SM14A-01
Large Dayside Geosynchronous Magnetic Field Compressions: Model Expectations vs. Observations
The geosynchronous magnetic field has been measured routinely for nearly 40 years. It responds to the magnetosphere's major current systems including the magnetopause current, the ring current, field-aligned currents, and the tail current. As a consequence, these measurements are valuable for probing many aspects of solar wind-magnetosphere coupling. In this presentation we will show puzzling observations of large-amplitude dayside magnetic fields at geosynchronous orbit that aren't easily explained by the observed solar wind conditions. We will present an overview of the geosynchronous magnetic field variations and the related solar wind conditions. Then we compare the observations to both empirical models and results from the Lyon-Fedder-Mobarry global scale magnetospheric model. This work has two important outcomes. First, by making these model-data comparisons, we are able to validate the models' performance during these particular conditions. And, second, the diagnostic capabilities of the models enable an assessment of the dominant current systems that leads to the distinctive signatures measured in geosynchronous orbit.
SM14A-02
Spatio-temporal Features of Magnetic Storms Inferred From a High-resolution Empirical Magnetic Field Model and Birkeland Current Data
We report results of empirical modeling of the geomagnetic field and underlying current systems during magnetic storms using the new high-resolution dynamical empirical magnetic field model TS07D and Birkeland current images obtained with the help of the Iridium constellation. Many details of the morphology and dynamics of magnetic storms inferred from the new empirical magnetic field model are found to be consistent with earlier results of the ring current modeling and observations, which form now a coherent picture of the whole phenomenon. New findings include the double partial ring current during the main storm phase and the domination of the tail current over the conventional partial ring current during the second dip of the double-dip storms. The former effect is consistent with Image data and may be an integrated result of the substorm current wedge. Field aligned currents are derived from the TS07D model and show significant distortions of a conventional Birkeland current pattern, when compared with those during conventional single- dip storms. These currents are compared with Birkeland current distributions derived from Iridium magnetometer data which reveal comparable differences in double-dip storms relative to single-dip storms.
SM14A-03
Storm-time Inner Magnetosphere: Self-consistent Kinetic Simulation Driven by the Space Weather Modeling Framework
Accurately modeling inner magnetosphere dynamics requires proper treatment of both the kinetic drift physics as well as the interaction between particles and fields. Observations consistently show the inner magnetosphere magnetic field to be significantly depressed during geomagnetic storms. The field changes are caused by large amounts of injected ring current plasma, which in turn strongly influence the dynamic evolution of the plasma. We have developed a self-consistent inner magnetosphere code that treats this self- consistent interaction, through coupling a kinetic ring current model (RAM) with an Euler potential-based 3D plasma equilibrium code; in our approach, the magnetic field is computed in force balance with the kinetic model anisotropic pressures (anisotropy being critically important for the excitation of EMIC waves), and then fed back into the kinetic code. Here we report results from simulating a geomagnetic storm using this model, with plasma and magnetic field on the boundary supplied from the global BATSRUS MHD code from the Space Weather Modeling Framework (SWMF); we focus in particular on the following aspects: 1). the effect of the MHD model boundary vs. observation-based (from LANL satellites) boundary conditions; 2). the effect of magnetic self-consistency on ring current plasma pressure, anisotropy and EMIC wave instability; and 3). the relative magnitude of the induced vs. convective electric fields in the inner magnetosphere during the storm.
SM14A-04 INVITED
Progress in Plasmaspheric Models Based on CLUSTER and IMAGE Observations
With the innovative observational techniques employed by CLUSTER and IMAGE spacecraft, new light has being shed on the plasmasphere. This presentation reviews some recent progress made in plasmaspheric physics-based models on the basis of these modern observations. In particular, dynamical simulations have been developed to study the mechanisms of plasmapause formation and the influence of the electric field evolution during geomagnetic storms. The position of the plasmapause is determined as a function of the level of geomagnetic activity. The deformation of the plasmasphere during quiet and disturbed geomagnetic periods is illustrated. The dynamic model has been generalized in three dimensions and is constrained by realistic data. The core of the plasmasphere is obtained from the kinetic exospheric approach assuming a kappa velocity distribution function for the particles. The relative abundance of trapped particles is constrained in such way that the density profiles correspond to Carpenter and Anderson (1992) observations. Model predictions are compared with the results of other plasmaspheric models and observations of IMAGE and CLUSTER.
SM14A-05
Empirical Characterization of Plasmaspheric Plumes
The formation and subsequent development of plasmaspheric plumes in a given convection event is well
characterized by a series of distinct phases, each triggered by a change in the strength of global
magnetospheric convection. For example, after a prolonged quiet period, an increase in convection strength
triggers erosion, and the formation of a sunward-pointing plume that typically spans at least a few hours of
dayside magnetic local time (MLT). On the other hand, a convection decrease causes a pre-existing plume
to begin rotating eastward, eventually becoming wrapped around the main plasmaspheric torus. Predicted
by computational models, plume phases have since proven to be a consistent feature of plasmaspheric
dynamics in numerous observations made by the Imager for Magnetopause-to-Aurora Global Exploration
(IMAGE) spacecraft during the years 2000-2005. However, currently-existing empirical models for the
plasmasphere do not include plumes or plume phases. We present first results of an empirical model of
plume density and location using (respectively) measurements by the IMAGE radio plasma imager (RPI) and
extreme ultraviolet (EUV) instruments. This new model framework differs differs from current models in two
ways. First, it represents the plasmapause as a multi-valued function of L versus MLT. Second, it
incorporates the concept of plume phases by parameterizing plasmaspheric density based on superposed
epoch analysis. An empirical characterization of plasmaspheric plume density and location is an important
step toward better knowledge of the spatial and temporal dependence of critical wave-particle interactions
affecting ring current ions and outer radiation belt electrons.
http://tinyurl.com/5lewk5
SM14A-06
Ion composition in the Plasma Trough and Plasma Plume Derived From a CRRES Magnetoseismic Study
The mass and energy carried in the magnetosphere by heavy ions, O+ in particular, are known to increase as geomagnetic activity increases. However, the ion composition in the magnetosphere has not been fully specified, since measurements of the flux of different ion species from the ionospheric thermal energy (below 1 eV) to the ring current energy (above 100 keV) is difficult with single particle instruments. We used mass density determined by a magnetoseismology technique and the electron density derived from measured plasma wave spectra to investigate the ion composition and total mass density for CRRES orbit 962 (August 27-28, 1991). This orbit occurred during a geomagnetic storm and included afternoon passes through the plasmasphere, the plasma trough, and a plasma plume, where these plasma regions were identified using the electron density. In the magnetoseismology analysis we determined the fundamental frequency of the toroidal standing Alfven waves from the electric and magnetic field data and then inferred the corresponding total mass density at the satellite by solving an MHD wave equation with a realistic magnetic field model and a realistic assumption for the mass distribution along the field line. The toroidal frequency changed little when the spacecraft moved between the plasma trough and the plasma plume, implying the dominance of heavy ions in the plasma trough. From the electron density and the mass density we derived quantities associated with O+ by assuming that the plasma consisted of H+, He+, and O+. In the plasma trough, O+ ions are found to carry a number density of ~10/cc, ~50 percent of the number density, and ~90 percent of the mass density. On the other hand, O+ is found to be much less dominant in the plasma plume. Our results are consistent with DE-1 studies of the formation of an oxygen torus at the outer edge of the H+ plasmapause during geomagnetic active periods and with GEOS-1 and GEOS-2 studies that reported strong dependence of O+ density on geomagnetic activity and on solar extreme ultraviolet flux. In addition, our events indicate that the plasma plume boundary, defined in terms of the electron density may not exhibit similar structure in the total mass density that can be readily detected using magnetoseismology techniques.
SM14A-07
Detection of plasmaspheric wind in the Earth's magnetosphere by the Cluster spacecraft
The existence of a plasmaspheric wind in the Earth's magnetosphere, steadily transporting cold plasmaspheric plasma outwards across the geomagnetic field lines, has been predicted on theoretical basis (Lemaire and Shunk, 1992; André and Lemaire, 2006). Direct detection of this wind has, however, eluded observation in the past. Analysis of ion measurements, acquired in the outer plasmasphere by the CIS experiment onboard the four Cluster spacecraft, provide now the first experimental confirmation of a plasmaspheric wind. This wind was systematically detected during quiet and moderately active conditions, and could provide a substantial contribution to the magnetospheric populations outside the Earth's plasmasphere.
SM14A-08
Modeling the Excitation of Whistler Mode Chorus and EMIC Waves During the April 21, 2001 Magnetic Storm.
The global dynamic evolution of ring current ions and electrons during the April 21-24, 2001 magnetic storm is modeled with the RAM code using global electric fields, and particle fluxes near geostationary orbit obtained from the RCM code with the tail plasma sheet boundary conditions based on Geotail observations. The coupled codes allow us to investigate the influence of solar wind variability on the inner magnetosphere, and also identify the spatial locations for wave excitation during different phases of the storm. At locations, where wave instability is expected, the particle distributions from the RAM code are used to model the path integrated amplification of chorus and EMIC waves using the HOTRAY code. Our results are the first attempt to model the global distribution of chorus and EMIC waves from a source population originating in the plasma sheet obtained from the RCM driven by interplanetary conditions. Comparison will be made with available satellite data and statistical models of wave intensity during active conditions.