SM11A-1562
STEREO Observations of the Earth's Quiet-Time Ring Current using Energetic Neutrals
On November 6, 2006 the two STEREO spacecraft successively observed Energetic Neutral Atoms (ENA) from the night side magnetosphere with their Supra-Thermal Electrons (STE) Solid State Telescopes. STE was designed to study solar wind electrons in the 2-100keV with ~1keV FWHM energy resolution, but has recently demonstrated its sensitivity for imaging 4-20keV ENAs (Hydrogen) from the heliosheath [Wang et al 2008, Nature]. STEREO A and B made close passes separated by approximately 50 minutes at ~600km on the Earth's night side and near the equator. We present here the ENA spectra and spatial distribution of the observations. Further, we invert the ENA spectrum to give an L-integrated ion flux from 4- 100keV and compare this result to in situ observations of the quiet-time ring current. Preliminary analysis suggests that this detector can make the most sensitive ENA measurements of the ring current to date from low Earth orbit.
SM11A-1563
Probing Ring Current Properties From Multiple Satellite Data and Numerical Analyses
In this paper, ring current energy content, angular distribution of ring current particle fluxes and accompanying fields characteristics will be examined in detail using THEMIS and Geotail measurements through case studies, aided with simulation results from the Comprehensive Ring Current Model. In particular, we will investigate the relationship between the ring current and SAPS electric fields in a global context, using the electric field measurements from THEMIS and simultaneous DMSP & radar observations of subauroral flows.
SM11A-1564
Ring Current asymmetry and ASY-H: an analysis using IMAGE/HENA data
The ground station-based index ASY-H is commonly used as a indicator of ring current asymmetry. Recent research has indicated that the behavior of current systems other than the ring current significantly affect ground station-based indices. The current availability of Energetic Neutral Atom (ENA) measurements provides the opportunity to examine the accuracy and utility of these indices. In order to facilitate the use of ENA data, a simplified automated inversion technique that has good agreement with the usual more complicated inversion processes is used. ASY-H is evaluated using this procedure by comparing to HENA- derived ring current energy.
SM11A-1565
Increased local time accuracy of the corrected Dst index
The Dst index is one of the most used geomagnetic indices which has been constructed to monitor the most dramatic events in the near-Earth space, the geomagnetic storms. However, it has been known for some time that the Dst index includes random and systematic errors, e.g., an excessive, seasonally varying quiet-time level, the so called "non-storm component" which is unrelated to the intensity of the ring current or magnetic storms. Therefore, we have developed a corrected and extended version of the Dst index, the so called Dcx index which exists now in 1932-2007. So far, the Dcx index, in analogy with the Dst index, is based only on four stations, roughly evenly distributed over the longitude. Such a coarse longitudinal accuracy does not allow for a detailed study of the local time structure of global disturbances during storms, in particular the current systems like the symmetric and asymmetric ring current or the tail current. Here we reconstruct, based on the corrected method implemented in the Dcx index, a longitudinally enhanced index called the Dcx16 index, which is based on the data from 16 low and mid-latitude stations. We study the detailed local time structure of storm-time disturbances and calculate the maximum momentary asymmetry in the disturbance level. We compare our results with similar results based on the four stations and the conventional Dst index during recent years. We also compare the local time properties during storms driven by high speed streams and coronal mass ejcetions.
SM11A-1566
Dst and a map of average equivalent ring current: 1958-2007
A new Dst index construction is made using the original hourly magnetic-observatory data collected over the years 1958-2007; stations: Hermanus South Africa, Kakioka Japan, Honolulu Hawaii, and San Juan Puerto Rico. The construction method we use is generally consistent with the algorithm defined by Sugiura (1964), and which forms the basis for the standard Kyoto Dst index. This involves corrections for observatory baseline shifts, subtraction of the main-field secular variation, and subtraction of specific harmonics that approximate the solar-quiet (Sq) variation. Fourier analysis of the observatory data reveals the nature of Sq: it consists primarily of periodic variation driven by the Earth's rotation, the Moon's orbit, the Earth's orbit, and, to some extent, the solar cycle. Cross coupling of the harmonics associated with each of the external periodic driving forces results in a seemingly complicated Sq time series that is sometimes considered to be relatively random and unpredictable, but which is, in fact, well described in terms of Fourier series. Working in the frequency domain, Sq can be filtered out, and, upon return to the time domain, the local disturbance time series (Dist) for each observatory can be recovered. After averaging the local disturbance time series from each observatory, the global magnetic disturbance time series Dst is obtained. Analysis of this new Dst index is compared with that produced by Kyoto, and various biases and differences are discussed. The combination of the Dist and Dst time series can be used to explore the local-time/universal-time symmetry of an equivalent ring current. Individual magnetic storms can have a complicated disturbance field that is asymmetrical in longitude, presumably due to partial ring currents. Using 50 years of data we map the average local-time magnetic disturbance, finding that it is very nearly proportional to Dst. To our surprise, the primary asymmetry in mean magnetic disturbance is not between midnight and noon, but rather between dawn and dusk, with greatest mean disturbance occurring at dusk. As a result, proposed corrections to Dst for magnetopause and tail currents might be reasonably reconsidered.
SM11A-1567
The Energization of Ions in the Inner Magnetosphere by Sudden Storm Commencement
We have investigated the impact of coronal mass ejection (CME)-caused sudden storm commencements (SSCs) on magnetospheric ion populations by using a combination of global magnetohydrodynamic (MHD) simulations and large-scale kinetic particle tracing calculations. To do so, we have selected three moderate to large CME-driven geomagnetic storms for which upstream solar wind and interplanetary magnetic field (IMF) data and observations in the magnetotail and near-Earth plasma sheet are available. For each event, we have run a global MHD simulation of the event using upstream solar wind and IMF data. Ion trajectories are then traced from the solar wind, upstream of the bow shock, and from the ionosphere beginning 3-4 hours prior to the SSC to obtain global distributions of ions in the magnetotail and inner magnetosphere just prior to, during, and immediately after the SSC. Of particular interest is the energization evident in ion velocity distribution functions, and the dependence of this energization on distance from Earth and on local time. We further ascertain the effect of the shock impact on the acceleration and transport of ions in the seed region of the ion radiation belts, and determine the differences, if any, in the energization of protons and heavy ions in the inner magnetosphere.
SM11A-1568
Magnetic Storm Simulation With Multiple Ion Fluids: Algorithm
We describe our progress in extending the capabilities of the BATS-R-US MHD code to model multiple ion fluids. We solve the full multiion equations with no assumptions about the relative motion of the ion fluids. We discuss the numerical difficulties and the algorithmic solutions: the use of a total ion fluid in combination with the individual ion fluids, the use of point-implicit source terms with analytic Jacobian, using a simple criterion to separate the single-ion and multiion regions in our magnetosphere applications, and an artificial friction term to limit the relative velocities of the ion fluids to reasonable values. This latter term is used to mimic the effect of two-stream instabilities in a crude manner. The new code is fully integrated into the Space Weather Modeling Framework and it has been coupled with the ionosphere, inner magnetosphere and polar wind models to simulate the May 4 1998 magnetic storm.
SM11A-1569
Magnetic storm simulation with multiple ion fluids: results and analysis
Ionosheric outflow can be a significant contributor to the plasma population of the magnetosphere during active geomagnetic conditions. We present preliminary results and analysis of new efforts to model the source and effects of out-flowing plasma in the Space Weather Modeling Framework (SWMF). In particular, we use the Polar Wind Outflow Model (PWOM), a field-aligned multi-fluid polar wind code to study the ionospheric outflow, and a newly developed multi-fluid version of the BATS-R-US model of the magnetosphere to track the fate of that outflow. We present our methodology and a description of the evolution of magnetospheric composition during the May 4th 1998 geomagnetic storm.
SM11A-1570
Real-Time WINDMI Predictions of Geomagnetic Storm and Substorms
Real-Time WINMDI is plasma physics-based, nonlinear dynamical model of
the coupled solar WIND Magentosphere-Ionosphere system. Using
upstream solar wind particle and field data, a system of nonlinear
ordinary differential equations is solved numerically to describe the
energy transfer from the solar wind to the magnetosphere-ionosphere
system. The physics model WINMDI divides the incoming power into
energy stored in multiple regions of M-I system and has been verified
on GEM storm data in Spencer et al. (2007). The system of nonlinear
ordinary differential equations, which describes energy transfer into,
and between dominant components of the nightside magnetosphere and
ionosphere, is solved numerically to determine the state of each
component. The low-dimensional model characterizes the energy stored
in the ring current and the region 1 field-aligned current which are
use to compute model Dst and AL values. Real-time solar wind plasma
parameters, available from ACE, are downloaded every 10 minutes to
compute the input solar wind driving voltage for the model. Real-Time
WINDMI computes model Dst and AL values about 1-2 hours before index
data is available at the Kyoto WDC Quicklook website. Results are
shown on the Real-Time WINDMI website. We present
statistics for Real-Time WINDMI performance from 2006 to present and
also compare the results for different input driving voltages. We
plan to compare the database of Real-Time WINDMI Dst predictions with
other ring current models which contain different loss and
energization processes.
The work is supported by NSF grant ATM-0638480.
http://orion.ph.utexas.edu/~windmi/realtime/
SM11A-1571
Inner magnetosphere--global MHD coupled code: initial results
We present results of a one-way coupling between a global MHD model (BATSRUS) and a ring current model with ionosphere feedback (CRCM). The MHD model provides magnetic field in all computational regions and electric field potential, temperature and density at the outer boundary. The ring current model calculates the plasma distribution (H+ and e-) in the energy range 1-200keV, field-aligned currents of Region-2 and electric fields. We consider inner magnetosphere dynamics during an idealized case with south-north-south Bz turning as well as a real event during the 12 August 2000 storm. For the idealized case, we reproduce basic features of the electric field in the inner magnetosphere: strong convection during southward IMF and shielding, weak convection during northward IMF and overshielding. Additionally, we estimate characteristic times for shielding/overshielding formation. For the 12 August 2000 event we calculate ring current 3D fluxes and reconstruct energetic neutral atom (ENA) images. We compare the modeled ENA images with those observed by IMAGE HENA imager and investigate global ring current dynamics during 12 August 2000 event.
SM11A-1572
Modeling Observed Plasma Sheet Asymmetries During Intervals of Northward Interplanetary Magnetic Field
We apply a Lorentz force particle tracing code to investigate observed asymmetries and other features in the averaged plasma sheet parameters obtained from Geotail observations. Our study focuses on intervals of northward interplanetary magnetic field (IMF), which play an important role in pre-conditioning the plasma sheet for more active times. We are primarily concerned with the variations in the phase space densities with respect to the GSM Y axis, such as dawn-dusk asymmetries and the differences between flank and midnight populations. We have developed a plasma transport model that computes the drift trajectories of particles in the magnetosheath and magnetosphere using the relativistic Lorentz force equation. For our magnetic field, we combine an observation-based Tsyganenko magnetospheric magnetic field model with a theoretical magnetosheath magnetic field model that we have developed. Our electric field is obtained by tracing the potential along magenetic field lines (assumed to be equipotentials) to either the unshocked solar wind (where the electric field is assumed uniform) or the ionosphere (where we specify a Weimer potential). Our model is used to trace the drift paths of plasma sheet particles of different energies backward in time to estimate their source locations and thereby explain observed features of the plasma sheet. The limitations of the model are examined in order to assess the potential role that non-modeled processes could play in the particle transport and their potential impact on the results.
SM11A-1573
The Effect of Smoothed Solar Wind Inputs on Global Modeling Results
This study investigates the role of fluctuations in the solar wind parameters in triggering a magnetic storm and assesses the storm simulation ability of Space Weather Modeling Framework (SWMF) through model- data comparison. The event of September 22, 1999 is examined through global magnetosphere simulations, using as input ACE observations (16 sec temporal resolution) along with running averages of this data with windows of 4, 60, 120 and 180 minutes. It is noted that averaged solar wind input produces a double dip, fast recovery phase with a shorter main phase compared with the 16 second resolution input. Also, smoothing the input with a window larger than 60 minutes changes the entire magnetosphere and reduces the plasma sheet density/pressure, therefore a less intense storm develops. Is is worth to mention that the main phase for this magnetic storm lasted 3 hours, while the rapid drop in Dst index took less than one hour. This explains the change in the Dst profile for the 120 and 180 minutes averaged input. Also, comparison with the Dst predictions (O'Brien and McPherron, 2000) are presented and discussed. For all cases studied, there are no significant differences for Cross Polar Cap Potential (CPCP) in both hemispheres, while midnight plasma sheet density shows a sharp drop when the input is averaged over 4 minutes or more. Moreover, 4 minutes and 60 minutes temporal resolution inputs produce a larger disturbance than the 16 seconds resolution solar wind input.
SM11A-1574
Role of plasma sheet boundary conditions in simulations of severe geomagnetic storms with the Rice Convection Model
Rice Convection Model (RCM) is a first-principles inner magnetospheric code that evolves the particle distribution function using electric fields computed self-consistently. In our most recent work, we have modified the model, which has served for several decades as a theoretical tool for investigating the physics of the inner magnetosphere, to the level of a prediction tool. As part of this work, we now have the ability to use different empirical plasma sheet models to specify plasma inflow boundary conditions on the high-L boundary. When a time-dependent magnetic field model and time variations of the plasma sheet moments are used as inputs to the model (both driven by solar wind and IMF parameters), the inner magnetosphere is found to undergo severe perturbations, including strong ring current injection, supersonic ionospheric plasma drifts, and highly structured interchange-driven transport of plasma sheet particles into the ring current region. In this paper, we use comprehensive simulations of the severe magnetic storms of March 31, 2001 and November 7-11, 2004 with the RCM, to quantify the role of different plasma boundary conditions on the storm-time ring current dynamics and the magnetosphere-ionosphere coupling.
SM11A-1575
Initial model results of the inner magnetosphere obtained with OpenGGCM coupled with CRCM
We present initial simulation results of the stormtime inner magnetosphere obtained with OpenGGCM coupled with the Comprehensive Ring Current Model (CRCM), which self-consistently solves the kinetic equation of ring current protons. We model two events: the intense magnetic storm on 12 August 2000 and the 23 March 2007 substorm event. We compare our model results with previous studies which used either only global MHD modeling or only standalone ring current models to simulate disturbed-time events. In the case of an intense storm we observe that the boundary conditions provided by the OpenGGCM greatly influence the dynamics of the CRCM ring current proton flux. The during the substorm event simulation we observe particle inflow from the tail region which is consistent with previous studies.
SM11A-1576
Unequal compression of the geomagnetic field by the solar wind
The total pressure is balanced at the magnetopause where separates the shocked solar wind and the compressed geomagnetic field. In this study, we use the magnetic fields from five THEMIS probes and the theoretical dipole magnetic field model to calculate the ratio of the compressed geomagnetic field just inside the magnetopause to the dipole magnetic field. Here we find that the ratio is linearly proportional to the subsolar standoff distance. In addition, we also study the relation between the compressed geomagnetic field and the subsolar distance. Here we also find that the compressed geomagnetic field varies with the subsolar distance in a power law of -2.3, which is different from that estimated from the dipole magnetic field (-3.0). Furthermore, this relation can be turned into a function of the compressed geomagnetic field in terms of the subsolar distance. The function can be served as a boundary condition in the global modeling of the magnetosphere and can advance our understandings of the loss of electrons of the radiation belt at the magnetopause and the interaction between the solar wind and the magnetosphere.
SM11A-1577
Dispersive and dispersionless spatial structures at the inner edge of the plasma sheet simultaneously encountered by 3 Themis spacecraft at geomagnetically quiet time
The inner boundary of the electron plasma sheet at quiet times is known to vary in distance from the Earth as a function of electron energy. Thus a spacecraft inbound through the plasma sheet on the night side observes sharp decreases of electron flux first at high energies and later at lower energies. This dispersed cut-off is explained by an Alfvén layer model in which the separatrix between drift orbits that close around the earth and those that do not depends on particle thermal energy and associated gradient drift. Sometimes a spacecraft observes the cutoff boundary simultaneously at all energies, and this is referred to as a dispersionless boundary. Dispersionless signatures are common at disturbed times and are usually attributed to rapid motion of the boundary. We have surveyed Themis plasma data from 2007 to 2008 in order to identify boundary crossings observed by more than one spacecraft. On Jan. 1, 2008 with the provisional AL index below 20 nT, three Themis spacecraft crossed the inner edge of the plasma sheet within a limited time interval near 1900 UT. Two of the spacecraft observed dispersive boundaries whereas the third observed a dispersionless boundary. The trajectory of the latter spacecraft was at lower latitude than the other two. It seems unlikely that temporal variations could have greatly differed at the three spacecraft, so we attribute the differing observations to three-dimensional spatial structure of the plasma- sheet's inner edge. We will design a model to reproduce the observations. This unusual event requires us to reconsider whether observation of a dispersionless injection necessarily implies dynamics.
SM11A-1578
The modeling of a substorm event using the Rice Convection Model with an equilibrium magnetic field
We present a simulation of a non-storm-time substorm event on 29 Oct 2004 using the Rice Convection Model coupled with the Magneto-Friction code for the first time. The model includes the self-consistent feedback of both electric field and magnetic field. The modeling of the growth phase during fairly stable southward solar wind driving confirms the classic picture of the substorm growth phase. The expansion phase is modeled by non-adiabatically reducing the entropy parameter PV5/3 along the tailward boundary of the RCM. It confirms the idea that the reduction of the entropy parameter PV5/3 plays an important role in the plasma injection and the magnetic field dipolarization following substorm onset. The modeling results are compared with multipoint observations with good consistency, including the magnetic field, plasma moments, magnetic flux transport and the estimated local flux tube volume V and the entropy parameter PV5/3 in the near-Earth plasma sheet, as well as the magnetic field, plasma moments and energetic- particle fluxes at geosynchronous orbit. This simulation provides a global view of the changing of magnetic field configuration and the plasma transportation throughout an entire substorm cycle.
SM11A-1579
OpenGGCM/RCM simulation of the March 23, 2007 substorm event
We will report on recent progress in merging the OpenGGCM global magnetosphere model with the Rice Convection Model (RCM) by presenting results of a simulation of the March 23, 2007 substorm event. In these simulations, the OpenGGCM was used as input to the RCM. We will compare model results with previous stand-alone MHD code simulations of the same event and also with in situ satellite observations. In the RCM simulation, we find that particles are injected into inner magnetosphere after the substorm onset with low PV5/3. The simulation suggests that a reduction in PV5/3 and the resulting effect of interchange plays important role in substorm particle injection.
SM11A-1580
Radiation Belt Data-Assimilation Using Self-Consistent Storm-Time Magnetic Fields
The lack of suitably realistic magnetic field models for use in radiation belt data assimilation remains a critical unresolved problem in space weather specification and prediction. Although the high-energy radiation belt particles themselves do not significantly alter the magnetic fields in which they drift, the lower-energy ring current populations do. And the deviation (especially during storms) of the real magnetic field from that computed even with the best of the presently available empirical models can be very large. To overcome this problem, the LANL DREAM code has been modified to use magnetic fields that are self-consistently maintained in force balance with the plasma. We compare second and third adiabatic invariants computed from the self-consistent fields to those obtained with empirical B-field models, and we utilize a phase-space density matching technique in order to test the various field models. Finally, the PSD at constant mu and K in a data-assimilation model obtained with the self-consistent and non-self-consistent magnetic field models will be compared.
SM11A-1581
Inner Radiation Belt Data / Model Comparisons
We present detailed comparisons of a time-dependent inner radiation belt model with in-situ proton observations made by a variety of spacecraft during solar cycle 23. The recently-developed model (Selesnick et al., 2007) computes proton intensities as a function of time and of the three adiabatic invariants in the inner belt, which we convert to the observable count rate in a detector at the location of the satellite by using instrument response functions. These comparisons and initial data-assimilation efforts suggest that the model performance can be improved especially during injections of solar protons, and at L-shells above 2.
SM11A-1582
Radiation Belt Drift Shell Modeling for Real-Time and Long Duration Applications: L* a Million Times Faster
Radiation belt modeling and forecasts require accurate calculations of particle drift shells and their spatial/temporal variation which is commonly represented by the third adiabatic invariant, L*. These calculations in realistic geomagnetic fields typically involve three-dimensional numerical integration of the global field. For recent, empirical magnetic field models it can take a long time to calculate L* particularly using more sophisticated models [McCollough et al., 2008]. Because of these long computing times, researchers tend to pick simplistic models over more accurate ones risking large inaccuracies and even wrong conclusions [Huang et al., 2008]. Real-time radiation belt modeling and forecasting requires efficient algorithms without sacrifice of numerical accuracy. Likewise, long-duration calculations (e.g. solar-cycle scales) are impractical when finite element integrations are applied. We will present a newly developed method for calculating accurate L* values up to 106 times faster than the standard integration and interpolation technique. While the technique is applicable for any closed drift shell, we will present results of a detailed validation at geosynchronous orbit where there is extensive data for independent tests of accuracy. We will also present results from validating our prototype against various empirical field models including the TSK03 model [Tsyganenko et al., 2003].
SM11A-1583
Electron Precipitation Loss due to Pitch-Angle Scattering by Whistler-Mode Hiss in Plasmaspheric Plumes
Wave-particle interactions occurring in plasmaspheric plumes can significantly influence particle dynamics in the Earth's inner magnetosphere. Here we analyze electron precipitation loss to the atmosphere due to pitch- angle scattering by whistler-mode ELF hiss in plasmaspheric plumes.Using wave observations and inferred plasma densities from CRRES we analyze plume intervals for which well-determined hiss spectral intensities are available.We then select 14 representative plumes for detailed study,comprising 10 duskside plumes and 4 nonduskside plumes,with local hiss amplitudes ranging from maximum values of above 300 pT to minimum values of less than 1 pT.We estimate the electron loss timescale T due to pitch-angle scattering by hiss in each chosen plume as a function of L-shell and electron energy.We find that pitch-angle scattering by hiss in plumes can be efficient for inducing precipitation loss of outer-zone electrons with energies throughout the range 100 keV to 1 MeV,though the magnitude of T can be highly dependent on wave power,L-shell and electron energy. For 100- to 200-keV electrons,typically T is about 1 day while the minimum loss timescale (T)min is of the order of hours. For 500-keV to 1-MeV electrons, typically (T)min is of the order of days,while (T)min is less than 1 day in the case of large wave amplitude (~100's pT).Apart from inducing direct precipitation loss of MeV electrons,scattering by hiss in plumes may reduce the generation of MeV electrons by depleting the lower energy electron seed population. Comprehensive models of electron dynamics in Earth's inner magnetosphere should incorporate electron precipitation loss induced by ELF hiss scattering in plasmaspheric plumes.
SM11A-1584
Electron Maps for LEO using CEASE/TSX-5 electron data
Maps of the South Atlantic Anomaly (SAA) and high-latitude cutoff rigidities for energetic protons detrimental to satellite operations have previously been produced by the Space Vehicles Directorate of the Air Force Research Laboratory (AFRL/RVBXR) and others. AFRL has since recognized a need for a similar application to detail Low Earth Orbit (LEO) energetic electrons that might also negatively impact operational systems. Current work on this effort, specifically dealing with the outer radiation belt, will be presented. A set of flux intensity maps for electrons is shown for the epoch 2000-2006, based on data from the Compact Environment Anomaly Sensor (CEASE) flown onboard the Tri-Service Experiment-5 (TSX-5) satellite in a 410 km x 1710 km, 69 degree inclination orbit. To eliminate any proton contamination, >10 MeV particles and all particles in the SAA have been removed from the data. Scatter plots of counts/sec versus magnetic latitude are examined to ensure only data for the outer radiation belt is being used. Intensity maps of the integral flux in latitude versus altitude for seven of the instrument channels (0.11 MeV to 6.46 MeV energies) have been constructed. These maps are then compared to the AE-8 and average CRRESELE values and distribution functions examined.
SM11A-1585
Non-adiabatic Effects on Energetic Particles Drifts Near the Dayside Magnetopause
Near the dayside magnetopause, the magnetospheric magnetic field is compressed, resulting in so-called "W-shaped" magnetic field regions where the strength of the field has two local minima at off-equatorial points. When charged particles in the radiation-belts energy range drift through the region, they undergo drift-shell bifurcation resulting in bifurcating shells, also known as Shabansky orbits. In this paper, we analyze violations of the second adiabatic invariant due to drift-shell bifurcation. The effect was previously shown to be small if the magnetic field is symmetric in the north-south and east-west directions, for particles with gyroradii very small compared to the scale size of the magnetosphere. In this paper, we present results showing that if the magnetic field does not possess such symmetry, mainly due to the presence of the IMF By component, the effect becomes significant even for particles with small gyroradii, and we quantify violations of the second invariant for typical magnetospheric and solar wind conditions.
SM11A-1586
Simulations and Observations of Trapped Solar Energetic Particles in the Inner Magnetosphere
A combination of MHD simulations driven by the solar wind and interplanetary magnetic field (IMF) upstream of the magnetosphere and particle tracing calculations in the time dependent electric and magnetic fields from the MHD simulation showed the trapping of solar energetic particles (SEPs) in the inner magnetosphere within geosynchronous orbit. The differential flux of the particles in the inner magnetosphere was computed by using measured upstream differential fluxes to normalize the contribution of the test particles. The calculation results have shown reasonably good agreement with observations in the inner magnetosphere. Also the results indicate that at times the trapped particle population is dominated by particles that were trapped for a short time (less than an hour). Longer term particle trapping and the loss of these trapped particles is correlated with changes in the solar wind dynamic pressure, and the IMF.
SM11A-1587
Solar Cycle Dependence of Relativistic Electrons at Geostationary Orbit
We examined the behavior of relativistic electron fluxes, measured with the GEOS-8 and GOES-10 satellites at geostationary orbit, for the period from 1995 through 2006. With the measured actual electron fluxes, we presented also the values of the electron fluxes computed from our recent model for relativistic electrons at geostationary orbit. The simulation results are very well consistent with the actual fluxes, and both show a strong dependence on solar activity: the relativistic electron fluxes on average tend to be significantly reduced near the solar maximum, though the solar wind parameters that may affect the relativistic electron population, were changed insignificantly. A possible cause for the decrease in relativistic electrons in the outer radiation belt during high solar activity may be a specific regime of the solar wind for these time intervals when the solar wind velocity and density show the fast short-periodic variations that prevent from the acceleration of electrons in the outer radiation belt to high energies.
SM11A-1588
Study of the Influence of the Solar Wind Dynamic Pressure to the Variation of Pressure in the Inner Magnetosphere.
Knowledge about the distribution of plasma pressure is crucial for evaluation of stability of any plasma configuration. The solar wind-magnetosphere interaction affects this distribution in the inner magnetosphere. In this study we used the precipitating particle flux data obtained by the Aureol-3 satellite to reconstruct the radial plasma pressure profiles in the night-side inner magnetosphere with high space and time resolution. The dynamics of these profiles has been compared with the main parameters of the solar wind, inferred from the NSSDC data base. In particular, it was found that the maximum value of the static plasma pressure in the nigh-side inner magnetosphere correlates with the value of dynamic pressure of the solar wind. The position of the maximum is also affected by the solar wind dynamic pressure, being closer to the Earth in case of high dynamic pressure. This fact is important for understanding the dynamics of geomagnetic substorms and storms.
SM11A-1589
Ballooning instability in the near-Earth plasma sheet: Simulations and Observations
In the ionosphere, substorm expansive phase onset begins with the sudden brightening of a pre-existing or new auroral arc. Observational evidence proves that in many cases this arc is on field lines that thread the transition region between dipolar field lines. The objective of this study is to examine the hypothesis that the ballooning instability triggers these substorms. We present the results of direct numerical simulations of the ballooning instability development in the near-Earth plasma sheet mapped onto a high-resolution 3D computational grid. The simulations capture the evolution of the ballooning instability in numerically obtained tail equilibrium configurations calibrated with observational satellite data. We also discuss the implementation details of the numerical schemes used and significant challenges related to the boundary conditions and treatment of the curvilinear magnetic field topology.
SM11A-1590
The sub-auroral electric field as observed by DMSP and the new SuperDARN mid-latitude radars
In this paper we present analyses of the sub-auroral electric field environment as observed from both space and ground. We discuss the dependency of the configuration and strength of the sub-auroral electric field on IMF and geomagnetic activity, longitudinal, seasonal, and solar cycle variability. Primarily, e use ~20 years of electric field measurement dataset derived from the suite of DMSP ion drift meters. A major component of our analysis is correctly specifying the aurora boundary, as the behavior and magnitude of these fields will be drastically different away from the high-conductance auroral oval. As such, we use the coincident particle flux measurements from the DMSP SSJ4 monitors. We also present the solar minimum observations of the sub-auroral flow newly available from the mid-latitude SuperDARN radars at Wallops and Blackstone in Virginia. Preliminary comparisons between these flows and the DMSP climatology are discussed.
SM11A-1591
Quantifying the Accuracy of Inner Magnetospheric Electric Field Descriptions With Data- Model Comparisons for All Intense Storms of Solar Cycle 23
All of the intense magnetic storms (minimum Dst value of < -100 nT) from solar cycle 23 (1996 - 2005) were simulated using the hot electron and ion drift integrator (HEIDI) model. The simulations were run using two electric field descriptions: a Kp-driven shielded Volland-Stern electric field and a self-consistent electric field calculated from the HEIDI-generated field-aligned currents. Of the 90 events, 69 had acceptable boundary condition inputs (nightside plasma data from LANL and upstream solar wind data during the main phase), and are included in the analysis. Storms were classified according to their solar wind driver and means and correlations were examined. Data-model comparisons are made against Dst* time series and dayside LANL plasma data (plasmaspheric plume, hot ion moments and fluxes). It is found, for example, with Dst* comparisons, that the self-consistent electric field simulations are, on average, more accurate than the Volland-Stern-driven simulations. This is especially true for magnetic cloud-driven storm events. For other storm driver categories, the self-consistent results are, on average, more precise than the Volland-Stern results, with less variability in the data-model comparisons from one storm to the next. Other aspects of the data-model comparisons are presented and discussed.
SM11A-1592
Effect of the tail plasma sheet conditions on the penetration of the convection electric field in the inner magnetosphere: the RCM simulations
Transport of plasma sheet particles into the inner magnetosphere is an important source for the ring current. This transport is strongly affected by the large-scale electromagnetic coupling between the magnetosphere and ionosphere. In this study we focus on how the penetration of the plasma sheet particles into the inner magnetosphere, in response to a convection enhancement, depends on the state of the plasma sheet at the time of the enhancement. We have run simulations with the Rice Convection Model (RCM) using the Tsyganenko 96 magnetic field model. Outer proton and electron sources at r = 20 RE, are based on 11 years of Geotail data, and realistically represent the mixture of cold and hot plasma sheet population as a function of MLT and interplanetary conditions. We found that shielding is more efficient for a colder and denser plasma sheet, which is found following northward IMF, than for the hotter and more tenuous plasma sheet found following southward IMF. Although in both cases the pressures and the associated field aligned currents (FAC) in the plasma sheet are similar, the lower auroral conductance, which is computed from the simulated precipitating electron energy flux in these RCM runs, in the colder and denser plasma sheet requires enhanced shielding of the penetration electric field. Therefore, our simulation results indicate that the plasma sheet can penetrate further inside the ring current region in response to enhanced convection if the preceding IMF is southward, which leads to higher auroral conductance and weaker shielding.
SM11A-1593
Characteristics of Storm-time Electric Fields in the Inner Magnetosphere Derived From Cluster Data
We report storm-time electric fields in the inner magnetosphere at L=4-10 and full magnetic local time measured by Cluster. Here we use merged data from the Electron Drift Instrument (EDI) and the Electric Field and Wave (EFW) instrument. Data are analyzed statistically by picking storm periods during March 2001 and November 2007. Superposed epoch analysis with an epoch at Dst minimum is performed to reveal dependence of electric fields on epoch time and spacecraft locations. Strong electric fields are detected right around the Dst minimum for all magnetic local times, even though the data acquisition rate is not always large during these periods. The magnitude of electric fields often increases as L value decreases, although this is not always the case. The data are further examined in terms of the location of the inner edge of plasmasheet electrons and controlling parameters such as geomagnetic indices and interplanetary parameters.
SM11A-1594
Response of the convection electric field on southward turning of the IMF
We have investigated the response of convection electric fields in the inner magnetosphere on southward turning of the interplanetary magnetic field (IMF), and its spatial dependence using the CRRES spacecraft data measured in the inner magnetosphere. When the southward turning of IMF to -20 nT was measured by IMP-8 twice at 3:12 and 5:52 UT, which was accompanied by a storm with the minimum SYM-H of -216 nT, the CRRES spacecraft was located in the dusk inner magnetosphere and detected enhancements of the convection electric field within 1 min after the southward IMF Bz reaches the dayside magnetopause. The amplitude of the electric field is well reproduced by the Weimer model. These results indicate that plasma convection in the inner magnetosphere quickly responds to the energy input from the solar wind to the magnetosphere, and the time variation can be described by simple mapping of two-cell convection in the ionosphere. However, when the spacecraft is located in the midnight sector, convection electric fields do not quickly respond to southward turning of the IMF. CRRES measured a 20 min delay of enhancements of the electric field at 6.6 RE and 21.5 MLT on March 21, 1991. The amplitude is about a half of the Weimer model electric field mapped onto the spacecraft location. A statistical analysis using 165 events of southward and northward turning of the IMF has clarified that the electric field quickly (< 5 min) responds to IMF variations at the earthward of the inner edge of the electron plasma sheet, while it takes more than 30 min in the plasma sheet. This tendency indicates that plasma convection has a different behavior in and earthward of the plasmasheet.
SM11A-1595
Specification of the Earth's Plasmasphere with Data Assimilation
The plasmasphere is an important component of the intricate web of interacting processes which cause and are space weather. It is the medium of propagation for waves which are responsible for acceleration and decay of the radiation belts, it causes surface charging, and even affects orbital decay. Although the time-scales in the plasmasphere are significantly larger than for many other magnetospheric regions, the plasmasphere still exhibits significant dynamics, and capturing these dynamics is important in predicting the effects of the plasmasphere. In this paper we will discuss using data assimilation techniques to model the plasmasphere. In particular we will explore using a simple plasmasphere model (Ober et al., 1997) in combination with ensemble Kalman filtering techniques (e.g. Evensen, 2003). The ultimate goal is to produce a physics-based model in which only unknown external inputs are adjusted to maximize agreement between model and data. We will discuss data sources as well as progress to date.
SM11A-1596
Image-Based Empirical Modeling of the Plasmasphere
A new suite of empirical models of plasmaspheric plasma based on remote, global images from the IMAGE EUV instrument is proposed for development. The purpose of these empirical models is to establish the statistical properties of the plasmasphere as a function of conditions. This suite of models will mark the first time the plasmaspheric plume is included in an empirical model. Development of these empirical plasmaspheric models will support synoptic studies (such as for wave propagation and growth, energetic particle loss through collisions and dust transport as influenced by charging) and serves as a benchmark against which physical models can be tested. The ability to know that a specific global density distribution occurs in response to specific magnetospheric and solar wind factors is a huge advantage over all previous in-situ based empirical models. The consequence of creating these new plasmaspheric models will be to provide much higher fidelity and much richer quantitative descriptions of the statistical properties of plasmaspheric plasma in the inner magnetosphere, whether that plasma is in the main body of the plasmasphere, nearby during recovery or in the plasmaspheric plume. Model products to be presented include statistical probabilities for being in the plasmasphere, near thermal He+ density boundaries and the complexity of its spatial structure.
SM11A-1597
Plasmasphere from the Moon
We have succeeded in observations by the Telescope of Extreme Ultraviolet (TEX) aboard Japanfs lunar orbiter KAGUYA to characterize the evolution of the near-Earth plasma torus. The view afforded by the KAGUYA orbit encompasses the plasma torus in a single exposure, enabling us to examine for the first time the globally-averaged properties of the torus. We focus on a study period that began with a moderate erosion event, and follow the plasma refilling from the upper atmosphere for a period of 3 days. The refilling rate (the expansion rate of the cold dense plasma onto the equatorial plane) ranges from approximately 1600 km per day to 4800 km per day. A flux transfer event was identified from the gside viewh of the Earth, in which cold dense plasmas (90 cm-3) on geomagnetic flux tube was transferred to the outer magnetosphere of the Earth. This is called gGeoscience from the Moonh.
SM11A-1598
Observation of the Plasmaspheric Depletion and Refilling: Comparison Between ULF Waves and IMAGE-EUV Measurements
In order to study depletion and refilling of the plasmasphere, we studied magnetic storm events using two different measurements. The first way is cross-phase analysis of Ultra-Low Frequency (ULF) waves. Measurements of the eigenfrequency of geomagnetic field lines can provide information on the plasma mass density near the equatorial plane of the magnetosphere. Data of ULF waves from an extended meridional array of ground magnetometers therefore allows the radial density distribution, and its temporal variation, to be remotely monitored. Using cross-phase analysis of ground magnetometer array data, we studied temporal variation of the plasma mass density in a range of L shells and determined the depletion and subsequent refilling during the magnetic storms. The second way is analysis of the Extreme Ultraviolet (EUV) images from a polar orbit. He+ ions scatter light at its resonance wavelength of 30.4 nm. The EUV camera on the Imager for Magnetopause-to-Aurora Global Exploration satellite recorded its brightness and mapped the distribution of He+ ions in the plasmasphere. Using the global images of the plasmasphere, we observed inward motion of the plasmapause driven by the southward turning of the interplanetary magnetic field. We further studied temporal variation of He+ density in flux tubes which are fixed on several ground-based points. In this paper, we will compare these two measurements and discuss the results in the context of (i) the location of ions loss into the open field, (ii) supply and hold of ions into depleted flux tubes, (iii) different of movements between ion species.
SM11A-1599
Density and Magnetic Field Structure in the Plasmasphere: Comparison Between CLUSTER Data and Models
The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. This allows to study the geometry and orientation of its overall density structure and magnetic field distribution. We present several CLUSTER plasmasphere crossings for which we compute the four-point spatial gradient of the electron density (WHISPER data) and of the magnetic field strength (FGM data), and we compare the direction of both gradients with the local field vector. We compare our CLUSTER results with models of the density and of the magnetic field inside the plasmasphere. We discuss in particular the density and magnetic field distribution along and transverse to field lines.
SM11A-1600
MAGNETOSPHERICALLY REFLECTED CHORUS WAVES CAPTURED BY THEMIS
Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves observed in the radiation belts of the Earth magnetosphere. Chorus propagates from its well localized source in the vicinity of the magnetic equator to polar regions roughly along magnetic field lines and can be reflected at low altitudes. After reflection, wave packets can return to the equatorial plane region. The characteristics of the reflection process are very important for the correct description of wave-particle interaction. We focus our study on the properties of the reflected chorus emissions registered by the THEMIS spacecraft Search Coil Magnetometer (SCM) and Electric Field Instrument (EFI) at low magnetic latitudes. Three axis waveform measurements of SCM and EFI in the burst mode cover the same frequency bandwidth, from 0.1 Hz to 4 kHz, in the ULF/ELF frequency range. Most of the measurements in this mode were carried out in the regions of L greater then 7. Typical time intervals of measurements in the burst mode were less then 2 minutes. Using the measurements of the electric and magnetic field fluctuations we determine the direction of the Poynting flux and wave vector distribution for direct and reflected waves. The reflected chorus emissions captured in the vicinity of the magnetic equator have discrete structure roughly similar to direct chorus structure, however the amplitude of the reflected signal is significantly (ten - thirty times) smaller. Reflected emissions observed by the particular spacecraft have frequency shift with respect to chorus propagating from magnetic equator. For each direct and reflected chorus registered event we model chorus propagation and reflection by means of ray-tracing technique employing WHAMP - based geometrical optics tracer. Ray tracing study allowed us to reconstruct chorus source region and to explain observed frequency shifts and propagation characteristic. Typically reflected waves return to magnetic equator plane with wave vector oriented nearly parallel to the field lines.