karratha and Dampier on the NW coast of Australia and then on to Kauai, Hawaii, ∼10.6 Mm from NWC. Observations from the 8.1-Mm path NPM (21.4 kHz, Hawaii) to Dunedin, NZ, are also used. The sunspot number increase from ∼5 to ∼60 was found to coincide with a decrease in the height, H′, of the midday tropical ionosphere by 0.75 ± 0.25 km (from H′ ≈ 70.5 km to H′ ≈ 69.7 km) while the sharpness, β increased by 0.025 ± 0.01 km−1 (from β ≈ 0.47 km−1 to β ≈ 0.49 km−1) where H′ and β are the traditional height and sharpness parameters used by Wait and by the U.S. Navy in their Earth-ionosphere VLF radio waveguide programs.

Description: The growth of magnetic field fluctuations driven by the injection of pickup ions perpendicular to a background magnetic field in a homogeneous, collisionless plasma is studied using one-dimensional hybrid simulations. Freshly ionized protons are continuously injected into the simulations at constant rates and relative speeds consistent with conditions in the distant solar wind and the outer heliosheath. The pickup protons initially form a ring-velocity distribution unstable to the electromagnetic proton cyclotron instability and lead to enhanced magnetic fluctuations. After an exponential growth phase of the instability, the fluctuating magnetic fields exhibit linear temporal growth followed by a more-slowly growing quasi-steady phase. The excited fluctuations pitch angle scatter the pickup protons toward an isotropic shell velocity distribution with the most significant scattering occurring in the exponential growth phase. The scattering rate of the freshly injected pickup protons during the linear temporal growth phase remains relatively constant and it increases with the pickup proton injection rate. More importantly, significant pitch angle scattering only occurs after the accumulated pickup proton density exceeds a critical value, the scattering-onset density. The scattering-onset density also increases with the pickup proton injection rate and the scattering onset typically occurs during the exponential growth phase of the magnetic fluctuations. Scaling relations for the scattering rate and the scattering-onset density versus the pickup proton injection rate are derived from the simulation results. These relations suggest that significant scattering of pickup protons in the outer heliosheath occurs in a relatively limited spatial range close to the heliopause, related to the issue of whether the “secondary ENA” mechanism is a possible explanation for the ENA ribbon observed by IBEX. Implications of the results on pickup proton dynamics in the distant solar wind are also discussed.

Description: Relativistic electron microbursts, which are bursty enhancements of the precipitation of relativistic electrons, are often observed by low-altitude satellite measurements. These microbursts are likely to play an important role in high-energy electron flux loss in the outer radiation belt. Some observations suggest that whistler chorus waves are a cause of relativistic electron microbursts. First, we derived the relativistic time of flight model considering the propagation of whistler mode waves, and then investigated characteristics of the precipitations. We found that relativistic electron precipitation has a positive energy dispersion at low altitude. The duration of electron precipitation by one whistler chorus element decreases when the energy of the precipitated electrons is increased. We then performed three-dimensional test particle simulation with a newly developed wave-particle interaction model using realistic plasma parameters in the inner magnetosphere. The test particle simulation showed for the first time that the resonant interactions with whistler chorus elements at high-latitudes produce bursty enhancements of relativistic electron precipitation, thus confirming the results of the TOF analysis. A few Hz modulations are embedded in the precipitating electron flux variations, which is associated with the repetition period of the whistler chorus elements. The simulation results indicate that microbursts of relativistic electrons of the outer belt are caused by chorus wave-particle interactions at high latitudes and a series of rising tone elements of chorus waves produce a few Hz modulation of microbursts observed by the SAMPEX satellite.

Description: The passage of an interplanetary (IP) shock was detected by Wind, ACE, Geotail, and THEMIS-B in the solar wind on 24 November 2008. From the propagation time of the IP shock at the spacecraft, it is expected that the IP shock front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using multipoint observations of the sudden commencement (SC) at THEMIS probes, GOES 11, and ETS in the dayside magnetosphere, we confirmed that the magnetospheric response to the IP shock starts earlier in the postnoon sector than in the prenoon sector. We found that the estimated normal direction of the SC front is nearly aligned with the estimated IP shock normal. We also found that the SC front normal speed is much slower than the fast mode speed and is about 22–56% of the IP shock speed traveling in the solar wind. Thus, we suggest that the major field changes of the SC in the dayside magnetosphere are not due to the magnetic flux carried by hydromagnetic waves but to the increased solar wind dynamic pressure behind the shock front sweeping the magnetopause. The SC event appears as a step-like increase in the H component at the low-latitude Bohyun station and a negative-then-positive variation in the H component at the high-latitude Chokurdakh (CHD) station in the morning sector. During the negative perturbation at CHD, the SuperDARN Hokkaido radar detected a downward motion in the ionosphere, implying westward electric field enhancement. Using the THEMIS electric field data, it is confirmed that the westward electric field corresponds to the inward plasma motion in the dayside magnetosphere due to the magnetospheric compression.

Description: Quasi-linear bounce-averaged diffusion coefficients for interactions between electrons and parallel propagating whistler waves in a dipole field are compared with test particle simulations. We solve equations of motion for a large number of electrons interacting with waves with a Gaussian distribution of wave power. For broadband and small amplitude waves, which are assumed by the quasi-linear analysis, our test particle simulation results agree well with quasi-linear theory predictions. We then demonstrate the effect of the wave amplitude on diffusion coefficients. We show that as the amplitude increases, the bounce-averaged quasi-linear diffusion coefficients become invalid. Critical wave amplitudes for the breakdown of the bounce-averaged diffusion coefficients for a range of energies and pitch angles are calculated for the set of wave parameters we used. Finally, we investigate the effect of wave bandwidth on bounce-averaged diffusion coefficients. Consistent with a previous theoretical prediction, bounce-averaged quasi-linear diffusion coefficients are still valid for narrowband waves, as long as the wave amplitude is small. When the amplitude of the narrowband wavefield increases, nonlinear effects such as phase-bunching and trapping become dominant and correspondingly quasi-linear theory becomes invalid. Our results demonstrate the validity of applying quasi-linear theory to interactions between electrons and small amplitude plasma waves in the radiation belt.

Description: We investigate the evolution of waves driven by the linearly polarized Alfvén wave in the magnetic field-aligned cross-field shear flow. The generated electric field is derived in ideal MHD using analytical solutions for the driven waves. A single particle dynamics in the generated electromagnetic field is considered and governing equations for the particle's total kinetic energy and particle parallel velocity are obtained. Our goal is to show how the driven wave inclusion modifies the evolution of these quantities. It is shown that the total kinetic energy of the particle as well as the particle's parallel velocity is not conserved in the driven wave fields and there is a force exerted on particles. A specific example is considered using solar coronal hole plasma parameters. The process presented in this work might also be important in the laboratory, terrestrial and astrophysical plasma processes where the inhomogeneous flows are present.

Description: To address the mechanism and factors controlling the injection of energetic particles to the geostationary orbit (GEO), we analyzed the appearance of injections at the GEO drift shell as observed by LANL spacecraft in the cases where the flow bursts and associated transient dipolarization were detected at the entry to the inner magnetosphere, in the high beta plasma sheet region on the nightside between 8 and 13 Re. We analyzed two different data sets, one including Geotail observations in 1995–2005 and another including a set of Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations in 2008–2009. We found that only a small portion of all flow bursts at 8–13 Re were associated with particle injection at GEO but that those injection-associated flows had smaller values of plasma tube entropy parameter (PV5/3) as well as larger change of magnetic field north-south component (dBz). This confirms a scenario that the bursty flows at the entry of the inner magnetosphere (8–13 Re) penetrate into GEO and produce there the energetic particles flux increase. According to the bubble theory of magnetotail plasma flows, the probability of the deep plasma penetration critically depends on how stretched the magnetospheric configuration is, and this dependence is statistically confirmed in a large database to be the major factor controlling the occurrence of GEO injections. We suggest using the background plasma tube entropy value in the nightside part of the GEO drift shell as a suitable parameter to predict the probability of particle injection to GEO. One more outcome of this study is that the energetic particle injections cannot reliably serve as a tool to identify the substorm onset times, as has been done in many past studies.

Description: The solar wind and the Earth's magnetosheath are often characterized by proton temperature anisotropies that cannot be discussed by adiabatic fluid theory. An excessive perpendicular temperature anisotropy may result when the plasma undergoes compression. The proton temperature anisotropy, T⊥/T∥ 〉 1, leads to the proton cyclotron and mirror instabilities. Marginal stability conditions for these instabilities may be expressed as inverse correlations between T⊥/T∥ and parallel beta, β∥. In the literature, these correlations are constructed on the basis of linear theory, hybrid simulations, or observational fitting. The present paper makes use of quasilinear theory for the proton cyclotron and mirror instabilities. In such an approach the inverse correlation naturally emerges as the time-asymptotic states of self-consistent evolution. The inverse correlation thus constructed shows the predominance of proton cyclotron instability for low β∥ regime, while for high β∥ values, the mirror instability dictates the inverse correlation.

Description: We report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (Ssp and Ssh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RDsp and RDsh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer.

Description: Statistical analysis of Dst behavior during recovery phase of magnetic storms induced by different types of interplanetary drivers is made on the basis of OMNI data in period 1976–2000. We study storms induced by ICMEs (including magnetic clouds (MC) and Ejecta) and both types of compressed regions: corotating interaction regions (CIR) and Sheaths. The shortest, moderate and longest durations of recovery phase are observed in ICME-, CIR- , and Sheath-induced storms, respectively. Recovery phases of strong (Dstmin ≤ −100 nT) magnetic storms are well approximated by hyperbolic functions Dst(t) = a/(1 + t/τh) with constant τh times for each types of drivers while for moderate (−100 

Description: An empirical model of subauroral polarization streams (SAPS) has been incorporated into the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). This SAPS driven TIEGCM is used to simulate the effect of SAPS on the global thermosphere and ionosphere during a moderate geomagnetically active period between day of year (DOY) 329 and 333 in 2008. Model results show: (1) SAPS caused an increase in global thermospheric temperature which became stronger with time. This neutral temperature increase was more significant in subauroral and auroral regions. Joule heating by the SAPS and the redistribution of this heat by dynamic processes were the primary mechanisms for the simulated global neutral temperature changes. (2) In the SAPS driven TIEGCM, the strong ion drag effect in the subauroral SAPS channel drove large changes in thermospheric winds. Zonal neutral winds had either an extra, separate channel of westward flow in the subauroral region in the afternoon-midnight sector or a broad westward wind jet that merged with the regular duskside auroral westward zonal neutral wind driven by the high latitude convection pattern. The exact latitudinal profile of the zonal winds depended on local time. (3) The response of neutral temperature and wind to SAPS was more significant at higher altitudes and exhibited seasonal/hemispheric asymmetry. (4) The heating to the thermosphere by SAPS also resulted in changes in thermospheric composition with upwelling of molecular rich air in subauroral and auroral regions and downwelling of atomic oxygen rich air at other latitudes. These changes in thermospheric composition contributed to the deeper and more extended ionospheric electron density depletions in subauroral middle latitude regions, as well as electron density increases along the equatorward edge of the SAPS channel in the afternoon sector.

Description: Kinetic Alfvén waves (KAWs) with highly oblique wave vectors, k⊥ ≫ k∥, are believed to form an integral part of the turbulent energy cascade in the solar wind near the proton gyroradius scale k⊥ρi ∼ 1. At wave numbers k⊥ρi 〉 1, where linear theory predicts kinetic Alfvén waves undergo strong Landau damping, mode coupling with ion-Bernstein waves (IBWs) occurs. This mode coupling enables energy exchange between KAWs and IBWs that may be relevant for turbulent dissipation processes in the solar wind and other collisionless plasmas. It is pointed out that for plasmas having Gaussian velocity distributions, also known as Maxwellian plasmas, the dispersion relation of IBWs exhibits a fine structure or splitting into multiple branches that causes the dispersion relation of IBWs to intersect a given branch of the KAW dispersion relation several times, thus providing multiple channels of energy exchange between KAWs and IBWs (for a given angle of wave propagation). It is also shown that the collisionless damping rate of IBWs can exceed that of KAWs in certain regions of parameter space and that IBWs exhibit different ratios of proton to electron heating than KAWs. Consequently, the role of IBWs in the dissipation of solar wind turbulence requires more careful study. Gyrokinetic theory, gyrokinetic simulations, and other physical models of solar wind dissipation processes which ignore the coupling between KAWs and IBWs may be missing important physics.

Description: It has been found that the DMSP spacecraft at 840 km can charge to very large negative voltages (up to −2000 V) when encountering intense precipitating electron events (auroral arcs). We present an 11-year study of over 1600 charging events, defined as when the spacecraft charged to levels exceeding 100 V negative during an auroral crossing. The occurrence frequency of events was highly correlated with the 11-year solar cycle with the largest number of events occurring during solar minimum. This was due to the requirement that the background thermal plasma density be low, at most 104 cm−3. During solar maximum, the plasma density is typically well above that level due to the solar EUV ionizing radiation, and although the occurrence frequency of auroral arcs is considerably greater than at solar minimum, the occurrence of high-level charging is minimal. As a result of this study, we produced a model spectrum for precipitating electrons that can be used as a specification for the low-altitude auroral charging environment. There are implications from this study on a number of LEO satellite programs, including the International Space Station, which does enter the auroral zone, particularly during geomagnetic activity when the auroral boundary can penetrate to very low latitudes. The plasma density in the ISS orbit is usually well above the minimum required density for charging. However, in the wake of the ISS, the plasma density can be 2 orders of magnitude or more lower than the background density and thus conditions are ripe for charging.

Description: A full kinetic elve model with a wide time range from microseconds to seconds and its spectral range from UV, visible to near-infrared wavelengths is developed. Not only the fast electron-impact emissions N2 1P (B3Πg - A3Σu+), N2 2P(C3Πu - B3Πg), N2 Lyman-Birge-Hopfield (a1Πg - X1Σg+), N2+ 1N (B2Σu+ - X2Σg+) and O2+ 1N (b4Σg− – a4Πu) but also the post-impulse chemiluminescenses, O2 atmospheric band (b1Σg+ – X3Σg−), O(1S – 1D) at 557.7 nm and O(1D – 3P) at 630 nm, are considered in the elve model. We calculate the dominant emissions and possible weak emissions in our elves model to analyze the relative importance of emission intensity, measured by the ISUAL imager with 5 selectable band pass filters (N21P, 762, 630, 557.7, 427.8 nm filter). The modeling emission intensities were well consistent with the measurements by Imager with different filters. This comparison could also be useful in designing the imager filters for future TLE survey missions in Earth orbit.

Description: The magnetic local time and latitude dependence of amplitude of the main impulse (MI) of geomagnetic sudden commencements (SCs) and its seasonal variation have been investigated using high time resolution (1–3 sec) geomagnetic data in the latitudinal range 27–70 degrees for the period 1996–2010. The daytime distribution of the SC-MI amplitude in the sub-auroral and middle latitudes (35–60 degrees) is similar to the DP-2 type geomagnetic variation which shows negative and positive changes in the morning and afternoon, respectively. The magnetic field variation is reversed around the magnetic latitude of 63–65 degrees. This suggests that a pair of field-aligned currents (FACs), resembling the region-1 (R-1) FACs, is located near the magnetic latitude of 63–65 degrees. The nighttime SC amplitude is enhanced significantly in the low and middle latitudes (27–60 degrees). The enhancement is due to the magnetic effect produced by the SC-MI FACs. In the nighttime auroral latitude (63–65 degrees), the SC amplitude decreases steeply due to the enhanced westward auroral electrojet associated with the compression of the magnetosphere. The size of the diurnal variation tends to increase significantly during the summer, compared with that during the winter. This seasonal variation suggests that the DP-2 type ionospheric currents (ICs) and FACs generated during the SC-MI phase are intensified by increased ionospheric conductivities during the summer. It can be concluded that the large-scale MI current system in the ionosphere and magnetosphere is voltage generator.

Description: Recent case studies on the precursor signatures of equatorial spread-F (ESF) have shown a one-to-one correspondence between the large-scale wave structures (LSWS) and ESF development at equatorial latitude. In this study, the LSWS and the onset and development of the ESF are investigated over Sanya (18°N, 109°E), a station located at 13° north of the magnetic equator, during both geomagnetic quiet and disturbed conditions in September–October 2011. High-time-resolution ionograms from Digisonde Portable Sounder (DPS-4D) provided the satellite trace measurements that were used to indicate the occurrence of the LSWS. The development of local ESF activity was identified using GPS scintillation and VHF coherent radar echo measurements from the same site, together with the range type spread-F (RSF) in ionograms. Additionally, the Sanya VHF radar five-beam scanning measurements in east–west direction were used to characterize the longitudinal difference in establishing the initial conditions for ESF development. Correlative studies between the LSWS and ESF activities during the observational period offer consolidated evidence that the LSWS is a necessary precursor for the ESF development. It is shown that the LSWS and ESF have nearly a one-to-one relationship when the F layer undergoes an abrupt post-sunset rise (PSSR), revealing that the magnitude of the pre-reversal enhancement in zonal electric field (PRE) that elevates the F layer to a high enough altitude is an important parameter controlling the generation of post-sunset ESF. However, in the absence of the PSSR, the ESF and GPS scintillation did not always occur following the appearance of LSWS. Sometimes the LSWS events preceded the generation of bottom type spread-F (BSF) that did not develop vertically into ESF and radar plumes. This result may indicate that under inexpressive, weak, or even moderate PRE conditions, the appearance of the LSWS alone may not be sufficient to produce the post-sunset F region irregularities responsible for ionospheric scintillations. More factors, other than the LSWS, could play crucial roles favoring the growth of ESF instabilities responsible for ionospheric scintillations.

Description: It is pointed out that interactions between the solar wind and the dusty magnetospheres of planets and comets give rise to nonlinear electrostatic drift waves. It is assumed that after transient processes a local steady state is attained with the same sheared flow of electrons and ions Vi0(x) = Ve0(x) = V0(x)z^ along the initial constant component of B0z of the total sheared magnetic field B0=B0zz^+B0y(x)y^. The nonlinear perturbation caused by the electron temperature gradient forms solitary and shock structures, depending upon the dominant role of either the wave dispersion or dissipation, respectively. The theoretical model has been applied to the magnetosphere of Jupiter that contains positively charged dust grains. This investigation predicts the formation of short scale electrostatic solitons having width of the order of 1 m and shocks having widths of the order of 2 m.

Description: The dynamics of inner radiation belt electrons are governed by competing source, loss, and transport processes. However, during the recent extended solar minimum period the source was inactive and electron intensity was characterized by steady decay. This provided an opportunity to determine contributions to the decay rate of losses by precipitation into the atmosphere and of diffusive radial transport. To this end, a stochastic simulation of inner radiation belt electron transport is compared to data taken by the IDP instrument on the DEMETER satellite during 2009. For quasi-trapped, 200 keV electrons at L = 1.3, observed in the drift loss cone (DLC), results are consistent with electron precipitation losses by atmospheric scattering alone, provided account is taken of non-diffusive wide-angle scattering. Such scattering is included in the stochastic simulation using a Markov jump process. Diffusive small-angle atmospheric scattering, while causing most of the precipitation losses, is too slow relative to azimuthal drift to contribute significantly to DLC intensity. Similarly there is no contribution from scattering by VLF plasma waves. Energy loss, energy diffusion, and azimuthal drift are also included in the model. Even so, observed decay rates of stably-trapped electrons with L 〈 1.5 are slower than predicted by scattering losses alone, requiring radial diffusion with coefficient DLL ∼ 3 × 10−10 s−1 to replenish electrons lost to the atmosphere at low L values.

Description: A recent two-dimensional (radial distance r and solar longitude ϕ) model for the solar wind is driven using 1 h average data from the Wind spacecraft. We extend the treatment of the Sun's magnetic field in comparison with previous models to allow a nonzero intrinsic azimuthal component Bϕ at the solar source surface, in addition to the radial component Br. We find nonzero azimuthal magnetic fields at the source surface which dominate the variability in B(r, ϕ) at 1 AU and beyond. The averages 〈|Bϕ(Rs)|〉 and 〈|Br(Rs)|〉 inferred over solar cycle 23 were 0.44 ± 0.48 μT (4.4 ± 4.8 mG) and 120 ± 30 μT (1.2 ± 0.3 G) at the photosphere, respectively, where Rs equals one solar radius. While the surface magnetic field is closely radial on average as expected, it is sometimes over 20° from radial. Both Bϕ and Br vary smoothly on periods of order of a day, with evidence for relatively narrow current sheets, and vary differently with the solar cycle: Br(Rs) is correlated with the sunspot number while Bϕ(Rs) has a two-level behavior. The typical fields |Br(Rs)| are consistent with previous estimates. This consistency, the finding of a linear relation between the data-smoothing time period and the average transition time for each component and other arguments support the contention that the Bϕ(Rs) fields found are intrinsic. Our results and model can account naturally for non-Parker-like magnetic field directions at 1 AU and all r above the source surface.

Description: We study the solar wind proton velocity space distribution functions on the lunar nightside at low altitudes (∼100 km) above the lunar surface using a three-dimensional hybrid plasma solver, when the Moon is in the unperturbed solar wind. When the solar wind encounters a passive obstacle, such as the Moon, without any strong magnetic field and no atmosphere, solar wind protons that impact the obstacle's surface are absorbed and removed from the velocity space distribution functions. We show first that a hybrid model of plasma is applicable to study the low-altitude lunar plasma wake by comparing the simulation results with observations. Then we examine the effects of a solar wind bi-Maxwellian velocity space distribution function and the lunar surface plasma absorption on the solar wind protons' velocity space distribution functions and their entry in the direction parallel to the interplanetary magnetic field lines into the low-altitude lunar wake. We present a backward Liouville method for particle-in-cell solvers that improves velocity space resolution. The results show that the lunar surface plasma absorption and anisotropic solar wind velocity space distributions result in substantial changes in the solar wind proton distribution functions in the low-altitude lunar plasma wake, modifying proton number density, velocity, and temperature there. Additionally, a large temperature anisotropy is found at close distances to the Moon on the lunar nightside as a consequence of the lunar surface plasma absorption effect.

Description: We report on nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed at Kototabang, Indonesia (geographic longitude: 100.3°E; geographic latitude: 0.2°S; and geomagnetic latitude: 10.6°S) during a 7-year period from October 2002 to October 2009. MSTIDs were observed in 630-nm nighttime airglow images by using a highly sensitive all-sky airglow imager at Kototabang. The averages and standard deviations of horizontal phase velocity, period, and horizontal wavelength of MSTIDs observed during the 7 years were 320 ± 170 m/s, 42 ± 11 min, and 790 ± 440 km, respectively. The occurrence rate of the observed MSTIDs decreased with decreasing solar activity. The average horizontal wavelength of MSTIDs increased with decreasing solar activity. Southward MSTIDs were dominant throughout the 7 years of observations. These facts are consistent with the hypothesis that the observed MSTIDs are caused by gravity waves in the thermosphere. Moreover, we compared the propagation directions of the observed MSTIDs with the locations of tropospheric convection activity for the events where gravity waves producing the observed MSTIDs could have existed in the lower atmosphere. Strong tropospheric convection was found within ±30 degrees from the source directions of MSTIDs in 81% of the MSTID events. In such events, gravity waves were possibly generated from deep convection in the troposphere and directly propagated into the thermosphere.

Description: Jovian anomalous continuum is a narrowband electromagnetic radiation near 10 kHz that can escape from Jupiter's magnetosphere to interplanetary space. One possible source mechanism is the magnetosheath re-radiation of the Jovian low frequency radio emissions such as the quasiperiodic (QP) radio emissions, broadband kilometric radiation (bKOM) and non-thermal continuum. Jovian anomalous continuum was consistently observed by the Cassini Radio and Plasma Wave Science instrument from 2000 to 2004, right before the Saturn orbit insertion, which means the radiation can be detected as far as 8 AU away from Jupiter. An analysis of intensity versus radial distance shows that the Jovian anomalous continuum has a line source rather than a point source, consistent with the theory that the emission is radiated by the whole length of the magnetotail. The emissions are modulated at the system III period of Jupiter and are unpolarized. Since the lower cutoff frequency of the anomalous continuum is related to the plasma frequency in the magnetosheath of Jupiter, which is a function of solar wind density, the recurrent variations of the lower cutoff frequency can be used as a remote diagnostic of the solar wind condition at Jupiter. We propose that the frequency dispersion, a unique characteristic of the anomalous continuum, is likely a comprehensive effect of both the slow group velocity near the local plasma frequency and the refraction/scattering of the waves by density structures as they propagate in the magnetosheath.

Description: A self-consistent theory of relatively thin anisotropic current sheets (TCS) in collisionless plasma is developed, taking into account the presence of a guiding field By (all notations are used in the GSM coordinate system). TCS configurations with a finite value of guiding field By are often observed in Earth's magnetotail and are typical for Earth's magnetopause. A characteristic signature of such configurations is the existence of a magnetic field component along the direction of TCS current. A general case is considered in this paper with global sheared magnetic field By = const. Analytical and numerical (particle-in-cell) models for such plasma equilibria are analyzed and compared with each other as well as with Cluster observations. It is shown that, in contrast to the case with By = 0, the character of “particle-current sheet” interaction is drastically changed in the case of a global magnetic shear. Specifically, serpentine-like parts of ion trajectories in the neutral plane become more tortuous, leading to a thicker current sheet. The reflection coefficient of particles coming from northern and southern sources also becomes asymmetric and depends upon the value of the By component. As a result, the degree of asymmetry of magnetic field, plasma, and current density profiles appears characteristic of current sheets with a constant By. In addition, in the presence of nonzero guiding field, the curvature current of electrons in the center of the current sheet decreases, yielding an effective thickening of the sheet. Implications of these results for current sheets in Earth's magnetosphere are discussed.