SM13B-01
The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) NASA Mission-of- Opportunity - Up and Operational
*Presented on behalf of the entire TWINS Team
Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a NASA Explorer
Mission-of-Opportunity to stereoscopically image the Earth's magnetosphere for the first time [McComas et
al., 2008]. TWINS extends our understanding of magnetospheric structure and processes by providing
simultaneous Energetic Neutral Atom (ENA) imaging from two widely separated locations. TWINS observes
ENAs from 1-100 keV with high angular (~4° x 4°) and time (~1-minute) resolution. The
TWINS Ly-α monitor measures the geocoronal hydrogen density to aid in ENA analysis while
environmental sensors provide contemporaneous measurements of the local charged particle environments.
By imaging ENAs with identical instruments from two widely spaced, high-altitude, high-inclination spacecraft,
TWINS enables three-dimensional visualization of the large-scale structures and dynamics within the
magnetosphere for the first time. As of the summer of 2008, both TWINS instruments are finally on orbit and
operational and stereo imaging of the magnetosphere has begun. This talk briefly summarizes the TWINS
mission and instruments and shows some of the 'first-light' observations. More information about TWINS and
access to these data are available at http://twins.swri.edu.
Reference:
McComas, D.J., F. Allegrini, J. Baldonado, B. Blake, P. C. Brandt, J. Burch, J. Clemmons, W. Crain, D.
Delapp, R. DeMajistre, D. Everett, H. Fahr, L. Friesen, H. Funsten, J. Goldstein, M. Gruntman, R. Harbaugh,
R. Harper, H. Henkel, C. Holmlund, G. Lay, D. Mabry, D. Mitchell, U. Nass, C. Pollock, S. Pope, M. Reno, S.
Ritzau, E. Roelof, E. Scime, M. Sivjee, R. Skoug, T. S. Sotirelis, M. Thomsen, C. Urdiales, P. Valek, K.
Viherkanto, S. Weidner, T. Ylikorpi, M. Young, J. Zoennchen, The Two Wide-angle Imaging Neutral-atom
Spectrometers (TWINS) NASA Mission-of-Opportunity, Submitted to Space Science Reviews, 2008.
http://twins.swri.edu
SM13B-02 INVITED
The Storm-Time Access of Ionospheric Ions to the Near-Earth Magnetotail
We have examined the contribution of the ionosphere to the plasma population of the magnetotail during three moderate to strong coronal mass ejection-driven geomagnetic storms. For each event, we carried out a global magnetohydrodynamic (MHD) simulation of the storm by using solar wind and interplanetary magnetic field data from spacecraft upstream of Earth. Next, we launched large numbers of ions from sources in the solar wind and ionosphere and followed their trajectories in the three-dimensional, global, time-dependent fields obtained from the MHD simulation for that event. Solar wind ion flux was normalized to the measured solar wind velocity and density, and the ionospheric ion outflow was determined by using empirical models. We thus obtained ion distribution functions and moments of the distribution (density, pressure, etc.) for ions of solar wind and ionospheric origin, allowing us to assess the importance of ionospheric ions, specifically O+, in the magnetotail as a function of storm phase. The effect of the sudden storm commencement, pre-storm and storm-time substorms on ion heating and injection into the inner magnetosphere were also evaluated. This talk will present and compare results from the September 24, 1998, October 28, 2001, and April 17, 2002 geomagnetic storms.
SM13B-03 INVITED
Effects of Field-aligned Potential Drops on the Inner Magnetosphere
The ability of inner magnetospheric numerical models to predict storm- and substorm-associated disturbances in the ring current region depends, among other things, on inclusion of essential plasma physics processes. One such numerical model, the Rice Convection Model (RCM), is a first-principles inner magnetospheric code that evolves the particle distribution function using electric fields computed self- consistently. We have recently extended the RCM by including a module for estimating field-line potential drops and auroral electron precipitation using the well-known Knight relation. We also developed a module to represent the effects of ion outflows along auroral field lines. Using this new capability, we present RCM event simulations of an isolated substorm and a large geomagnetic storm to evaluate the role of field-line potential drops and the effect of ion outflows on the ring current, field-aligned currents, and the structure of the aurora.
SM13B-04
Rice Convection Model Simulation of Injection of an Observed Plasma Bubble Into the Inner Magnetosphere
An RCM simulation has been carried out for the growth and early expansion phase of a substorm that occurred on July 22, 1998. This is the first substorm simulation for which the RCM boundary conditions and the inputted magnetic field model have been carefully tailored for consistency with measurements made in the inner plasma sheet during the event (Geotail near X=-9, Y=0 in GSM coordinates). The simulation focuses on the injection into the inner magnetosphere of a bubble (region with low specific entropy) that was observed by Geotail. Potential and inductive contributions to the magnetospheric electric field are both important, and their patterns are compared and discussed. One preliminary conclusion from the simulation is that the bubble drifts in a channel that narrows as it approaches the inner magnetosphere, which results in a plasma-sheet inner edge that resembles the injection boundary proposed many years ago by Carl McIlwain. The corresponding distinctive pattern in the auroral electric field is compared with published substorm observations. The model also predicts a distinctive substorm-onset-associated prompt-penetration electric field in the low- and mid-latitude ionosphere.
SM13B-05 INVITED
Comparisons of Simulated and Observed Stormtime Magnetic Intensities and Ion Densities in the Ring Current
Recent progress in ring current and plasma sheet modeling has shown the importance of a self-consistent treatment of particle transport and magnetic and electric fields in the inner magnetosphere. For example, the feedback of the ring current tends to mitigate the build-up of the asymmetric ring current and associated magnetic depressions during storm main phase. Models with and without self-consistency can lead to significantly different magnitudes and spatial distributions of plasma pressure and magnetic intensity during disturbed times. In this study we compare simulated and observed stormtime magnetic intensities and ion densities at geosynchronous altitude to test how well self-consistent simulations can simultaneously reproduce these quantities. We simulate the ring current and plasma sheet for conditions corresponding to the 12-14 August 2000 storm using the self-consistent Rice Convection Model-Equilibrium (RCM-E) [ Lemon et al., JGR, 2004]. Using the empirical IMF-dependent model of Tsyganenko and Mukai [JGR, 2003], we specify the plasma sheet pressure and density at 10 RE as the plasma boundary location in the RCM- E. We compare the simulated magnetic intensity at geosynchronous altitude (6.6 RE) with the magnetic intensity measured by magnetometers on the GOES G8, G10, and G11 satellites. The simulated ion densities at different magnetic local times are compared with those from the re-analysis model of LANL/MPA densities of O'Brien and Lemon [Space Weather, 2007]. This is a first step towards a more extensive comparison that will include other datasets, such as ion and magnetic field data from Polar, at locations closer to the Earth than geosynchronous altitude.
SM13B-06
Dynamical property of storm-time subauroral rapid flows as a manifestation of complex structures of the plasma pressure in the inner magnetosphere: Simulation and SuperDARN Hokkaido radar observation
During the intense magnetic storm of 15 December 2006, the mid-latitude SuperDARN Hokkaido radar observed a dynamical character of rapid, westward flows (at 50-56 MLAT) which may be referred to as the subauroral polarization stream (SAPS). The simulation that couples the inner magnetosphere and the subauroral ionosphere was performed using a realistic boundary condition of the hot-ion distribution determined from four LANL satellites at 6.6 Re. Temporal changes in the hot-ion distribution were gradually brought by the convection electric field from the plasma sheet to L~2, resulting in a complex structure of the plasma pressure in the inner magnetosphere. Field-aligned currents that were generated by a longitudinal gradient of the plasma pressure resulted in rapid plasma flows in the subauroral ionosphere. The simulated velocity shows good agreement with the radar observation in terms of the temporal and spatial variations of the rapid flows as well as the flow velocity. For example, the simulation result shows that a temporal increase in the hot-ion density in the plasma sheet results in the temporal reduction and subsequent intensification of the rapid flow at certain subauroral latitudes. It is suggested that the subauroral plasma flow is likely a good measure for widely monitoring and deeply understanding the coupling process between the inner magnetosphere (ring current) and the subauroral ionosphere.
SM13B-07
Effects of Self-Consistent Magnetic Coupling on Ring Current Development
Satellite observations indicate that the magnetic field may be significantly depressed compared to dipolar near the equatorial plane in the inner magnetosphere during storm time. We investigate the effect of non- dipolar magnetic field geometry and the feedback of a self-consistently computed magnetic field on ring current dynamics during the 31 August 2005 geomagnetic storm. This large storm with maximum Kp=7 at 18 UT and minimum Dst=-131 nT at 20 UT on 31 August was selected for detailed study by the LWS TR&T Focus Team on ionospheric-magnetospheric plasma storm time redistribution. We use our kinetic ring current-atmosphere interactions model (RAM) that has been extended for non-dipolar magnetic field geometry. The RAM is coupled with a 3-D model that calculates self-consistently the three-dimensional magnetic field in force balance with the anisotropic ring current ion distributions. We find that the ring current fluxes calculated with a self-consistent B field are smaller compared to the dipolar B field calculations. We show an initial computation of the electric fields induced by the time change of the self- consistent magnetic fields. We simulate the sunward transport, acceleration, and loss of ring current ions using our improved RAM and investigate the effects of 1) various O+/H+ composition ratios applied at the outer boundary, and 2) the induced electric fields on ring current dynamics. We discuss ring current morphology, ion composition, pitch angle anisotropy, source and loss processes during various storm phases.
SM13B-08
Statistical properties of the multiple ion band structures observed by the FAST satellite
Data of low energy (< 28 keV) H+ and O+ ions obtained by the FAST satellite were used to investigate the statistical properties of multiple ion band structures (MIBS) that are characterized by multiple O+/H+ components with discrete energies. MIBS distributions for H+ and O+ ions had different relationships with the AL/ index, invariant latitude (ILAT) and magnetic local time, suggesting different formation mechanisms. O+ MIBSs were observed during magnetically active periods around the equatorward boundary of the auroral oval mainly in the dusk and midnight sectors, while H+ MIBSs were observed during quiet times at higher latitudes in the dawn and dusk sectors. O+ MIBSs shifted toward lower latitudes with decreasing AL/ index due to the expansion of the auroral oval during magnetically active periods. Both maximum and minimum energies of O+ MIBSs decrease with decreasing ILAT, which is consistent with velocity filter effects caused by convective transport from high to low latitudes in the nightside. The statistical properties obtained from the FAST observations suggest that O+ MIBSs supply O+ ions from the ionosphere to the inner magnetosphere during magnetic storms and contribute to the storm time ring current development.