SM11A-0304
The Statistics of Foreshock Cavities Results of a Cluster Survey
Kinetic processes occurring upstream of the terrestrial bow shock can greatly perturb the parameters of the Solar Wind incident on the dayside magnetosphere. Foreshock cavities are believed to form when isolated magnetic field bundles connect to to quasi-parallel bow shock. This allows energetic ions to stream back against the Solar Wind flow excavating depressions in density and magnetic field magnitude. It has been suggested that these foreshock cavities may be the most important source of transient events in the outer dayside magnetosphere and high-latitude ionosphere. We present the results of a survey of foreshock cavities conducted with Cluster II magnetic field, plasma and energetic particle instruments. Cavities were observed at a rate of almost one per day when Cluster was upstream of the bow shock. Statistically, there is no significant difference between the solar wind before and after the cavities: they do occur on isolated bundles of flux. Mapping the observed positions of foreshock cavities against previously reported boundaries of the contiguous foreshock yields a puzzling result.
SM11A-0305
THEMIS observations of a Hot Flow Anomaly at the Earth's bow shock and its impact on the magnetosphere
Hot Flow Anomalies are generated at the bow shock by otherwise unremarkable discontinuities in the solar wind magnetic field (measured at 1AU). They drastically reduce the solar wind ram pressure on minute timescales, and are thought to be responsible for a variety of magnetospheric signatures. Despite their intrinsic interest as a plasma physics phenomenon, and their impact on space weather prediction, a number of questions remain concerning thermalization mechanisms, occurrence rates, and their overall impact on the magnetosphere. Here, we present THEMIS observations of a Hot Flow Anomaly (HFA) at the Earth's bow shock on 4 July 2007 at 10:26UT. At this time, the five THEMIS spacecraft were in a configuration unique to the first dayside season; three spacecraft were separated by a few hundred kilometers with the other two 1Re up and downstream. At the time of observation, THEMIS A was upstream of the bow shock, with the other spacecraft in the magnetosheath; this is a rare example where the event was observed on both sides of the bow shock. We show that THEMIS A observed classical HFA signatures; we use field and particle data to study the orientation and motion of the underlying discontinuity and examine in new detail the plasma thermalization mechanisms inside the HFA. Data from the other THEMIS spacecraft are used to study the evolution of the HFA in the magnetosheath. We also calculate the impact of the HFA on the magnetopause, and present THEMIS ground based data, complemented by other datasets, showing its impact on the magnetosphere as a whole.
SM11A-0306
Cluster observations of the Earth's quasi-parallel bow shock
Cluster observations of the Earth's quasi-parallel shock are used to investigate properties of the transition and the role of magnetic pulsations in the shock process. Previous studies have shown that the parallel shock is both extended in space and rapidly varying in time. Embedded within it are magnetic pulsations that grow from upstream waves and are thought to play a key role in the thermalisation process. We use crossings at small spacecraft separations to show that pulsations grow on a timescale of only a few seconds. We then use an example of a shock crossing when the spacecraft were a few thousand kilometers apart to demonstrate that the transition was, in this case, confined to a distance of less than 2500 km. In particular, in the context of data showing that the overall extent of the pulsations exceeds 1000 km, this suggests that the thickness of the shock layer over which the bulk of plasma thermalisation occurs is narrow, containing only one or at most a few pulsations. The small scale spatial properties of structures within the shock are difficult to extract independently of their time evolution, but we present a crossing with a favourable tetrahedron formation at which two pairs of spacecraft observed the same magnetic signatures simultaneously. We show that signatures of these pulsations are consistent with their refraction as they are convected anti-sunwards, as predicted by simulation work, and that they are coherent over a distance of at least 1300 km parallel to the expected shock surface.
SM11A-0307
Cluster Observations of Scales in the Quasi-perpendicular Collisionless Shocks
The scale of the collisionless shock is important to study the shocks because it is directly connected with the nature of the shock and with its formation due to the balance between the steepening of a nonlinear waves in the plasma and some counteracting process. The shock scale is also one of the key parameters to determine the acceleration of the particles in astrophysical shocks. In this paper, we analyze a number of bow shocks observed by magnetic field measurement by Cluster satellites. Several different methods are used to determine accurately the shock normal directions such as based on co-planarity theorem, minimum variance analysis, modelled normal, and timing difference between the satellites. Experimentally derived shock scales based on the accurately estimated shock normal directions and velocity are compared with the electron and ion scales such as inertial length and convected gyro-radius for different plasma conditions (e.g. Mach number) to determine predominant formation process of the shock.
SM11A-0308
Multipoint Observations Of Ions In The Energy Range 30 - 90 KeV Upstream Of Earth's Bow Shock.
We used multipoint observations by the four Cluster spacecraft during time periods when the spacecraft separation was between 1 and 1.5 Earth radii to study diffusive transport in the upstream region and the efficiency of ion acceleration at the bow shock. We determined spatial gradients by measuring partial proton intensities in the energy range 27.7 keV to 92.2 keV as a function of distance from the bow shock along the magnetic field, using data from the RAPID (Research with Adaptive Particle Imaging Detectors) experiments onboard Cluster 1 and Cluster 3. Combining RAPID data with CIS data at lower energies (Kis et al., 2004), we find that the e-folding distance increases from lower to higher energies, with an approximately linear dependence on energy. Assuming that upstream diffusion is balanced by downstream convection we determine the spatial diffusion mean free path parallel to the magnetic field as a function of energy.
SM11A-0309
Evidence of quasi perpendicular shock front nonstationarity from CLUSTER data: comparative approach with numerical simulation results
Both numerical simulations and experimental observations (CLUSTER) have evidenced that the front of quasi perpendicular shocks may be strongly stationary or nonstationary. Simulations have evidenced several different mechanisms responsible for this nonstationarity both on macro- (ion) and micro- scales and but no detailed comparison has been performed with experimental data until now. The fact that several mechanisms can coexist together make a clear diagnosis quite difficult. On the other hand, multi satellites CLUSTER mission reveals to be helpful for clarifying the situation. The present work focuses on experimental CLUSTER data where macroscale nonstationarity is evidenced and identified as being due to the shock front self reformation driven by the accumulation of reflected ions. Detailed analysis is performed based on many criteria accumulated from a collection of previous 1D and 2D PIC simulation (changes both in ramp-foot scales and typical changes in the local ion distribution function). In particular, it accounts the surprising experimental results where the shock ramp can be very thin and access to a few inertial electron lengths only. Present detailed results are also completed by an additional statistical analysis. These experimental data confirm that the shock front can be nonstationary and that the identified responsible process strongly competes with another self reformation process driven by nonlinear dispersive waves activity.
SM11A-0310
Cluster Observations of Magnetosheath Plasmoids
We use Cluster multi-point measurements to identify magnetosheath plasmoids, which we define as localized plasma blobs with a higher density than the background plasma, and some associated variation in the magnetic field. Several criteria are used to discriminate between blobs convecting together with the plasma flow from signatures associated with motion of the magnetopause or bow shock. Having identified such plasmoids, we determine their geometry along and perpendicular to the plasma flow and magnetic field, and their orientation relative to the bow shock and magnetopause. We also determine the dynamic beta value (the ratio of the kinetic and magnetic energy densities) and ratio of the scale size perpendicular to the flow to the ion gyro radius (evaluated using the drift velocity). These are critical parameters for determining the penetration of such plasmoids into the magnetosphere during impulsive penetration events. Determination of these parameters enables a comparison with theoretical and laboratory results, showing if typical plasmoids can penetrate into the magnetosphere, and what type of penetration mechanism will be likely.
SM11A-0311
THEMIS Observations of Mirror Mode Structures in the Magnetosheath
Mirror modes structures are commonly observed in planetary magnetosheaths, cometary sheaths, and other plasmas with anisotropic temperature distributions. Here we present the preliminary analysis of a wave train event observed by the five THEMIS spacecraft on May 19, 2007 from 02:40 to 02:50 UT. During this event, all of the spacecraft returned high time resolution magnetic field and plasma data. All five spacecraft observed compressional fluctuations in the magnetic field that are in anti-phase with the plasma pressure fluctuations, as is expected for mirror modes. The two spacecraft closest to the Earth, and presumably closest to the magnetopause, observed magnetic field dips (decreases relative to the background field). The other three spacecraft were closely spaced approximately 2.5 RE further from the Earth. These more distant spacecraft observed a train of quasi-periodic field fluctuations with possibly a few magnetic peaks (increases relative to the background field) near the end of the event. We will present the plasma distribution functions and anisotropies for each of the spacecraft before, during, and after the event and relate them to the type of magnetic structures observed. In addition, we will discuss how these data compare to our observations of mirror mode structures in the Jovian magnetosheath.
SM11A-0312
Movement of magnetospheric boundaries in response to an interplanetary shock: Themis contribution
Recently, several studies have been devoted to the interaction of interplanetary shocks (IPS) with the Earth's magnetospheric boundaries - the bow shock and the magnetopause. Non-stationarity of interaction of these large structures requires multi-spacecraft observations with good space and temporal coverage. The first half-year after the Themis fleet launch offers rich multi- spacecraft observations of the bow shock and magnetopause structures and their reaction to the interplanetary shocks with very suitable space configuration. In the contribution we analyze selected interplanetary shocks observed by multiple spacecraft in the solar wind and their passage through the bow shock - magnetosheath - magnetopause structure. Themis multi-spacecraft measurements allow us to study the deformation of the IP shock and movement of the magnetospheric boundaries, estimate their orientation and speed and compare them with various theoretical and simulation models.
SM11A-0313
The altered solar wind - magnetosphere coupling during low Mach number CMEs: Highlights from MHD simulations
In this paper we illustrate some expectations for the interaction between low Mach number solar wind (often characteristic of CMEs) and the magnetosphere. A result of the low (Alfven) Mach number solar wind is the formation of a low thermal beta magnetosheath downstream of the bow shock. Because of such properties, magnetic forces become prominent and largely rule the properties of the magnetosheath flow and of its coupling with the magnetosphere. We illustrate such effects by use of spacecraft data and MHD simulations for such a low-beta magnetosheath case. We generally predict (a) high-velocity flow jets in the magnetosheath adjacent to the magnetopause, (b) reduced flows in other regions of the magnetosheath, (c) asymmetric shapes for the magnetopause, (d) polar cap saturation and Alfven wings, and (d) anomalous magnetic field stretching of the dipolar portions of the magnetosphere, which we relate to the occurrence of sawtooth events. These effects have generally been overlooked and will deserve both small- and large-scale multi-spacecraft observations to be investigated.
SM11A-0314
Travel time of impulsive signals in the magnetosphere: Modeling and observations
The calculation of travel time for impulsive signals has many uses in magneotspheric physics, such as understanding the propagation of sudden impulses, helping identify the causes of substorm onsets, and inferring the global plasma density and temperature from inverting the signal arrival time at multiple locations. Because impulsive signals can propagate rapidly as MHD waves, it is necessary for calculations and observations to have a time resolution of the order of one sec to yield useful results. To avoid time-consuming global simulations at this high cadence, we have developed a numerical model that focuses on wavefront construction to compute the travel time of impulsive signals. Following the Huygens principle, the algorithm allows the user to define the shape of the initial impulse and tracks the first arrival of wavefront in two dimensions. We will demonstrate, in both equatorial and meridian planes, how the wavefront of sudden impulses propagates tailward from the dayside magnetopause and how the wavefront of substorm onsets in the magnetotail evolves as it propagates earthward. We compare our calculations with the magnetic field observations from the armada of satellites, including Polar and THEMIS, in orbit, as well as the data from various ground magnetometer networks such as McMAC, THEMIS-GBO/EPO, and CARISMA.
SM11A-0315
Magnetospheric Variations Resulting From the Propagation of an Interplanetary Shock
When an interplanetary shock interacts with the bow shock and magnetopause, its properties are modified and new discontinuities appear in the magnetosheath. Using results from a global magnetospheric MHD code, we study the propagation of a forward fast shock in the magnetosphere. We find that this forward fast shock reflects somewhere inside the magnetosphere and investigate the location of the reflecting boundary. An additional one- dimensional model has been developed to study interaction of the fast shock with the plasmapause. The forward and reflected shocks generate significant variations of the magnetic field and plasma parameters in the magnetosphere, which are confirmed by observations. The reflected fast shock passes through the magnetopause and magnetosheath and finally reaches the bow shock, where it forces the bow shock to move outward.
SM11A-0316
THEMIS Multi-Spacecraft Survey of Reconnection and Flux Transfer Events at the Magnetopause
The pearls-on-a-string formation of the five THEMIS spacecraft in a near-equatorial orbit provides unprecedented opportunities to study the spatial structure and temporal evolution of reconnection and flux transfer events at the subsolar and flank magnetopause. Probes B, C, D are at separations comparable to the magnetopause layer thickness (100-500km), while the two outer probes, A and B, are at 1-2Re scale separations, providing the opportunity to monitor the pristine magnetosheath and magnetosphere. We present events observed with multiple THEMIS probes traversing different parts of the FTE core and the reconnection layer. We survey of the occurrence rates of such phenomena as a function of the solar wind plasma and magnetic field conditions.
SM11A-0317
3D Global Hybrid Simulation of Flux Transfer Events at the Dayside Magnetopause
Magnetic reconnection at the dayside magnetopause is simulated using a 3-D global hybrid code, in which ions are treated as fully-kinetic particles, while electrons are treated a massless fluid. The simulation domain contains mainly the dayside plasma regions from r=4-25\ RE, and the simulation is performed for cases with a southward interplanetary magnetic field (IMF). Both quasi-steady reconnection structure and flux transfer events (FTEs) are obtained. (1) The magnetic field and corresponding plasma structures of FTEs at various latitudes and longitudes are analyzed. In FTEs, the twisted magnetic flux tubes extend a finite length in the east-west direction, with magnetosheath ions trapped in the tube. The spatial profiles of FTEs on either the magnetosheath or the magnetospheric edge of the reconnected flux tubes resemble those observed by satellites. (2) The growth, evolution, and propagation of the FTEs and their resulting waves in the magnetosphere are investigated. (3) D-shaped as well as multi-beam distributions of the transmitted magnetosheath ions are obtained in the magnetopause. The ion particle distribution and ion transport in the magnetopause reconnection are studied. (4) The magnetic field structure in the magnetopause FTEs is compared with that in 2-D reconnection.
SM11A-0318
Localized Reconnection and Plasma Structures at the Magnetopause
The magnetopause current sheet is known to have a thickness comparable to an ion gyro-radius/skin depth and such processes while neglected in MHD are the focal point to multi-spacecraft missions such as THEMIS and Cluster. Multi-fluid/multi-scale modeling is used to examined the structure of magnetopause down to a resolution of 200-300 km. Attention is focused on southward interplanetary magnetic field (IMF) and when there is a non- zero component IMF By. It is shown that with the inclusion of ion gyro-radius/skin depth the reconnection on the magnetopause is very patchy, with a significant (10-20 nT) core magnetic field being generated by the Hall term in the generalized Ohm's law, that is orthogonal to the incident IMF (even when IMF By is non-zero). This magnetic field component means that the question of whether the reconnection is parallel or component is not well posed because the core magnetic field modifies the overall structure of the magnetopause. It is shown though that the strongest acceleration of particles occurs within the vicinity of the subsolar region through with the reconnection being localized to structures less that 0.5 Re in width, a few Re in breadth and varying in time and space. A comparison of the signatures of this reconnection is made between equator and polar orbiting spacecraft.
SM11A-0319
Two-dimensional MHD reconstruction for studying magnetic reconnection at the magnetopause
A new method for the reconstruction of two-dimensional, coherent structures in a space plasma is developed, using the ideal MHD equations. The reconstruction algorithm is similar to that used in Grad-Shafranov (GS) reconstruction, which is to solve the equations as a spatial initial-value problem. It is benchmarked with an exact analytical solution, in which the pressure, density, all three magnetic field and flow components are functions of radius only, and in which isentropic flow at an angle to the magnetic field is present. The reconstruction results show good agreement with the exact solution, with acceptably small errors within a strip of substantial width around the spacecraft trajectory. The reconstruction scheme is then applied to previously studied magnetopause reconnection events seen by Cluster. In contrast to the case of GS reconstruction, which is performed in the deHoffmann-Teller frame, we now use a frame co-moving with the X-line, in which the axial electric field should ideally be constant. The new reconstruction results are generally consistent with earlier interpretations. We also examine the possibility of including the Hall term in Ohm's law by use of an iterative procedure.
SM11A-0320
Evidence for Magnetic Reconnection in Kelvin-Helmholtz Vortices
While the Cluster spacecraft (separated by 2500 km) were skimming the dusk equatorial magnetopause during a period of northward interplanetary magnetic field and of large solar wind speed, all the plasma and magnetic field data displayed a periodicity of several minutes. The comparison between the observations and published MHD simulations allowed to interpret the Cluster data in terms of passages through fully evolved Kelvin-Helmholtz vortices. Evidence for reconnection occurring within the vortices and for plasma transport across the vortices, detected by the CIS plasma analyser, will be discussed.
SM11A-0321
Signatures of Resonant Mode Conversion at the Magnetopause
At low frequency, the MHD equations describe coupling between the compressional and Alfvén wave near the Alfvén resonance. Coupling between the modes occurs when there is a gradient in the Alfvén velocity at the location where the wave frequency matches the Alfvén resonant frequency (k\parallel VA). However, the modes are coupled only in the case where there is a wave perturbation (ky) perpendicular to the magnetic field (z) and to the direction of the Alfven velocity gradient (x). At higher frequency, f > 0.1 fci) coupling may also occur due to the polarization drift. We solve the full fluid wave equations for a 1D magnetopause equilibrium model to determine the efficiency of mode conversion including coupling due to (f/fci) effects and ky. Wave absorption is quantified by comparing the incoming and reflected compressional wave Poynting fluxes for numerical solutions obtained by solving the corresponding difference equation on a grid with appropriate boundary conditions. For the magnetopause equilibrium model, we find that mode conversion efficient peaks where (ky VA/ ω) ~ 0.4 and f/fci ~ 0.3 with nearly total absorption. The efficiency is significantly weaker (10%) in the limit f \ll fci as in the MHD approach. We also discuss the effect of heavy ions on the mode conversion process. We compare the mode conversion efficiency with hybrid simulations and discuss kinetic effects on the mode conversion process. Finally, we consider these results in the context of magnetopause wave measurements and discuss implications for particle transport. http://w3.pppl.gov/~jrj/magnetopause.html
SM11A-0322
Hybrid Simulation of Mode Conversion at the Magnetopause
A 2-D hybrid simulation is performed for interaction between an incident compressional wave and the magnetopause current layer, across which the plasma density gradually decreases and magnetic field strength increases from the magnetosheath to magnetosphere. The simulation is carried out in the xz plane, where x is along the magnetopause normal. The initial magnetic field is assumed to be in the yz plane, with an arbitrary tilt angle θ relative to z. A fast-mode compressional MHD wave is launched from the magnetosheath boundary, propagating toward the magnetospause with kx>0 and kz>0. As the incident wave propagates to the magnetopause and thus encounters a gradiant in the Alfven speed VA, the compressional wave is found to mode convert to the short wavelength (k\perp ρi ~ 1) kinetic Alfven waves (KAWs) at the location where the Alfven resonance conditon is satisfied, as predicted by theories. In addition to the transverse magnetic field and velocity perturbations, a parallel electric field is generated locally in the KAW due to \nabla pe. The absorption rate of the incident wave is estimated by calculating the change of Poynting fluxes averaged over the wave period. The simulation is performed for cases with various field angle θ, electron-to-ion temperature ratio Te/Ti, and wave vector, amplitude, and frequency ω/(k\parallel VA) of the incident wave. The associated ion heating and diffusion are also investigated. The resulting properties of mode conversion are compared with a theoretical model that solves an analytic solution of the full fluid wave equations in a system containing an equilibrium structure of the magnetopause (see companion paper by Johnson and Lin).
SM11A-0323
Kinetic Alfven waves at the low-latitude boundary layer
In the LLBL for northward IMF, plasma is usually found to be "mixed" with both a low energy magnetosheath component and high energy magnetospheric component. Recent observations have found dawn-dusk asymmetries in the density and temperature of the ion populations, and in situ particle distributions show perpendicular ion heating of low energy ions on the dawnside associated with strong compressional wave activity in the magnetosheath. It is the purpose of this study to investigate energy transport processes that would occur due to mode conversion from compressional waves to kinetic Alfven waves (KAWs) at the LLBL. Using a time- dependent fluid simulation code, we show how such mode conversion at the sharp boundary layer occurs for continuous and impulsive incoming compressional waves from the magnetosheath. In addition, by adopting Kelvin-Helmholtz (KH) vortex structure at the boundary layer, we also examine the wave properties in the small scale plasma structure. Time histories of electric and magnetic field at different spatial locations and wave spectra are presented. The role of KAW on the ion perpendicular heating at the dawnside LLBL is discussed. The results are expected to help further understanding of observed ULF waves by multiple satellites passing through boundary layers.
SM11A-0324
Energetic Ion Bursts and Associated Polar Rain Electron Flux Enhancements During Magnetic Cloud Passage: A WIND-POLAR-DMSP Study
We present correlated Wind-Polar -DMSP observations of precipitation features in the northern, summer polar cap obtained during the passage of the sheath region of an interplanetary magnetic cloud. The sheath was characterized by an strong magnetic field whose direction spanned a wide range of orientations. Distinct field and flow discontinuities allow us to interpret a series of energetic (maximum E ~20 kV) ion bursts, flowing predominantly against the field direction and which are accompanied by enhanced polar rain electron fluxes. The underlying convection pattern is inferred from DMSP passes. Generating mechanisms involving overdraped lobe/dual reconnection are examined in the light of the observations.
SM11A-0325
Field-Aligned Current Dynamics and Its Dependence on Solar Wind Conditions
Field-aligned currents (FACs) are the currents flowing into and out of the ionosphere which connect to themagnetosphere. They provide an essential linkage between the solarwind-magnetosphere system and the ionosphere, and the understanding of these currents is important for global magnetosphere dynamics and space weather prediction. The three spacecraft ST5 constellation provides an unprecedented opportunity to study in situ FAC dynamics in time scales that can not be achieved by earlier studies with single spacecraft studies or large-spaced conjugate spacecraft studies. In this study, we use the magnetic field observations during the whole ST5 mission to study the dependence of FAC dynamics on solar wind conditions. FAC peak current densities show very good correlations with some solar wind parameters, including IMF Bz, dynamic pressure, Ey, and some IMF angles, but not with other parameters. Instant FAC speeds show generally much weaker dependence on solar wind conditions comparing to FAC peak current densities. This obvious dislinkage between FAC peak current densities and speeds implies that FAC peak current densities are more controlled by solar wind conditions, while FAC speeds are more strongly controlled by internal magnetosphere-ionosphere processes which can not be substantially representated by the conventional solar wind parameters tested in this study.
SM11A-0326
The Auroral Acceleration Region: FAST Observations in the THEMIS Era
More than 11 years after being launched in August 1996, the FAST spacecraft continues to acquire data within the auroral acceleration region (AAR). With the launch of the THEMIS spacecraft and the building of the associated ground-station network, these observations take on added significance. In particular the THEMIS spacecraft provide observations of the "drivers" of the field-aligned currents, Alfvén waves, and plasma populations that ultimately result in the emissions and magnetic field perturbations observed by the THEMIS ground-stations, but only after the particles and fields have been processed through the AAR. FAST is ideally suited to provide the observations of the AAR, where the electromagnetic energy flux associated with large-scale field-aligned currents and Alfvén waves is partially converted to particle energy flux (e.g., inverted-V and wave-accelerated electrons). FAST also observes the consequences of these energy fluxes as ionospheric plasma outflows. As part of the instrument commissioning phase the THEMIS spacecraft were fortunate to observe a substorm on March 23, 2007. Shortly after the substorm onset FAST flew through the AAR. FAST observed a strong westward flow channel, together with typical signatures of the AAR. The flow channel was bounded by a pair of field-aligned currents. A similar signature was observed at THEMIS altitudes, but this appeared to be associated with the passage over the THEMIS spacecraft of the western most edge of the substorm current-wedge system. In this presentation we explore how field-aligned currents and related particle signatures as observed at FAST are related to magnetospheric dynamics as observed by the THEMIS spacecraft and ground-stations.
SM11A-0327
Quantification of the Precipitation of Outer Radiation Belt Relativistic Electrons
Quantifying critical physical processes controlling relativistic electron dynamics in the Earth’s outer radiation belt is the prerequisite for the development of space weather models. It is well known that a balance of competing source and loss processes determines the radiation belt electron dynamics. Although recent progress has been made on source processes, a complete model prediction of relativistic electrons still requires quantitative determination of loss processes, especially the effects of precipitation into the atmosphere due to wave-particle interactions. We will perform a statistical study of the decade-long multi-satellite electron observations from SAMPEX, LANL GEO and GPS. First we will develop an empirical model that describes the precipitation as functions of electron energy, longitude, latitude/L shell, local time, seasons, storm phases and sunspot phases. Then by comparing the decay rate of trapped electrons observed at the equatorial plane to the precipitation rates observed at low altitude, we can quantitatively determine the role of precipitation on the loss of relativistic electrons, especially for the portion of radiation belt with L>4.
SM11A-0328
Multispacecraft observations of chorus dispersion and source location
Measurements from the Polar spacecraft have put an upper limit of a few thousand kilometers to the size of the magnetospheric chorus generation region along the magnetic field line in agreement with earlier theoretical estimates. Multipoint observations from the four Cluster spacecraft reveal that a single chorus wave packet can appear differently between spacecraft. One spacecraft observes a chorus element which is frequency shifted and time delayed relative to another. Since the dispersion relation for chorus waves is known, these differences provide a new opportunity to refine the parallel dimension of these source regions. A cross-correlation analysis is used to identify common chorus events between the Cluster spacecraft and to quantify their timing delays. The timing arrival differences and frequency accessibility are then simulated with a ray-tracing technique. Locations in the magnetosphere where the simulated frequency shift and time delay match the observed frequency shift and time delay for a single chorus event are determined as possible source regions. The identified source locations for multiple chorus events are presented as is a preliminary statistical survey of source emission characteristics of these regions.
SM11A-0329
Extreme Drainage of Plasmasphere as Ionosphere Strives to Replenish
We present a case study of a global scale restructuring of plasmasphere under an extreme solar wind condition using measurements from THEMIS, Polar, ACE spacecraft, and ground magnetograms. In a case when a coronal mass ejection (CME) with number density 40-60 cm-3 and dynamic pressure 6-12 nPa interacted with the Earth's magnetic field, we found that a section of plasmasphere disappeared from its usual location as observed by THEMIS, in association with unusual enhancements of ionospheric outflows in the polar cap regions as observed by the Polar spacecraft. In the meantime, large detached regions of dense ions and electrons of plasmaspheric like characteristics were observed along the path of THEMIS as it approached or encountered the magnetosheath plasma at the magnetopause. The event illuminates the formation/erosion of the plasmasphere as well as the physical processes involving the more direct interaction of solar wind and ionospheric plasmas at the magnetopause. We will estimate the rate of the ionospheric outflow and its contribution to the recovery of the plasmasphere and interpret how the plasmaspheric/ionospheric plasma interacts more directly with solar wind plasma at the magnetopause.
SM11A-0330
Antarctic Ground-based Observations During Selected THEMIS Satellite Event Studies
In Antarctica, the Polar Experiment Network for Geospace Upper-atmosphere Investigations (PENGUIn) team operates a suite of optical and radio wave imagers, magnetometers, riometers, and ELF-HF receivers at South Pole and McMurdo stations, as well as from the Automated Geophysical Observatories (AGOs) on the Antarctic polar plateau. These stations span locations from the auroral zone to deep in the polar cap. Employing data from this array, ground-based observations during several THEMIS satellite event studies will be discussed. These include: a flux transfer event (FTE) on May 20, 2007; a solar wind shock propagation on June 21; a hot flow anomaly on July 4; high latitude optical events on August 8th and 10th; and substorm events on March 23rd and 24th. Of particular interest is the FTE event where the magnetometer Z-component appears to have the signature of a line current passing overhead at South Pole and a sharp cutoff of 2-4 kHz VLF signals is also observed at the time the current moved overhead. Cosmic noise absorption and 630 nm optical signals also began about the time the currents moved overhead, and then tracked the H-component of the magnetometer. The enhanced optical signal was coincident with increased ionosphere currents as shown by the H-component. In this presentation, a southern hemisphere contextual description of this event, and the others listed above, will be presented. http://www.antarcticspacescience.org
SM11A-0331
Cluster Active Archive products and multipoint magnetospheric investigations
The four-satellite Cluster mission investigates the small-scale structures (in three dimensions) of the Earth's plasma environment, such as those involved in the interaction between the solar wind and the magnetospheric plasma, in global magnetotail dynamics, in cross-tail currents, and in the formation and dynamics of the neutral line and of plasmoids. The Cluster Active Archive CAA (http://caa.estec.esa.int/) contains the entire set of Cluster high resolution data and other allied products in a standard format. The CAA currently has data from most of the Cluster instruments for at least the first three years of operations (2001-2003). The coverage and range of products is being continually improved with more than 200 datasets available from each spacecraft including high-resolution magnetic & electric DC fields and wave spectra; full 3D electron & ion distributions from a few eV to hundreds of keV; and various ancillary & browse products to help with spacecraft and event location. The data archived are (1) publicly accessible, (2) of the best quality achievable with the given resources, and (3) suitable for science use and publication by both the Cluster and broader scientific community. The presentation contains examples of user friendly services of the CAA for searching and accessing these data and ancillary products and of online capabilities of the system.
SM11A-0332
THEMIS Orbits and Data at SPDF
The Space Physics Data Facility (SPDF) within Goddard's Heliospheric Physics Laboratory has worked closely with the THEMIS team to adapt SPDF's orbit and data tools/services to the special needs of the THEMIS mission. We will explain and demonstrate these systems that now include Level-2 data from the THEMIS ground and space instruments and the latest orbits and orbit predictions. CDAWeb now serves current FluxGate Magnetometer (FGM), ElectroStatic Analyzer (ESA), Solid-State Telescope (SST), Electric Field Instrument (EFI) and Search Coil Magnetometer (SCM) data from all 5 THEMIS spacecraft and magnetometer data from 20+ THEMIS ground stations. CDAWeb displays include line plots and spectrograms and outputs are now also available in PDF and Postscript. The latest version of the 3-D interactive orbit viewer now includes the capability to follow the magnetic ground tracks of the THEMIS satellites and their relation to the THEMIS ground stations making it an excellent tool for the coordinated analysis of THEMIS space and ground data. The SSCWeb system allows complex queries involving magnetic conjunctions between satellites and between satellites and ground stations, and region occupancy. Several THEMIS-specific queries were set up and saved and are now available for easy (one click) usage. THEMIS is utilizing the Common Data Format (CDF) for its data products, a format developed and maintained by SPDF and the backbone of the CDAWeb system. A number of CDF routines were customized for most efficient use by the THEMIS team. http://spdf.gsfc.nasa.gov/