ALBERT

Description: [1]  Neutron monitors have recorded the flux of high energy Galactic cosmic rays for more than half a century. During the recent prolonged, deep minimum in solar activity many sources indicate that modulated Galactic cosmic rays have attained new space-age highs. However reported neutron monitor rates are ambiguous; some record new highs while others do not. This work examines the record of 15 long-running neutron monitors to evaluate cosmic ray fluxes during the recent extraordinary solar minimum in a long-term context. We show that ground-level neutron rates did reach a historic high during the recent solar minimum, and we present a new analysis of the cosmic ray energy spectrum in the year 2009 versus year 1987. To do this we define a reference as the average of eight high-latitude neutron monitors, four in the northern hemisphere (Apatity, Inuvik, Oulu, Thule) and four in the southern hemisphere (Kerguelen, McMurdo, Sanae, Terre Adelie). Most stations display changes in sensitivity, which we characterize by a simple linear trend. After correcting for the change in sensitivity, a consistent picture emerges. With our correction all stations considered display new highs at the recent solar minimum, approximately 3% above the previous record high. These increases are shown to be consistent with spacecraft observations.

Description: [1]  We present the occurrence frequency of downgoing auroral electron beams in magnetic local time and invariant latitude, and the dependence on solar cycle, as indicated by F10.7, on whether the ionospheric footpoint of the satellite is illuminated or dark, and on the energy flux carried by the electrons. As previously reported, we find that the occurrence of electron beams peaks in the pre-midnight local time sector and that solar illumination at the footpoint (solar zenith angle) reduces both the occurrence and energy of the electron beams. The effect of solar maximum conditions (indicated by F10.7) is almost as large as the effect of the solar zenith angle. The characteristic energy of the electron beams is dependent on the energy flux carried, in addition to both solar zenith angle and F10.7. The beam energy (and therefore the parallel potential drop) is ~1.6 times higher for during solar minimum than during solar maximum for both dark and illuminated footpoints. The beam energy during dark solar minimum conditions is a factor of ~3 more than during sunlit minimum conditions. The ‘area’ covered by intense aurora is also reduced during solar maximum, for both sunlit and dark conditions. There is no evidence that the statistical results are due to the fact that acceleration via parallel electric fields moves to lower latitudes during solar maximum.

Description: [1]  In this paper we describe and quantify the energy transfer, flow and distribution. Our high-resolution data-set covers 13 years of OMNI, SuperMAG and Kyoto data. We employ what we consider to be the best estimates for energy sinks, and relate these to SuperMAG indices for better coverage and spatial resolution. For the energy input we have used the method of dimensional analysis [ Vasyliunas et al ., 1982] that is presented in unit power and makes it appropriate for energy analysis. A cross-correlation analysis parameterizes the magnetospheric response on the solar wind parameters during a wide range of conditions, ranging from substorms and storms up to a decade. The determined functional form is then evaluated and scaled using superposed epoch analysis of geomagnetic storms, revealing that the effective area of interaction can not be considered static. Instead we present a dynamic area which depends to the first order on the cube of the IMF B z component. Also, we find that for longer time periods this area must be increased compared to the area used for geomagnetic storms. We argue that some of the terms in the energy coupling function are contributory to describing magnetosheath conditions, and discuss how our coupling function can be related to Maxwell stress components. Also, we quantify the relative importance of the different energy sinks during substorms, geomagnetic storms and long time series, and present the coupling efficiency of the solar wind. Our energy coupling functions is compared with the ɛ parameter [ Akasofu and Perreault , 1978] and performs better for almost any event.

Description: [1]  Plasma sheet flow bursts have been suggested to correspond to different types of auroral activity, such as poleward boundary intensifications (PBIs), ensuing auroral streamers, and substorms. The flow-aurora association leads to the important question of identifying the magnetotail source region for the flow bursts and how this region depends on magnetic activity. The present study uses the ARTEMIS spacecraft coordinated with conjugate ground-based auroral imager observations to identify flow bursts beyond 45 R E downtail and corresponding auroral forms. We find that quiet-time flows are directed dominantly earthward with a one-to-one correspondence with PBIs. Flow bursts during the substorm recovery phase, and during steady magnetospheric convection (SMC) periods are also directed earthward, and these flows are associated with a series of PBIs/streamers lasting for tens of minutes with similar durations to that of the series of earthward flows. Pre-substorm onset flows are also earthward and associated with PBIs/streamers. The earthward flows during those magnetic conditions suggest that the flow bursts, which lead to PBIs and streamers, originate from further downtail of ARTEMIS, possibly from the distant tail neutral line (DNL) or tailward-retreated near-Earth neutral line (NENL) rather than from the nominal NENL location in the mid-tail. We find that tailward flows are limited primarily to the substorm expansion phase. They continue throughout the period of auroral poleward expansion, indicating that the expansion-phase flows originate from the NENL and that NENL activity is closely related to the auroral expansion of the substorm expansion phase.

Description: [1]  The solar eclipse on 15 January 2010 traversed Asia and completed its travel on the Shandong Peninsula in China at sunset. Two vertical-incidence ionosondes at Wuhan and Beijing and the oblique-incidence ionosonde network in North China were implemented to record the ionospheric response to the solar eclipse. Following the initial electron density decrease caused by the eclipse, the ionosphere was characterized by a strong pre-midnight enhancement, and a subsequent ionospheric decay, and a ~10 hour later post-midnight enhancement. Neither geomagnetic disturbance occurred during the eclipse day, nor did obvious nighttime peak appear for the ten-day mean of the F2-layer critical frequency ( fo F2). The electron density profilogram of the Beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere, possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse. The two-dimensional differential fo F2 maps present the regional variations of the nighttime electron density peaks and decay. Both the pre- and post-midnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward. The different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux. The ionospheric decay following the pre-midnight enhancement is also considered as a consequence of the eclipse shade.

Description: [1]  We study a statistics of ∂  B z /∂  x in a thin stretching current sheet (substorm growth phases) observed by Cluster between 8 and 18 R E downtail. After 2005 spacecraft separation allowed to measure directly this derivative of B z along the tail axis. The near-tail events (within 14 R E ) exhibited a straight decrease of an initially large positive ∂  B z /∂  x to ∼ 1–2 nT/ R E . In the more stretched middle tail, usually the small | ∂  B z /∂  x | 〈 0.5 − 1 nT/ R E had no clear trend and fluctuated around zero with time scales 5–15 min. In general, negative ∂  B z /∂  x were ubiquitous. At some onsets larger negative ∂  B z /∂  x  〈 − 1 nT/ R E were associated with transient dipolarizations, propagating Earthward. There was no clear association of local plasma sheet activity onset with any value of ∂  B z /∂  x . We discuss relation of observations and recent modeling results.

Description: [1]  ELF/VLF radio waves are difficult to generate with conventional antennas. Ionospheric HF heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet, creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW HAARP facility near Gakona, Alaska, and provide a baseline reference of ELF/VLF generation capabilities with HF heating. Between February 2007 and August 2008, HAARP was operated on close to 100 days for ELF/VLF wave generation experiments, at a variety of ELF/VLF frequencies, seasons and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker, but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30 dB. Generation strengthens by ~5 dB during the first ~30 minutes of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching250 km. The median power generated by HAARP and injected into the waveguide is ~0.05-0.1 W in this base-line configuration (vertical beam, 3.25 MHz, amplitude modulation), but may have generated hundreds of Watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.

Description: [1]  An inversion technique for estimating the properties of the magnetospheric plasma from the harmonic frequencies of the toroidal standing Alfvén waves has been used to derive the global equatorial mass density covering radial distances from 4 to 9 Earth radii ( R E ), within the local time sector spanning from 0300 to 1900 hours. This broad range of L shell extending to the outer magnetosphere allows us to examine the local time and radial dependence of the quiet-time equatorial mass density during solar minimum and thereby construct a global distribution of the equatorial mass density. The toroidal Alfvén waves were detected with magnetometers on the Active Magnetospheric Particle Tracer Explorers (AMPTE)/Charge Composition Explorer (CCE) during the nearly 5 year interval from August 1984 to January 1989 and on the Geostationary Operational Environmental Satellites (GOES) (10, 11 and 12) for 2 years from 2007 to 2008, both of which were operating during solar minimum years. The derived equatorial mass density, ρ eq , at geosynchronous orbit (GEO) monotonically increases with increasing magnetic local time (MLT) from the nightside towards the dusk sector. At other radial distances, ρ eq has the same MLT variation as that of GEO, while the magnitude logarithmically decreases with increasing L value. An investigation of the Dst and Kp dependence shows that the median value of ρ eq varies little in the daytime sector during moderately disturbed times, which agrees with previous studies. ρ eq calculated from the F 10.7 dependent empirical model shows good agreement with that of CCE but overestimates that of GOES probably due to the extreme solar cycle minimum in years 2007–2008.

Description: [1]  In this paper we compare observations of the high latitude cusp from DMSP data to simulations conducted using the Lyon-Fedder-Mobarry (LFM) global magnetosphere simulation. The LFM simulation is run for the 31 Aug 2005 to 02 Sep 2005 moderate storm, from which the solar wind data exhibits a wide range of conditions that enable a statistical representation of the cusp to be obtained. The location of the cusp is identified using traditional magnetic depression and plasma density enhancement at high altitude. A new diagnostic using the parallel ion number flux is also tested for cusp identification. The correlation of the cusp latitude and various solar wind IMF coupling functions is explored using the three different cusp identification methods. The analysis shows 1) the three methods give approximately the same location and size of the simulated cusp at high altitude; 2) the variations of the simulated cusp are remarkably consistent with the observed statistical variations of the low-altitude cusp. In agreement with observations a higher correlation is obtained using other solar wind coupling functions such as the Kan-Lee electric field. The MLT position of the simulated cusp is found to depend upon the IMF By component, with a lower linear correlation. The width of the simulated cusp in both latitude and MLT is also examined. The size of the cusp is found to increase with the solar wind dynamic pressure with saturation seen when the dynamic pressure is greater than 3 nPa.

Description: [1]  Daily profiles of phase measurements as observed on fixed VLF-paths generally show a transient phase advance, followed by a phase delay, for about 90 minutes after sunrise hours. This is indicative of a reflecting ionospheric C-region developing along the terminator line at an altitude below the normal D-region. The suggested occurrence of a C-region is consistent with rocket measurements made in the 1960's, showing a maximum of the electron density between 64 and 68 km, and by radio sounding in the 1980's. In order to correctly describe the properties of the phase effect associated with the presence of a C-region, it is important to understand the subionospheric propagation characteristics of the VLF-paths. In this paper, we analyze the variations presented by the temporal properties of the VLF narrow-band phase effect, and determined a parameter associated with the appearance of the C-region at sunrise hours observed by receivers from the South America VLF Network (SAVNET). Periodic patterns emerge from the parameter curves. Two distinct temporal behavior regimes can be identified: one exhibiting slow variations between March and October, and another one exhibiting faster variations between October and March. Solar illumination conditions and the geometrical configuration of the VLF paths relative to the sunrise terminator partly explain the slow variation regime. During periods of faster variations, we have observed good association with atmospheric temperature variability found in the measurements of the TIMED-SABER satellite instrument, which we assume to be related to the Winter Anomaly atmospheric phenomenon. However, when comparing the parameter time series with temperature curves, no direct one-to-one correspondence was found for transient events.

Description: [1]  On 21 January 2005, one of the fastest interplanetary coronal mass ejections (ICME) of solar cycle 23, containing exceptionally dense plasma directly behind the sheath, hit the magnetosphere. We show from charge-state analysis that this material was a piece of the erupting solar filament, and further, based on comparisons to the simulation of a fast CME, that the unusual location of the filament material was a consequence of three processes. As the ICME decelerated, the momentum of the dense filament material caused it to push through the flux rope towards the nose. Diverging non-radial flows in front of the filament moved magnetic flux to the sides of the ICME. At the same time reconnection between the leading edge of the ICME and the sheath magnetic fields worked to peel away the outer layers of the flux rope creating a remnant flux rope and a trailing region of newly opened magnetic field lines. These processes combined to move the filament material into direct contact with the ICME sheath region. Within one hour after impact and under northward IMF conditions, a cold dense plasma sheet formed within the magnetosphere from the filament material. Dense plasma sheet material continued to move through the magnetosphere for more than 6 hours as the filament passed by the Earth. Densities were high enough to produce strong diamagnetic stretching of the magnetotail despite the northward IMF conditions and low levels of magnetic activity. The disruptions from the filament collision are linked to an array of unusual features throughout the magnetosphere, ionosphere and atmosphere. These results raise questions about whether rare collisions with solar filaments may, under the right conditions, be a factor in producing even more extreme events.

Description: [1]  We present observations from the Falkland Islands SuperDARN radar of the propagation of HF radio waves via the Weddell Sea ionospheric Anomaly (WSA), a region of enhanced austral summer nighttime ionospheric electron densities covering the southern Pacific and South Americas region. This anomaly is thought to be produced by uplift of the ionosphere by prevailing equatorwards thermospheric winds. Of particular interest are perturbations of the WSA-supported propagation, which suggest that during periods of geomagnetic disturbance the ionospheric layer can be lowered by several 10s of km and subsequently recover over a period of 1 to 2 hours. Perturbations can appear singly or as a train of 2 to 3 events. We discuss possible causes of the perturbations, and conclude that they are associated with equatorward-propagating large-scale atmospheric waves produced by magnetospheric energy deposition in the auroral or sub-auroral ionosphere. Changes in high/mid-latitude electrodynamics during geomagnetic storms may also account for the perturbations, but further modeling is required to fully understand their cause.

Description: [1]  Inner magnetosphere magnetic field and plasma flow data are examined during 228 steady magnetospheric convection events. We find that the B Z component of the magnetic field around geostationary orbit is weaker than during average conditions and the plasma flow speeds are higher than average in the dusk sector just beyond geostationary orbit. The SMC periods include more enhanced Earthward and tailward flow intervals than during average conditions. The steady convection period magnetic field is not steady: The near-geostationary nightside field grows increasingly taillike throughout the steady convection period. In the midtail, Earthward flows are enhanced in a wide region around the midnight sector, which leads to enhanced magnetic flux transport toward the Earth during the steady convection periods. Compared to well-known characteristics during magnetospheric substorms, the inner tail evolution resembles that during the substorm growth phase, while the midtail flow characteristics duringsteady convection periods are similar to those found during substorm recovery phases.

Description: [1]  A global total electron content (TEC) model response to geomagnetic activity described by the K p -index is built by using the Center for Orbit Determination of Europe (CODE) TEC data for full 13 years, January 1999 - December 2011. The model describes the most probable spatial distribution and temporal variability of the geomagnetically forced TEC anomalies assuming that these anomalies at a given modip latitude depend mainly on the K p -index, local time (LT) and longitude. The geomagnetic anomalies are expressed by the relative deviation of TEC from its 15-day median and are denoted as rTEC. The rTEC response to the geomagnetic activity is presented by a sum of two responses with different time delay constants and different sign of the cross-correlation function. It has been found that the mean dependence of rTEC on K p -index can be expressed by a cubic function. The LT dependence of rTEC is described by Fourier time series which includes the contribution of four diurnal components with periods 24, 12, 8 and 6 hours. The rTEC dependence on longitude is presented by Fourier series which includes the contribution of zonal waves with zonal wavenumbers up to 6. In order to demonstrate how the model is able to reproduce the rTEC response to geomagnetic activity three geomagnetic storms at different seasons and solar activity conditions are presented. The model residuals clearly reveal two types of the model deviation from the data: some underestimation of the largest TEC response to the geomagnetic activity and randomly distributed errors which are the data noise or anomalies generated by other sources. The presented TEC model fits to the CODE TEC input data with small negative bias of -0.204, root mean squares error RMSE  = 4.592 and standard deviation error STDE  = 4.588. The model offers TEC maps which depend on geographic coordinates (5 o x5 o in latitude and longitude), and universal time (UT) at given geomagnetic activity and day of the year. It could be used for both science and possible service (nowcasting and short-term prediction); for the latter a detailed validation of the model at different geophysical conditions has to be performed in order to clarify the model predicting quality.

Description: [1]  Magnetic reconnection (MR), a fundamental process in space plasmas that changes magnetic topology and converts magnetic energy into kinetic and thermal energies, is an ultimate driver of space weather. There exist two models of MR in the literatures, anti-parallel and component, associated with intensive studies of their generation and applications. In this paper we report an MR event observed by Cluster constellation in the geo-magnetotail where both types of MR were detected. By reconstructing the three-dimensional (3D) MR configuration we find that a pair of A-B nulls existed in both types of MR cases with two fan surfaces intersecting each other to form a separator line connecting the nulls. A weak or sizable magnetic field exists along the separator in the anti-parallel or component case, respectively. In the latter case, field strength is finite away from the two nulls and vanishes close to the nulls. Therefore, at least in the two cases observed, both anti-parallel and component MR geometries are local presentation of the separator MR configuration. This result supports the expectation that 3D nulls often occur as a crucial element of MR at least in the magnetotail and separator MR may play an important role in dynamics and reconfiguration of magnetic field in 3D MR processes.

Description: [1]  The development of equatorial plasma irregularity plumes can be well recorded by steerable backscatter radars operated at and off the magnetic equator due to the fact that the vertically extended plume structures are tracers of magnetically north-south aligned larger scale structures. From observations during March 2012, using two low latitude steerable backscatter radars in Southeast Asia, the Equatorial Atmosphere Radar (EAR) (0.2ºS, 100.3ºE; dip lat 10.4ºS) and the Sanya VHF radar (18.4ºN, 109.6ºE; dip lat 12.8ºN), the characteristics of backscatter plumes over the two sites separated in longitude by ~1000 km were simultaneously investigated. The beam steering measurements reveal frequent occurrences of multiple plumes over both radar sites, of which two cases are analyzed here. The observations on 30 March 2012 show plume structures initiated within the radar scanned area, followed by others drifting from the west of the radar beam over both stations. A tracing analysis on the onset locations of plasma plumes reveals spatially well-separated backscatter plumes, with a maximum east-west wavelength of about 1000 km, periodically generated in longitudes between 85ºE and 110ºE. The post-sunset backscatter plumes seen by the Sanya VHF radar are found to be due to the passage of sunset plumes initiated around the longitude of EAR. Most interestingly, the EAR measurements on the night of 21 March 2012 show multiple plume structures that developed successively in the radar scanned area with east-west separation of ~50 km, with however, no sunset plasma plume over Sanya. Co-located ionogram measurements show that spread F irregularities occurred mainly in the bottomside F-region at Sanya, whereas satellite traces in ionograms that are indications of large-scale wave structures, were observed on that night at both stations. Possible causes for the longitudinal difference in the characteristics of radar backscatter plumes are discussed.

Description: [1]  The solar wind impacting the Earth varies over a wide range of time scales, driving a corresponding range of geomagnetic activity. Past work has strongly indicated the rate of merging on the frontside magnetosphere is the most important predictor for magnetospheric activity, especially over a few hours. However the magnetosphere exhibits variations on other time scales, including UT, seasonal, and solar cycle variations. Much of this geomagnetic variation cannot be reasonably attributed to changes in the solar wind driving – that is, it is not created by the original Russell-McPherron effect or any generalization thereof. In this paper we examine the solar cycle, seasonal, and diurnal effects based upon the frequency of substorm onsets, using a data set of 53,000 substorm onsets. These were identified through the SuperMAG collaboration and span three decades with continuous coverage. Solar cycle variations include a profound minima in 2009 (448 substorms) and peak in 2003 (3727). The magnitude of this variation (a factor of 8.3) is not explained through variations in estimators of the frontside merging rate (such as d Φ MP / dt ), even when the more detailed probability distribution functions are examined. Instead, v , or better, n 1/2 v 2 seems to be implicated in the dramatic difference between active and quiet years, even beyond the role of velocity in modulating merging. Moreover, we find that although most substorms are preceded by flux loading (78.5% are above the mean and 83.8% above median solar wind driving) a high solar wind v is almost as important (68.3% above mean, 74.8% above median). This and other evidence suggests either v or n 1/2 v 2 (but probably not p ) plays a strong secondary role in substorm onset. As for the seasonal and diurnal effects, the elliptical nature of the Earth's orbit, which is closest to the Sun in January, leads to a larger solar wind driving (measured by Bs , vBs , or d Φ MP / dt ) in November, as is confirmed by 22 years of solar wind observations. However substorms peak in October and March, and have a UT dependence best explained by whether a conducting path established by solar illumination exists in at least one hemisphere in the region where substorm onsets typically occur.

Description: [1]  The primary sources of energetic electron precipitation (EEP) which affect altitudes 〈100 km (〉30 keV) are expected to be from the radiation belts, and during substorms. EEP from the radiation belts should be restricted to locations between L  = 1.5-8, while substorm produced EEP is expected to range from L  = 4-9.5 during quiet geomagnetic conditions. Therefore, one would not expect any significant D-region impact due to electron precipitation at geomagnetic latitudes beyond about L  = 10. In this study we report on large unexpectedly high latitude D-region ionization enhancements, detected by an incoherent scatter radar at L  ≈ 16, which appear to be caused by electron precipitation from substorms. We go on to reexamine the latitudinal limits of substorm produced EEP using data from multiple low-Earth orbiting spacecraft, and demonstrate that the precipitation stretches many hundreds of kilometers polewards of the previously suggested limits. We find that a typical substorm will produce significant EEP over the IGRF L -shell range L  = 4.6 ± 0.2-14.5 ± 1.2, peaking at L  = 6-7. However, there is significant variability from event to event; in contrast to the median case, the strongest 25% of substorms have significant EEP in the range spaning L  = 4.1 ± 0.1-20.7 ± 2.2, while the weakest 25% of substorms have significant EEP in the range spaning L  = 5.5 ± 0.1-10.1 ± 0.7. We also examine the occurrence probability of very large substorms, focusing on those events which appear to be able to disable geostationary satellites when they are located near midnight MLT. On average these large substorms occur approximately 1-6 times per year, a significant rate given the potential impact on satellites.

Description: [1]  This paper presents new observations of the behaviour of simulated dust particles in space plasma based on a 3D particle in cell code. Multistep Monte Carlo collision is employed to simulate the dust charging process which is validated for the cases of charging of isolated dust particle and ensemble dust particles, where results indicate good agreement between simulation and theories. The code is then used to investigate plasma properties near a charged surface in a vicinity of a cloud of dust particles. The simulation reveals that a cloud of dust particle close to a spacecraft surface affects plasma densities around the spacecraft as well the spacecraft's surface potential. It is suggested that dust cloud causes the surface to charge to higher negative potential. The simulation also suggests that the combination of surface potential and dust cloud potential produces a region of trapped low energy electrons.

Description: [1]  We here document with magnetic field observations a passage of the MESSENGER spacecraft through Mercury's magnetosphere under conditions of a quasi-parallel bow shock, i.e., when the direction of the upstream interplanetary magnetic field (IMF) was within 45° of the bow shock normal. The spacecraft's fast transition of the magnetosheath and the steady solar wind conditions during the period analyzed allow both spatial and temporal properties of the shock crossing to be investigated. The observations show that the shock reformation process can be nearly periodic under stable solar wind conditions. Throughout the 25-min-long observation period, the pulsation duration deviated by at most ~10% from the average 10 s period measured. This quasi-periodicity allows us to study all aspects of the shock reconfiguration, including ultra-low-frequency waves in the upstream region and large-amplitude magnetic structures observed in the vicinity of the magnetosheath − solar wind transition region and inside the magnetosheath. We also show that bow shock reformation can be a substantial source of wave activity in the magnetosphere, on this occasion having given rise to oscillations in the magnetic field with peak-to-peak amplitudes of 40–50 nT over large parts of the dayside magnetosphere. The clean and cyclic behavior observed throughout the magnetosphere, the magnetosheath, and the upstream region indicates that the subsolar region was primarily influenced by a cyclic reformation of the shock front, rather than by a spatial and temporal patchwork of short large-amplitude magnetic structures (SLAMS), as is generally the case at the terrestrial bow shock under quasi-parallel conditions.

Description: [1]  The entry of solar wind into the magnetosphere is strongly influenced by kinetic-scale boundary layers where the rapid variation in the magnetic field and/or velocity can drive transport. In current layers with strong Alfvénic velocity shear, the generation of vortices from the Kelvin-Helmholtz instability can drive magnetic reconnection even in broader current sheets by locally compressing these layers as the vortices develop. Previous two-dimensional (2D) fully kinetic simulations of this vortex-induced reconnection process have demonstrated the copious formation of magnetic islands in regions of strongly compressed current between the vortices. Here we describe the first three-dimensional (3D) fully kinetic simulations of this process and demonstrate that the compressed current sheets give rise to magnetic flux ropes over a range of oblique angles and along the entire extent of the compressed current layer around the periphery of the vortex. These flux ropes propagate with the shear flow and eventually merge with the vortex. Over longer time scales, this basic scenario is repeated as the vortices drive new compressed current sheets. In the final stage, the vortices undergo a merging process that drives new compressed current sheets and flux ropes. Based on these simulations, a simple model is proposed that predicts the size of these flux ropes relative to their parent vortex. Both the relative sizes as well as the structure of the profiles across the vortex are in reasonable agreement with THEMIS observations at the Earth's low-latitude magnetopause.

Description: [1]  We survey the properties of electron pitch angle distributions in the magnetotail plasma sheet at a distance between 15 and 19 R E from the Earth, using data from the Cluster PEACE instrument. We limit our survey to those pitch angle distributions measured when the IMF had been steadily northward or steadily southward for the previous three hours. We find that, at sub-keV energies the plasma sheet electron pitch angle distribution has an anisotropy such that there is a higher differential energyflux of electrons in the (anti-) field-aligned directions. Fitting the measured pitch angle distributions with both a single and two component kappa distribution reveals that this anisotropy is the result of the presence of a second, cold, component of electrons that is observed more often than not, and occurs during both the northward and southward IMF intervals. We present evidence that suggests the cold electron component has an ionospheric, rather than magnetosheath, source and is linked tothe large scale field aligned current systems that couple the magnetosphere and ionosphere.

Description: [1]  Driver functions for the Earth's magnetosphere-ionosphere system are derived from physical principles. Two processes act simultaneously: a reconnection-coupled MHD generator G and a viscous interaction. G accounts for the dayside reconnection rate, the length of the reconnection X-line, and current-saturation limits for the solar-wind generator. Two viscous drivers are derived: Bohm viscosity B and the freestream-turbulence effect F. A problematic proxy effect is uncovered wherein the viscous driver functions also describe the strength of reconnection. Two magnetospheric-driver functions written in terms of upstream-solar-wind parameters are constructed: G+B and G+F. The driver functions are tested against 7 geomagnetic indices. The reaction of the geomagnetic indices to G+B and G+F is nonlinear: nonlinear versions of the driver functions are supplied. Applying the driver functions at multiple timesteps yields correlation coefficients of ~85% with the AE and Kp indices; it is argued that multiple timestepping removes high-frequency uncorrelated signal from the drivers. Autocorrelation-function analysis shows strong 1-d and 1-yr periodicities in the AE index that are not in the solar-wind driver functions; correspondingly, highpass and lowpass filtering finds uncorrelated signal at 1-d and 1-yr timescales. Residuals (unpredicted variance) between the geomagnetic indices and the driver functions are analyzed: the residuals are anti-correlated with the solar-wind velocity, the solar F 10.7 radio flux, and the solar-wind current-saturation parameter. Removing diurnal, semiannual, and annual trends from the indices improves their correlation with the solar-wind driver functions. Simplified versions of the driver functions are constructed: the simplified drivers perform approximately as well as the full drivers.

Description: [1]  Plasma properties of Saturn's pre-midnight tail region are surveyed using Cassini/CAPS ion observations from 2010. Only low-latitude (|lat| 〈 6°) intervals in which the CAPS viewing was roughly symmetric inward and outward around the corotation direction are used. Our numerical moments algorithm returns nonzero ion density for 70% (999) of the intervals selected. Of these, 642 had detectable water-group ion densities, and the remainder were dominantly, if not entirely, light ions. The derived plasma parameters are similar to those found in an earlier study for the post-midnight tail region, except that we find little evidence for the systematic outflows identified in that study, and we do find numerous significant inflow events. One such inflow is identified as a dipolarization event, the first reported plasma properties of such a structure at Saturn. A second, long-lasting event may be evidence for the existence at times of a quasi-steady reconnection region in the pre-midnight tail. The large majority of the plasma flows are found to be within 20° of the corotation direction, though with flow speeds significantly lower than full corotation. While the inflow events represent plausible evidence for internally-driven mass loss in the pre-midnight region, the absence of significant outflow events suggests that in the region surveyed here, tail reconnection has not yet proceeded to involve lobe field lines, so the disconnected plasma continues its general motion in the corotation direction.

Description: [1]  Following the first-time ionospheric imaging of a seismic fault, here we perform a case-study on retrieval of parameters of the extended seismic source ruptured during the great M9.0 Tohoku-oki earthquake. Using 1Hz ionospheric GPS data from the Japanese network of GPS receivers (GEONET) and several GPS satellites, we analyze spatio-temporal characteristics of co-seismic ionospheric perturbations and we obtain information on the dimensions and location of the sea surface uplift (seismic source). We further assess the criterion for the successful determination of seismic parameters from the ionosphere: the detection is possible when the line-of-sights from satellites to receivers cross the ionosphere above the seismic fault region. Besides, we demonstrate that the multi-segment structure of the seismic fault of the Tohoku-oki earthquake can be seen in high-rate ionospheric GPS-data. Overall, our results show that, under certain conditions, ionospheric GPS-derived TEC measurements could complement the currently working systems, or independent ionospherically-based system might be developed in the future.

Description: [1]  The non-dipolar portions of the Earth's main magnetic field constitute substantial differences between the two hemispheres. Beside the magnetic flux densities and patterns being different in the Northern Hemisphere (NH) and Southern Hemisphere (SH), also the offset between the invariant magnetic and the geographic poles is larger in the SH than in the NH. We investigated the effects of this magnetic field asymmetry on the high-latitude thermosphere and ionosphere using global numerical simulations, and compared our results with recent observations. While the effects on the high-latitude plasma convection are small, the consequences for the neutral wind circulation are substantial. The cross-polar neutral wind and ion drift velocities are generally larger in the NH than the SH, and the hemispheric difference shows a semidiurnal variation. The neutral wind vorticity is likewise larger in the NH than in the SH, with the difference probably becoming larger for higher solar activity. In contrast, the spatial variance of the neutral wind is considerably larger in the SH polar region, with the hemispheric difference showing a strong semidiurnal variation. Its phase is similar to the phase of the semidiurnal variation of the hemispheric magnitude differences. Hemispheric differences in ion drift and neutral wind magnitude are most likely caused partly by the larger magnetic flux densities in the near-polar regions of the SH, and partly by the larger offset between the invariant and geographic pole in the SH, while differences in spatial variance are probably just caused by the latter. We conclude that the asymmetry of the magnetic field, both in strength and in orientation, establishes substantial hemispheric differences in the neutral wind and plasma drift in the high-latitude upper atmosphere, which can help to explain observed hemispheric differences with EDI/Cluster and CHAMP.

Description: [1]  We have identified 8 events with double-belt structure in the outer radiation belt from 110 CME-driven magnetic storms and 223 CIR-driven storms during 1994 to 2003 based on the SAMPEX data sets. Among them, 3 cases are related to CME-driven magnetic storms and 5 cases are related CIR-driven storms. All double-belt structure events in the outer radiation belt are found during the recovery phase of a magnetic storm for both CME- and CIR-related events—they usually start to form within 3–4 days after the onset of the magnetic storm. The pre-conditions needed to form a double-belt structure, for all the CME-related events, are found to be high solar wind dynamic pressure ( P dy ) and southward IMF Bz; Nevertheless, for the CIR-related events, they are found to be associated with high speed stream with southward interplanetary magnetic field, which is enhanced by a suitably orientated B y component.It is further found that the flux distributions of the double-belt structure can be fitted well with a simply exponential decay function of L ∗ . Based on the RBC index, the proportion of the total number of 1.5-6.0 MeV electrons inside the position of maximum fluxes to that outside the maximum fluxes keeps rising during the double-belt period, which implies that the acceleration mainly occurs at regions inside the location of maximum fluxes. We suggest that the plasmapause and the strong wave-particle interactions with VLF and ULF waves near it, play an important role in the development of the double-belt structures.

Description: [1]  The solar minimum period during 2008–2009 was characterized by lower thermospheric density than the previous solar minimum, and lower than any previously measured. Recent work [ Solomon et al ., 2010; 2011] used the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model to show that the primary cause of density changes from 1996 to 2008 was a small reduction in solar extreme-ultraviolet irradiance (EUV), causing a decrease in thermospheric temperature and hence a contracted thermosphere. There are similar effects in the ionosphere, with most measurements showing an F -region ionosphere that is unusually low in density, and in peak altitude. This paper addresses the question of whether model simulations previously conducted, and their solar, geomagnetic, and anthropogenic inputs, produce ionospheric changes commensurate with observations. We conducted a 15-year model run and obtained good agreement with observations of the global mean thermospheric density at 400 km throughout the solar cycle, with a reduction of ~30% from the 1996 solar minimum to 2008–2009. We then compared ionosonde measurements of the mid-day peak density of the ionospheric F -region ( N m F 2 ) to the model simulations at various locations. Reasonable agreement was obtained between measurements and the model, supporting the validity of the neutral density comparisons. The global average N m F 2 was estimated to have declined between the two solar minima by ~15%. In these simulations, a 10% reduction of solar EUV plays the largest role in causing the ionospheric change, with a minor contribution from lower geomagnetic activity, and a very small additional effect from anthropogenic increase in CO 2 .

Description: [1]  We report the statistical features of sporadic sodium layers (SSLs) and the thermospheric enhanced sodium layers (TeSLs) observed by a lidar chain located at Beijing (40.2°N, 116.2°E), Hefei (31.8°N, 117.3°E), Wuhan (30.5°N, 114.4°E), and Haikou (19.5°N, 109.1°E). The average SSL occurrence rate was approximately 46.0, 12.3, 13.8, and 15.0 hr per SSL at Beijing, Hefei, Wuhan, and Haikou, respectively. However, the TeSLs occurred relatively infrequently and were more likely to appear at low and high latitudinal sites. Both the SSLs and TeSLs at four lidar sites showed evident summer enhancements and correlated well with Es ( f o E s  〉  4  MHz ). The co-observations of SSLs at three lidar site pairs, i.e., Hefei – Beijing, Hefei – Wuhan and Hefei – Beijing, indicated that a large-scale SSL extended horizontally for at least a few hundred kilometers and exhibited a tidal-induced modulation. Moreover, the SSLs were better correlated for the Hefei – Wuhan and Hefei – Haikou pairs than the Hefei – Beijing pair, which suggested a difference in the dynamical/chemical process in mesosphere and lower thermosphere (MLT) between the Beijing site and the other sites.

Description: [1]  A highly sensitive all-sky EMCCD airglow imager has been operative in Longyearbyen, Norway (78.1°N, 15.5°E) since October 2011. The imager obtains the 630.0 nm all-sky images with an exposure time of 4 sec, which is about 10 times shorter than the conventional cooled CCD airglow imagers. This new equipment allows us to image the on-going structuring of polar cap patches in 2D fashion. Here, we report a case in which faint undulations appeared along the trailing edge of patches propagating in the central polar cap. The separation between the fingers in the undulations was about 50–100 km and the e -folding time of their growth was ~5 min. We suggest that the gradient-drift instability (GDI) is one of the possible generation mechanisms of the undulating structures. The reasons for this interpretation are 1) the asymmetry in the preference of structuring between the leading and trailing edges is qualitatively consistent with the GDI mechanism, and 2) the linear growth rate of GDI calculated by using electron density estimates from simultaneous EISCAT Svalbard radar observations is roughly consistent with the observed growth time of the fingers. Such “unstable polar cap patches" could be important sources of seed irregularities, which would eventually be broken down to smaller-scale density perturbations affecting the trans-ionospheric satellite communications in the central polar cap.

Description: [1]  As the Polar spacecraft apogee precessed through the magnetic equator in 2001, Polar encountered numerous substorm events in the region between geosynchronous orbit and 10 Re geocentric distance; most of them in the plasma sheet boundary layers. Of these, a small number were recorded near the neutral sheet in the evening sector. Polar/TIDE provides a unique perspective on the lowest energy ion plasma, showing that these events exhibited a damped wavelike character, initiated by a burst of radially outward flow transverse to the local magnetic field at ~ 80 km/sec. They then exhibit strongly damped cycles of inward/outward flow with a period of several minutes. After one or two cycles, they culminated in a hot plasma electron and ion injection, quite similar to those observed at geosynchronous orbit. Cold plasmaspheric plasmas comprise the outward flow cycles, while the inward flow cycles contain counter-streaming field-parallel polar wind like flows. The observed wave-like structure, preceding the arrival of an Earthward moving substorm injection front, suggests an outward displacement driven by the inward motion at local times closer to midnight, that is, a “snowplow” effect. The damped in/out flows are consistent with interchange oscillations driven by the arrival at the observed local time by an injection originating at greater radius and local time.

Description: [1]  Accurate knowledge of the global distribution of magnetospheric chorus waves is essential for radiation belt modeling because it provides a direct link to understanding radiation belt losses and acceleration processes. In this paper, we report on newly developed models of the global distribution of chorus amplitudes based on in-situ measurements of IMF and solar wind parameters as well as geomagnetic indices using an artificial neural network technique. We find that solar wind speed and IMF B Z are the most influential parameters that affect the evolution of the magnetospheric chorus. The variations of chorus amplitudes in the outer ( L  ≥ 7) and in the inner (5 ≤  L  〈 7) regions, respectively, are well correlated with the variations of solar wind speed and IMF B Z . In addition, the solar wind parameter-based chorus model generally results in a slightly higher correlation between measured and modeled chorus amplitudes than any other models including geomagnetic indices AE, Kp, and Dst. The developed model shows that the chorus is amplified near the pre-noon sector during the geomagnetically disturbed conditions. With increasing southward IMF B Z the location of peak chorus amplitude moves from the pre-noon sector to the midnight sector, which is due to the enhanced electron injection near midnight. We also present a comparison of diffusive transport simulations for radiation belt electrons interacting with two newly developed chorus models, solar wind parameter-based and geomagnetic index-based chorus models. The comparison between two models shows that the modeling outside the plasmapause can affect the dynamic even inside the plasmasphere because the populations outside the plasmapause can act as seed population to radiation belt particles inside the plasmapause. One weakness of our chorus modeling is that it is trained during the early phase of solar cycle 24 where very few strong storms occurred. Therefore, our model might not be valid in reproducing the chorus activity under extremely disturbed conditions, which should be updated in the future once chorus measurements for such conditions become available.

Description: [1]  We investigate the storm-scale morphology of the magnetospheric magnetic field as well as underlying distributions of electric currents, equatorial plasma pressure and entropy for four Steady Magnetospheric Convection (SMC) events that occurred during the May 2000 and October 2011 magnetic storms. The analysis is made using the empirical geomagnetic field model TS07D, in which the structure of equatorial currents is not predefined and it is dictated by data. The model also combines the strengths of statistical and event-oriented approaches in mining data for the reconstruction of the magnetic field. The formation of a near-Earth minimum of the equatorial magnetic field in the midnight sector is inferred from data without ad hoc assumptions of a special current system postulated in earlier empirical reconstructions. In addition, a new SMC class is discovered where the minimum equatorial field is substantially larger and located closer to Earth. The magnetic field tailward of the minimumis also much larger, and the corresponding area of accumulated magnetic flux may occupy a very short tail region. The equatorial current and plasma pressure are found to be strongly enhanced far beyond geosynchronous orbit and in a broad local time interval covering the whole nightside region. This picture is consistent with independent recent statistical studies of the SMC pressure distributions, global MHD and kinetic RCM-E simulations. Distributions of the flux tube volume and entropy inferred from data reveal different mechanisms of the magnetotail convection crisis resolution for two classes of SMC events.

Description: [1]  Drifts in the Parker spiral interplanetary magnetic field are known to be an important component in the propagation of galactic cosmic rays, while they are thought to be negligible for Solar Energetic Particles (SEPs). As a result they have so far been ignored in SEP propagation modelling and data analysis. We examine drift velocities in the Parker spiral within single particle first-order adiabatic theory, in a local coordinate system with an axis parallel to the magnetic field. We show that, in the presence of scattering in interplanetary space, protons at the high end of the SEP energy range experience significant gradient and curvature drift. In the scatter-free case, drift due to magnetic field curvature is present. The magnitude of drift velocity increases by more than an order of magnitude at high heliographic latitudes compared to near the ecliptic; it has a strong dependence on radial distance r from the Sun, reaching a maximum at r ~1 AU at low heliolatitudes and r ~10 AU at high heliolatitudes. Due to the mass over charge dependence of drift velocities, the effect of drift for partially ionised SEP heavy ions is stronger than for protons. Drift is therefore likely to be a considerable source of cross field transport for high energy SEPs.

Description: [1]  We present a novel method for the automatic retrieval of local plasma density measurements from the Mars advanced radar for sub-surface and ionospheric sounding (MARSIS) active ionospheric sounder (AIS) instrument. The resulting large data set is then used to study the configuration of the Martian ionosphere at altitudes above ~300 km. An empirical calibration routine is used, which relates the local plasma density to the measured intensity of multiple harmonics of the local plasma-frequency oscillation, excited in the plasma surrounding the antenna in response to the transmission of ionospheric sounding pulses. Enhanced accuracy is achieved in higher-density ( n e  〉 150 cm − 3 ) plasmas, when MARSIS AIS is able to directly measure the fundamental frequency of the local plasma oscillation. To demonstrate the usefulness of this data set, the derived plasma densities are binned by altitude and solar zenith angle (SZA) in regions over weak ( nT) and strong ( nT) crustal magnetic fields, and we find clear and consistent evidence for a significant asymmetry between these two regions. We show that within the ~300-1200 km altitude range sampled, the median plasma density is substantially higher on the dayside in regions of relatively stronger crustal fields than under equivalent illuminations in regions of relatively weaker crustal fields. Conversely, on the nightside, median plasma densities are found to be higher in regions of relatively weaker crustal fields. We suggest that the observed asymmetry arises as a result of the modulation of the efficiency of plasma transport processes by the irregular crustal fields, and the generally horizontal draped interplanetary magnetic field (IMF).

Description: [1]  Global models of the Van Allen radiation belts usually include resonant wave-particle interactions as a diffusion process, but there is a large uncertainty over the diffusion rates. Here we present a new diffusion matrix for whistler mode chorus waves that can be used in such models. Data from seven satellites are used to construct 3,536 power spectra for upper and lower band chorus for 1.5 ≤  L ∗  ≤ 10, MLT, magnetic latitude 0 o  ≤ | λ m | ≤ 60 o and five levels of K p . Five density models are also constructed from the data. Gaussian functions are fitted to the spectra and capture typically 90% of the wave power. The frequency maxima of the power spectra vary with L ∗ and are typically lower than that used previously. Lower band chorus diffusion increases with geomagnetic activity and is largest between 21:00 and 09:00 MLT. Energy diffusion extends to a few MeV at large pitch angles 〉 60 o and at high energies exceeds pitch angle diffusion at the loss cone. Most electron diffusion occurs close to the geomagnetic equator (〈 12 o ). Pitch angle diffusion rates for lower band chorus increase with L ∗ and are significant at L ∗  = 8 even for low levels of geomagnetic activitywhile upper band chorus is restricted to mainly L ∗  〈 6. The combined drift and bounce averaged diffusion rates for upper and lower band chorus extend from a few keV near the loss cone up to several MeV at large pitch angles indicating loss at low energies and net acceleration at high energies.

Description: [1]  We report that radio science (RS) experiment onboard Mars Express (MEX) have observed three plasma layers in the nighttime ionosphere of Mars at altitudes ~80-100 km, ~120 km and ~160 km, which are reproduced by model calculation due to impact of meteoroid, solar wind proton and electron respectively. The densities of 21 ions (Mg + , Fe + , Si + , MgO + , MgCO 2 + , MgO 2 + , MgN 2 + , FeO + , FeO 2 + , FeN 2 + , FeCO 2 + , SiO + , SiCO 2 + , SiN 2 + , SiO 2 + , CO 2 + , N 2 + , O + , O 2 + , CO + , and NO + ) have been computed between altitude 50 km and 200 km. The model shows that all atmospheric ions (CO 2 + , N 2 + , O + , CO + , O 2 + and NO + ) are produced above 100 km due to solar wind electron and proton impact ionizations. The metallic ions are formed between 50 km and 100 km due to ablation of micrometeoroids. It is found that mass ~3.0 × 10 -4  g of incoming meteoroid is sufficient for meteor ablation and its characteristic flux ~4.0 × 10 -15  cm -2  s -1 could produce the nighttime metallic layer observed by MEX. The calculated electron densities are also compared with the occultation measurements made by Mars 4/5 in the nighttime ionosphere of Mars.

Description: [1]  Ultra Low Frequency (ULF) waves transfer energy in the Earth's magnetosphere through a variety of mechanisms that impact the Earth's ionosphere, radiation belts, and other plasma populations. Measurements of the electromagnetic portion of the energy transfer rate are an important source of information for assessing the importance of ULF waves relative to other energy transfer mechanisms as well as a diagnostic for studying the behavior of ULF waves. Using THEMIS satellite data, we examine the time averaged electromagnetic energy transfer rate, or Poynting vector, as a function of frequency and region of the magnetosphere; for this study, we focus on the direction and rate of energy transfer relative to the background magnetic field, comparing perpendicular and parallel transfer rates. This study extends earlier studies of the ULF wave Poynting vector that focused on narrower frequency ranges or specific regions of the magnetosphere; here, we consider the 3–50 mHz frequency range, all local time sectors, radial distances from 3 to 13 Re, and magnetic latitudes close to the equatorial plane. We measure time averaged Poynting vectors that range from  10 − 11 to 10 − 5 W / m 2 , with larger Poynting vector magnitudes occurring at largerradial distances and smaller frequencies. In every spatial region and frequency we examined, we found a large degree of scatter in both the Poynting vector magnitude and direction. The Poynting vector tends to be anisotropic at all frequencies,with more energy transferred along rather than across the background magnetic field. This preference for parallel energy transfer near the magnetic equator suggests that Joule dissipation in the ionosphere and the acceleration of auroral electrons are the largest sinks of ULF wave energy in the magnetosphere.

Description: [1]  Previous statistical studies have found a close relationship between high speed streams and high latitude geomagnetic activity. The speed by itself would increase the geoeffectivity of the solar wind. But it is also believed that pure Alfvénic fluctuations, often found in the trailing part of the streams, play a role in the solar wind driving of geomagnetic activity by amplifying the north-south component of the magnetic field ( B Z ), and thereby the dayside reconnection electric field. By automatically identifying slow and fast solar wind streams and by analysing them for more than one solar cycle, we aimed to study the relation between speed, Alfvénicity and B Z in the solar wind. It was found out that streams whose trailing parts are dominated by pure Alfvénic fluctuations, are the most geoeffective streams, on average. However, it is not the pure Alfvénic fluctuations themselves which cause the streams to be more geoeffective. There is only a variation of about 10 % in B Z due to the Alfvénicity of the fluctuations. Instead the streams are more geoeffective because the pure Alfvénic fluctuations tend to occur during high solar wind speed and strong IMF. There is a substantial variation within the solar cycle of how Alfvénic the solar wind streams are, and years with many extremely Alfvénic streams tends to have more days with moderately large geoeffectivity. The list of solar wind streams is included as extra material to this paper.

Description: [1]  Data Interpolating Empirical Orthogonal Functions (DINEOFs) are a data-based method for determining a few orthogonal basis functions that optimally reproduce a given data set. This technique is applied to meridional drift measurements performed by the Coupled Ion Neutral Dynamics Investigation (CINDI) onboard the Communication/Navigation Outage Forecasting System (C/NOFS) as well as electron density profiles derived from GPS Radio Occulations (RO) performed by COSMIC. The low densities of the equatorial ionosphere spanning 2009 - 2010 restricted quality drift measurements by CINDI to altitudes near perigee, limiting the local time coverage of measurements. Full local time descriptions may be obtained as perigee moves through all local times though this requires a minimum 67 day season. To increase the data coverage of the ionosphere CINDI data is supplemented with COSMIC GPS RO data. DINEOFs are applied to median meridional drift measurements as well as COSMIC measurements spanning 2009-10 and are used to make a best estimate of the equatorial ionosphere at locations not observed. The scattered distribution of COSMIC profiles as well as the physical relationship between meridional ion drifts and the distribution of density with altitude improve thequality of the reconstructions compared to using CINDI alone. The DINEOF reconstructions demonstrate that the annual anomomly of reduced ionospheric densities in June compared to December measured by COSMIC is coincident with a change in the meridional ion drifts at the geomagnetic equator measured by CINDI.

Description: [1]  It is well accepted that the propagation of electromagnetic ion cyclotron (EMIC) waves are bidirectional near their source regions and unidirectional when away from these regions. The generally believed source region for EMIC waves is around the magnetic equatorial plane. Here we describe a series of EMIC waves in the Pc1 (0.2-5 Hz) frequency band above the local He + cyclotron frequency observed in situ by all four Cluster spacecraft on 9 April 2005 at mid-magnetic latitudes (MLAT = ~33°-49°) with L = 10.7-11.5 on the dayside (MLT = 10.3-10.4). A Poynting vector spectrum shows that the wave packets consist of multiple groups of packets propagating bidirectionally, rather than unidirectionally, away from the equator, while the local plasma conditions indicate that the spacecraft are entering into a region sufficient for local wave excitation. One possible interpretation is that, while part of the observed waves are inside their source region, the others are either close enough to the source region, or mixed with the wave packets from multiple source regions at different latitudes.

Description: [1]  Using mesospheric temperature information obtained by Rayleigh lidar observations over Gadanki (13.5°N, 79.2°E) and temperature, chemical constituents and their exothermic chemical reaction heating rates obtained by Sounding of Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite over and near to Gadanki location, it is demonstrated that, the dominant role of chemical heating for the occurrence of a few large mesospheric inversion layer (MIL) events during January-February 2011. The heating rates due to exothermic chemical reactions among atomic oxygen (O), atomic hydrogen (H), molecular oxygen (O 2 ), ozone (O 3 ) and hydroxyl (OH) species are the key factors involved in the MIL formation. As relatively larger (lower) ozone mixing ratios are observed at the top (bottom) of the inversion layers, large heating rate (~ 15 K/day) is found to occur between 80 and 85 km due to the exothermic reaction between atomic hydrogen and ozone H + O 3  → OH + O 2 , which dominates all other important exothermic chemical reactions during these MIL events and the large volume emission rates of energy of O 2 , OH are found to be mostly due to the reaction between H and O 3. It is also demonstrated that dynamics plays a negligible role in the formation of these MILs as conditions for the convective and dynamic instability are found to be not satisfied during these MIL events.

Description: [1]  Bursty bulk flows (BBFs) play an important role for the mass, energy and magnetic flux transport in the plasma sheet, and the flow pattern in and around a BBF has important consequences for the localized energy conversion between the electromagnetic and plasma mechanical energy forms. The plasma flow signature in and around BBFs is often rather complicated. Return flows and plasma vortices are expected to exist at the flanks of the main flow channel, especially near the inner plasma sheet boundary, but also further down-tail. A dipolarization front (DF) is often observed at the leading edge of a BBF, and a flux pileup region (FPR) behind the DF. Here we present Cluster data of three FPRs associated with vortex flows observed in the mid-tail plasma sheet on August 15, 2001. According to the principles of Fu et al . [2011] and Fu et al . [2012c], two of the FPRs are considered to be in an early stage of evolution (growing FPRs). The third FPR is in a later stage of evolution (decaying FPR). For the first time, the detailed energy conversion properties during various stages of the FPR evolution have been measured. We show that the later stage FPR has a more complex vortex pattern than the two earlier stage FPRs. The two early stage FPR correspond to generators, E  ⋅  J  〈 0, while the later stage FPR only shows weak generator characteristics and is instead dominated by load signatures at the DF, E  ⋅  J  〉 0. Moreover, to our knowledge this is one of the first times BBF related plasma vortices have been observed to propagate over the spacecraft in the mid-tail plasma sheet at geocentric distances of about 18 R E . Our observations are compared to recent simulation results [ Wiltberger et al ., 2000; Birn et al ., 2011] and previous observations [ Fu et al ., 2011, 2012c; Pang et al ., 2012].

Description: [1]  We use the measurements by the Vector Electric Field Investigation (VEFI) on board the C/NOFS satellite to study the local time, seasonal, and longitudinal dependent climatology of equatorial F region zonal plasma drifts during 2008-2011. These drifts are essentially westward during the day and eastward at night. Over Jicamarca, the satellite measurements are in good agreement with incoherent scatter radar drifts. Our data show strong longitudinal variations, particularly in the South American sector during the solstices. The equinoctial data exhibit short-lived and largely enhanced westward drifts near sunrise, and wave-4 structures from theearly afternoon to late night equinoctial periods. The nighttime eastward drifts are largest near the western American sector at all seasons. The June solstice post-midnight eastward drifts decrease sharply at longitudes of about 310˚ and have much smaller values in the entire eastern hemisphere. We also briefly discuss the relationship between the longitude dependent vertical and zonal plasma drifts.

Description: [1]  Long-term variation in the geomagnetic Sq field and the cause of the variation were examined. 　The amplitude of the geomagnetic Y component (Sq(Y)) in equinox was averaged for each year, and adopted as a proxy of the Sq field. Sq(Y) was combined with the ionospheric conductivity estimated by the IRI model to determine the dynamo electric field and neutral wind velocity by using the geomagnetic main field strength. It was found that the solar activity dependence of the Sq field could be almost completely attributed to the conductivity variation, and neutral winds tend to decrease when the solar activity increases Although the long-term variation in the dynamo field differed among observatories, these differences were mostly attributed to the locality of the geomagnetic secular variation, whereas the variations in neutral wind amplitude were nearly the same in all regions. On the other hand, no clear long-term variation in neutral wind was detected other than that by solar activity.

Description: [1]  We analyze data recorded from October 2010 to September 2011, during the ascending phase of the 24 th solar cycle, from an AIS-INGV (Advanced Ionospheric Sounder - Istituto Nazionale di Geofisica e Vulcanologia) ionosonde and a GISTM (GPS Ionospheric Scintillation and TEC Monitor) scintillation receiver, co-located at low-latitude in the Southern American longitudinal sector (Tucumán, 26.9°S, 294.6°E, mag. Lat. 15.5°S, Argentina). The site offers the opportunity to perform spread-F and GPS scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly. Spread-F signatures, classified into four types (strong range spread-F (SSF), range spread-F (RSF), frequency spread-F (FSF) and mixed spread-F (MSF)), the phase and amplitude scintillation index ( σ Φ and S 4 , respectively), the total electron content ( TEC ) and the rate of TEC ( ROT ) parameter, marker of the TEC gradients, that can cause scintillations, are considered. The seasonal behavior results as follows: the occurrence of all four types of spread-F is higher in summer and lower in winter, while the occurrence of scintillations peaks at equinoxes in the post-sunset sector and shows a minimum in winter. The correspondence between SSF and scintillations seems to be systematic, and a possible correlation between S 4 and FSF peaks is envisaged at the terminator. The investigation focused also on two particular periods, from 12 to 16 March 2011, and from 23 to 29 September 2011, both characterized by the simultaneous presence of SSF signatures and scintillation phenomena allowing to discuss the role of Travelling Ionospheric Disturbances as a strong candidate causing ionospheric irregularities.

Description: ABSTRACT [1]  Neutrons contribute a significant radiation dose at commercial passenger airplane altitudes. With cosmic ray energies 〉 1  GeV , these effects could in principle be propagated to ground level. Under current conditions, the cosmic ray spectrum incident on the Earth is dominated by particles with energies 〈 1  GeV . Astrophysical shocks from events such as supernovae accelerate high energy cosmic rays (HECRs) well above this range. The Earth is likely episodically exposed to a greatly increased HECR flux from such events. Solar events of smaller energies are much more common and short lived, but still remain a topic of interest due to the ground level enhancements (GLEs) they produce. The air showers produced by cosmic rays (CRs) ionize the atmosphere and produce harmful secondary particles such as muons and neutrons. Although the secondary spectra from current day terrestrial cosmic ray flux are well known, this is not true for spectra produced by many astrophysical events. This work shows the results of Monte Carlo simulations quantifying the neutron flux due to CRs at various primary energies and altitudes. We provide here lookup tables (described later) that can be used to determine neutron fluxes from proton primaries with total energies 1  MeV – 1 PeV . By convolution, one can compute the neutron flux for any arbitrary CR spectrum. This contrasts with all other similar work, which is spectrum dependent. Our results demonstrate the difficulty in deducing the nature of primaries from the spectrum of ground level neutron enhancements.

Description: [1]  Rayleigh lidar temperature observations over Gadanki show a few mesospheric inversion layer (MIL) events during 20-25 January 2007. The zonal mean removed SABER temperature shows warm anomalies around 50°E and 275°E indicating the presence of planetary wave of zonal wavenumber 2. The MIL amplitudes in SABER temperature averaged for 10°N-15°N and 70°E-90°E show a clear 2-day wave modulation during 20-28 January 2007. Prior to 20 January 2007, a strong 2-day wave (zonal wavenumber 2) is observed in the height region of 80-90 km and it gets largely suppressed during 20-26 January 2007 as the condition for vertical propagation is not favourable, though it prevails at lower heights. The 10-day mean zonal wind over Tiruneveli shows deceleration of eastward winds indicating the westward drag due to wave dissipation. The nightly mean MF radar observed zonal winds show the presence of alternating eastward and westward winds during the period of 20-26 January 2007. The two dimensional spectrum of Rayleigh lidar temperature observations available for the nights of 20, 22 and 24 January 2007 shows the presence of gravity wave activity with periods 18 min, 38 min, 38 min, and vertical wavelengths 6.4 km, 4.0 km, 6.4 km respectively. From the dispersion relation of gravity waves, it is inferred that, these waves are internal gravity waves rather than inertia gravity waves with the horizontal phase speeds of ~40 m/s, ~37 m/s and ~50 m/s respectively. Assuming the gravity waves are eastward propagating waves, they get absorbed only in the eastward local wind fields of the planetary wave thereby causing turbulence and eddy diffusion which can be inferred from the estimation of large drag force due to the breaking of gravity wave leading to the formation of large amplitude inversion events in alternate nights. The present study shows that, the mesospheric temperature inversion is caused mainly due to the gravity wave breaking and the inversion amplitude may get modulated by the interaction between gravity waves and planetary waves. The eddy diffusion associated with gravity wave drag may also cause suppression in the planetary wave activity.

Description: [1]  To evaluate whether ground magnetic responses traditionally viewed as signatures of substorm onset may be related to post-onset auroral streamers rather than to substorm onset seen in aurora, we have analyzed ground magnetic and all-sky image responses for 14 substorm onsets selected solely on imager coverage. We find evidence supporting this possibility, the response being approximately coincident for mid-latitude positive bay and Pi2 pulsation enhancements and for abrupt auroral zone H decreases at stations near a streamer. These are all signatures of current wedge formation, indicating that substorm current wedge formation may be more of a response to plasma sheet flow channels associated with post-onset streamers than to the process leading to auroral onset, and that the current wedge may develop via a series of distinctly narrower wedge-like structures. We also find evidence that periods of streamers can occur more than once during a substorm expansion phase, and can give magnetic signatures of multiple onsets even if there are no additional auroral onsets. Furthermore, the peak auroral zone H decreases are seen in association with streamers and at times varying from just a few minutes to well over a half hour after substorm auroral onset if there is a prolonged period of streamers. This indicates peak substorm AE and AL values are likely related to features of post-onset streamers and their locations relative to observing stations, and are not a measure of the strength of the substorm auroral onset processes. We discuss possible additional implications on substorm expansion phase development.

Description: [1]  We statistically examine the occurrence rate of electromagnetic ion cyclotron (EMIC) waves observed by AMPTE/CCE. We use the 8-Hz magnetic field dataset that covers the whole CCE mission period of nearly 4.5 years from Augutst 1984 to Janauary 1989, which is more than three times the period studied by Anderson et al. [1992] (~452 days). The large data volume allows us to evaluate the storm phase dependence of the spatial occurence pattern of EMIC waves. The major results of this study are summarized as follows. (a) The occurrence rate is below 5% on the nightside at all L. On the dayside the rate is 〈5% in the inner magnetosphere (L 〈 6), while it is higher than 5% in the outer magnetosphere (L ≥ 6), up to 25%. The highest rate appears in the afternoon sector. (b) The overall occurrence rate is higher for H-band events than He-band events, except for the opposite feature seen in the inner magnetosphere on the early afternoon-to-post midnight side (L 〈 6, 14 h 〈 MLT 〈 22 h). (c) H-band events occur frequently in the outer magnetosphere (L ≥ 7) in the afternoon sector, regardless of geomagnetic activity. Under quiet conditions, H-band events also occur in the outer magnetosphere on the morning side (4 h ≤ MLT 〈 8 h). (d) He-band events frequently occur in the inner magnetosphere (L 〈 7) on the pre-noon to dusk side (10 h ≤ MLT 〈 19 h) under disturbed conditions (Dst ≤ −50 nT). (e) The storm-time He-band waves are generated more frequently during the main phase than the recovery phase, with the main-phase wave excitation seen toward the afternoon-side outer magnetosphere (L 〉 7). The results indicate two independent major processes that cause EMIC wave excitation in the Earth's magnetosphere: one externally triggers H-band waves on the dayside, and the other internally excites He-band waves on the dusk to afternoon side. We suggest that the former is due to solar wind compression which leads to perpendicular adiabatic ion heating and in turn an increase in temperature anisotropy, and that the latter is caused by injections of new, highly energetic ion population from the plasma sheet, with its velocity distributions becoming pancake-like on the dusk-to-afternoon side. The frequent occurrence seen on the afternoon side, at a wide L range, and during the main/development phase, strongly suggests the significant role of the sunward surge of the plasmasphere and plasma plumes in the injection-associated (i.e., storm-time) EMIC wave generation.

Description: [1]  We performed a statistical study of downward moving protons and alpha particles of ~ keV energy (assumed to be of solar wind origin), inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package onboard Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses the occurrence frequency of observed proton precipitation events is reduced by a factor ~3 and for He 2+ events the occurrence frequency is reduced by a factor ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pile-up of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H + /He 2+ precipitations.

Description: [1]  We present THEMIS observations of a " Spontaneous Hot Flow Anomaly" (SHFA) upstream from the pre-noon bow shock at 0431 UT on August 12, 2007. Although the SHFA exhibited the greatly heated and deflected solar wind plasmas used to identify hot flow anomalies (HFAs), it did not result from the standard mechanism invoked for the formation of HFAs, namely the interaction of an interplanetary magnetic field (IMF) discontinuity with the bow shock. We employ THEMIS A, B, C, and D observations to describe the evolution of the event from a proto-SHFA exhibiting regions of depressed magnetic field strength and density but little evidence for plasma heating or flow deflection, to a well-developed SHFA further downstream. These observations show that SHFA can be generated without the presence of an IMF discontinuity and are therefore a new category of HFAs.

Description: [1]  The two primary methods responsible for solar wind magnetosphere coupling are magnetic reconnection and the viscous interaction. The viscous interaction is generated due to the antisunward dragging of plasma inside the magnetopause by the plasma flowing in the magnetosheath, creating a return flow deeper inside the magnetosphere and producing a circulation pattern. This viscous circulation pattern is mapped into the ionosphere via magnetic field lines, which results in ionospheric electric field in the non-rotating Earth's frame. We measure this interaction in terms of an electric potential, the viscous potential. In this paper, we use the results obtained from the LFM simulation model during periods of purely northward IMF for different solar wind velocity and ionospheric conductivity, showing a reduction of the viscous potential with increasing magnitude of northward IMF. The viscous potential is found to settle around 5-10 kV for large + B z values. The decrease in viscous potential was found to be associated with a weak or non-existent sunward plasma flow in the nightside plasmasheet. Instead, the return flow to the dayside occurs at high latitudes and is associated with the reconnection topology and dynamics that occur during northward IMF periods. We also show that the magnetosphere remains closed during purely northward IMF, except for two small regions-one on each hemisphere, where the magnetic reconnection occur. We argue that the reduction of the viscous potential is due to a reduction of the velocity shear across the magnetopause and the lack of sunward convection in the equatorial tail.

Description: [1]  We present an analytical model of the Poynting flux that is generated by the interaction between the plume of Enceladus and Saturn's magnetospheric plasma. Our purpose is to analyze the influence of two key elements of Enceladus’ magnetospheric interaction on the electromagnetic energy radiated away in the moon's Alfvén wings. First, the north-south asymmetry of the obstacle generates a system of hemisphere coupling currents which allows a transport of electromagnetic energy into Saturn's northern hemisphere, even if the field-aligned currents connecting to the plume are completely blocked at the non-conducting icy crust of Enceladus. Second, the presence of electron-absorbing dust grains within the plume was recently found to drastically modify the electromagnetic field configuration within Enceladus’ Alfvén wings (Anti-Hall effect), thereby also altering the energy flux radiated away from the interaction region. By systematically studying the impact of varying strengths of the hemisphere coupling currents and varying electron absorption fractions on the energy flux, we come to the following conclusions: (1) The integrated Poynting flux into Saturn's southern hemisphere always exceeds the integrated flux into the northern hemisphere. In particular, the power transmitted towards the south may become several orders of magnitude larger than the power transmitted towards the north. (2) The search for Enceladus’ auroral footprint has so far mainly focused on Saturn's northern hemisphere. However, based on the Poynting fluxes radiated away by the interaction, detections of the footprint should occur more likely in the giant planet's southern hemisphere, if no other far-field effects play a role. (3) Electron absorption by the dust grains within the plume makes a measurable contribution to the energy flux. Thus, changes in the brightness of the observed footprints cannot exclusively be ascribed to variations in the incident magnetospheric flow conditions or the neutral gas content of the plume, but variations in the properties of the dust component need to be taken into account as well.

Description: [1]  Suprathermal singly-charged molecular ions, O 2 + (at ~32 Da/e) and the Mass-28 ion group 28 M + (ions at ~28 Da/e, with possible contributions from C 2 H 5 + , HCNH + , N 2 + , and/or CO + ), are present throughout Saturn's ~4-20 Rs (1 Saturn radius, Rs = 60,268 km) near-equatorial magnetosphere from mid-2004 until mid-2012. These ~83-167 keV/e heavy ions measured by Cassini's CHarge-Energy-Mass Spectrometer, CHEMS, have long-term temporal profiles that differ from each other and differ relative to the dominant water group ions, W + (O + , OH + , H 2 O + , and H 3 O + ). O 2 + /W + , initially ~0.05, declined steadily until equinox in mid-2009 by a factor of ~6, and 28 M + /W + , initially ~0.007, declined similarly until early-2007 by a factor of ~2. The O 2 + /W + decline is consistent with Cassini's in-situ ring-ionosphere thermal ion measurements, and with proposed and modeled seasonal photolysis of Saturn's rings for thermal O 2 and O 2 + . The water ice dominated main rings and Enceladus plume depositions thereon are the two most likely O 2 + sources. Enceladus' dynamic plumes, though, have no known long-term dependence. After declining, O 2 + /W + and 28 M + /W + levels remained low until late-2011 when O 2 + /W + increased, but 28 M + /W + did not. The O 2 + /W + increase was steady and became statistically significant by mid-2012, indicating a clear increase after a decline, that is, a possibly delayed O 2 + “seasonal” recovery. Ring insolation is driven by solar UV flux which itself varies with the sun's 11-year activity cycle. The O 2 + /W + and 28 M + /W + declines are consistent with seasonal ring insolation. No O 2 + /W + response to the late-2008 solar-cycle UV minimum and recovery is evident. However, the O 2 + /W + recovery from the post-equinox baseline levels in late-2011 coincided with a strong solar UV enhancement. We suggest a scenario/framework in which the O 2 + observations can be understood.

Description: [1]  We analyze ion temperature data near 350 km altitude over the years 1966–2012 to seek explanations for three outstanding questions concerning the long-term cooling observed in the upper thermosphere: (1) why is the cooling so much larger than expected, (2) why has the cooling lasted so long, and (3) why is the thermospheric density response to the cooling so small? We speculate that gravity waves may cause this cooling and provide answers to these questions. Recent simulations have shown that gravity waves are expected to cool the upper thermosphere by an amount comparable to that observed over our data timeline. A gravity-wave proxy formed from the non-tidal fluctuations in temperature shows a positive long-term trend throughout its timeline, consistent with the increasing cooling observed. The time scales of the long-term trend and its decadal fluctuations are characteristic of the ocean, not the atmosphere. We suggest that the following scenario may explain these behaviors: (a) the climate regime shift of 1976–1977 launched slow Rossby waves across the oceans which continue to propagate to this day, (b) winds over this increasingly corrugated ocean have launched increasing fluxes of gravity waves into the atmosphere, (c) these increasing fluxes of gravity waves have propagated to the thermosphere to produced increasing amounts of cooling. The strong thermospheric cooling seen would be expected to produce thermospheric density declines much larger than those observed via satellite drag. These temperature and density results would be compatible if the turbopause were lowered 4 km over the time span of observations.

Description: [1]  We introduce a new model to study Jupiter's magnetosphere and how it interacts with the solar wind. We first derive a set of one-fluid MHD equations to consistently include the ion-neutral collisions in Jupiter's ionosphere, and the mass-loading in the Io torus. The mass-loading and the subsequent radial mass transport in Jupiter's magnetosphere leads to a deviation from full corotation of the magnetospheric plasma. Ion-neutral collisions in Jupiter's ionosphere and subsequent transport of angular momentum out into the magnetosphere acts to spin up the magnetosphere's plasma. Our model explicitly includes mass-loading in the Io plasma torus and an inner boundary region, which represents the effects of Jupiter's ionosphere. We present the results of five model runs where different mass-loading rates and ionospheric conductances are used. For these model runs, we consider an anti-parallel interplanetary magnetic field and a strong solar wind dynamic pressure, resulting in a compressed magnetosphere. The results are compared with analytical models, in situ measurements, and remote-sensing observations. Our azimuthal velocity profiles and the position of the corotation break-down are in quantitative agreement with theoretical predictions by Hill [1979, 2001] and Saur et al . [2004a], and Voyager observations [ McNutt et al ., 1981]. The total current flowing into and out of the ionosphere is 48.7 MA, which is in agreement with estimates from measurements and analytical models. Using the field aligned electric current j ║ to determine the position of the aurorae, we find that our main auroral oval is associated, as expected, with the position of the corotation break-down (between 20.6 R J and 30.1 R J for the different model runs). The discontinuity in the main oval observed by Radioti et al . [2008] is also present in our results, where it is caused by an asymmetry in the pressure distribution, due to the interaction between the rotating plasma and the magnetopause.

Description: [1]  In this study we quantify the contribution of individual large-scale waves to ionospheric electrodynamics, and examine the dependence of the ionospheric perturbations on solar activity. We focus on migrating diurnal tide (DW1) plus mean winds, migrating semidiurnal tide (SW2), quasi-stationary planetary wave 1 (QSPW1), and nonmigrating semidiurnal westward wave 1 (SW1) under northern winter conditions, when QSPW1 and SW1 are climatologically strong. From TIME-GCM simulations under solar minimum conditions, it is found that the mean winds and DW1 produce a wave 2 pattern in equatorial vertical E  ×  B drift that is upward in the morning and around dusk. The modeled SW2 also produces a wave 2 pattern in the ionospheric vertical drift that is nearly a half wave cycle out of phase with that due to mean winds and DW1. SW1 can cause large vertical drifts around dawn, while QSPW1 does not have any direct impact on the vertical drift. Wind components of both SW2 and SW1 become large at mid to high latitudes in the E-region, and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift, likely through modulating the E-region wind dynamo. The most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk, reflecting the more dominant role of large F-region Pedersen conductivity and of the F-region dynamo under high solar activity. Therefore, the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions, not only because variability is more identifiable in a quieter background, but also because the E-region wind dynamo is more significant. These numerical experiments also demonstrate that the amplitudes, phases and latitudinal and vertical structures of large-scale waves are important in quantifying the ionospheric responses.

Description: [1]  An improved dispersion relation, with thermal corrections retained, for parallel propagating electromagnetic waves in a warm plasma is developed for both left-hand (L-) and right-hand (R-) polarized modes. Compared with the cold plasma dispersion relation, the derived dispersion relation is in much better agreement with the full hot plasma dispersion relation (including the wave growth rate). The pitch angle scattering rates of energetic electrons are compared between using cold and full dispersion relation. Significant differences are found when evaluating pitch angle scattering rate of MeV electron caused by He + band waves in multiple ion plasmas. Due to He + ion cyclotron absorption, the He + band EMIC waves, which are able to resonate with MeV electrons (at large wave number), tend to be strongly suppressed. Less significant differences in scattering rate of electrons between using cold and hot dispersion relation are found in the case of L-mode waves in single H + ion plasma, and in the case of R-mode waves.

Description: [1]  The fundamental features of ~0.1–0.2 s duration ~0.5 s spaced ionospheric electron precipitation “microbursts”, ~5 to 15 s microburst “trains”, and 5–15 s electron precipitation pulsations are reviewed in light of similar temporal structures of electromagnetic whistler mode “chorus” waves detected in the outer magnetosphere. Past observations of microbursts point to extremely rapid (ms timescale) wave-particle interactions, probably between lower-band chorus subelements (durations of ~10 to 100 ms) and energetic ~10 to 100 keV electrons. A recent theory explaining such rapid interaction rates observed in microbursts is briefly reviewed. Arguments are given why ~5–15 s x-ray (and optical) pulsations are also associated with chorus scattering of energetic electrons. Comments about relativistic (E 〉 1 MeV) microbursts are also provided. There are, however, many other unsolved problems of outer zone energetic electron precipitation. The authors will attempt to indicate several of these for the interested reader. Finally an appendix is provided for a brief review of two-frequency chorus and some current problems with that topic.

Description: [1]  A real-time mapping model of f o F 2 in northern China was established using neural networks (NNs). To avoid the local minimum problem associated with traditional NNs, a newly improved genetic algorithm-based NN (GA-NN) was developed using the input parameters of solar activities, geomagnetic activities, neutral winds, seasonal information, and geographical coordinates. The f o F 2 data were extracted by inversing the oblique ionograms obtained from the oblique ionosondes of the China Ground-based Seismo-ionospheric Monitoring Network every 30 minutes for the period from August 2009 to December 2011. The data associated with five transmitter stations (Beijing, Changchun, Qingdao, Xinxiang, and Suzhou) and one receiver station in Binzhou were considered the input parameters for the real-time f o F 2 mapping model, and the data from the Dalian and Jinyang transmitter stations were used to verify the results. The Jining transmitter station data were used to test the capability of the model. The root-mean-square error (RMSE) and percent deviation (PD) were calculated to estimate the performance of the model. The correlation coefficient was used to evaluate the correlation of observed and predicted values. In addition, observations of f o F 2 from the vertical ionosondes at Beijing, Changchun, Qingdao, and Suzhou stations are compared with the model prediction of f o F 2 . The results indicate that the developed real-time f o F 2 mapping model based upon GA-NN is very promising for ionospheric studies.

Description: [1]  The total electron content (TEC) is a primary ionospheric parameter as it can be studied globally using signals of GNSS satellites. Lean et al . [2011, JGR] in the first study of long-term trends in TEC found positive trends for the period 1995–2010 based on TEC derived from global GPS observations. However, the positive trends seem to be inconsistent with both observed and modeled trends in foF2. Here we try to shed light on this puzzle using historical Faraday rotation TEC measurements and foF2 data over the period 1995–2010. We use data from European area where Lean et al . [2011] report remarkably stronger than average positive trend of TEC. These data suggest no trend of TEC in this region in the past but also almost no trend of foF2 over 1995–2010 compared with a negative trend in solar cycles 21 and 22. This means that the trends for 1995–2010 are more positive than trends for the period 1976–1996 and that the trends for 1995–2010 are not representative for the previous period. The magnitude of trends for 1995–2010 is to some extent uncertain due to the uncertain level of the solar EUV flux in the deep solar minimum in 2008 and 2009.

Description: [1]  We devise an approach to calculate the polarization electric field in the ionosphere, when the ionospheric conductances, the primary (modeled) or the total (measured) electric field, and the Cowling efficiency are given. In contrast to previous studies, our approach is a general solution which is not limited to specific geometrical setups, and all parameters may have any kind of spatial dependence. The solution technique is based on spherical elementary current (vector) systems (SECS). This way, we avoid the need to specify explicit boundary conditions for the searched polarization electric field of its potential which would be required if the problem was solved in a differential equation approach. Instead, we solve an algebraic matrix equation, and the implicit boundary condition that the divergence of the polarization electric field vanishes outside our analysis area is sufficient. In order to illustrate our theory, we then apply it to two simple models of auroral electrodynamic situations, the first being a mesoscale strong conductance enhancement in the early morning sector within a relatively weak southward primary electric field, and a morning sector auroral arc with only a weak conductance enhancement, but a large southward primary electric field at the poleward flank of the arc. While the significance of the polarization electric field for maximum Cowling efficiency is large for the first case, it is rather minor for the second one. Both models show that the polarization electric field effect may not only change the magnitude of the current systems, but also their overall geometry. Further, the polarization electric field may extend into regions where the primary electric field is small, thus even dominating the total electric field in these regions. For the first model case, the total Joule heating integrated over the analysis area decreases by a factor of about 4 for maximum Cowling efficiency as compared to the case of vanishing Cowling efficiency. Further, for this case the resulting total electric field structurally shows a strong resemblance to that frequently observed during auroral omega band events.

Description: [1]  In this paper the CHAMP and GRACE observations during 2002–2010 are utilized to study the variation of the annual asymmetry in thermospheric density at 400 km under low solar activity condition (F10.7 = 80) based on the method of empirical orthogonal functions (EOFs). The derived asymmetry index (AI) in thermospheric density from the EOF analysis shows a strong latitudinal variation at night, but varies a little with latitudes in daytime. Moreover, it exhibits a terdiurnal tidal signature at low-middle latitudes. The global mean value of the AI is 0.191, indicating that a 47% difference in thermosphere between December and June solstices in the global average. In addition, the NCAR Thermosphere-Ionosphere Electrodynamics Global Circulation Model (TIEGCM) is used to explore the possible mechanisms responsible for the observed annual asymmetry in thermospheric density. It is found that the standard simulations give a lower AI and also a weaker day-to-night difference. The simulated AI shows a semidiurnal pattern in the equatorial and low latitude regions in contrast with the terdiurnal tide signature seen in the observed AI. The daily mean AI obtained from the simulation is 0.125, corresponding to a 29% December to June difference in thermospheric density at 400 km. Further sensitivity simulations demonstrated that the effect of the varying Sun-Earth distance between the December and June solstices is the main process responsible for the annual asymmetry in thermospheric density, while the magnetic field configuration and tides from the lower atmosphere contribute to the temporal and spatial variations of the AI. Specifically, the simulations show that the Sun-Earth distance effect explains 93% of the difference in thermospheric density between December and June, which is mainly associated with the corresponding changes in neutral temperature. However, our calculation from the density observations reveals that the varying Sun-Earth distance effect only accounts for ~67% of the December to June difference in thermosphere density, indicating that the TIEGCM might significantly underestimate the forcing originating from the lower atmosphere.

Description: [1]  Recently, efforts have been undertaken to develop a coupled thermosphere-ionosphere-plasmasphere model based on two well-established models, namely, the Thermosphere-Ionosphere-Mesosphere General Circulation Model (TIMEGCM) developed at the National Center for Atmospheric Research (NCAR) and the SAMI3 ionosphere model developed at the Naval Research Laboratory. This paper presents the first results from the coupled model on the investigation of a prompt penetration electric field (PPEF) event that took place on 9 November 2004. The coupled model eliminates two major upper boundary limitations of the stand-alone TIMEGCM, e.g., the upper boundary height and the prescribed O + fluxes at the upper boundary. It is found that the F -layer peak height is raised above 800 km in response to the large PPEF. The O + fluxes in the top ionosphere vary drastically during the course of the PPEF, with strong upward and downward fluxes with a magnitude greater than 10 9  cm -2  s -1 in localized regions. For the first time, the coupled model allows us to simulate and visualize the super-fountain effect on a global scale. Future model development is also envisaged, including the implementation of a more realistic magnetic field model and a fully two-way coupling between neutrals and ions.

Description: [1]  We report the first observations of long-lasting daytime equatorial plasma bubbles with the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The most unusual features of the plasma bubbles are the persistence from the post-midnight sector through the afternoon sector and the extremely long lifetime of 12 hours. In one case, the plasma bubbles were generated at 02:00–03:00 LT near the end of the main phase of a moderate magnetic storm and detected by C/NOFS over eight successive orbits, and the decrease of the ion density inside the bubbles was still as large as ~30% at 14:00–15:00 LT. In another case, one group of plasma bubbles was generated near the sunset terminator and existed over the entire nighttime until the post-sunrise sector (06:00–08:00 LT), and another group of plasma bubbles were first detected at 04:00–06:00 LT and lasted until ~11:00 LT. The latter group of bubbles occurred following a sharp northward turning of the interplanetary magnetic field (IMF) near the end of the main phase of a weak magnetic storm, and the over-shielding electric field caused by the IMF northward turning and the storm-time disturbance dynamo might both have contributed to the generation of the bubbles. The plasma bubbles reached 800 km or higher in altitude during daytime. The high altitudes may be critical for the long lifetime of the bubbles: the photo-ionization rate decreases rapidly with altitude. The photo-ionization process may take a long time to produce enough new plasma particles to fill the daytime bubbles at high altitudes.

Description: [1]  The open magnetic flux ( F PC ) is a key parameter to study magnetospheric dynamical process, which is closely related to magnetic recon nections in the dayside magnetopause and magnetotail. Using global MHD simulations, we find that the open magnetic flux F PC can be estimated through a combined parameter f by F PC  = 0.89 f /( f  + 0.20) + 0.52, where the parameter is a function of the solar wind velocity ( v SW ), the solar wind number density ( n SW ), the southern interplanetary magnetic field (IMF) strength ( B S ) , and the ionospheric Pederson conductance (Σ P ). The comparison with the limited observational F PC data available in the literature shows its promising in estimating the open magnetic flux from the interplanetary and ionospheric conditions. The open magnetic flux ( F PC ) may be served as a key space weather forecast element in the future.

Description: [1]  In this paper we demonstrate how magnetic control of ion-neutral interactions in the ionosphere-thermosphere (IT) system effectively produces source terms for non-migrating solar tides in the neutral momentum equations for the thermosphere. The National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is utilized to quantify these tides, and to assess their importance relative to those that propagate upwards from lower atmospheric regions. The primary diurnal tides excited in-situ by the above mechanism include DE1, D0 and DW2, with zonal wind amplitudes on the order of 20 m s –1 (5 - 10 m s –1 ) at ~500 km (~350 km) under solar maximum (minimum) conditions. Smaller amplitude semidiurnal non-migrating tides, mainly SE1, S0, SW1, and SW3, are also generated under solar maximum conditions. The aggregate effect of these tidal components is to produce extrema ranging from -110 to +140 m s –1 in a typical illustration of latitude versus longitude at a constant local time. The associated wind circulations include vertical wind perturbations that drive temperature perturbations through adiabatic heating and cooling effects. At high latitudes hydromagnetic coupling effects generate non-migrating tidal components including DE1, D0, DW2, SE1, S0, and SW1, which show interhemispheric differences in both amplitude and latitudinal structure due to interhemispheric differences in the offset between the geographic and geomagnetic poles. Our computational results show that the in-situ generated non-migrating tidal components dominate some parts of the tidal spectrum at high levels of solar activity and suggest that in-situ generated non-migrating tides must be taken into account in order to reconcile differences in data-model comparisons.

Description: [1]  The orientation of the heliospheric magnetic field (HMF) in near-Earth space is generally a good indicator of the polarity of HMF foot points at the photosphere. There are times, however, when the HMF folds back on itself (is inverted), as indicated by suprathermal electrons locally moving sunward, even though they must ultimately be carrying the heat flux away from the Sun. Analysis of the near-Earth solar wind during the period 1998–2011 reveals that inverted HMF is present approximately 5.5% of the time and is generally associated with slow, dense solar wind and relatively weak HMF intensity. Inverted HMF is mapped to the coronal source surface, where a new method is used to estimate coronal structure from the potential-field source-surface model. We find a strong association with bipolar streamers containing the heliospheric current sheet, as expected, but also with unipolar or pseudostreamers, which contain no current sheet. Because large-scale inverted HMF is a widely-accepted signature of interchange reconnection at the Sun, this finding provides strong evidence for models of the slow solar wind which involve coronal loop opening by reconnection within pseudostreamer belts as well as the bipolar streamer belt. Occurrence rates of bipolar- and pseudostreamers suggest that they are equally likely to result in inverted HMF and, therefore, presumably undergo interchange reconnection at approximately the same rate. Given the different magnetic topologies involved, this suggests the rate of reconnection is set externally, possibly by the differential rotation rate which governs the circulation of open solar flux.

Description: [1]  Subauroral ion drifts (SAID) are the prominent feature of the active subauroral geospace, just earthward of the electron plasma sheet (PS) boundary in the premidnight sector. We explore magnetically-conjugate satellite observations of substorm SAID near the magnetic equator and in the topside ionosphere confirming and expanding on our previous results. The SAID channels reside between the hot electron (PS/auroral) boundary at the plasmapause and the drop in the hot ion flux inside the plasmasphere. The overall features are inconsistent with the paradigm of voltage and current generators. Rather, they are explained in terms of a short-circuiting of substorm-injected hot plasma jets over the plasmapause and formation of a turbulent plasmaspheric boundary layer. The short-circuiting occurs when the cold plasma density exceeds a critical value of 5-10 cm -3 . As the polarization field at the front of the hot plasma jet is shorted out, the hot electrons are arrested, while the hot ions yet move inward. This provides a natural explanation of the long-known dispersionless auroral precipitation boundary. Enhanced plasma turbulence within the SAID channel provides anomalous circuit resistivity and magnetic diffusion, as with the well-documented plasmoid-magnetic barrier problem.

Description: [1]  It is commonly assumed that geomagnetic activity is symmetrical between interhemispheric conjugate locations. However, in many cases, such an assumption proved to be wrong. Especially in high-latitude regions where the magnetosphere and the ionosphere are coupled in a more complex and dynamic fashion, asymmetrical features in geomagnetic phenomena are often observed. This paper presents investigations of geomagnetic responses to sudden change in solar wind pressure to examine interhemispheric conjugate behavior of magnetic field variations, which have rarely been made mainly due to the difficulty of facilitating conjugate-point measurements. In this study, using magnetometer data from three conjugate stations in Greenland and Antarctica, solar wind pressure impulse events (〉5 nPa in 〈16 min) and their geomagnetic responses, typically seen as magnetic impulse events (MIEs), have been examined. Out results suggest that asymmetry in ground response patterns between the conjugatelocations often shows little correlation with IMF orientation, season, and ionospheric conductivity, indicating that much more complex mechanism might be involved in creating interhemispheric conjugate behavior.

Description: [1]  We provide evidence of the simultaneous occurrence of large amplitude, quasi-parallel whistler mode waves and ion-scale magnetic structures, which have been observed by the Cluster spacecraft in the plasma sheet at 17 Earth radii, during a substorm event. It is shown that the magnetic structures are characterized by both a magnetic field strength minimum and a density hump, and that they propagate in a direction quasi perpendicular to the average magnetic field. The observed whistler mode waves are efficiently ducted by the inhomogeneity associated with such ion-scale magnetic structures. The large amplitude of the confined whistler waves suggests that electron precipitations could be enhanced locally via strong pitch-angle scattering. Furthermore, electron distribution functions indicate that a strong parallel heating of electrons occurs within these ion-scale structures. This study provides new insights on the possible multi-scale coupling of plasma dynamics during the substorm expansion, on the basis of the whistler mode wave trapping by coherent ion-scale structures.

Description: [1]  As a response to the Geospace Environment Modeling (GEM) ‘Global Radiation Belt Modeling Challenge’, a 3D diffusion model is used to simulate the radiation belt electron dynamics during two intervals of the Combined Release and Radiation Effects Satellite (CRRES) mission, 1990 August 15-October 15 and 1991 February 1-July 31. The 3D diffusion model, developed as part of the Dynamic Radiation Environment Assimilation Model (DREAM) project, includes radial, pitch angle, and momentum diffusion and mixed pitch angle-momentum diffusion, which are driven by dynamic wave databases from the statistical CRRES wave data, including plasmaspheric hiss, lower-band and upper-band chorus. By comparing the DREAM3D model outputs to the CRRES electron phase space density (PSD) data, we find that, with a data-driven boundary condition at L max  = 5.5, the electron enhancements can generally be explained by radial diffusion, though additional local heating from chorus waves is required. Because the PSD reductions are included in the boundary condition at L max  = 5.5, our model captures the fast electron dropouts over a large L range, producing better model performance compared to previous published results. Plasmaspheric hiss produces electron losses inside the plasmasphere, but the model still sometimes overestimates the PSD there. Test simulations using reduced radial diffusion coefficients or increased pitch angle diffusion coefficients inside the plasmasphere suggest that better wave models and more realistic radial diffusion coefficients, both inside and outside the plasmasphere, are needed to improve the model performance. Statistically, the results show that, with the data-driven outer boundary condition, including radial diffusion and plasmaspheric hiss is sufficient to model the electrons during geomagnetically quiet times, but to best capture the radiation belt variations during active times, pitch angle and momentum diffusion from chorus waves is required.

Description: [1]  Exploiting eight years of magnetic field data from the Cluster mission, we employ an automated magnetopause crossing detection routine to determine the magnetopause location over varying magnetic latitude and local time. For a period spanning nearly one solar cycle we build a database of 2709 magnetopause crossings and compare these locations to the magnetopause models of Petrinec and Russell (1996), Shue et al. (1998), Dmitrievand Suvorova (2000) and Lin et al. (2010). We compare our detected locations with the predicted locations for a variety of solar wind conditions and positions on the magnetopause. We find that, on average, the Petrinec and Russell (1996) and Shue et al. (1998) models overestimate the radial distance to the magnetopause by ~1 R E (9%) whilst the Dmitriev and Suvorova (2000) and Lin et al. (2010) models underestimates it by 0.5 R E (4.5%) and 0.25 R E (2.3%) respectively. Some varying degree of control on the differences between the predicted and encountered locations, by the solar wind and location parameters, are found.

Description: [1]  Possible enhancement of ionospheric Total Electron Content (TEC) immediately before the 2011 Tohoku-oki earthquake (M w 9.0) has been reported by Heki (2011). Critical responses to it often come in two stages; they first doubt the enhancement itself and attribute it to an artifact. Secondly (when they accept the enhancement), they doubt the significance of the enhancement among natural variability of space weather origin. For example, Kamogawa and Kakinami (2013) attributed the enhancement to an artifact falsely detected by the combined effect of the highly variable TEC under active geomagnetic condition and the occurrence of a tsunamigenic ionospheric hole (Kakinami et al., 2012). Here we closely examine the time series of vertical TEC before and after the 2011 Tohoku-oki earthquake. We first demonstrate that the tsunami did not make an ionospheric hole, and next confirm the reality of the enhancement using data of two other sensors, ionosonde and magnetometers. The amplitude of the preseismic TEC enhancement is within the natural variability, and its snapshot resembles to large-scale traveling ionospheric disturbances. However, distinction could be made by examining their propagation properties. Similar TEC anomalies occurred before all the M ≥ 8.5 earthquakes in this century, suggesting their seismic origin.

Description: [1]  We have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms (RGSs), which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008. It is shown that total electron content (TEC) has a tendency to minimize before the beginning of RGSs and to peak 3 to 4 days after, i.e. on the RGS recovery phase produced by high-intensity long-duration continuous auroral activity. The maximum of TEC coincides with the maximum of solar wind velocity within high-speed solar wind streams. An analysis of electron content vertical profiles, derived from two independent methods using ionosondes and COSMIC/FORMOSAT-3 radio occultation, showed that in the maximum of an ionospheric storm on 28 March 2008, the F2 layer thickens, NmF2 increases by ~50% and hmF2 elevates by a few tens of kilometers. The response of positive ionospheric storms to solar, heliospheric and geomagnetic drivers reveals a prominent longitudinal asymmetry. In the longitudinal range from –90° to 90°, the solar illumination plays a major role, and in the range from 90° to –120°, the influence of heliospheric and geomagnetic drivers becomes significant. The highest correlations of the TEC enhancements with the heliospheric and geomagnetic drivers were found during December - February period ( r increased from ~ 0.3 to ~0.5). We speculate that the dynamics controlling this might result from an effect of solar zenith angle, storm-time effects of thermospheric ΣO/N 2 enhancement, and penetrating electric fields of interplanetary and magnetospheric origin.

Description: [1]  We analyzed the Very Large Array (VLA) archived data observed in 2000 to determine whether solar UV/EUV heating of the Jovian thermosphere causes variations in the total flux density and dawn-dusk asymmetry (the characteristic differences between the peak emissions at dawn and dusk) of Jupiter ' s synchrotron radiation (JSR). The total flux density varied by 10% over six days of observations and accorded with theoretical expectations. The average dawn-dusk peak emission ratio indicated that the dawn side emissions were brighter than those on the dusk side, and this was expected to have been caused by diurnal wind induced by the solar UV/EUV. The daily variations in the dawn-dusk ratio did not correspond to the solar UV/EUV, and this finding did not support the theoretical expectation that the dawn-dusk ratio and diurnal wind velocity varies in correspondence with the solar UV/EUV. We tried to determine whether the average dawn-dusk ratio could be explained by a reasonable diurnal wind velocity. We constructed an equatorial brightness distribution model of JSR using the revised Divine-Garrett particle distribution model and used it to derive a relation between the dawn-dusk ratio and diurnal wind velocity. The estimated diurnal wind velocity reasonably corresponded to a numerical simulation of the Jovian thermosphere. We also found that realistic changes in the diurnal wind velocity could not cause the daily variations in the dawn-dusk ratio. Hence, we propose that the solar UV/EUV related variations were below the detection limit and some other processes dominated the daily variations in the dawn-dusk ratio.

Description: : [1]  The ionospheric F2–region is known to show a large day- to-day and hour-to-hour variability. Some of this variability has recently being linked to sudden stratospheric warmings (SSWs). We therefore investigate the extent of ionospheric changes following SSWs of 2007, 2008 and 2009 using ionosonde data from six different stations in the Asian zone thus covering a broad latitudinal range from 23.2ºN to 45.1ºN. We find that ionospheric F2-region shows some significant perturbations soon after the start of the warming. However characteristics of these perturbations vary from event to event and from station to station. We also examine the data on equatorial electrojet strength (EEJ) during these warmings and find there are significant changes in the EEJ strength during the SSW events. A counter electrojet (CEJ) coincident with the start of warming was observed for the SSW event of 2008. We then compare this SSWs linked variability observed by us to the normal day-to-day and hour-to-hour variability seen in the ionospheric data. We find that even during times when there are no SSWs and solar and magnetic indices are quite stable and close to their minimum values, the ionospheric variability is comparable to the variability attributed to these warmings. Further, it seems to us that it is difficult to quantify with precision the changes in foF2, as well as in the ionospheric response times involved, following these events.

Description: [1]  The electric structure of dipolarization fronts (DFs) is very important to both DF dynamics and particle acceleration. We performed two-dimensional Hall MHD simulation to study the electric structure of DF produced by interchange instability on the scale of ion inertial length in the flow braking region of near-Earth tail. The results indicate that Hall effect makes the structures of plasma density and magnetic field deformed in the dawn-dusk direction. This deformation is caused by the induced Lorentz force along the tangent plane of DF, which is associated with the outward moving of demagnetized ions driven by the ion-scale Earthward electric field on DF. In addition, the x component of electric field contributed jointly by Hall and electron pressure gradient terms along with Bz can produce a dawnward E  ×  B drift to the whole “mushroom” structure. Inside the DF, the electric field is mainly produced by Hall term, and the contributions from the convectional and electron pressure gradient electric fields are very small. This indicates that the ion frozen-in condition of magnetic field is violated inside the DF. Therefore it is the electric field contributed by Hall term inside the DF that changes the overall MHD “mushroom” pattern. The comparison between the simulation results and the observations of THEMIS satellites demonstrates that the model of Hall MHD simulation can reproduce the plasma and electric field observed at DF.

Description: [1]  It has been reported that Pi2 pulsations can be excited under extremely quiet geomagnetic conditions ( Kp  = 0). However, there have been few comprehensive reports of Pi2 pulsations in such a near ground state magnetosphere. To understand the characteristics of quiet-time Pi2 pulsations, we statistically examined Pi2 events observed on the nightside between 1800 and 0600 local time at the low-latitude Bohyun (BOH, L = 1.35) station in South Korea. We chose year 2008 for analysis because geomagnetic activity was unusually low in that year. A total of 982 Pi2 events were identified when Kp  ≤ 1. About 80% of the Pi2 pulsations had a period between 110 and 300 s, which significantly differs from the conventional Pi2 period from 40 to 150 s. Comparing Pi2 periods and solar wind conditions, we found that Pi2 periods decrease with increasing solar wind speed, consistent with the result of Troitskaya (1967). The observed wave properties are discussed in terms of plasmaspheric resonance, which has been proposed for Pi2 pulsations in the inner magnetosphere. We also found that Pi2 pulsations occur quasi-periodically with a repetition period of ~23–38 min. We will discuss what determines such a recurrence time of Pi2 pulsations under quiet geomagnetic conditions.

Description: [1]  The observed γ -ray fluence distribution of Terrestrial Gamma-ray Flashes (TGFs) detected by the Fermi Gamma-ray Burst Monitor (GBM) is altered by instrumental effects. We perform corrections for deadtime, pulse pile-up and detection efficiency in a model independent manner. A sample of 106 GBM TGFs is selected to include both TGFs which triggered GBM and weaker TGFs found using an offline search. Detector deadtime and pulse pile-up lower the observed fluence of each TGF and the detection efficiency causes weaker TGFs to have a lower probability of detection than brighter TGFs. Monte Carlo simulations are performed in each case to correct for these effects. The corrected fluence distribution is well fit with a power-law of index α  = –2.20 ± 0.13. This is consistent with previous estimates using other techniques. Neither a high-fluence cut-off nor a low-fluence limit is found. The fluence distribution is also expressed in units of TGF hour –1  km –2 versus photons cm –2 per TGF.

Description: [1]  The wave-3 and wave-4 modulations of the Equatorial Ionization Anomalies (EIAs) are a robust feature of the low latitude ionosphere, when viewed at constant local time. Although initially associated respectively with DE2 and DE3 nonmigrating diurnal tides in the mesosphere and lower thermosphere (MLT) region, recent results have suggested that the wave-3 and wave-4 may also have significant contributions from other tidal and stationary planetary wave (SPW) signatures. We present observations of total electron content (TEC) variations associated with tidal and SPW signatures comprising the ionospheric wave-3 and wave-4 structures from FORMOSAT-3 / COSMIC from 2007-2011. We find that the wave-3 (wave-4) feature is comprised predominately by DE2 (DE3) and SPW3 (SPW4) signatures in TEC throughout all five years, with contributions from SE1 (SE2) being less significant. The wave-3 component also has recurring contributions from DW4 during December/January. The absolute amplitudes of all theaforementioned tidal and SPW signatures are directly related to the level of solar activity and the semiannual variation in zonal mean TEC. After normalizing by the zonal mean, the relative amplitudes of the wave-4 signatures are inversely related to solar activity through 2010, which is not seen with the wave-3 related signatures. The seasonal variation and phases of the main constituents of wave-3 and wave-4 are consistent from year to year, as evidenced by the inter-annual recurrence in the peak and trough locations of wave-3 and wave-4.

Description: [1]  The MEPED instruments onboard the NOAA/POES satellites have provided a valuable long-term database of low altitude energetic particle observations spanning from 1978 to present. Here we study the instrumental problems of the NOAA/MEPED electron detectors and present methods to correct them. It is well known that the MEPED electron detectors are contaminated by protons of certain energy range. Using the recently corrected MEPED proton fluxes we are now able to reliably remove this contamination. Using a simple simulation model to estimate the response of the MEPED electron detectors to incoming electrons and protons we show that efficiencies of SEM-1 and SEM-2 versions of the detectors have large differences due to different detector designs. This leads to a systematic difference between the SEM-1 and SEM-2 measurements and causes a significant long-term inhomogeneity in measured MEPED electron fluxes. Using the estimated efficiencies we remove the proton contamination and correct the electron measurements for non-ideal detector efficiency. We discuss the entire 34-year time series of MEPED measurements and show that, on an average, the correction affects different energy channels and SEM-1 and SEM-2 instruments differently. Accordingly, the uncorrected electron fluxes and electron spectra are severely distorted by non-ideal detector efficiency and proton contamination, and their long-term evolution is misrepresented without the correction. The present correction of the MEPED electron fluxes over the whole interval of NOAA/POES measurements covering several solar cycles is important for long-term studies of, e.g., magnetospheric dynamics, solar activity, ionospheric research and atmospheric effects of energetic electrons.

Description: [1]  In this paper, temporal and spatial analyses are employed to detect seismo-ionospheric precursors (SIPs) in the ionospheric total electron content (TEC) during 16 October 1999 M w 7.1 Hector Mine earthquake. To discriminate anomalies caused by global effects, such as solar radiations, magnetic storms, etc., and local effects, such as earthquake, we cross-examine the GPS TECs and their gradients in the eastward and northward directions at epicenter/centers of the Hector Mine area and the other two reference areas at similar magnetic latitudes in Europe and Japan. Temporal variations of the northward TEC gradient suggest SIPs most likely appearing day 6-5 before the earthquake. A global search by using the TEC of GIM (global ionosphere map) shows that the TEC increase and decrease anomalies continuously and specifically appear around the epicenter day 5 before the earthquake.

Description: [1]  A three-dimensional (3D) magnetic field configuration in force balance with a realistic plasma pressure distribution can provide more accurate evaluation of the role of magnetic field on plasma sheet dynamics and M-I coupling. We used Geotail and THEMIS data to establish an empirical model for nightside equatorial isotropic plasma pressure to r  = 30 R E for Kp = 0–5 and for solar wind dynamic pressure (P SW ) = 1.5 and 3 nPa. The model pressure is used in the companion paper for modeling a 3D force-balanced pressure and magnetic field equilibrium. Larger convection during higher Kp drives the plasma sheet further earthward, resulting in larger increase of pressure and pressure gradient at smaller radial distance. On the other hand, magnetosphere compression by increasing P SW enhances pressure and pressure gradient mainly in the tail plasma sheet. While both pressure and radial gradients are enhanced with increasing Kp or P SW , there is no significant azimuthal pressure variation statistically under all Kp and P SW conditions. The empirical pressures well reproduce these statistical profiles with very high correlation coefficients. Additionally, comparisons with pressure gradients computed using two simultaneous measurements from two THEMIS spacecraft show reasonable agreement. Furthermore, our model provides more accurate pressure gradients than previous empirical models. The model magnetic field distributions obtained in the companion paper from requiring force balance with these empirical pressure profiles are also found to be consistent with the magnetic field observations, indicating that our equilibria well represent realistic 3D pressure and magnetic field configurations.

Description: [1]  Mode conversion at the magnetopause has been suggested to lead to the generation of kinetic Alfvén waves (KAWs) and effective mass transport from the solar wind into the magnetosphere. To investigate the mode conversion process in the dynamic dayside system, a 3-D global hybrid simulation associated with a quasi-parallel shock under a radial interplanetary magnetic field (IMF) is carried out, in which the foreshock compressional pulses are self-consistently generated by the interaction between the solarwind and the geomagnetic field. The results show that as the compressional pulses propagate from the magnetosheath to the magnetopause, short wavelength structures of k ⊥ ρ i  ∼ 0.5 - 1 with enhanced parallel electric field E ∥ are excited in the subsolar magnetopause boundary layer (MPBL), where k ⊥  ≃  k x is the perpendicular waves number nearly along the GSE x direction, and ρ i is the ion Larmor radius. The wave phase relationship between the magnetic field and the density changes from in-phase in the magnetosheath to anti-phase in the short-wavelength MPBL perturbations. The wave polarization is predominantly compressive in the magnetosheath, whereas strong transverse wave powers appear abruptly around the MPBL. The mode conversion from the compressional pulses to KAWs is identified around the predicted Alfvén resonance surface in the MPBL. As these KAWs evolve, KAW modes dominated by azimuthal wave number with k y ρ i  ∼ 1 are also generated. The KAWs in the MPBL are identified by the sharp increases in E ∥ and the electromagnetic field polarization relations of Alfvén mode, as well as a spectral analysis. The KAW perturbations propagate poleward into the cusps along the MPBL. Due to the differential flow convection speeds at various latitudes, the KAW packets expand along the north-south direction, while they may also merge with newly formed KAWs due to newly arrived compressional waves.

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

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

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

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

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

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

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

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

Description: Ground-based observations have shown Pi1B magnetic pulsations are associated with substorm onset. These pulsations can also be observed at geosynchronous orbit, suggesting that they propagate from (or beyond) geosynchronous orbit to the ionosphere at substorm onset. Independently, investigations have shown that the initial brightening of an arc at subtorm onset is Alfvénic in nature (i.e., that the aurora during the initial brightening is wave-driven). These results raise the question of whether Pi1B pulsations might drive Alfvénic aurora at substorm onset. In this paper, data from a single event are presented that show Pi1B pulsations observed simultaneously at geosynchronous orbit, by FAST just above the ionosphere and by various ground stations. The event is observed by FAST within a few minutes of the onset of Pi1B pulsations, with an electron signature of the onset arc that is quite characteristic of Alfvénic aurora, showing that at least a portion of the initial brightening is wave-driven and associating this with the presence of Pi1B pulsations. The implication of this work is that Pi1B pulsations propagate to the ionosphere from beyond geosynchronous orbit and provide the wave power to drive Alfvénic aurora at substorm onset, at least for this single, isolated event. The luminosity associated with the Alfvénic aurora, however, may only provide a small contribution to the total brightness.

Description: We report observations of very large amplitude whistler mode waves in the Earth's nightside inner radiation belt enabled by the STEREO Time Domain Sampler. Amplitudes range from 30–110 mV/m (zero-peak), 2 to 3 orders of magnitude larger than previously observed in this region. Measurements from the peak electric field detector (TDSMax) indicate that these large-amplitude waves are prevalent throughout the plasmasphere. A detailed examination of high time resolution electric field waveforms is undertaken on a subset of these whistlers at L 〈 2, associated with pump waves from lightning flashes and the naval transmitter NPM in Hawaii, that become unstable after propagation through the ionosphere and grow to large amplitudes. Many of the waveforms undergo periodic polarization reversals near the lower hybrid and NPM naval transmitter frequencies. The reversals may be related to finite plasma temperature and gradients in density induced by ion cyclotron heating of the plasma at 200 Hz, the modulation frequency of the continuous-mode NPM naval transmitter signal. Test particle simulations using the amplitudes and durations of the waves observed herein suggest that they can interact strongly with high-energy (〉100 keV) electrons on a time scale of

Description: In this paper, we report a long-term study of medium-scale traveling ionospheric disturbance (MSTID) occurrence using all-sky images of O I 630 nm airglow emission. Our study is based on a 10.5 year data series in which 5.5 years compound a new data set. The images were obtained by an all-sky imager installed at Cachoeira Paulista (22.7°S, 45°W, 15°S magnetic latitude). Our results show the greatest occurrence of MSTIDs during solar minimum and a minor occurrence rate during descending and ascending solar activity periods. During solar maximum, we have not detected MSTID signatures on all-sky images. All detected events have occurred during geomagnetically quiet conditions. Simultaneous measurements using both all-sky images and ionograms obtained at the same site show the occurrence of spread F and a sharp rise in the ionospheric F layer at the same time as dark bands are optically registered over the zenith. It is possible that for certain weaker events, the ionosonde may resolve bands that are not sufficiently raised to cause darkening of the all-sky images. In order to investigate this possibility, we have conducted a study using only ionograms for a 1 year period (March 2000–February 2001) during solar maximum, when we have not seen any MSTID events in the all-sky images. As we conjectured, MSTIDs also occur during solar maximum, and the risings of the ionospheric F layer are not able to disturb the airglow layer during such events.

Description: We reproduce a magnetospheric reconfiguration under southward interplanetary magnetic field (IMF) conditions using numerical magnetohydrodynamic simulations. To investigate the relative displacements of the geomagnetic conjugate points, we trace both footprints of the geomagnetic field lines during the magnetospheric reconfiguration under positive and negative IMF By conditions. Several substormlike features, namely, the formation of a near-Earth neutral line, a fast earthward flow, and tailward releases of the plasmoid, occur about 1 h after a southward turning of the IMF. The surveyed field line traced from the near-Earth magnetotail was strongly distorted duskward in the north and south after the substorm onset for positive and negative IMF By, respectively. The maximum of the relative longitudinal displacement of both footprints is 4.5 and 5.5 h in magnetic local time for positive and negative IMF By, respectively. While observational studies have indicated that the IMF orientation is the main factor controlling the relative displacement of the conjugate points, the present simulation-based study with a constant IMF orientation shows for the first time that the combined effects of plasma pressure, magnetic field intensity, and the field-aligned current density distribution along the field line are likely to be major factors controlling the relative displacement of conjugate points.

Description: Motivated by recent attempts to derive geomagnetic activity from hourly mean data in long-term studies, we test the recursive Kalman filter method to obtain the regular solar variation curve of the geomagnetic field. Using a simple algorithm, we are able to assign a quiet day curve to every day separately, without the need for additional input parameter(s) to define the geomagnetically quiet days. We derive a digital counterpart AhK of the analog range index Ak at the subauroral Sodankylä station and compare it to the earlier digital estimate Ah and the local Ak index. We find that the new method outperforms the former estimate in every aspect studied and provides a robust, straightforward manner of estimating and verifying the manually scaled Ak index, based on readily available hourly values. The model is independent of sampling; thus, for shorter-term studies where high-sampling data are available, more accurate estimates can also be obtained when needed. Therefore, in contrast to other recent approaches, we do not provide a method to quantify irregular activity directly but derive the actual quiet day curves in the traditional manner. In future applications the same algorithm may be used to define a wide variety of geomagnetic indices (such as Ak, Dst, or AE).