ALBERT

Description: This study focuses on the 15 May 2005 geomagnetic superstorm, and aims to investigate the global variation of positive and negative storm phases and their development. Observations are provided by a series of global total electron content (TEC) maps, and multi-instrument line plots. Coupled Thermosphere-Ionosphere-Plasmasphere electrodynamics (CTIPe) simulations are also employed. Results reveal some sunward streaming plumes of storm-enhanced density (SED) over Asia and a well-developed mid-latitude trough over North America forming isolated positive and negative storms respectively. The simultaneous development of positive and negative storms over North America is also shown. Then, some enhanced auroral ionizations maintained by strong equatorward neutral winds appeared in the depleted night-time ionosphere. Meanwhile, the northern night-time polar region became significantly depleted as the SED plume plasma could not progress further than the dayside cusp. Oppositely, a polar tongue of ionization (TOI) developed in the daytime southern polar region. According to CTIP simulations, solar heating locally maximized (minimized) over the southern (northern) magnetic pole. Furthermore, strong upward surges of molecular rich air created O/N 2 decreases both in the auroral zone and in the trough region while some SED related downward surges produced O/N 2 increases. From these results we conclude for the time period studied that 1) composition changes contributed to the formation of positive and negative storms, 2) strengthening polar convection and increasing solar heating of the polar cap supported polar TOI development, and 3) a weaker polar convection and minimized solar heating of the polar cap aided the depletion of polar plasma.

Description: We develop a new analytical model of the Alfvén wing that is generated by the interaction between a planetary moon's ionosphere and its magnetospheric environment. While preceding analytical approaches assumed the obstacle's height-integrated ionospheric conductivities to be spatially constant, the model presented here can take into account a continuous conductance profile that follows a power law. The electric potential in the interaction region, determining the electromagnetic fields of the Alfvén wing, can then be calculated from an Euler-type differential equation. In this way, the model allows to include a realistic representation of the “suspension bridge”-like conductance profile expected for the moon's ionosphere. The major drawback of this approach is its restriction to interaction scenarios where the ionospheric Pedersen conductance is large compared to the Hall conductance and thus, the Alfvénic perturbations are approximately symmetric between the planet-facing and the planet-averted hemispheres of the moon. The model is applied to the hemisphere coupling effect observed at Enceladus, i.e., to the surface currents and the associated magnetic discontinuities that arise from a north-south asymmetry of the obstacle to the plasma flow. We show that the occurrence of this effect is very robust against changes in the conductance profile of Enceladus' plume and we derive upper limits for the strength of the magnetic field jumps generated by the hemisphere coupling effect. During all eleven reported detections of the hemisphere coupling currents at Enceladus, the observed magnetic field jumps were clearly weaker than the proposed limits. Our findings are also relevant for future in-situ studies of putative plumes at the Jovian moon Europa.

Description: Ground magnetic measurements provide a unique database in understanding space weather. The continuous geomagnetic records from Colaba-Alibag observatories in India contain historically longest and continuous observations from 1847 to present date. Some of the super intense geomagnetic storms occurred prior to 1900 have been revisited and investigated in order to understand the probable interplanetary conditions associated with intense storms. Following the Burton et al . [1975], an empirical relationship is derived for estimation of interplanetary electric field (IEFy) from the variations of Dst index and ΔH at Colaba-Alibag observatories. The estimated IEFy values using Dst and ΔH ABG variations agree well with the observed IEFy, calculated using ACE (Advanced Composition Explorer) satellite observations for intense geomagnetic storms in solar cycle 23. This study will provide the uniqueness of each event and provide important insights into possible interplanetary conditions for intense geomagnetic storms and probable frequency of their occurrence.

Description: We report sub-packet structures found in electromagnetic ion cyclotron (EMIC) rising tone emissions observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probles. We investigate three typical cases in detail. The first case shows a continuous single rising tone with obvious four sub-packets, and the second case is characterized by a patchy emission with multiple sub-packets triggered in a broadband frequency. The third case looks like a smooth rising tone without any obvious sub-packet in the FFT spectrum, while its amplitude contains small peaks with increasing frequencies. The degree of polarization of each sub-packet is generally higher than 0.8 with a left-handed polarization, and the wave direction of the sub-packets is typically field-aligned. We show that the time evolution of the observed frequency and amplitude can be reproduced consistently by nonlinear growth theory. We also compare the observed time span of each sub-packet structure with the theoretical trapping time for second-order cyclotron resonance. They are consistent, indicating that an individual sub-packet is generated through a nonlinear wave growth process which excites an element in accordance with the theoretically predicted optimum amplitude.

Description: Lunar mini-magnetosphere formed by the interaction between the solar wind and a local crustal field often has a scale size comparable to the ion inertia length, in which the Hall effect is very important. In this paper, the general characteristics of lunar mini-magnetosphere are investigated by three-dimensional Hall MHD simulations. It is found that the solar wind ions can penetrate across the magnetopause to reduce the density depletion and cause the merging of the shock and magnetopause, but the electrons are still blocked at the boundary. Besides, asymmetric convection occurs, resulting in the magnetic field piles up on one side while the plasma gathers on the other side. The size of the mini-magnetosphere is determined by both the solar zenith angle and the magnetosonic Mach number, while the Hall effect is determined by the ratio of the pressure balance distance to the ion inertia length. When the ratio gets small, the shock may disappear. Finally, we present a global Hall MHD simulation for comparison with the observation from Chang'E-2 satellite on Oct 11, 2010 and confirm that Chang'E-2 flew across compression regions of two separate mini-magnetospheres.

Description: Accurate evaluation of the physical processes during the substorm growth phase, including formation of field-aligned currents (FACs), isotropization by current sheet scattering, instabilities, and ionosphere-magnetosphere connection relies on knowing the realistic 3 dimensional (3D) magnetic field configuration, which cannot be reliably provided by current available empirical models. We have established a 3D substorm growth phase magnetic field model, which is uniquely constructed from empirical plasma sheet pressures under the constraint of force balance. We investigated the evolution of model pressure and magnetic field responding to increasing energy loading, and their configurations under different solar wind dynamic pressure (P SW ) and sunspot number. Our model reproduces the typical growth phase evolution signatures: plasma pressure increases, magnetic field lines become more stretched, current sheet becomes thinner, and the Region-2 FACs are enhanced. The model magnetic fields agree quantitatively well with observed fields. The magnetic field is substantially more stretched under higher P SW while the dependence on sunspot number is non-linear and less substantial. By applying our modeling to a substorm event, we found that (1) the equatorward movement of proton aurora during the growth phase is mainly due to continuous stretching of magnetic field lines, (2) the ballooning instability is more favorable during late growth phase around midnight tail where there is a localized plasma beta peak, and (3) the equatorial mapping of the breakup auroral arc is at X ~ –14 R E near midnight, coinciding with the location of the maximum growth rate for the ballooning instability.

Description: We investigate localized magnetosheath and solar wind density enhancements, associated with clear magnetic field changes, and therefore referred to as magnetosheath/solar wind plasmoids, respectively. Using Cluster data, we show that there are two distinct populations of magnetosheath plasmoids, one associated with a decrease of magnetic field strength (diamagnetic plasmoids), and one with an increased magnetic field strength (paramagnetic plasmoids). The diamagnetic magnetosheath plasmoids have scale sizes of the order of 1–10 R E , while the paramagnetic ones are an order of magnitude smaller. The diamagnetic plasmoids are not associated with any change in the magnetosheath plasma flow velocity, and they are classified as embedded plasmoids in the terminology of Karlsson et al. (2012). The paramagnetic plasmoids may either be embedded or associated with increases in flow velocity (fast plasmoids). A search for plasmoids in the pristine solar wind resulted in identification of62 diamagnetic plasmoids with very similar properties to the magnetosheath diamagnetic plasmoids, making it probable that the solar wind is the source of these structures. No paramagnetic plasmoids are found in the pristine solar wind, indicating that these are instead created at the bow shock or in the magnetosheath. We discuss the relation of the plasmoids to the phenomenon of magnetosheath jets, with which they have many properties in common, and suggest that the paramagnetic plasmoids can be regarded as a subset of these, or a closely related phenomenon. We also discuss how the results from this study relate to theories addressing the formation of magnetosheath jets.

Description: We present an empirical model of the high-latitude air density at 450 km, derived from accelerometer measurements by CHAMP and GRACE satellites during 2002–2006, which we call HANDY ( H igh-latitude A tmospheric N eutral D ensit Y ). HANDY consists of a quiet model and disturbance model. The quiet model represents the background thermospheric density for “zero geomagnetic activity” conditions. The disturbance model represents the response of the thermospheric density to solar wind forcing at high latitudes. The solar wind inputs used are the following: (1) solar wind electric field E SW , (2) interplanetary magnetic field (IMF) clock angle C SW , and (3) solar wind dynamic pressure P SW . Both quiet and disturbance models are constructed on the basis of spherical harmonic function fitting to the data. Magnetic coordinates are used for the disturbance model, while geographical coordinates are used for the quiet model. HANDY reproduces main features of the solar wind influence on the high-latitude thermospheric density, such as the IMF B y effect that produces a hemispheric asymmetry in the density distribution.

Description: Using the OMNI data for period 1976–2000 we investigate the temporal profiles of 20 plasma and field parameters in the disturbed large-scale types of solar wind (SW): CIR, ICME (both MC and Ejecta) and Sheath as well as the interplanetary shock (IS). To take into account the different durations of SW types we use the double superposed epoch analysis (DSEA) method: re-scaling the duration of the interval for all types in such a manner that, respectively, beginning and end for all intervals of selected type coincide. As the analyzed SW types can interact with each other and change parameters as a result of such interaction, we investigate separately 8 sequences of SW types: (1) CIR, (2) IS/CIR, (3) Ejecta, (4) Sheath/Ejecta, (5) IS/Sheath/Ejecta, (6) MC, (7) Sheath/MC, and (8) IS/Sheath/MC. The main conclusion is that the behavior of parameters in Sheath and in CIR are very similar both qualitatively and quantitatively. Both the high-speed stream (HSS) and the fast ICME play a role of pistons which push the plasma located ahead them. The increase of speed in HSS and ICME leads at first to formation of compression regions (CIR and Sheath, respectively), and then to IS. The occurrence of compression regions and IS increases the probability of growth of magnetospheric activity.

Description: Using fully kinetic simulations, we study the x-line orientation of magnetic reconnection in an asymmetric configuration. A spatially localized perturbation is employed to induce a single x-line, that has sufficient freedom to choose its orientation in three-dimensional systems. The effect of ion to electron mass ratio is investigated, and the x-line appears to bisect the magnetic shear angle across the current sheet in the large mass ratio limit. The orientation can generally be deduced by scanning through the corresponding 2D simulations to find the reconnection plane that maximizes the peak reconnection electric field. The deviation from the bisection angle in the lower mass ratio limit is consistent with the orientation shift of the most unstable linear tearing mode in a electron-scale current sheet.

Description: Understanding how the relativistic electron fluxes drop out in the outer radiation belt under different conditions is of great importance. To investigate which mechanisms may affect the dropouts under different solar wind conditions, 1.5-6.0 MeV electron flux dropout events associated with 223 Corotating Interaction Regions (CIRs) from 1994 to 2003 are studied using the observations of SAMPEX satellite. According to the superposed epoch analysis, it is found that high solar wind dynamic pressure with the peak median value of about 7 nPa, is corresponding to the dropout of the median of the Radiation Belt Content (RBC) index to 20 percent of the level before stream interface arrival; whereas low dynamic pressure with the peak median value of about 3 nPa, is related to the dropout of the median of RBC index to 40 percent of the level before stream interface arrival. Furthermore, the influences of Russell-McPherron effect with respect to Interplanetary Magnetic Field (IMF) orientation on dropouts is considered. It is pointed out that under positive Russell-McPherron effect (+RM effect) condition, the median of RBC index can drop to 23 percent of the level before stream interface arrival; while for negative Russell-McPherron-effect (-RM effect) events, the median of RBC index only drops to 37 percent of the level before stream interface arrival. From the evolution of phase space density profiles, the effect of +RM on dropouts can be through non-adiabatic loss.

Description: This study presents a statistical overview of coherent wave activity in Mercury's magnetosheath. Left-handed electromagnetic ion-cyclotron waves are commonly found behind the quasi-perpendicular section of the bow shock, where they are present in ~50% of the spacecraft crossings of the magnetosheath. Their occurrence distribution maximizes within the magnetosheath, approximately half-way between the bow shock and the magnetopause, and the waves are generally strongly Doppler shifted up to frequencies above the local ion-cyclotron frequency. Downstream of the quasi-parallel shock, the magnetosheath often exhibit large-amplitude pulsations with wave periods around 10 s and peak-to-peak amplitudes of up to 100 nT that dominate the magnetic field structure. These waves are circularly left-hand polarized with wave vectors in the direction of the local shock normal. The data suggest that they have been generated upstream of the shock and transmitted into the downstream region. Their occurrence rates maximize at the near-parallel shock, where they are present approximately 10% of the time, and where they also show their largest wave powers. Some evidence is also found of waves with a right-handed polarization in the spacecraft frame. These consist of both whistler waves above the local ion-cyclotron frequency and ion-cyclotron waves propagating against the magnetosheath flow with Doppler shifts exceeding the intrinsic wave frequency, which results in a change in their apparent polarization. These waves are in minority compared to the left-handed observations, which indicates a preference for ion-cyclotron waves propagating in the direction of the plasma flow.

Description: A comprehensive study of the solar wind interaction with the Martian upper atmosphere is presented. Three global models: the 3-D Mars multi-fluid Block Adaptive Tree Solar-wind Roe Upwind Scheme (BATS-R-US) MHD code (MF-MHD), the 3-D Mars Global Ionosphere Thermosphere Model (M-GITM) and the Mars exosphere Monte Carlo model Adaptive Mesh Particle Simulator (M-AMPS) were used in this study. These models are one-way coupled, i.e., the MF-MHD model uses the 3-D neutral inputs from M-GITM and the 3-D hot oxygen corona distribution from M-AMPS. By adopting this one-way coupling approach, the Martian upper atmosphere ion escape rates are investigated in detail with the combined variations of crustal field orientation, solar cycle and Martian seasonal conditions. The calculated ion escape rates are compared with Mars Express (MEX) observational data and show reasonable agreement. The variations in solar cycles and seasons can affect the ion loss by a factor of ~ 3.3 and ~ 1.3, respectively. The crustal magnetic field has a shielding effect to protect Mars from solar wind interaction, and this effect is the strongest for perihelion conditions, with the crustal field facing the Sun. Furthermore, the fraction of cold escaping heavy ionospheric molecular ions [(O and/or CO )/Total] are inversely proportional to the fraction of the escaping (ionospheric and corona) atomic ion [O + /Total], whereas O and CO ion escape fractions show a positive linear correlation since both ion species are ionospheric ions that follow the same escaping path.

Description: Observations performed by the Earth Observing System Microwave Limb Sounder instrument on-board the Aura satellite from 2004 – 2009 (2004–2014) were used to investigate the 27-day solar rotational cycle in mesospheric OH (O 3 ) and the physical connection to geomagnetic activity. Data analysis was focused on nighttime measurements at geomagnetic latitudes connected to the outer radiation belts (55° - 75°N/S). The applied superposed epoch analysis reveals a distinct 27-day solar rotational signal in OH and O 3 during winter in both hemispheres at altitudes 〉70 km. The OH response is positive and in-phase with the respective geomagnetic activity signal, lasting for 1 – 2 days. In contrast the O 3 feedback is negative, delayed by one day, and is present up to 4 days afterward. Largest OH (O 3 ) peaks are found at ~75 km, exceeding the 95% significance level and the measurement noise of 〈2% (〈0.5%), while reaching variations of +14% (−7%) with respect to their corresponding background. OH at 75 km is observed to respond to particle precipitation only after a certain threshold of geomagnetic activity is exceeded, depending on the respective OH background. The relation between OH and O 3 at 75 km in both hemispheres is found to be non-linear. In particular OH has a strong impact on O 3 for relatively weak geomagnetic disturbances and accompanying small absolute OH variations (〈0.04 ppb). In contrast catalytic O 3 depletion is seen to slow down for stronger geomagnetic variations and OH anomalies (0.04 - 0.13 ppb), revealing small variations around −0.11 ppm.

Description: A tsunami propagating in open ocean can produce gravity waves and thus perturb the ionosphere. In this study, we employ a second-order numerical difference method using GPS total electron content observed in New Zealand to detect the ionospheric disturbances triggered by the Chile tsunami that occurred on 1 April 2014. We observe travelling ionospheric disturbances (TIDs), which have similar horizontal velocity and direction as the tsunami waves, at different times after the event. According to the arrival times, the latter TIDs (about 14.5-15 h after earthquake) can be attributed to the tsunami waves whereas the former one (about 12 h 30 min after earthquake) could be related to other sources. This suggests that, besides the propagation velocity and direction, the arrival time is also necessary to distinguish tsunami-driven TIDs correctly. Furthermore, we observe the phenomenon that the detected tsunami-driven TIDs are superimposed upon other non-tsunami-driven ionospheric perturbations far away from the epicenter. The superimposed TIDs eventually separate due to their different propagation velocities.

Description: To improve our understanding of the role of EMIC waves in radiation belt electron dynamics, we perform a comprehensive analysis of EMIC wave induced resonant scattering of outer zone relativistic (〉0.5 MeV) electrons and resultant electron loss timescales with respect to EMIC wave band, L-shell, and wave normal angle model. The results demonstrate that while H + -band EMIC waves dominate the scattering losses of ~1–4 MeV outer zone relativistic electrons, it is He + -band and O + -band waves that prevail over the pitch angle diffusion of ultra-relativistic electrons at higher energies. Given the wave amplitude, EMIC waves at higher L-shells tend to resonantly interact with a larger population of outer zone relativistic electrons and drive their pitch angle scattering more efficiently. Obliquity of EMIC waves can reduce the efficiency of wave induced relativistic electron pitch angle scattering. Compared to the frequently adopted parallel or quasi-parallel model, use of the latitudinally varying wave normal angle model produces the largest decrease in H + -band EMIC wave scattering rates at pitch angles 〈~ 40° for electrons 〉~ 5 MeV. At a representative nominal amplitude of 1 nT, EMIC wave scattering produces the equilibrium state (i.e., the lowest normal mode under which electrons at the same energy but different pitch angles decay exponentially on the same timescale) of outer belt relativistic electrons within several to tens of minutes, and the following exponential decay extending to higher pitch angles on timescales from 〈1 minute to ~1 hour. The electron loss cone can be either empty as a result of the weak diffusion or heavily/fully filled due to approaching the strong diffusion limit, while the trapped electron population at high pitch angles close to 90° remains intact because of no resonant scattering. In this manner, EMIC wave scattering has the potential to deepen the anisotropic distribution of outer zone relativistic electrons by reshaping their pitch angle profiles to “top-hat”. Overall, H + -band and He + -band EMIC waves are most efficient in producing the pitch angle scattering loss of relativistic electrons at ~1–2 MeV. In contrast, the presence of O + -band EMIC waves, while at a smaller occurrence rate, can dominate the scattering loss of 5–10 MeV electrons in the entire region of the outer zone, which should be considered in future modeling of the outer zone relativistic electron dynamics.

Description: Initial brightening of the aurora is an optical manifestation of the beginning of a substorm expansion, and is accompanied by large-amplitude upward field-aligned currents (FACs). Based on global magnetohydrodynamic (MHD) simulation, we suggest the possible generation mechanism of the upward FAC that may manifest the initial brightening. (1) A formation of the near-Earth neutral line (NENL) releases the tension force that accelerates plasma earthward. (2) The earthward (perpendicular) flow is converted to a field-aligned flow when flow braking takes place. (3) A high-pressure region propagates earthward along a field line. (4) The off-equatorial high-pressure region pulls in and discharges ambient plasma, which generates a flow vorticity around it. (5) Region 1-sense FAC is generated in the upper part of the off-equatorial high-pressure region. (6) The upward FAC is connected with the ionosphere in the center of the Harang discontinuity, causing the initial brightening. Additional dynamo is generated in the near-Earth region, which transmits electromagnetic energy. Upward FAC that manifests the initial brightening seems to be necessarily originated in the near-Earth off-equatorial region where the magnitude of the perpendicular (diamagnetic) current is relatively small in comparison with that of the FAC. Near the equatorial plane, the perpendicular current is comparable to or larger than FAC, so that a current line is diverted from a magnetic field line and that the FAC generated near the equatorial plane is not necessarily connected with the ionosphere. The proposed mechanism occurs regardless of the location of the NENL, and may explain some of auroral forms.

Description: Satellite measurements suggest that space plasmas often exhibit bi-kappa particle distributions with high-energy tails instead of simple Maxwellians. The presence of suprathermal particles significantly alters the plasmas’ dispersion properties compared to purely Maxwellian scenarios. In the past, wave propagation in magnetized, bi-kappa plasmas was almost exclusively addressed for parallel propagating modes only. To enable a systematic study of both parallel and oblique wave propagation, the new kinetic dispersion relation solver DSHARK was developed and is presented in this work. DSHARK is an iterative root finding algorithm which is based on Summers et al. [1994] who derived the dielectric tensor for plasmas with bi-kappa distributed particles. After a brief discussion of kappa distributions, we present the kinetic theory and the numerical methods implemented in DSHARK and verify the code by considering several test cases. Then, we apply DSHARK to the oblique firehose instability to initiate a more extensive work which will be addressed in the future. A systematic investigation of the dispersion properties of bi-kappa distributed plasmas is expected to lead to a deeper understanding of wave propagation and instability growth in the solar wind.

Description: Magnetic reconnection at the Earth's magnetopause plays an important role in magnetospheric dynamics. Understanding the dynamics requires theory and observations. Previous theoretical work suggests that for no guide field, ions in the exhaust region on the magnetosheath side of the boundary counterstream with a velocity separation that is twice the upstream Alfvén speed ( v A ) and that the counterstreaming velocity decreases with increasing guide field. These theoretical predictions are tested for reconnection at the Earth's magnetopause using observations from the Cluster spacecraft. The difference between the incident and reflected ion velocities ( v sep ) in the magnetosheath boundary layer (MSBL) ion populations is used to determine the exhaust velocity. The ratio of v sep over twice the Alfvén speed ( R V = v sep /2 v A,L ) is predicted to approach 1 for reconnection with shear angles near 180° (no guide field), but is observed to reach a value of approximately 0.84 for the magnetopause crossings analyzed with shear angles near 180°. This value is consistent with previous observations of ion velocities from reconnection at the magnetopause investigated using the Walén relation. While magnetic shear angle can contribute to the disagreement between observations and the Walén relation, it does not play a large role, given the reduced ratio for the events near 180° in this study.

Description: An all-sky imaging system at the McDonald Observatory (30.67 o N, 104.02 o W, 40 o MLAT) showed dramatic ionospheric effects during a moderate geomagnetic storm on June 1, 2013. The auroral zone expanded, leading to the observation of a Stable Auroral Red (SAR) arc. Airglow depletions associated with Equatorial Spread F (ESF) were also seen for the first time at such high magnetic latitude. Total electron content (TEC) measurements from a global positioning system (GPS) receiver exhibited ionospheric irregularities typically associated with ESF. We explore why this moderate geomagnetic disturbance lead to such dramatic ionospheric perturbations at mid-latitudes. A corotating interaction region (CIR)-like driver and a highly contracted plasmasphere caused the SAR arc to occur at L-shell ~ 2.3. For ESF at L ~2.1, timing of the storm intensification, alignment of the sunset terminator with the central magnetic meridian, and sudden variations in the westward auroral electrojet, all combined to trigger equatorial irregularities that reached altitudes of ~ 7000 km. The SAR arc and ESF signatures at the ionospheric footpoins of inner magnetosphere L-shells (L~ 2) represent a dramatic convergence of pole to equator/equator to pole coupling at midlatitudes.

Description: The response of the vertical plasma drift (Vz) and the electron density (NmF2) during different solar eclipses were investigated. The Diurnal values of the direct scaled measurement of F2 peak height and the one derived from M(3000)F2 data, acquired over an equatorial/low-latitude stations have been used to determine the vertical plasma drift. The ionosphere during a solar eclipse is significantly affected by the E×B vertical drift; the large depletion of electron density at low altitudes can be transported to high altitudes through the plasma vertical drift. The loss in ionization density during the eclipse phase decreases the electron density, which was accompanied by rapid increase in hmF2. This deviation in the NmF2 during eclipse compared to control days can be related to the increase in the loss rate due to recombination, as a result of reduction in thermal energy. However, the maximum reduction in NmF2 is not synchronous with the time of maximum totality but some minutes later. The differences in the solar epochs may contribute to the observed relative changes in the ionospheric F2 region behavior during the eclipse window. Lastly, it is very difficult to separate the influence of magnetic disturbances from solar eclipse. The deviation in NmF2 is higher during magnetic disturbed days than the quiet day. The reverse is the case for hmF2 observation. However, the NmF2 variation increases with an increase in solar activity.

Description: The Resolute Bay incoherent scatter radar North (RISR-N) data collected between January 2012 and June 2013 are employed to identify and analyze 14 events with significant plasma density depressions ( N e  〈 4× 10 10 m − 3 ) in the winter polar cap ionosphere. The RISR-N observations near a magnetic latitude (MLAT) of 85 ∘ N refer to the region poleward of the previously-identified polar hole-auroral cavity region 70 ∘  − − 80 ∘ MLAT where extremely low densities (down to 2 × 10 8 m − 3 near 300 km in altitude) are found at times. Multi-point observations by RISR-N are also characterized by multiple series of propagating local density enhancements (plasma structures) both well outside and in the vicinity of polar holes. A superposed epoch analysis of plasma density and convection reveals that the density depressions tend to reach their minimum near the reversal of the meridional convection component. The wavelet analysis of plasma density time series shows that the wave power is enhanced within the depressions and tends to peak near the density minimum. The plasma structures are more elongated at mesoscales (〉 150 km), with no apparent differences between structure shapes outside and insidelow-density regions. The structure propagation velocity is perpendicular to its elongation direction and consistent with that of the large-scale plasma convection. The observations indicate that large-scale density depressions can form under a variety of convection conditions and that plasma structuring processes outside the depressions may be responsible for their partial filling.

Description: Low-latitude Pi2 pulsations in the topside ionosphere are investigated using vector magnetic field measurements from LEO satellite, CHAMP and underneath ground station. Substorm-associated Pi2s are initially identified using high-resolution data from Indian station Shillong, during 2007-2009, and are further classified into three sub-groups of Pi2-band (6-15mHz), based on its frequency. During nighttime, coherent in-phase oscillations are observed in the compressional component at satellite and horizontal-component at underneath ground-station for all the Pi2 events, irrespective of the Pi2 frequency. We observe that the identification of daytime Pi2s at CHAMP (compressional component) depends on the frequency of Pi2 oscillation i.e., 40%, 45% and 100% of Pi2 events observed in dayside ground station with frequency between 6-10mHz, 10-15mHz and 15-25mHz were identified at satellite respectively. At CHAMP during daytime, the presence of a dominant power in the lower frequencies of Pi2-band, which is unique to satellite is consistently observed and can modify the Pi2-oscillations. Pi2s having frequency 〉15mHz are less affected by these background frequencies and a clear signature of daytime Pi2s at CHAMP is possible to observe, provided contribution from non-Pi2 frequencies at satellite from the lower end of Pi2 band is eliminated. Daytime Pi2s identified in the topside ionosphere showed coherent but mostly opposite-phase oscillations with underneath ground station, and satellite-to-ground amplitude ratio is in general found to be less than one. Present results indicate that a combination of fast-cavity-mode oscillations and an instantaneous transmission of Pi2 electric field from high-to-low latitude ionosphere is responsible for the observation of daytime Pi2s.

Description: Bursty (a few minutes) enhancements of hot electrons (1-10 keV) in the tail magnetosheath, which we name hot electron enhancements (HEEs), are sometimes observed. To understand the processes leading to HEEs, we have used 4 years of measurements from Acceleration Reconnection Turbulence & Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) mission to statistically investigate the dawn-dusk asymmetry of HEEs in the mid-tail ( X from –30 to –70 R E ) magnetosheath and their correlations with the solar wind/interplanetary magnetic field (IMF) conditions. We find two strong dawn-dusk asymmetries associated with HEEs: (1) They occur about 3 to 4 times more frequently on the dawnside. (2) Their fluxes on the dawnside are about twice as large as those on the duskside. The magnitudes of HEE fluxes are similar to those of the magnetosphere fluxes near the magnetopause, which are also a factor of 2 higher on the dawnside, indicating that the magnetosphere electrons are likely the source for HEEs and the cause for the HEE flux asymmetry. HEEs occur preferentially during higher solar wind speed and the majority of HEEs are associated with sharp IMF direction changes and are accompanied by large and transient magnetosheath density changes. These correlations are stronger on the dawnside, suggesting that perturbations created near the quasi-parallel bow shock, which is most of the time on the dawnside, associated with IMF discontinuities is a possible process leading to HEEs and could account for the higher HEE occurrence on the dawnside.

Description: We have analyzed the Cassini Radio and Plasma Wave (RPWS) Wideband Receiver (WBR) data specifically looking for the presence of bipolar Electrostatic Solitary Waves (ESWs). Typical examples of these ESWs are provided to show that when they are present, several of them may be detected over a few to several ms time span. We carried out an event study of an Enceladus encounter which took place on October 9, 2008. Approximately 30 minutes prior to and during the crossing of the Enceladus dust plume, several ESWs are observed with amplitudes of about 100 μV/m up to about 140 mV/m, and time durations of several tens of µs up to 250 µs. The highest amplitudes (over 10 mV/m) were observed only during the closest approach to Enceladus. We also carried out an ESW survey using the WBR for all years from 2004 through 2008 for distances less than 10 R S . The survey clearly shows that most of the ESWs are found on the night side, with a high percentage of them in the range of 4–6 R S . This location is consistent with the densest part of Saturn's E ring and Enceladus' orbit. These are the first extended survey results of ESWs near Saturn and the first reported ESWs in connection with Enceladus. We discuss possibilities for the generation of these nonlinear ESWs, which involve current, beam, and acoustic, including dust, instabilities.

Description: Hong Kong (22.3°N, 114.2°E, dip: 30.5°N; Geomagnetic 15.7°N, 173.4°W, Declination: 2.7°W) is a low latitude area and the Hong Kong Continuously Operating Reference Station (CORS) network has been developed and maintained by Lands Department of Hong Kong government since 2001. Based on the collected GPS observations of a whole solar cycle from 2001 to 2012, a method is proposed to estimate the zonal drift velocity as well as the tilt of the observed plasma bubbles and the estimated results are statistically analyzed. It is found that though the plasma bubbles are basically vertical within the equatorial plane, the tilt can be as big as more than 60° eastward or westward sometimes. And the tilt and the zonal drift velocity are correlated. When the velocity is large, the tilt is also large generally. Another finding is that large velocity and tilt generally occur in spring and autumn and in solar active years.

Description: We have studied the statistical properties of toroidal mode standing Alfvén waves with a fundamental eigenmode structure along the field line, denoted T1 waves, in the L range 7–12, using THEMIS-D data for 2008–2013. T1 wave events were identified in hourly data segments using an automated procedure that detects narrowband oscillations in the azimuthal component of the ion bulk velocity. For each event we determined the frequency, amplitude, ellipticity, and the orientation angle of the polarization ellipse, and we examined the L and magnetic local time dependence of the detection rate and physical properties of the T1 waves. Confirming previous observations in space and on the ground, we found a pronounced dawn–dusk asymmetry in the wave detection rate and amplitude. The detection rate in the dawn sector is approximately twice as high as that in the dusk sector, and the amplitude in the dawn sector is larger by ∼50 % . The same asymmetry is also evident in the velocity amplitude averaged in the fixed Pc5 band (1.7–6.7 mHz) and in the amplitude of the electric field and field line displacement that are derived from the velocity amplitude. The ellipticity and the orientation angle of the polarization ellipse are organized by local time, in accordance with the theoretical prediction of toroidal mode waves excited by field line resonance with tailward propagating waves in the magnetosphere, which are in turn driven by external sources. Although infrequently, T1 waves are also detected in the midnight sector, suggesting magnetotail sources for this subset of events.

Description: Cause of substorm expansion onset is one of the major problems in the magnetospheric study. On the basis of a global magnetohydrodynamic (MHD) simulation, Tanaka et al. [2010] suggested that formation and evolution of a high-pressure region (HPR) in the near-Earth plasma sheet could result in sudden intensification of the Region 1 field-aligned current and the westward auroral electrojet. In this sense, the formation and evolution of the HPR are a key in understanding the cause of the onset. On 5 April 2009, three probes of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) were located at X GSM ~ −11 Re around the equator, which provide unique opportunity to investigate the spatial-temporal evolution of the HPR near the substorm expansion onset. Just before the onset, a positive excursion of the plasma pressure appeared at the outermost probe first, followed by the inner ones. Just after the onset, the opposite sequence took place. A positive excursion of the Y-component of the current density was observed near the onset by the THEMIS probes, and followed by a decrease trend. A similar variation was also found in the MHD simulation. All these features are consistent with the simulation result that a squeeze of the plasma from the plasma sheet results in the formation of the HPR before the onset, and that the accumulated plasma spreads outward after the onset. The HPR is shown to be important for the dynamics of the magnetosphere during a substorm.

Description: A Monte Carlo simulation was used to study the outflow of O + and H + ions along three flight trajectories above the polar cap up to altitudes of about 15 R E . Barghouthi [2008] developed a model on the basis of altitude and velocity dependent wave-particle interactions, and a radial geomagnetic field which includes the effects of ambipolar electric field and gravitational and mirror forces. In the present work we improve this model to include the effect of the centrifugal force, with the use of relevant boundary conditions. In addition, the magnetic field and flight trajectories, namely the central polar cap (CPC), nightside polar cap (NPC) and cusp, were calculated using the Tsyganenko T96 model. To simulate wave-particle interactions, the perpendicular velocity diffusion coefficients for O + ions in each region were determined such that the simulation results fit the observations. For H + ions, a constant perpendicular velocity diffusion coefficient was assumed for all altitudes in all regions as recommended by Nilsson et al . [2013]. The effect of centrifugal acceleration was simulated by considering three values for the ionospheric electric field: 0 (no centrifugal acceleration), 50, and 100 mV/m. It was found that the centrifugal acceleration increases the parallel bulk velocity and decreases the parallel and perpendicular temperatures of both ion species at altitudes above about 4 R E . Centrifugal acceleration also increases the temperature anisotropy at high altitudes. At a given altitude, centrifugal acceleration decreases the density of H + ions while it increases the density of O + ions. This implies that with higher centrifugal acceleration more O + ions overcome the potential barrier. It was also found that aside from two exceptions centrifugal acceleration has the same effect on the velocities of both ions. This implies that the centrifugal acceleration is universal for all particles. The parallel bulk velocities at a given value of ionospheric electric field were highest in the cusp followed by the CPC followed by the NPC. In this study a region of no wave-particle interaction was assumed in the CPC and NPC between 3.7 and 7.5 R E . In this region the perpendicular temperature was found to decrease with altitude due to perpendicular adiabatic cooling.

Description: We present an analysis of 23 years of thermal plasma measurements in the topside ionosphere from the DMSP spacecraft. The H + /O + ratio and density vary dramatically with the solar cycle; cross-correlation coefficients between E10.7 and the daily averaged densities are greater than 0.85. The ionospheric parameters also vary dramatically with season, particularly at latitudes away from the equator where the solar zenith angle varies greatly with season. There are also 27-day solar rotation periodicities in the density, associated with periodicities in the directly-measured solar EUV flux. Empirical Orthogonal Function (EOF) analysis captures over 95% of the variation in the density in the first two principal components. The first principal component (PC1) is clearly associated with the solar EUV while the second principal component (PC2) is clearly associated with the SZA variation. The magnitude of the variation of the response of the topside ionosphere to solar EUV variability is shown to be closely related to the ionospheric composition. This is interpreted as the result of the effect of composition on the scale height in the topside ionosphere and the "pivot effect" in which the variation in density near the F2 peak is amplified by a factor of e at an altitude a scale height above the F2 peak. When the topside ionosphere is H + dominated during solar minimum, DMSP may be much less than a scale height above the F2 peak while during solar maximum , when it is O + dominated, DMSP may be several scale heights above the F2 peak.

Description: Ultra-low frequency (ULF) waves play an important role in transferring energy by buffeting the magnetosphere with solar wind pressure impulses. The amplitudes of magnetospheric ULF waves, which are induced by solar wind dynamic pressure enhancements or shocks, are thought to damp in one half a wave cycle or an entire wave cycle. We report in situ observations of solar wind dynamic pressure impulse-induced magnetospheric ULF waves with increasing amplitudes. We found six ULF wave events induced by solar wind dynamic pressure enhancements with slow but clear wave amplitude increase. During three or four wave cycles, the amplitudes of ion velocities and electric field of these waves increased continuously by 1.3 ~ 4.4 times. Two significant events were selected to further study the characteristics of these ULF waves. We found that the wave amplitude growth is mainly contributed by the toroidal mode wave. Three possible mechanisms of causing the wave amplitude increase are discussed. Firstly, solar wind dynamic pressure perturbations, which are observed in a duration of 20 ~ 30 minutes, might transfer energy to the magnetospheric ULF waves continually. Secondly, the wave amplitude increase in the radial electric field may becaused by superposition of two wave modes, a standing wave excited by the solar wind dynamic impulse and a propagating compressional wave directly induced by solar wind oscillations. When superposed, the two wave modes fit observations as does a calculation that superposes electric fields from two wave sources. Thirdly, the normal of the solar wind discontinuity is at an angle to the Sun-Earth line. Thus, the discontinuity will affect the dayside magnetopause continuously for a long time.

Description: Access of solar and galactic cosmic rays to the Earth's magnetosphere is quantified in terms of geomagnetic cutoff rigidity. Numerically computed grids of cutoff rigidities are used to model cosmic ray flux in Earth's atmosphere and in low Earthorbit. In recent years, the development of more accurate dynamic geomagnetic field models and an increase in computer power have made a real-time data-driven geomagnetic cutoff computation extending over the inner magnetosphere possible. For computational efficiency, numerically computed cutoffs may be scaled to different altitudes and directions of arrival using the known analytic variation of cutoff in a pure dipole magnetic field. This paper is a presentation of numerical techniques developed to compute effective cutoff rigidities for space weather applications. Numerical tests to determine the error associated with scaling vertical cutoff rigidities with altitude in a realistic geomagnetic field model are included. The tests were performed to guide the development of spatial grids for modeling cosmic ray access to the inner magnetosphere and to gain a better understanding of the accuracy of numerically modeled cutoffs.

Description: Using in situ observations from the ROCSAT-1 spacecraft, we investigated the time response and local time dependence of the ionospheric electric field at mid–low latitudes associated with geomagnetic sudden commencements (SCs) that occurred from 1999 to 2004. We found that the ionospheric electric field variation associated with SCs instantaneously responds to the PI signature on the ground regardless of spacecraft local time. Our statistical analysis also supports the global instant transmission of electric field from the polar region. In contrast, the peak time detected in the ionospheric electric field is earlier than that of the equatorial geomagnetic field (~20 s before in the PI phase). Based on the ground–ionosphere waveguide model, this time lag can be attributed to the latitudinal difference of ionospheric conductivity. However, the local time distribution of the initial excursion of ionospheric electric field shows that dusk-to-dawn ionospheric electric fields develop during the PI phase. Moreover, the westward electric field in the ionosphere, which produces the preliminary reverse impulse of the geomagnetic field on the dayside feature, appears at 18–22 h LT where the ionospheric conductivity beyond the duskside terminator (18 h LT) is lower than on the dayside. The result of a magnetohydrodynamic simulation for an ideal SC shows that the electric potential distribution is asymmetric with respect to the noon–midnight meridian. This produces the local time distribution of ionospheric electric fields similar to the observed result, which can be explained by the divergence of the Hall current under non-uniform ionospheric conductivity.

Description: Energetic O + ions are rapidly enhanced in the inner magnetosphere because of abrupt intensification of the dawn-to-dusk electric field, and significantly contribute to the ring current during substorms. Here, we examine the generation mechanism of the dawn-to-dusk electric field that accelerates the O + ions, and the spatial and temporal evolution of the differential flux of the O + ions by using a test particle simulation in the electric and magnetic fields that are provided by a global magnetohydrodynamics (MHD) simulation. In the MHD simulation, strong dawn-to-dusk electric field appears in the near-Earth tail region by a joint action of the earthward tension force and pile-up of magnetic flux near an onset of substorm expansion. The peak of the electric field is ~9 − 13 mV/m, and is located ~1 – 2 R E earthward of the peak of the plasma bulk speed because of the pile-up. O + ions coming from the lobe are accelerated from ~ eV to 〉100 keV in ~10 minutes. The reconstructed flux of the O + ions shows that, at ~7 R E near midnight, the flux has a peak near a few tens-of-keV and the flux below ~10 keV is small. This structure, called a “void” structure, is consistent with the Polar observation, and can be regarded as a manifestation of the acceleration of unmagnetized ions perpendicular to the magnetic field. In the inner magnetosphere (at 6.0 R E ), reconstructed energy-time spectrograms show the nose dispersion structure that is also consistent with satellite observations.

Description: The efficiencies of pathways of thermospheric heating via soft electron precipitation in the dayside cusp region are investigated using the coupled magnetosphere-ionosphere-thermosphere model (CMIT). Event-based data-model comparisons show that the CMITmodel is capable of reproducing the thermospheric mass density variations measured by the CHAMP satellite during both quite and active periods. During blackthe 24 Aug 2005 storm event (Kp = 6-) while intense Joule heating rate occurs in the polar cusp region, including soft electron precipitation is important for accurately modelling the F -region thermospheric mass density distribution near the cusp region. blackDuring the 27 Jul 2007 event (Kp = 2-) while little Joule heating rate occurs in the polar cusp region, the controlled CMIT simulations suggest that the direct blackpathway through the energy exchange between soft electrons and thermospheric neutrals is the dominant process during this event, which only has a small effecton the neutral temperature and mass density at 400 km altitude. blackComparisons between the two case studies show that the indirect pathway via increasing the F-region Joule heating rate is a dominant process during the 24 Aug 2005 storm event, which is much more efficient than the direct heating process.

Description: Fifteen months of pitch angle resolved Van Allen Probes REPT measurements of differential electron flux are analyzed to investigate the characteristic variability of the pitch angle distribution (PAD) of radiation belt ultra-relativistic (〉2 MeV) electrons during storm conditions and during the long-term post-storm decay. By modeling the ultra-relativistic electron pitch angle distribution as sin n α , where α is the equatorial pitch angle, we examine the spatio-temporal variations of the n-value. The results show that in general n-values increase with the level of geomagnetic activity. In principle, ultra-relativistic electrons respond to geomagnetic storms by becoming more peaked at 90° pitch angle with n-values of 2–3 as a supportive signature of chorus acceleration outside the plasmasphere. High n-values also exist inside the plasmasphere, being localized adjacent to the plasmapause and exhibiting energy dependence, which suggests a significant contribution from EMIC waves scattering. During quiet periods, n-values generally evolve to become small, i.e., 0–1. The slow and long-term decays of the ultra-relativistic electrons after geomagnetic storms, while prominent, produce energy and L-shell dependent decay timescales in association with the solar and geomagnetic activity and wave-particle interaction processes. At lower L shells inside the plasmasphere, the decay timescales τ d for electrons at REPT energies are generally larger, varying from tens of days to hundreds of days, which can be mainly attributed to the combined effect of hiss induced pitch angle scattering and inward radial diffusion. As L shell increases to L ~ 3.5, a narrow region exists (with a width of ~0.5 L) where the observed ultra-relativistic electrons decay fastest, possibly resulting from efficient EMIC wave scattering. As L shell continues to increase, τ d generally becomes larger again, indicating an overall slower loss process by waves at high L shells. Our investigation based upon the sin n α function fitting and the estimate of decay timescale offers a convenient and useful means to evaluate the underlying physical processes that play a role in driving the acceleration and loss of ultra-relativistic electrons and to assess their relative contributions.

Description: Thermospheric winds and temperatures must be correctly specified to understand the impacts of lower-atmosphere processes on the upper atmosphere, and to measure the global effects of high-latitude magnetospheric processes. Fabry-Perot interferometers can estimate these parameters by measuring the characteristic 630.0-nm emission that is produced at around 250-km altitude. These sophisticated instruments exist at only a few locations globally, so models are often employed to provide wind and temperature estimates elsewhere. This study is composed of two parts. First, observing system simulation experiments estimate the accuracy of Fabry-Perot interferometer observations using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) and the Whole Atmosphere Community Climate Model eXtended (WACCM-X). Atmospheric observational error sources are found to be very small across two test periods (September 2000 and September 2010) and using two different ‘truth’ models. The largest magnitude wind observation error is found to be 16.9 m/s, root-mean-square errors are 2.3 m/s and the bias is 0.9 m/s. The largest magnitude temperature observation error is found to be 63.7 K, root-mean-square errors over the test period are 6.7 K and the bias is 2.8 K. Modeled redline emission altitudes vary by over 100 km, far more than was expected. Second, several models (TIEGCM, WACCM-X, the Horizontal Wind Model and the Mass Spectrometer Incoherent Scatter model) are assessed using interferometer winds and temperatures from Cariri and Cajazeiras, Brazil, as ground truth. In the best cases, the models reproduce wind variability without systematic biases, but show no ability to predict instantaneous values, though temperatures are modeled more accurately.

Description: Although the zeroth order picture of the Moon–solar-wind interaction involves no upstream perturbation, the presence of the Moon does affect the upstream plasma in a variety of ways. In this paper, a large volume of data obtained by the dual-probe Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission are used to characterize the large-scale morphology of the “foremoon,”which is defined as the region upstream of the Moon and its wake that contains Moon-related particles and waves. Solar-wind ions reflected from the unshielded surface and by crustal magnetic fields, together with heavy ions of lunar surface/exospheric origin, are picked up by the solar wind magnetic and electric fields. Partially coinciding with populations of these Moon-related ions, ~0.01 Hz and ~1 Hz magnetic field fluctuations are observed. The morphology of the Moon-related ion and wave distributions is well organized by the upstream magnetic field direction. In addition, the low-frequency wave distributions depend on the upstream Alfvén Mach numbers, suggesting that propagation effects also play a role in determining the wave foremoon morphology. Occurrence of modified electron velocity distributions and higher-frequency, electromagnetic and electrostatic waves is primarily controlled by magnetic connection to the Moon and its wake. These statistical results observationally demonstrate the large-scale properties of the foremoon and upstream-parameter control thereof.

Description: We address the claim that an increase in the flux of neutrons detected by the Neutron Spectrometer (NS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft in orbit about Mercury at 15:45 UTC on 4 June 2011 was generated by the impact of energetic ions onto spacecraft. We find this claim to be unwarranted. The claim is grounded on the erroneous assumption that the NS singles count rate is triggered only by energetic ions. Rather, because any mix of energetic ions, electrons, photons, and neutrons can trigger NS singles, these data do not provide a reliable constraint on the presence of energetic ions. The absence of an enhancement in the count rate of 1635-keV gamma rays, as monitored by the MESSENGER Gamma-Ray Spectrometer, provides independent evidence that a fluence of energetic protons sufficiently high to generate the neutron enhancement was not present during the neutron event. The interpretation that currently best matches the available data is that the neutron enhancement on 4 June 2011 was the result of solar neutrons.

Description: We describe an automated computer algorithm designed to remove background contamination from the Van Allen Probes MagEIS electron flux measurements. We provide a detailed description of the algorithm with illustrative examples from on-orbit data. We find two primary sources of background contamination in the MagEIS electron data: inner zone protons and bremsstrahlung X-rays generated by energetic electrons interacting with the spacecraft material. Bremsstrahlung X-rays primarily produce contamination in the lower energy MagEIS electron channels (~30-500 keV) and in regions of geospace where multi-MeV electrons are present. Inner zone protons produce contamination in all MagEIS energy channels at roughly L  〈 2.5. The background corrected MagEIS electron data produce a more accurate measurement of the electron radiation belts, as most earlier measurements suffer from unquantifiable and uncorrectable contamination in this harsh region of the near-Earth space environment. These background-corrected data will also be useful for spacecraft engineering purposes, providing ground truth for the near-Earth electron environment and informing the next generation of spacecraft design models (e.g., AE9).

Description: The Van-Allen probes, low-altitude NOAA satellite, MetOp satellite and riometer are used to analyze variations of precipitating energetic electron fluxes and cosmic radio noise absorption (CNA) driven by plasmaspheric hiss with respect to geomagnetic activities. The hiss-driven energetic electron precipitations (at L ~4.7-5.3, MLT~8-9) are observed during geomagnetic quiet condition and substorms, respectively. We find that the CNA detected by riometers increased very little in the hiss-driven event during quiet condition on September 06, 2012. The hiss-driven enhancement of riometer was still little during the first substorm on September 30, 2012. However, the absorption detected by the riometer largely increased while the energies of the injected electrons became higher during the second substorm on September 30, 2012. The enhancement of CNA (ΔCNA) observed by the riometer and calculated with precipitating energetic electrons are in agreement during the second substorm, implying that the precipitating energetic electrons increase CNA to an obviously detectable level of the riometer during the second substorm on September 30, 2012. The conclusion is consistent with Rodger et al . (2012), which suggests that the higher level of ΔCNA prefer to occur in the substorms, because substorms may produce more intense energetic electron precipitation associated with electron injection. Furthermore, the combination of the observations and theory calculations also suggests that higher-energy electron (〉55 keV) precipitation contribute more to the ΔCNA than the lower-energy electron precipitation. In this paper, the higher-energy electron precipitation is related to lower-frequency hiss.

Description: The present study investigates the ionospheric Total Electron Content (TEC) and F-layer response in the Southern Hemisphere equatorial, low-latitude, and mid-latitude due to major sudden stratospheric warming (SSW) event, which took place during January-February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual-frequency GPS stations and 2 ionosonde stations spanning latitudes from 2.8 o N to 53.8 o S, longitudes from 36.7 o W to 67.8 o W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from Equator to the mid-latitudes. During DOY 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The VTEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSW temperature peak. Using one GPS station located at Rio Grande (53.8 o S, 67.8 o W, mid-latitude-South America sector), it is reported for the first time that the mid-latitude in southern hemisphere was disturbed by the SSW event in the Northern hemisphere.

Description: Large amplitude variations in GPS total electron content (TEC) at Pc5-6 (〈6.67 mHz) frequencies have been observed, using a high data rate Global Positioning System (GPS) receiver of the Canadian High Arctic Ionospheric Network (CHAIN). TEC variations with peak-to-peak amplitudes of 2-7 TEC units (TECU) were observed over a 2.5 hour period in the post-noon sector on 09 September 2011, during a period of high auroral activity within a moderate geomagnetic storm. TEC observations were from the Sanikiluaq, Nunavut (56.54°N, 280.77°E) GPS receiver located in the auroral region. Over this same time period, compressional Pc5-6 magnetic field variations were observed by the geosynchronous GOES 13 magnetometer and the ground-based Sanikiluaq magnetometer. GOES 13 has a northern magnetic footprint in close proximity to Sanikiluaq. Cross correlation analysis indicates that magnetic field and TEC variations were possibly linked. No natural hazards or nuclear explosions capable of exciting TEC perturbations were reported on this day. Using a triangulation technique involving TEC measurements of multiple GPS satellites, the propagation velocity of TEC variations in the ionosphere was also calculated. This calculation revealed two distinct events: lower frequency (~0.9 mHz) TEC variations that propagated westward, consistent with the westward propagation of compressional Pc5 waves observed by GOES 13 and 15 satellites, and higher frequency (~3.3 mHz) TEC variations that propagated southward. This is the first report of variations in ionospheric TEC linked to satellite observations of Pc5-6 ULF waves.

Description: Modeling the spatio-temporal evolution of relativistic electron fluxes trapped in the Earth's radiation belts in the presence of radial diffusion coupled with wave-induced losses should address one important question: how deep can relativistic electrons penetrate into the inner magnetosphere? However, a full modelling requires extensive numerical simulations solving the comprehensive quasi-linear equations describing pitch-angle and radial diffusion of the electron distribution, making it rather difficult to perform parametric studies of the flux behavior. Here, we consider the particular situation where a localized flux peak (or storage ring) has been produced at low L 〈 4 during a period of strong disturbances, through a combination of chorus-induced energy diffusion (or direct injection) at low L together with enhanced wave-induced losses and outward radial transport at higher L . Assuming that radial diffusion can be further described as the spatial broadening within the plasmasphere of this pre-existing flux peak, simple approximate analytical solutions for the distribution of trapped relativistic electrons are derived. Such a simplified formalism provides a convenient means for easily determining whether radial diffusion actually prevails over atmospheric losses at any particular time for given electron energy E and location L . It is further used to infer favorable conditions for relativistic electron access to the inner belt, providing an explanation for the relative scarcity of such a feat under most circumstances. Comparisons with electron flux measurements on board the Van Allen Probes show a reasonable agreement between a few weeks and four months after the formation of a flux peak.

Description: We report the first comprehensive observations of Jovian synchrotron radiation (JSR) and H 3 + emission from the Jovian thermosphere to investigate the generation process of short term (days to weeks) variations in the Jovian radiation belt. The observations were made by the Giant Metrewave Radio Telescope and NASA Infrared Telescope Facility during November 2011. The total flux density of JSR increased by approximately 5% between Nov. 6–9 and Nov. 12–17, associated with the increased solar UV/EUV flux. From Nov. 7–14, a possible rise in the infrared H 3 + emission was observed in the middle latitude region, corresponding to a temperature variation of approximately 10 K. These results are consistent with the scenario that the solar UV/EUV heating causes variations in the thermospheric temperature and JSR. Radio images along the equatorial region showed that the JSR intensity decreased inside 1.5 Jovian Radii (Rj), and the peak position shifted outward. This implies that energetic electrons are attenuated by some internal loss process, despite the simultaneous increase in radial diffusion. A physical model for the radiation belt shows that such an internal loss process can explain the observed variation of brightness distribution. Typical loss time scale is longer than strong diffusion limit, which suggests the existence of some pitch angle diffusion process such as wave particle interaction. Thus, variations of the total JSR flux density and thermospheric temperature seems consistent with the scenario, and the brightness distribution of JSR can be explained by the increase in radial diffusion accompanied by internal loss processes.

Description: The Siple Transmitter Experiment operated from 1973 to 1988 and generated a wealth of observations of nonlinear wave-particle interactions including extensive recordings of triggered emissions generated by VLF signals injected into the magnetosphere from the transmitter at Siple Station, Antarctica. Due to their complex appearance and immensely varied behavior, triggered emissions remain poorly described and understood. This work provides a comprehensive statistical description of observed triggered emissions and establishes statistical bounds on triggered emission type (fallers, risers, and positive and negative hooks) and behavior (frequency changes between 1 kHz and 2.5 kHz with initial sweep rates between −2.5 kHz/s and 2.5 kHz/s, with risers undergoing a median frequency change of 556 Hz and fallers a median frequency change of −198 Hz). The statistical study also reveals an apparent dependence of the triggered emission behavior on the transmitted signal itself. Long tones and rising ramps generate more risers and positive hooks, while short tones and falling ramps produce more fallers and negative hooks. Triggered emissions also appear to favorably initiate with sweep rates similar to that of the triggering element, with the 1 kHz/s rising ramps triggering initial risers with a median sweep rate of 1.03 kHz/s and −1 kHz/s triggering initial fallers with a median sweep rate of −0.73 kHz/s. These results improve observations of wave modification resulting from wave-particle interactions in the radiation belts and can be used to validate numerical simulations of triggered emissions.

Description: Sensitivity of the global electric circuit (GEC) to variations of atmospheric conductivity and current sources is analyzed and discussed. When the undisturbed exponential conductivity profile is assumed all over the Earth, the most substantial changes in the ionospheric potential (IP) are caused by conductivity perturbations inside thunderstorms; if, in addition, conductivity reduction inside thunderstorms and nonelectrified clouds is assumed, the IP becomes less sensitive to conductivity perturbations; besides, the IP is even more sensitive to source current variations than to conductivity. Current-source and voltage-source descriptions of GEC generators are compared; it is shown that the IP variation may critically depend on the chosen description. As an application, the IP variation due to nuclear weapons testing is studied; it is shown that neither local nor global increase of conductivity in the stratosphere could alone explain the observed 40% IP increase in the 1960s; at the same time this increase might be accounted for by a 40% increase in the source current density or a 46% reduction of the conductivity inside thunderstorms, provided that it was not reduced initially. The IP variation due to solar activity and in particular due to solar modulation of galactic cosmic ray flux is also discussed and modeled, which required an adequate parameterization of the rate of atmospheric ion-pair production over the solar cycle. It is estimated that the maximum IP variation on the scale of the solar cycle does not exceed 5% of the mean value, unless source current perturbations are taken into account.

Description: The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellite mission has offered for the first time global snapshots of the geomagnetic field-aligned currents with unprecedented space and time resolution, thus providing an opportunity to feed an acknowledged first-principles model of the Earth's upper atmosphere such as the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (NCAR TIE-GCM). In a first step, Marsal et al. (2012) used AMPERE data in the current continuity equation between the magnetosphere and the ionosphere to drive the TIE-GCM electrodynamics. In the present work, ionospheric conductivities have been made consistent with enhanced upward field-aligned currents, which are assumed to correspond to electrons plunging as a result of downward acceleration by electric fields built up along the geomagnetic field lines. The resulting conductance distribution is reasonably commensurate with an independent model that has tried to quantify the ionizing effect of precipitating particles onto the auroral ionosphere. On the other hand, comparison of geomagnetic observatory data with the ground magnetic variations output by the model only shows a modest improvement with respect to our previous approach.

Description: Recent measurements of GPS-derived total electron content (TEC) reveal acoustic wave periods of ∼1-4 minutes in the F-region ionosphere following natural hazard events, such as earthquakes, severe weather, and volcanoes. Here, we simulate the ionospheric responses to infrasonic-acoustic waves, generated by vertical accelerations at the Earth's surface or within the lower atmosphere, using a compressible atmospheric dynamics model to perturb a multi-fluid ionospheric model. Response dependencies on wave source geometry and spectrum are investigated at mid, low, and equatorial latitudes. Results suggest constraints on wave amplitudes that are consistent with observations, and that provide insight on the geographical variability of TEC signatures, and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field. Asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side, due to alignments of acoustic wave velocities parallel and perpendicular to field lines, respectively. Acoustic wave-driven TEC perturbations are shown to have periods of ∼3-4 minutes, which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere. Furthermore, thermospheric acoustic waves couple with ion sound waves throughout the F-region and topside ionosphere, driving plasma disturbances with similar periods and faster phase speeds. The associated magnetic perturbations of the simulated waves are calculated to be observable, and may provide new observational insight in addition to that provided by GPS TEC measurements.

Description: Data from the Proton-Electron Telescope on the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite, taken during 1992–2009, are analyzed for evidence of inner radiation belt electrons with kinetic energy E 〉 1 MeV. It is found that most of the data from a detector combination with a nominal energy threshold of 1 MeV were, in fact, caused by a chance-coincidence response to lower energy electrons or high-energy protons. In particular, there was no detection of inner belt or slot-region electrons above 1 MeV following the 2003 Halloween storm injection, though they may have been present. However, by restricting data to a less-stable, low-altitude trapping region, a persistent presence of inner belt electrons in the energy range 1 to 1.6 MeV is demonstrated. Their soft, exponential energy spectra are consistent with extrapolation of lower energy measurements.

Description: We present observations of the equatorial plasma bubbles (EPB) in the topside ionosphere at early morning hours (05–08 LT) in the recovery phase of the 18–19 February 2014 geomagnetic storm. This rare type of irregularities was detected in the Pacific sector using GPS-measurements onboard several Low-Earth-Orbit (LEO) satellites. We use a multi-satellite constellation consisted of the three Swarm and one TerraSAR-X satellites, that on 19 February flew in the same region and at similar altitudes ~500 km. The EPB occurrence in the LEO GPS data was observed for several consecutive orbits from ~11 UT to 16–17 UT on 19 February 2014, which suggests: 1) rather long duration (hours) of favorable conditions for EPB generation, 2) formation and evolution of EPB over wide longitude range of the Pacific Ocean, 3) possible movement of the EPB region in the westward direction (with dawn). Registration of the early morning EPB in LEO GPS data was supported by concurrent in situ (Swarm and DMSP) and ground-based (ionosonde and GPS) measurements. LEO-based GPS technique is found to be essential and promising data-source to study the topside EPB over regions with lack of the ground-based facilities. In addition, we use the Prompt Penetration Model and the NCAR Thermosphere-Ionosphere Electrodynamics Global Circulation Model (TIE-GCM) to identify the possible mechanisms responsible for the observed phenomenon. The model simulation results indicate the occurrence of the zone with the enhanced vertical plasma drift (~40-45 m/s) owing to the disturbance dynamo action in the pre-dawn/dawn sector during 09–17 UT.

Description: We present an observational analysis of electron cooling/heating rates in the fast and slow solar wind between 0.3 and 1 AU. We fit electron velocity distribution functions acquired in situ by Helios 1 and 2 spacecraft by a three component (core-halo-strahl) analytical model. The resulting radial profiles of macroscopic characteristics (density, temperatures and heat fluxes) are employed to examine properties of theoretical energy balance equations and to estimate external cooling/heating terms. Our analysis indicates that in contrast to solar wind protons the electrons do not require important heating mechanisms to explain the observed temperature gradients. The electron heating rates are actually found to be negative for both the slow and fast solar wind, namely due to the significant degradation of the electron heat flux with increasing radial distance from the Sun. Cooling mechanisms acting on electrons are found to be significantly stronger in the slow wind than in the fast wind streams.

Description: We present the first statistical analysis of ELF/VLF emissions observed on the ground at subauroral latitudes that includes their features, occurrences and association with solar wind and geomagnetic variations. Using a 100 kHz sampling loop antenna located in Athabasca, Canada (54.60 ∘ N, 246.36 ∘ E, L=4.3) we monitored these emissions, including chorus, quasi-periodic emissions, and hiss, from November 2012 to October 2013. We found a maximum occurrence rate in the morning sector (06–07 MLT) and a minimum in the night sector (∼18 to 02 MLT), in agreement with previous satellite measurements in the inner magnetosphere. We also found correlation between the ongoing substorm and storm activity and the increase of occurrence rates. The observed waves usually had a central frequency ∼1–3 kHz lower than the half gyro-frequency at the conjugate equatorial plane, indicating a wave source at higher latitudes. A superposed epoch analysis showed that the starting time of the ELF/VLF emissions is preceded by a rise in AE both on short (hours) and long (days) terms. Solar wind speed also started slowly rising ∼1.5 days before, while density and dynamic pressure decreased shortly afterwards. This may signify that high-speed solar wind conditions also contribute to the generation of ELF/VLF emissions detected at subauroral latitudes.

Description: We present a novel technique for imaging and data assimilation of the topside ionosphere and plasmasphere. The methodology is based upon the 3 dimensional variational technique (3DVAR), where an empirical background model is utilized. However, to prevent non-physical vertical variation in density estimates, we devise statistical methods to enforce a roughness penalty in the traditional 3DVAR optimization. The upward looking total electron content (TEC) observations from the Global Positioning System (GPS) receiver onboard Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites are utilized in the assimilation algorithm. The estimation results show reasonable agreement with in-situ density measurements of Defense Meteorological Satellite Program satellites and Van Allen Probes derived densities during geomagnetically quiet and severe storm-time conditions, respectively. These preliminary results demonstrate great potential for the use of GPS TEC measurements from low-earth-orbit (LEO) satellites in monitoring and studying the morphology and dynamics of large-scale structures of the electron density in the topside ionosphere and plasmasphere.

Description: The excitation of magnetospheric whistler-mode chorus in response to interplanetary (IP) shocks is investigated using wave data from the THEMIS spacecraft. As an example, we show a typical chorus wave excitation following an IP shock event that was observed by THEMIS in the post-noon sector near the magnetopause on 3 August, 2010. We then analyze characteristic changes during this event and perform a survey of similar events during the period 2008 – 2014 using the THEMIS and OMNI dataset. Our statistical analysis demonstrates that the chorus wave excitation/intensification in response to IP shocks occurs only at high L shells (L 〉 8) on the dayside. We analyzed the variations of magnetic curvature following the arrival of the IP shock and found that IP shocks lead to more homogeneous background magnetic field configurations in the near-equatorial dayside magnetosphere, and therefore the threshold of nonlinear chorus wave growth is likely to be reduced, favoring chorus wave generation. Our results provide the observational evidence to support the concept that the geomagnetic field line configuration plays a key role in the excitation of dayside chorus.

Description: We present results from a numerical study of structure and dynamics of dispersive Alfvén waves in the near-earth magnetosphere containing proton radiation belt (near L = 1.5 dipole magnetic shell). The interest in this problem is motivated by numerous observations of magnetic oscillations with frequencies in the range of 0.1-4.0 Hz detected on the ground at low and middle latitudes. In a number of studies these oscillations interpreted as shear Alfvén waves standing inside the so-called ionopspheric Alfvén resonator (IAR). We present results from two-dimensional, time dependent simulations of the reduced two-fluid MHD model performed in the dipole magnetic field geometry with the realistic parameters of the magnetospheric plasma. These simulations show that these pulsations can be produced by the fundamental mode of the global field line resonator, spanning the entire magnetic field line in the low or middle magnetosphere. Simulations also show that even the waves with the highest considered frequencies (2.44 Hz) are not trapped inside the ionospheric resonator. Therefore, if these waves will be generated by some ionospheric source, then they can reach the equatorial magnetosphere and interact with energetic protons in the proton radiation belt.

Description: The period near sunset is a dynamic and critical time for the daily development of the equatorial nighttime ionosphere and the instabilities that occur there. It is during these hours that the pre-conditions necessary for the later development of Equatorial Spread F (ESF) plasma instabilities occur. The neutral dynamics of the sunset ionosphere are also of critical importance to the generation of currents and electric fields; however, the behavior of the neutrals is experimentally understood primarily through very limited single-altitude measurements or measurements that provide weighted altitude means of the winds as a function of time. To date, there have been very few vertically-resolved neutral wind measurements in the F region at sunset. We present two sets of sounding rocket chemical release measurements, one from a launch in the Marshall Islands on Kwajalein atoll and one from Alcantara, Brazil. Analysis of the release motions has yielded vertically-resolved neutral wind profiles that show both the mean horizontal winds and the vertical shears in the winds. In both experiments, we observe significant vertical gradients in the zonal wind that are unexpected by classical assumptions about the behavior of the neutral wind at these altitudes at sunset near the geomagnetic equator.

Description: We present a statistical study of the magnetic reconnection exhausts in solar wind. Observational data are compared with the analytical model based on Riemann analysis of tangential discontinuity decay forced by finite X -line reconnection of skewed magnetic fields. Statistical analysis is based on 51 events of the solar wind reconnection listed in [Phan et al., 2009]. The best agreement of the observed and analytically predicted values is achieved for the rotational angle of the tangential magnetic field component with correlation coefficient reaching the value of 0.97. The lowest correlation coefficient of 0.87 is obtained for the exhaust flow plasma temperature. It is found that proton temperature increases at the exhaust boundary while electron temperature stays unchanged. This may indicate that heating and acceleration processes operate on the proton scale. Exhaust boundaries are identified as tangential discontinuities, except one particular event, where Alfvén discontinuity and slow shock were detected instead. Hence, the impulsive reconnection may be supposed in that case rather than steady state one. Exhaust regions extending up to 690 R E , registered in some observations, do not necessarily imply X -lines of similar length. They could be explained alternatively by reconnection of skewed magnetic fields. The numerical modeling of the ICME propagating in the solar wind reveals that the resistance force, impeding the ICME motion, may be reduced significantly (three times in our simulations) by means of the magnetic reconnection at the leading edge. Thus, reconnection may substantially increase ICME velocity and travel distance.

Description: We use the time-dependent, two-dimensional (2-D), ideal MHD equations to simulate and investigate the evolution of magnetic field and plasma profiles of the typical (T) and crater (C) magnetic flux ropes (FRs). The T-FR has a magnetic pressure peak at the center of the flux rope while the C-FR has a local dip instead. The simulation starts with a 2-D magnetic flux rope in magnetohydrostatic equilibrium, where pressure gradient forces are balanced by Lorentz forces. The magnetic field and plasma pressure profiles for the initial flux rope are derived from the analytical solutions by Zhang et al. (2010). The initial flux rope starts to evolve when the force balance is broken by imposing pressure or magnetic field perturbations onto the equilibrium system. The pressure perturbations are produced by increasing/decreasing the internal plasma pressure of the flux rope, while the magnetic field perturbations are produced by increasing/decreasing the transverse magnetic fields across the flux rope. We conclude that a T-FR can be evolved into a C-FR and vice versa, if the perturbation strength is sufficient, and that the plasma pressure and density in the new equilibrium state could be either increased or decreased for the evolution of C-FR to T-FR and also for the evolution of T-FR to C-FR.

Description: We present simultaneous THEMIS observations of plasma parameters upstream in the solar wind and downstream in the magnetosheath (MSH) from 2007-2008. We discuss the connection of foreshock (FSH) processes and magnetospheric disturbances to transmission mechanisms in the MSH. In 60% of the analyzed cases, the MSH was strongly influenced by the FSH. We analyze the results as a function of location, time scale, spatial orientation of the observed structures, and the prevailing interplanetary magnetic field (IMF) and solar wind plasma parameters. We find that plasma structures with density enhancement are mostly observed during radial IMF orientations and for small θ B N , the angle between the upstream magnetic field and the local bow shock normal; the observed structures are pressure balanced with strong anti-correlation between density and temperature; the scale size of the density fluctuations is about 0.4 R E . We compare the observations with results from a 2.5-dimensional hybrid simulation to investigate the mechanisms by which the foreshock plasma structures are generated, propagate through the bow shock, and evolve.

Description: During the first several months of the three-spacecraft Swarm mission all three spacecraft came repeatedly into close alignment, providing an ideal opportunity for validating the proposed dual spacecraft method for estimating current density from the Swarm magnetic field data. Two of the Swarm spacecraft regularly fly side-by-side in closely similar orbits, while the third at times approaches the other two. This provides a data set which under certain assumptions of stationarity of the magnetic field, can produce 2, 3, 4, 5 (or more) point measurements, which can be cross-compared. We find that at low Earth orbit the use of time-shifted positions allow stable estimates of current density to be made and can verify temporal effects as well as validating the interpretation of the current components as arising predominantly from field aligned currents. In the case of four-spacecraft configurations we can resolve the full vector current and therefore can check the perpendicular as well as parallel current density components directly, together with the quality factor for the estimates directly (for the first time in situ at low earth orbit).

Description: During solar energetic particle (SEP) events, the inner heliosphere is bathed in MeV electrons. Through magnetic reconnection, these relativistic electrons can enter the magnetosphere of Mercury, nearly instantaneously filling the regions of open field lines with precipitating particles. With energies sufficient to penetrate solid aluminum shielding more than 1 mm thick, these electrons were observable by a number of sensors on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Because of its thin shielding, frequent sampling, and continuous temporal coverage, the Fast Imaging Plasma Spectrometer provided by far the most sensitive measurements of MeV electrons of all MESSENGER sensors. Sharp changes in energetic electron flux coincided with topological boundaries in the magnetosphere, including the magnetopause, polar cap, and central plasma sheet. Precipitating electrons with fluxes equal to ~40% of their corresponding upstream levels were measured over the entire polar cap, demonstrating that electron space weathering of Mercury's surface is not limited to the cusp region. We use these distinct precipitation signatures acquired over 33 orbits during 11 SEP events to map the full extent of Mercury's northern polar cap. We confirm a highly asymmetric polar cap, for which the dayside and nightside boundary latitudes range over ~50−70°N and ~30−60°N, respectively. These latitudinal ranges are consistent with average models of Mercury's magnetic field but exhibit a large variability indicative of active dayside and nightside magnetic reconnection processes. Finally, we observed enhanced electron fluxes within the central plasma sheet. Although these particles cannot form a stable ring current around the planet, their motion results in an apparent trapped electron population at low latitudes in the magnetotail.

Description: Utilizing associated observations of Geotail and ACE satellites from the year of 1998 to 2005, we investigated the X-lines in the near-Earth tail under different interplanetary magnetic field (IMF) conditions. The X-lines are recognized by the tailward fast flows (TFF) with negative Bz. Statistically, the X-lines in the tail can be observed for southward as well as northward IMF, but more frequently observed for southward IMF. A typical case on 26 Apr, 2005 showed clear evidence that the X-line can occur for northward IMF while the geomagnetic activity is particularly quiet. Further analysis showed that the X-line-related solar wind (SW) has stronger Ey and Bz components for southward than northward IMF. In addition, the X-line-related geomagnetic activities are stronger for southward than northward IMF.

Description: Diurnal variations of the horizontal component of the geomagnetic field ΔH on International Quiet days of 1999–2012, measured hourly at two stations in the same longitude zone in the Northern hemisphere, near and away from the dip equator, have been subjected to principal component analysis. This technique is also applied to the difference ΔH EEJ of ΔH at these two stations, which is attributed to the equatorial electrojet (EEJ). The first three principal components: PC1, PC2, and PC3, account for 91 - 96% of the variances in the data. Maximum contribution to the quiet day variations in ΔH around its peak in the morning hours at both the stations, and in the EEJ, comes from the day-to day variation of the amplitude of PC1. Patterns of day-to-day variations of PC1 amplitudes for the equatorial station and the EEJ are essentially semiannual modulated by solar EUV flux, superimposed on a longer time scale solar EUV flux-dependent trend. Contributions from PC2 and to a lesser extent from PC3 are seen to be responsible for the absence of semi-annual variations in ΔH in the afternoon hours at the equatorial station. Distribution of amplitudes of PC2 and PC3 for ΔH EEJ for weak electrojet days, shows seasonal features in accordance with greater occurrence of afternoon (morning) counter-electrojet during June (December) solstice. During the extended solar minimum, PC3 amplitudes for ΔH at the equatorial station and for the EEJ display annual variation. Possible sources for these seasonal features in the variations of equatorial ΔH are discussed.

Description: We investigate ion acceleration in dipolarization events in the magnetotail, using the electromagnetic fields of an MHD simulation of magnetotail reconnection and flow bursts as basis for test particle tracing. The simulation results are compared with “Time History of Events and Macroscale Interactions during Substorms" (THEMIS) observations. We provide quantitative answers to the relative importance of source regions and source energies. Flux decreases at proton energies up to 10-20 keV are found to be due to sources of lobe or plasma sheet boundary layer particles that enter the near tail via reconnection. Flux increases result from both thermal and suprathermal ion sources. Comparable numbers of accelerated protons enter the acceleration region via cross-tail drift from the dawn flanks of the near-tail plasma sheet and via reconnection of field lines extending into the more distant tail. We also demonstrate the presence of earthward plasma flow and accelerated suprathermal ions ahead of a dipolarization front. The flow acceleration stems from a net Lorentz force, resulting from reduced pressure gradients within a pressure pile-up region ahead of the front. Suprathermal precursor ions result from, typically multiple, reflections at the front. Low-energy ions also become accelerated due to inertial drift in the direction of the small precursor electric field.

Description: We perform a systematic theoretical and numerical study of anti-parallel two-dimensional magnetic reconnection with asymmetries in the plasma density and reconnecting magnetic field strength in addition to a bulk flow shear across the reconnection site in the plane of the reconnecting fields, which commonly occurs at planetary magnetospheres. We analytically predict the speed at which an isolated X-line is convected by the flow, the reconnection rate, and the critical flow speed at which reconnection no longer takes place for arbitrary reconnecting magnetic field strengths, densities, and upstream flow speeds, and we confirm the results with two-fluid numerical simulations. The predictions and simulation results counter the prevailing model of reconnection at Earth's dayside magnetopause which says reconnection occurs with a stationary X-line for sub-Alfvénic magnetosheath flow, reconnection occurs but the X-line convects for magnetosheath flows between the Alfvén speed and double the Alfvén speed, and reconnection does not occur for magnetosheath flows greater than double the Alfvén speed. In particular, we find that X-line motion is governed by momentum conservation from the upstream flows, which are weighted differently in asymmetric systems, so the X-line convects for generic conditions including sub-Alfvénic upstream speeds. For the reconnection rate, as with symmetric reconnection, it drops with increasing flow shear and there is a cutoff speed above which reconnection is not predominant. However, while the cutoff condition for symmetric reconnection is that the difference in flows on the two sides of the reconnection site is twice the Alfvén speed, we find asymmetries cause the cutoff speed for asymmetric reconnection to be higher than twice the asymmetric form of the Alfvén speed. The stronger the asymmetries, the more the cutoff exceeds double the asymmetric Alfvén speed. This is due to the fact that in asymmetric reconnection, the plasma with the smaller mass flux into the dissipation region contributes a smaller mass to the dissipation region, so the effect of its flow on opposing the release of energy by the reconnected magnetic fields is diminished and the reconnection is not suppressed to the extent previously thought. The results compare favorably with an observation of reconnection at Earth's polar cusps during a period of northward interplanetary magnetic field, where reconnection occurs despite the magnetosheath flow speed being more than twice the magnetosheath Alfvén speed, the previously proposed suppression condition. These results are expected to be of broad importance for magnetospheric physics of Earth and other planets; particular applications are discussed.

Description: For the period July 2003 to August 2010, the interplanetary coronal mass ejection (ICME) catalogue maintained by Richardson and Cane lists 106 Earth-directed events, which have been measured in-situ by plasma and field instruments on–board the ACE satellite. We present a statistical investigation of the Earth's thermospheric neutral density response by means of accelerometer measurements collected by the GRACE satellites, which are available for 104 ICMEs in the data set, and its relation to various geomagnetic indices and characteristic ICME parameters such as the impact speed ( v max ), southward magnetic field strength ( B z ). The majority of ICMEs causes a distinct density enhancement in the thermosphere, with up to a factor of eight compared to the pre–event level. We find high correlations between ICME B z and thermospheric density enhancements (≈ 0.9), while the correlation with the ICME impact speed is somewhat smaller ( ox 0.7). The geomagnetic indices revealing the highest correlations are Dst and SYM-H (≈ 0.9), the lowest correlations are obtained for k p and AE (≈ 0.7), which show a nonlinear relation with the thermospheric density enhancements. Separating the response for the shock sheath region and the magnetic structure of the ICME, we find that the Dst and SYM-H reveal a tighter relation to the B z minimum in the magnetic structure of the ICME, whereasthe polar cap indices show higher correlations with the B z minimum in the shock sheath region. Since the strength of the B z component—either in the sheath or the magnetic structure of the ICME—is highly correlated (≈ 0.9) with the neutral density enhancement, we discuss the possibility of satellite orbital decay estimates based on magnetic field measurements at L1, i.e. before the ICME hits the Earth magnetosphere. These results are expected to further stimulate progress in space weather understanding and applications regarding satellite operations.

Description: Propagation of Very Low Frequency (VLF) radio signal through the earth-ionosphere waveguide depends strongly on the plasma properties of the ionospheric D-layer. Solar extreme ultra-violet (EUV) radiation plays the central role in controlling physical and chemical properties of the lower ionospheric layers and hence determining the propagation characteristics of a VLF signal. The nature of interference among different propagating modes varies widely with the length of the propagation path. For a very long path, exposure of solar radiation and thus the degree of ionization varies by a large amount along the path. This influences the VLF signal profile by modulating the sky wave propagation. To understand the propagation characteristics over such a long path, we need a thorough investigation of the chemical reactions of the lower ionosphere which is lacking in the literature. Study of radio signal characteristics in the Antarctic region during summer period in the southern hemisphere gives us a unique opportunity to explore such a possibility. In addition, there is an extra feature in this path – the presence of solar radiation and hence the D-region for the whole day during summer in at least some sections of the path. In this paper, we present long distance propagation characteristics of VLF signals transmitted from VTX (18.2 kHz) and NWC (19.8 kHz) transmitters recorded at the Indian permanent station Maitri (Lat. 70 ∘ 45′S, Long. 114 ∘ 40′E) in 2007-2008. A very stable diurnal variation of the signal has been obtained with no signature of nighttime fluctuation due the presence of twenty-four hours of sunlight. Using ion production and recombination profiles by solar irradiance and incorporating D-region ion chemistry processes we calculate the electron density profile at different heights. Using this profile in the Long Wavelength Propagation Capability (LWPC) code we are able to reproduce the amplitude of VLF signal.

Description: Wave injection experiments provide an opportunity to explore and quantify aspects of nonlinear wave-particle phenomena in a controlled manner. Waves are injected into space from ground-based ELF/VLF transmitters and the modified waves are measured by radio receivers on the ground in the conjugate hemisphere. These experiments are expensive and challenging projects to build and to operate, and the transmitted waves are not always detected in the conjugate region. Even the powerful transmitter located at Siple Station, Antarctica in 1986, estimated to radiate over 1 kW, only reported a reception rate of ∼40%, indicating that a significant number of transmissions served no observable scientific purpose and reflecting the difficulty in determining suitable conditions for transmission and reception. Leveraging modern machine learning classification techniques, we apply two statistical techniques, a Bayes and a SVM classifier, to predict the occurrence of detectable 1-hop transmissions from Siple data with accuracies on the order of 80%-90%. Applying these classifiers to our 1986 Siple data set, we detect 406 receptions of Siple transmissions which we analyze to generate more robust statistics on nonlinear growth rates, 3 dB/s - 270 dB/s, and nonlinear total amplification, 3 dB - 41 dB.

Description: We analyse an equatorial plasma bubble (EPB) event observed in optical 630 nm image data simultaneously from Gadanki (13.5° N, 79.2° E), Kolhapur (16.8° N, 74.2° E), India. The total electron content data from Gadanki together with the ionosonde data from an equatorial Indian station, Tirunelveli (8.7°N, 77.8°E) confirmed the association of observed EPB event with equatorial spread-F (ESF). The optical 630 nm images from a farther low latitude Indian station Ranchi (23.3° N, 85.3° E) show clear signatures of tilted East–west wave structures propagating towards equator. Further, the upward wave energy noted in mesospheric airglow data was found to be negligible. These data suggest that possibly the off-equatorial tilted East–west structures triggered the observed EPB/ESF event.

Description: Linear kinetic dispersion theory is used to investigate a regime transition of the ion Bernstein instability driven by a proton velocity distribution with positive slopes with respect to the perpendicular velocity, ∂ f p ( v ∥ ∼0, v ⊥ )/ ∂ v ⊥ 〉0. The unstable waves arising from this instability are ion Bernstein waves with proton cyclotron harmonic dispersion. However, in the inner magnetosphere, particularly inside of the plasmapause where plasmas are dominated by a cold background, the instability leads to ion Bernstein waves which approximately follow the cold plasma dispersion relation for fast magnetosonic waves and are, therefore, fast magnetosonic-like. Subsequently, the relevant waves have been termed fast magnetosonic waves and many studies have assumed the cold plasma dispersion relation to describe them. On the other hand, how the dispersion properties of ion Bernstein waves become fast magnetosonic-like has not yet been well understood. To examine this regime transition of the instability, we perform linear dispersion analyses using a two-component proton model of f p ( v ) = f M ( v ) + f s ( v ), where f M is a Maxwellian velocity distribution and f s is an isotropic shell velocity distribution. The results show that the unstable waves are essentially ion Bernstein waves; however, when the shell proton concentration becomes sufficiently small (less than 10 % ), the unstable waves approach the cold plasma dispersion relation for fast magnetosonic waves and become fast magnetosonic-like. Although a reduced proton-to-electron mass ratio of 100 has been used for convenience, which reduces the number of unstable modes involved by lowering the lower hybrid frequency, this does not change the overall regime transition picture revealed in this study.

Description: We use the Cassini Radio and Plasma Wave Science/Langmuir Probe measurements of the electron density from the first 110 flybys of Titan to study how Saturn's magnetosphere influences Titan's ionosphere. The data is first corrected for biased sampling due to varying solar zenith angle (SZA) and solar energy flux (solar cycle effects). We then present results showing that the electron density in Titan's ionosphere, in the altitude range 1600 − 2400 km, is increased by about a factor 2.5 when Titan is located on the nightside of Saturn (Saturn local time (SLT) 21-03 h) compared to when on the dayside (SLT 09-15 h). For lower altitudes (1100 − 1600 km) the main dividing factor for the ionospheric density are the ambient magnetospheric conditions. When Titan is located in the magnetospheric current sheet, the electron density in Titan's ionosphere is about a factor 1.4 higher compared to when Titan is located in the magnetospheric lobes. The factor of 1.4 increase in between sheet and lobe flybys is interpreted as an effect of increased particle impact ionisation from ∼200 eV sheet electrons. The factor of 2.5 increase in electron density between flybys on Saturn's nightside and dayside is suggested to be an effect of the pressure balance between thermal plus magnetic pressure in Titan's ionosphere against the dynamic pressure and energetic particle pressure in Saturn's magnetosphere.

Description: We present a modeling study of interstellar pickup ion (PUI) distributions in co-rotating interaction regions (CIRs). We consider gradual compressions associated with CIRs formed when fast speed streams overtake slower streams in the inner heliosphere. For the analysis, we adopt a simplified magnetohydrodynamic model of a CIR [Giacalone et al., 2002]. The Energetic Particle Radiation Environment Module (EPREM) [Schwadron et al., 2010], a parallelized particle numerical kinetic code, is used to model PUI distributions using the focused transport equation, including adiabatic cooling/heating, adiabatic focusing, and parallel and perpendicular diffusion. The continuous injection of PUIs is handled as a source term with a ring distribution in velocity space that is produced from the local neutral density obtained from a hot model of the interstellar neutral gas. The simulated distributions exhibit a harder spectrum in the compression region and a softer spectrum in the rarefaction region than that in undisturbed solar wind. As an additional result, a v −5 power-law tail distribution above the PUI cut-off speed (a knee in the distribution) emerges for a particular velocity gradient in the CIR. The tail above the PUI cut-off is sensitive to the CIR velocity gradient, and in one observational case studied, this relationship adequately explains the observed spectrum from 2 to 4 times the solar wind speed. This suggests that the velocity gradient associated with the CIR formation can efficiently create a seed population of PUIs before a shock forms even without stochastic acceleration. Thus, local CIR compressions without shocks may play a significant role in the acceleration process as suggested previously [e.g., Chotoo et al., 2001; Giacalone et al., 2002; Ebert et al., 2012].

Description: We develop a single-fluid 2-D analytical model of the axially-symmetric thin heliospheric current sheet (HCS) embedded into the heliospheric plasma sheet (HPS). A HCS-HPS system has a shape of a relatively thin plasma disk limited by separatrices that also represent current sheets, which is in agreement with Ulysses observations in the aphelion, when it crossed the HCS perpendicular to its plane. Our model employs a differential rotation of the solar photosphere that leads to unipolar induction in the corona. Three components of the interplanetary magnetic field (IMF), the solar wind speed, and the thermal pressure are taken into account. Solar corona conditions and a HCS-HPS system state are tied by boundary conditions and the “frozen-in” equation. The model allows finding spatial distributions of the magnetic field, and the speed within the HPS, and electric currents within the HCS. An angular plasma speed is low within the HPS due to the angular momentum conservation (there is no significant co-rotation with the Sun), which is consistent with observations. We found that the HPS thickness L decreases with distance r , becoming a constant far from the Sun . L ~2.5 solar radii ( R 0 ) at 1 AU. Above the separatrices and at large heliocentric distances, the solar wind behavior obeys Parker's model, but the magnetic field spiral form may be different from Parker's one inside the HPS. At r ≤ 245 R 0 , the IMF spiral may undergo a turn simultaneously with a change of the poloidal current direction (from sunward to anti-sunward).

Description: Recent discoveries of higher harmonic cyclotron emissions in aurora occuring under daylit conditions motivated the modification of radio receivers at South Pole Station, Antarctica, to measure fine structure of such emissions during two consecutive austral summers, 2013-4 and 2014-5. The experiment recorded 347 emission events over 376 days of observation. The seasonal distribution of these events reveals that successively higher harmonics require higher solar zenith angles for occurrence, as expected if they are generated at the matching condition f u h = N f c e , which for higher N requires higher electron densities which are associated with higher solar zenith angles. This result implies that generation of higher harmonics from lower harmonics via wave-wave processes explains only a minority of events. Detailed examination of 21 cases in which two harmonics occur simultaneously shows that in almost all events the higher harmonic comes from higher altitudes, and only for a small fraction of events is it plausible that the frequencies of the fine structures of the emissions are correlated and in exact integer ratio. This observation puts an upper bound of 15-20% on the fraction of emissions which can be explained by wave-wave interactions involving Z-mode waves at f c e , and combined ith consideration of source altitudes puts an upper bound of 75% on the fraction explained by coalescence of Z-mode waves at 2 f c e . Taken together, these results suggest that the dominant mechanism for the higher harmonics is independent generation at the matching points f u h = N f c e , and that the wave-wave interaction mechanisms explain a relatively small fraction of events.

Description: Determining transport coefficients for galactic cosmic ray (GCR) propagation in the turbulent interplanetary magnetic field (IMF) poses a fundamental challenge in modeling cosmic ray modulation processes. GCR scattering in the solar wind involves wave-particle interaction, the waves being Alfven waves which propagate along the ambient field (B). Empirical values at 1 AU are determined for the components of the diffusion tensor for GCR propagation in the heliosphere using neutron monitor (NM) data. At high rigidities particle density gradients and mean free paths at 1 AU in B can only be computed from the solar diurnal anisotropy (SDA) represented by a vector A ( components Ar, A ϕ , A θ ) in a heliospherical polar coordinate system. Long-term changes in SDA components of NMs (with long track record and the median rigidity of response Rm ~ 20 GV) are used to compute yearly values of the transport coefficients for 1963–2013. We confirm the previously reported result that the product of the parallel (to B) mean free path (λ || ) and radial density gradient (Gr) computed from NM data exhibits a weak Schwabe cycle (11y) but strong Hale magnetic cycle (22y) dependence. Its value is most depressed in solar activity minima for positive (p-) polarity intervals (solar magnetic field in the northern hemisphere points outward from the sun) when GCRs drift from the polar regions toward the helio-equatorial plane and out along the heliospheric current sheet (HCS), setting up a symmetric gradient G θs pointing away from HCS. Gr drives all SDA components and λ || Gr contributes to the diffusive component (Ad) of the ecliptic plane anisotropy (A). GCR transport is commonly discussed in terms of an isotropic hard sphere scattering (a.k.a billiard-ball scattering) in the solar wind plasma. We use it with a flat HCS model and the Ahluwalia-Dorman master equations to compute the coefficients α (= λ⊥/λ || ) and ωτ (a measure of turbulence in the solar wind) and transport parameters λ || , λ⊥, Gr, G θs , and an asymmetric gradient G θa normal to the ecliptic plane. We study their dependence on rigidity (R), p-/n- intervals, sunspot numbers (SSNs), and solar wind parameters at 1 AU. λ || exhibits a strong 22y dependence but Gr does not, explaining solar polarity dependence of λ || Gr. The computed Gr values are an order of magnitude greater than those reported by colleagues making an ad hoc assumption that α is low (0.01). At high rigidities the drift contribution at 1 AU is small and unsteady. A new methodology is outlined to compute yearly GCR north–south anisotropy (A θ ) from the data for a single detector sorted for p-/n- intervals. We show that G θa is the main contributor to A θ in the steady state and G θa is shown not correlated with the north–south excess SSNs.

Description: We present the first multi-instrumental results on the ionospheric response to the geomagnetic storm of 17-18 March 2015 (the St. Patrick's Day storm) that was up to now the strongest in the 24 th solar cycle (minimum SYM-H value of -233 nT). The storm caused complex effects around the globe. The most dramatic positive ionospheric storm occurred at low-latitudes in the morning (~100-150% enhancement) and post-sunset (~80-100% enhancement) local sectors. These significant vertical total electron content (VTEC) increases were observed in different local time (LT) sectors and at different universal time (UT), but around the same area of the Eastern Pacific region, which indicates a regional impact of storm drivers. Our analysis revealed that this particular region was most concerned by the increase in the thermospheric O/N2 ratio. At mid-latitudes, we observe inverse hemispheric asymmetries that occurred, despite the equinoctial period, in different longitudinal regions. In the European-African sector, positive storm signatures were observed in the Northern Hemisphere (NH), whereas in the American sector, a large positive storm occurred in the Southern Hemisphere (SH), while the NH experienced a negative storm. The observed asymmetries can be partly explained by the thermospheric composition changes and partly by the hemispherically different non-dipolar portions of the geomagnetic field as well as by the IMF By component variations. At high-latitudes, negative ionospheric storm effects were recorded in all longitudinal regions, especially the NH of the Asian sector was concerned. The negative storm phase developed globally on March 18 at the beginning of the recovery phase.

Description: A new dynamic fluid-kinetic (DyFK) model is developed for investigating the plasma transport along a closed magnetic flux tube in the plasmasphere by coupling the field line interhemispheric plasma (FLIP) model with a generalized semi-kinetic (GSK) model. The coupling is achieved via an overlapped transition region (800 km-1100 km altitude) in each of the hemispheres. The flux tube is allowed to move both radially away from, toward, and azimuthally around the Earth. In addition to H + , ion species O + and He + are for the first time treated as simulation particles in a numerical model of the plasmasphere. The simulation particles are subjected to the field-aligned electric field, magnetic mirror force, gravity, centrifugal force, and inter and intra species Coulomb collisions. The plasmaspheric refilling processes as an application of the model are studied. The simulation results show that the behaviors of O + ions are substantially different from those of H + and He + ions.

Description: We present a low-altitude satellite survey of Power Line Harmonic Radiation (PLHR), i.e., electromagnetic waves radiated by electric power systems on the ground. We focus on frequencies corresponding to the first few harmonics of the base power system frequencies (50 Hz or 60 Hz, depending on the region). It is shown that the intensities of electromagnetic waves detected at these frequencies at an altitude of about 700 km are significantly enhanced above industrialized areas. The frequencies at which the wave intensities are increased are in excellent agreement with base power system frequencies just below the satellite location. We also investigate a possible presence of the weekend effect, i.e., if the situation is different during the weekends when the power consumption is lower than during the weekdays. Such an effect might be possibly present in the European region, but it is very weak. PLHR effects are less often detected in the summer, as the ionospheric absorption increases and also the radiation is obscured by lightning generated emissions. This difference is smaller in the U.S. region, in agreement with the monthly variations of the power consumption. The analysis of the measured frequency spectra reveals that although intensity increases at low odd harmonics of base power system frequencies are routinely detected, low even harmonics are generally absent. Finally, we verify the relation of PLHR intensities to the geomagnetically induced currents (GICs) proxy. It is shown that the PLHR intensity is increased at the times of higher GIC proxy values during the night.

Description: Scintillations on VHF radio signal are sparsely observed during daytime due to unavailability of strong electron density irregularities in equatorial E- or F-region. Type I/II irregularities observed at E-region altitudes during the daytime are linked with either two-stream or gradient drift instability. The occurrence of these irregularities in presence of strong blanketing Es (Esb) can produce weak-moderate scintillations on VHF signal during daytime. Such sparse daytime VHF scintillations are used in the present study to retrieve information about E-region irregularities, which are generally examined with radar observations. We use spaced receiver scintillation observations on 251 MHz signal transmitted from geostationary satellite UFO2 (71.2 ∘ E) and recorded at Tirunelveli (8.5 ∘ N, 77.8 ∘ E, dip latitude 0.6 ∘ N). Ionosonde data from Trivandrum (8.5 ∘ N, 76.6 ∘ E, dip latitude 0.5 ∘ N) during 2003-2005 is used to confirm the association of daytime scintillations with Esb. The daytime scintillations last for 15-45 minutes during post-noon hours. Their occurrence closely matches the peak occurrence time of Esb. For the first time, spatial scale lengths of E-region irregularities are obtained using the technique introduced by Bhattacharyya et al. [2003]. The observed spatial scales are validated using theoretical model. The theoretical model manifests 6-19% density fluctuations in the E-region to produce weak scintillations (0.15≤ S 4 ≤0.4) on 251 MHz. The study reveals that scale lengths of E-region irregularities are smaller on counter equatorial electrojet (CEEJ) days than non-CEEJ days, which could be resulting from lower electron temperatures in E-region on CEEJ days.

Description: This study focusses on meteor smoke particle (MSP) induced effects on the D-region ion-chemistry. Hereby, MSPs, represented with an eleven bin size distribution, have been included as an active component into the Sodankyä Ion and Neutral Chemistry model (SIC). By doing that, we model the diurnal variation of the negatively and positvely charged MSPs as well as ions and the electron density under quiet ionospheric conditions. Two distinct points in time are studied in more detail, i.e. one for sunlit conditions (Solar zenith angle is 72 ∘ ) and one for dark conditions (SZA is 103 ∘ ). We find nightly decrease of free electrons and negative ions, the positive ion density is enhanced at altitudes above 80 km and reduced below. During sunlit conditions the electron density is enhanced between 60 and 70 km altitude, while there is a reduction in negative and positive ions densities. In general, the MSP influence on the ion chemistry is caused by changes in the electron density. On the one hand, these changes occur due to nightly electron scavenging by MSPs resulting in a reduced electron-ion recombination. As a consequence positive ion density increase, especially water cluster ions are highly affected. On the other hand, the electron density is slightly increased during daytime by a MSP-related production due to solar radiation. Thus, more electrons attach to neutrals and short lived negative ions increase in number density. The direct attachment of ions to MSPs is a minor process, but important for long living ions.

Description: In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10's-100's km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 10-100 km scales using the all sky-imager, at 3 m scales using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August, 2014 by locating the radar scattering volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at sub-meter scales by the lower-hybrid-drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.

Description: Impacts of sudden stratospheric warming (SSW) on the thermosphere were studied using a gravity wave (GW)-resolving whole atmosphere model. During an SSW event, the mesosphere at high latitudes cools and the lower thermosphere becomes warm. At the peak of the SSW event, a temperature drop occurs above an altitude of 150 km at high latitudes. Our results indicate that the SSW event strongly affects meridional circulation and GW drag in the thermosphere. In the lower thermosphere, upward wind in the Arctic region, southward wind in the region between the North Pole and the South Pole, and downward wind in the Antarctic region are dominant before SSW occurs. The SSW event reverses meridional circulation at altitudes between 90 and 125 km in the northern hemisphere. During the SSW event, downward wind in the Arctic region and northward wind in the northern hemisphere prevail in the lower thermosphere. A detailed analysis revealed that during the SSW event, the change in meridional circulation is caused by the attenuation of the GW drag, and we identified the mechanism responsible for this attenuation. Moreover, we assessed the impacts of SSW on temperatures in the equatorial region and southern hemisphere.

Description: To prepare for when only single-view observations are available, we have made a test whether the 3-D parameters (radial velocity, angular width, and source location) of Halo Coronal Mass Ejections (HCMEs) from single-view observations are consistent with those from multi-view observations. For this test, we select 44 HCMEs from December 2010 to June 2011 with the following conditions: partial and full HCMEs by SOHO and limb CMEs by twin STEREO spacecraft when they were approximately in quadrature. In this study, we compare the 3-D parameters of the HCMEs from three different methods: (1) a geometrical triangulation method, the STEREO CAT tool developed by NASA/CCMC, for multi-view observations using STEREO/SECCHI and SOHO/LASCO data, (2) the Graduated Cylindrical Shell (GCS) flux rope model for multi-view observations using STEREO/SECCHI data, (3) an ice cream cone model for single-view observations using SOHO/LASCO data. We find that the radial velocities and the source locations of the HCMEs from three methods are well consistent with one another with high correlation coefficients (≥ 0.9). However, the angular widths by the ice-cream cone model are noticeably underestimated for broad CMEs larger than 100 ∘ and several partial HCMEs. A comparison between the 3-D CME parameters directly measured from twin STEREO spacecraft and the above 3-D parameters shows that the parameters from multi-view are more consistent with the STEREO measurements than those from single-view.

Description: Atmospheric tides are known to have a dramatic influence on thermospheric and ionospheric structure and variability. Considerable effort goes into understanding characteristics of tidal modes, their interactions with planetary and gravity waves and other tidal modes, as well as their influence on the background state of the thermosphere-ionosphere system. For the altitude interval between roughly 120 and 400 km, this effort is somewhat hindered by the lack of global observations. We propose a new method of determining tidal variability by making use of Dynasonde measurements. The NeXtYZ inversion procedure produces altitude profiles of the ionospheric parameters with a vertical resolution typically better than 1 km. This, together with the typical two minute cadence of the instrument results in extensive datasets with wide temporal and altitude coverage. At any given altitude we have non-uniform sampling due to the natural ionospheric variability. A Lomb-Scargle implementation is used to obtain equivalent results at all altitudes and locations. We report height profiles of the first three tidal harmonics derived from Dynasonde measurements. The data analyzed include the vertical electron density profiles, the ionospheric X (East-West) "tilt" measurement and the derived zonal plasma density gradient. Both the tilt and the gradient are shown to be sensitive tracers of atmospheric waves. We use data from Wallops Island and San Juan, for May-June and October-November 2013, thus capturing seasonal, latitudinal and altitude variations of tidal amplitude and phase. This proves the potential of using Dynasonde capable instruments as a data source for tidal studies in the thermosphere.

Description: In this manuscript, the authors show how the Global Navigation Satellite Systems, GNSS (exemplified in the Global Positioning System, GPS), can be efficiently used for a very different purpose from that for which it was designed; as an accurate Solar observational tool, already operational from the open global GPS measurements available in real-time, and with some advantages regarding dedicated instruments onboard spacecraft. The very high correlation of the solar Extreme Ultraviolet (EUV) photon flux rate in the 26-34 mm spectral band, obtained from the SEM instrument onboard the SOHO spacecraft during Solar flares, is shown with the GNSS Solar Flare Activity Indicator (GSFLAI). The GSFLAI is defined as the gradient of the ionospheric vertical total electron content (VTEC) rate versus the cosine of the Solar zenith angle in the day hemisphere (which filters out non-Solar over-ionization), and it is measured from data collected by a global network of dual frequency GPS receivers (giving in this way continuous coverage). GSFLAI for 60 X class flares, 320 M class flares and 300 C class flares, occurred since 2001, were directly compared with the EUV Solar flux rate data to show existing correlations. It was found that the GSFLAI and EUV flux rate present the same linear relationship for all classes of flares, not only the strong and medium intensity ones, X and M-class, as in previous works, but also for the weakest C-class Solar flares, which is a remarkable result.

Description: This paper presents solar wind data from the last five solar cycles. We review solar wind parameters over the four solar minima and five maxima for which spacecraft data are available and show the recovery from the last very weak minimum to the current solar maximum The solar wind magnetic field, speed, and density have remained anomalously low in this time period. However, the distributions of these parameters about the (lower than normal) average are similar to those from previous solar minima and maxima. This result suggests that the acceleration mechanism for the recent weak solar wind is probably not significantly different from earlier solar cycles. The He ++ /H + ratio variation with solar cycle continues to be a function of speed, but the most recent solar minimum has significantly lower ratios than in the previous solar cycle.

Description: We present a time-dependent MHD study of the controlling effects of the Mars crustal field on atmospheric escape. We calculate globally integrated planetary ion loss rates under quiet solar conditions considering the continuous rotation of crustal anomalies with the planet. It is found that the rotating crustal field plays an important role in controlling atmospheric escape. Significant time variation of ∼20 % and ∼50 % is observed during the entire rotation period for O + and for and , respectively. The control is exerted mainly through two processes. First, the crustal magnetic pressure over the subsolar regime controls solar wind penetration and mass loading and therefore the escaping planetary ion source. There is a strong negative correlation between the magnetic pressure and ion loss, with a time lag of 〈1 hr for O + and ∼2.5 hr for and . Second, the crustal magnetic pressure near the terminator region controls the cross section area between the induced magnetospheric boundary and 100 km altitude at the terminator. The change in day-night connection regulates the extent to which planetary ions created on the dayside can be ultimately carried away by the solar wind and escape Mars. There is a strong positive correlation between the cross section area and ion loss, with no significant time lag. As the planet rotates, the dayside process and the terminator process work together to control the total amount of escaping planetary ions. However, their relative importance changes with the local time of the strong crustal field region.

Description: A statistical based method combined with basis function expansion techniques is described in order to provide extensive maps of the ground level perturbation magnetic field from 40 0 magnetic latitude to the north magnetic pole for all longitudes. The method combines historical data from the SuperMAG data base, Principal Component Analysis and a spherical cap harmonic basis function expansion in order to fill in magnetic perturbation data where there are no magnetometers and produce the poloidal current potential. The maps have a regular grid with a 2 0 latitude and 1 hour longitude spacing. The statistical process uses SuperMAG data derived magnetic indices plus the solar zenith angle which orders the resulting spatial maps by geomagnetic activity indicators to enhance model agreement with the data. For quiet through to moderate magnetic activity intervals, the root mean square error between the input and the fitted data are 18 nT and 10 nT for the north-south and east-west components respectively, which are of similar magnitude to the statistical uncertainty in the SuperMAG data set.

Description: Plasmaspheric hiss is a whistler mode emission that permeates the Earth's plasmasphere and is a significant driver of energetic electron losses through cyclotron-resonant pitch angle scattering. The EMFISIS instrument on the Van Allen Probes mission provides vastly improved measurements of the hiss wave environment including continuous measurements of the wave magnetic field cross-spectral matrix and enhanced low frequency coverage. Here, we develop empirical models of hiss wave intensity using two years of Van Allen Probes data. First, we describe the construction of the hiss database. Then, we compare the hiss spectral distribution and integrated wave amplitude obtained from Van Allen Probes to those previously extracted from the CRRES mission. Next, we develop a cubic regression model of the average hiss magnetic field intensity as a function of Kp, L , magnetic latitude and magnetic local time. We use the full regression model to explore general trends in the data and use insights from the model to develop a simplified model of wave intensity for straightforward inclusion in quasi-linear diffusion calculations of electron scattering rates.

Description: Using a mechanical analogy of rolling a cylindrical barrel on a rough uneven surface, we developed a special method for detrending the GPS-derived total electron content (TEC) data. This method is specifically designed to recognize the presence of depletions in the TEC time series data, and handle them differently from wavelike features. We also demonstrate a potential application of this technique to map the detailed geographic profile of TEC depletions over the equatorial region, using the South American sector as an example.

Description: We present the results of a study of the azimuthal characteristics of ionospheric and seismic effects of the meteorite 'Chelyabinsk', based on the data from the network of GPS receivers, coherent decameter radar EKB and network of seismic stations, located near the meteorite fall trajectory. It is shown, that 6-14 minutes after the bolide explosion, GPS network observed the cone-shaped wavefront of TIDs that is interpreted as a ballistic acoustic wave. The typical TIDs propagation velocity were observed 661 ± 256 m/s, which corresponds to the expected acoustic wave speed for 240 km height. 14 minutes after the bolide explosion, at distances of 200 km we observed the emergence and propagation of a TID with annular wavefront, that is interpreted as gravitational mode of internal acoustic waves. The propagation velocity of this TID was 337 ± 89 m/s which corresponds to the propagation velocity of these waves in similar situations. At EKB radar, we observed TIDs in the sector of azimuthal angles close to the perpendicular to the meteorite trajectory. The observed TID velocity (400 m/s) and azimuthal properties correlate well with the model of ballistic wave propagating at 120-140 km altitude. It is shown, that the azimuthal distribution of the amplitude of vertical seismic oscillations with periods 3-60 s can be described qualitatively by the model of vertical strike-slip rupture, propagating at 1 km/s along the meteorite fall trajectory to distance of about 40 km. These parameters correspond to the direction and velocity of propagation of the ballistic wave peak by the ground. It is shown, that the model of ballistic wave caused by supersonic motion and burning of the meteorite in the upper atmosphere can satisfactorily explain the various azimuthal ionospheric effects, observed by the coherent decameter radar EKB, GPS-receivers network, as well as the azimuthal characteristics of seismic waves at large distances.

Description: In this research, we used numerical simulation to study the effect of Interhemispheric Field-aligned Currents (IHCs), going between two conjugate ionospheres in two hemispheres, on the Equivalent Ionospheric Currents (EICs). We computed the maps of these EICs in two hemispheres during summer-winter conditions, when the effect of the IHCs is especially significant. The main results may be summarized as follows: (1) In winter hemisphere, the IHCs may significantly exceed and be a substitute for the local R1 currents, and they may strongly affect the magnitude, location, and direction of the EICs in the nightside winter auroral ionosphere; (2) While in summer polar cap the EICs tend to flow sunward, in winter polar cap the EICs turn toward dawn due to the effect of the IHCs; (3) The well-known reversal in the direction of the EICs in the vicinity of the midnight meridian, in winter hemisphere is observed not at the polar caps boundary (as usually expected) but equatorward of this boundary in the region of the IHCs location; (4) The IHCs in winter hemisphere may be, in fact, not only a substitute for the R1 currents but also the major source of the Westward Auroral Electrojet, observed in both hemispheres during substorm activity.

Description: The solar minimum of 2007-2010 was unusually deep and long-lived. In the later stages of this period the electron fluxes in the radiation belts dropped to extremely low levels. The flux of relativistic electrons (〉1 MeV) was significantly diminished, and at times were below instrument thresholds both for spacecraft located in geostationary orbits and also those in low-Earth orbit. This period has been described as a natural "grand experiment" allowing us to test our understanding of basic radiation belt physics and in particular the acceleration mechanisms which lead to enhancements in outer belt relativistic electron fluxes. Here we test the hypothesis that processes which initiate repetitive substorm onsets drive magnetospheric convection, which in turn triggers enhancement in whistler mode chorus that accelerates radiation belt electrons to relativistic energies. Conversely, individual substorms would not be associated with radiation belt acceleration. Contrasting observations from multiple satellites of energetic and relativistic electrons with substorm event lists, as well as chorus measurements, shows that the data are consistent with the hypothesis. We show that repetitive substorms are associated with enhancements in the flux of energetic and relativistic electrons and enhanced whistler mode wave intensities. The enhancement in chorus wave power starts slightly before the repetitive substorm epoch onset. During the 2009/2010 period the only relativistic electron flux enhancements that occurred were preceded by repeated substorm onsets, consistent with enhanced magnetospheric convection as a trigger.

Description: The coronal mass ejection (CME) event on March 15, 2013 is one of the few solar events in Cycle 24 that produced a large solar energetic particle (SEP) event and severe geomagnetic activity. Observations of SEP from the ACE spacecraft show a complex time-intensity SEP profile that is not easily understood with current empirical SEP models. In this study, we employ a global three-dimensional (3-D) magnetohydrodynamic (MHD) simulation to help interpret the observations. The simulation is based on the H3DMHD code and incorporates extrapolations of photospheric magnetic field as the inner boundary condition at a solar radial distance ( r ) of 2.5 solar radii. A Gaussian-shaped velocity pulse is imposed at the inner boundary as a proxy for the complex physical conditions that initiated the CME. It is found that the time-intensity profile of the high-energy (〉 10 MeV) SEPs can be explained by the evolution of the CME-driven shock and its interaction with the heliospheric current sheet and the non-uniform solar wind. We also demonstrate in more detail that the simulated fast-mode shock Mach number at the magnetically connected shock location is well correlated ( r cc ≥ 0.7) with the concurrent 30-80 MeV proton flux. A better correlation occurs when the 30-80 MeV proton flux is scaled by r -1.4 ( r cc =0.87). When scaled by r -2.8, the correlation for 10-30 MeV proton flux improves significantly from r cc = 0.26 to r cc = 0.73, with one hour delay. The present study suggests that (1) Sector boundary can act as an obstacle to the propagation of SEPs; (2) The background solar wind is an important factor in the variation of IP shock strength thus plays an important role in manipulation of SEP flux; (3) At least 50% of the variance in SEP flux can be explained by the fast-mode shock Mach number. This study demonstrates that global MHD simulation, despite the limitation implied by its physics-based ideal fluid continuum assumption, can be a viable tool for SEP data analysis.

Description: For disturbed geosynchronous plasma, the onset of spacecraft charging and its evolution become more complex than quiet environment. A sudden jump of spacecraft potential can occur in specific environment conditions which can be detrimental to onboard electronics. In this paper, the potential jump for geosynchronous spacecraft charging is theoretically modeled and comprehensively characterized. Two types of potential jump in opposite directions are elucidated and the threshold conditions for both types of jump are determined. At both thresholds, the spacecraft potentials are semi-steady, but in opposite directions, with the possibility of a jump to a stable potential. The polarity of movement across the thresholds from different plasma will cause a spacecraft to experience irreversible charging histories which result in significant hysteresis. Generally, the jump to negative potential occurs with greater magnitude as compared to a potential jump in positive direction. Ion distribution has negligible influence to the threshold condition for jump to negative potential. However, ion distribution significantly affects the threshold for jump to positive potential and subsequently modifies the parametric domains of spacecraft charging.

Description: We have studied two Coronal Mass Ejections (CMEs) that occurred on September 25 and 28, 2012 and interacted near the Earth. By fitting the Graduated Cylindrical Shell (GCS) model on the SECCHI/COR2 images and applying the Stereoscopic Self-Similar Expansion (SSSE) method on the SECCHI/HI images, the initial direction of both the CMEs is estimated to be west of the Sun-Earth line. Further, the three-dimensional (3D) heliospheric kinematics of these CMEs have been estimated using Self-Similar Expansion (SSE) reconstruction method. We show that use of SSE method with different values of angular extent of the CMEs, leads to significantly different kinematics estimates for the CMEs propagating away from the observer. Using the estimated kinematics and true masses of the CMEs, we have derived the coefficient of restitution for the collision which is found to be close to elastic. The in situ measurements at 1 AU show two distinct structures of interplanetary CMEs, heating of the following CME, as well as ongoing interaction between the preceding and the following CME. We highlight the signatures of interaction in remote and in situ observations of these CMEs and the role of interaction in producing a major geomagnetic storm.

Description: DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite data have been used to investigate the global relationship between electron density (Ne) and electron temperature (Te) in the topside ionosphere (~680 km) from 2006-2009. Te and Ne were negatively correlated in most of the low and middle latitude regions at ~10:30 solar local time (LT). In these regions, photoelectron heating of the electrons was balanced by cooling through collisions with the ions. The negative correlation became weaker at mid-latitudes, due to the increasing influence of heat conduction. The correlation was negative in most seasons during the daytime except at high latitudes in the northern winter, where a positive correlation occurred. There were wave-like longitudinal structures in Ne and Te around the geomagnetic equator, but they had different patterns in the day and the night. However, no obvious longitudinal variations in the correlation were associated with these structures. A positive correlation occurred near the magnetic equator at ~22:30 LT, which depended on thermal equilibrium between the electrons, ions and neutrals. A negative correlation occurred at mid-latitudes. Around the September Equinox, at night around the magnetic equator, the positive correlation had a wider latitudinal range. At mid-latitudes, a negative correlation occurred in smaller areas than it did around the March Equinox. Around the December Solstice the direct night-time coupling between Ne and Te was weaker than it was around the June Solstice. The negative correlation depends on the collisions between the electrons and the ions and the heating source.

Description: The overall morphology and dynamics of magnetospheric substorms is well established in terms of the observed qualitative auroral features seen in ground based magnetometers. This paper focuses on the quantitative characterisation of substorm dynamics captured by ground based magnetometer stations. We present the first analysis of substorms using dynamical networks obtained from the full available set of ground based magnetometer observations in the northern hemisphere. The stations are connected in the network when the correlation between the vector magnetometer time series from pairs of stations within a running time window exceeds a threshold. Dimensionless parameters can then be obtained that characterise the network and by extension, the spatio-temporal dynamics of the substorm under observation. We analyse four isolated substorm test cases as well as a steady magnetic convection (SMC) event and a day in which no substorms occur. These test case substorms are found to give a consistent characteristic network response at onset in terms of their spatial correlation. Such responses are differentiable from responses to the SMC event and non-substorm times. We present a method to optimise network parametrisation with respect to the different individual station responses, the spatial inhomogeneity of stations in the northern hemisphere and the choice of correlation window sizes. Our results suggest that dynamical network analysis has potential to quantitatively categorise substorms.

Description: A curved shock is analyzed in the whole quasi-perpendicular propagation region (90° ≥ θ B n ≥ 45°) in a supercritical regime with the help of a 2D PIC code including self-consistent effects such as the shock front curvature and the time of flight effects. Two distinct ion populations are observed within the foreshock: a (gyrotropic) Field-Aligned Beam population, hereafter named "FAB”, and a (nongyrotropic) Gyro-Phase Bunched population, hereafter named “GPB”. The origin of these high energy particles and their corresponding acceleration mechanisms are analyzed in details in the present paper. Both “FAB” and “GPB” populations are shown to be produced by the shock front itself and more important, do have exactly the same origin. At the shock front, the two populations gain a non gyrotropic distribution, but “FAB” population looses its initial phase coherency after suffering several bounces along the curved front. This result has one main consequence: the time evolution of the two populations does not involve some distinct reflection processes as often claimed in the literature, but results only from the particle time history at the shock front. This important result was not expected and greatly simplifies the question of their origin. More precisely, a new parameter, the injection angle θ i n j has been defined between the shock normal direction and the ion gyrating velocity vector. We found that the“FAB” population is formed by ions injected almost along the shock front, while “GPB” population is formed by ions injected almost along the shock normal.