SM13E-01 INVITED
Outer Boundary Conditions for the Inner Magnetosphere: Global Simulation Perspective
Activity in the inner magnetosphere is a complex function of the driving solar wind, processes in the magnetotail, and coupling to the ionosphere. Global MHD simulations are great tools to study the solar wind – magnetosphere interaction on one hand and magnetosphere – ionosphere coupling on the other. Therefore, even if the MHD description does not give a full account of the complexity of the inner magnetosphere multi-component, multi- temperature plasmas, it does give self-consistent and dynamic boundary conditions of the driving solar wind and magnetotail as a source region. In this presentation we discuss magnetopause reconnection and energy entry in a series of global MHD simulations using the GUMICS-4 code. The simulation parameters have been selected to represent a variety of conditions: low and high Mach numbers, low and high solar wind speed, and small and large, northward and southward IMF conditions. We discuss the relationship between energy entry through the magnetopause and energy entry into the inner magnetosphere and the dependence of these processes on the driving solar wind and IMF conditions.
SM13E-02
Ring Current Morphology During Storm Main Phases
The morphology of the ring current during storm main phases is controlled by a variety of factors, including the solar wind driving and the pre-storm plasma sheet conditions. The ring current morphology in return is crucial for understanding further development in the inner magnetosphere (e.g., the ring current-plasamsphere overlap and its impact on the radiation belts). We present statistical results from ENA-derived equatorial plasma distributions for geomagnetic storms between 2000 and 2006. We discuss the penetration depth of the ring current and the position of the peak in response to possible controlling solar wind and magnetospheric factors.
SM13E-03
Ring Current Recovery: Electric Field and Plasma Sheet Density Effects
Recent simulation results agree that modifying the near-earth plasma sheet density at the start of the recovery phase of a magnetic storm ought to dramatically modify the recovery rate. Specifically, simulations predict that with lower plasma sheet density, the ring current recovers more quickly. Continued convection during the recovery phase can amplify this effect. We present an observational study that appears to contradict the simulations: the predominant controlling factor of the initial rate of recovery is the convection strength, while plasma sheet density plays at most a minor role.
SM13E-04
Ring current auroras
Ring current auroras (RCA) refer to the auroral emissions due to precipitating particles from the ring current. RCA are typically observed at sub-auroral latitudes due to precipitating protons or energetic neutral atomic hydrogen via charge-exchange. The electromagnetic ion cyclotron wave - particle interaction is the dominant mechanism for the precipitating protons. Change in the ambient magnetic field along the proton drift path could also cause the proton to precipitate. Different features of RCA will be shown by examples. A limited ring current simulation indicates that the structures in RCA are controlled by the proton pitch angle distribution. Observations of RCA not only reveal ring current dynamics but also serve as a tool to validate ring current models.
SM13E-05
Activity Dependent O+ Transport Paths From the Ionosphere to the Ring Current
Energetic O+ has important dynamic effects on the ring current. Insights into the effects of O+ on ring current dynamics have come primarily from models, not observations. Here we report observations made on the Polar spacecraft by the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) which has measured the flux and energy distribution of escaping O+, cast in auroral boundary coordinates. Comparison with ISEE -1 observations of O+ in the plasma sheet, other recent observations, and multi-fluid simulations of the magnetosphere suggest that there are two distinct pathways for the energization and transport of O+ from the dayside ionosphere to the plasma sheet: 1) Energization and transport over the polar cap into the central plasma sheet which our analysis suggests is significant only during geomagnetically active times; and 2) Energization and transport in three dimensional magnetospheric fields during geomagnetically quiet times that leads to a significant O+ population on the plasma sheet flanks. The consequences of the suggested activity-dependant O+ transport path and transport of O+ in boundary related coordinates have not been previously explored.
SM13E-06
Magnetospheric {ULF} Activity as a Function of Solar Wind Conditions: Toward a Quantitative Model of Radial Diffusion in the Magnetosphere
Magnetospheric ULF waves, with frequencies in the mHz range, are known to efficiently energize and transport relativistic electrons in the radiation belts through resonant interactions leading to enhanced rates of radial diffusion. However, the global occurrence and physical characteristics of the waves driving the transport, and the resulting rates of radial diffusion, are not well-characterized in terms of the solar wind conditions responsible for the ULF activity. In this effort we drive global MHD simulations of the magnetosphere using an idealized set of solar wind conditions, based on statistical characterizations of the solar wind pressure (and its variations) as a function of solar wind velocity. The simulated ULF wave distributions are analyzed as a function of radial position and global mode structure within the magnetosphere. By applying interpolation techniques to the resulting wave distributions, we create 'synthetic' maps of ULF activity as a function of solar wind velocity. We compare the synthetic rates of radial diffusion to commonly-used empirical diffusion coefficients, and to those derived from simulations driven by `real' solar wind conditions (observed by upstream solar wind monitors) representing CME- and CIR-driven storms. These comparisons are used to investigate the feasibility of using synthetic, solar wind-driven ULF maps to quantify rates of radial diffusion for real magnetospheric events.
SM13E-07
Geomagnetic Storms and Electromagnetic Ion Cyclotron Waves
Electromagnetic ion cyclotron (EMIC) waves are considered to play an important role in magnetosphere dynamics, including contributions to ring current ion losses and radiation belt electron losses. Theoretical studies suggest that some of these processes may be most effective during the main phase of geomagnetic storms. However, ground-based signatures of EMIC waves, Pc1-2 geomagnetic pulsations, are only occasionally observed during the main phase, and more frequently occur during the recovery phase. In this study using space-based data, we will investigate the association of EMIC waves with the various storm phases in case studies of up to 10 geomagnetic storms over 1996 – 2002. High resolution data from the GOES 8-12 geostationary satellite magnetometers provide information on EMIC wave activity in the 0 – 1 Hz band. Storm data includes Dst, Kp and upstream solar wind and IMF parameters. Other properties of the EMIC waves of interest to modellers including wave frequency, wave power and spectral energy density will be investigated with respect to the storm phase.
SM13E-08
Global Simulation of Electromagnetic Ion Cyclotron Waves
It is well known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and particles. Such a self-consistent model is being progressively developed by Khazanov et al. [2002 - 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. We will discuss the recent progress in understanding EMIC waves formation mechanisms in the inner magnetosphere. This problem remains unsettled in spite of many years of experimental and theoretical studies. Modern satellite observations by CRRES, Polar and Cluster still do not reveal the whole picture experimentally since they do not stay long enough in the generation region to give a full account of all the spatio-temporal structure of EMIC waves. The complete self-consistent theory taking into account all factors significant for EMIC waves generation remains to be developed. Several mechanisms are discussed with respect to formation of EMIC waves, among them are nonlinear modification of the ionospheric reflection by precipitating energetic protons, modulation of ion-cyclotron instability by long-period (Pc3/4) pulsations, reflection of waves from layers of heavy-ion gyroresonances, and nonlinearities of wave generation process. We show that each of these mechanisms have their attractive features and explains certain part experimental data but any of them, if taken alone, meets some difficulties when compared to observations. We conclude that development of a refined nonlinear theory and further correlated analysis of modern satellite and ground-based data is needed to solve this very intriguing problem.