SM12B-01 10:20h
Comparative study of post-midnight ENA flux enhancements during the August 2000 and April 2002 storms
The high energy neutral atom (HENA) imager on-board the IMAGE satellite captured remarkable images showing that the peak of the dominant ENA flux sometimes comes from the post-midnight region during magnetic storms(Brandt et al., GRL, 29(20), 1962, doi: 10.1029/2002GL015160, 2002). The peak of the 39-50 keV ENA flux occurred around 0500 MLT during the 12 August 2000 storm, while it peaked near midnight during the April 20, 2002 storm. This means that the post-midnight enhancement of the ENA flux does not always appear during all the magnetic storms. Fok et al. (Space Sci. Rev., 109, 77, 2003) performed the self-consistent ring current simulation that couples with the ionosphere, and found that the post-midnight enhancement appears when the ionospheric convection pattern is highly deformed by charge deposited by the strong Region 2 field-aligned current. Their calculations showed a robust reversal of the convection velocity equatorward of the auroral oval in the post-midnight sector due to the shielding electric field. Indeed, data from DMSP F13 shows that the ionospheric ion flow reversal occurred at -43 MLAT (0442 MLT) and the westward drift velocity reached around 600 m/s when IMAGE captured the post-midnight enhancement on August 12, 2000. The reversal occurred at -50 MLAT (0430 MLT) and the westward drift velocity reached only around 250 m/s when the midnight enhancement was observed on April 20, 2002. This may reflect the fact that the shielding electric field driven on August 12, 2000 is much stronger than on April 20, 2002 and the convection pattern is highly skewed during the August 2000 storm. We performed a self-consistent ring current simulation with realistic polar cap potential distribution from the Weimer 2001 model and a realistic auroral conductivity model derived from the IMAGE/FUV optical data. The result fairly accounts for the tendency of the DMSP observations and the HENA observations, likely meaning that the shielding electric field plays an important role in the formation of the post-midnight enhancement of the ENA flux.
SM12B-02 INVITED 10:35h
Modeling the Coupled Ring Current $--$ Plasmasphere System
We discuss the dynamics of charged particles in the coupled inner magnetosphere in response to the Sun's varying energy output. During periods of increased solar and geomagnetic activity charged particles are injected from the magnetotail, and being transported sunward and accelerated, build the storm time (main phase) ring current. During storm recovery phase the ring current decays through charge exchange with geocoronal hydrogen, Coulomb collisions with thermal plasma, ion precipitation, and convective dayside outflow. The anisotropic ring current populations generate plasma waves which could subsequently accelerate and/or scatter radiation belts particles. We simulate the temporal and spatial evolution of the ring current during the April and June 2001 geomagnetic storms using our kinetic drift-loss model coupled with a time-dependent plasmasphere model. We use geosynchronous data from LANL satellites to model the magnetospheric inflow of plasma on the nightside and demonstrate the importance of storm time plasma sheet enhancement and dropout for ring current buildup and decay. We discuss ring current morphology, ion composition, source and loss processes during various storm phases. Strong EMIC waves are excited near minimum $Dst$ and during the recovery phase of the storms and cause significant particle precipitation into the atmosphere and generation of detached proton auroral arcs.
SM12B-03 INVITED 10:55h
Coupling Processes in the Inner Magnetosphere Associated with Midlatitude Red Auroras during Superstorms
During recent superstorms, observations from IMAGE, Iridium, FAST, DMSP, TIMED, LANL Geo and ground-based photometers at vantage points throughout the geospace system are used to investigate, for the first time, features that map from the inner magnetosphere to strong red emissions at mid-latitudes, reaching as far equatorward as 33 deg MLAT. At the lowest latitudes, emissions have very little structure being described as a diffuse but intense red glow. The observations imply that these visible unstructured mid-latitude emissions are in fact extreme stable auroral red (SAR) arcs, and that large-scale coupling processes, within the inner magnetosphere are key to producing an enhanced energy source to drive SAR-arc intensities into the visible range. This presentation will focus on the 31 March 2001 and 11 April 2001 extreme events but draw upon a larger set of storms for supporting observations. New questions raised by these observations, as well as initial modeling results, will be presented.
SM12B-04 11:15h
Electrodynamics of M-I Coupling during the Main Phase of Superstorms
During the main phase of superstorms (Dst less than -200 nT) the mapping of magnetic field lines from the ionosphere to the magnetosphere is strongly and asymmetrically distorted by ring-current penetration close to Earth (Tsyganenko et al., 2003). Consequences of this distortion appear in plasma, particle and field measurements by DMSP satellites in low-Earth orbit and the CRRES satellite in the inner magnetosphere. They are manifest through the generation of low-energy ion populations and field-aligned currents with intensities above 1 A/m. The low energy ions are observed in both the ionosphere and magnetosphere near the dawn meridian below L = 2, well earthward/equatorward of the plasma sheet/auroral electron boundaries. DMSP satellites observe the intense paired sheets of field-aligned current in both the evening and dawn local time sectors. In some instances, precipitating electrons with energies well below 1 keV carry the upward current. Stopping at altitudes > 150 km, they support several tens of mhos of Pedersen but negligible Hall conductance. In such cases ground magnetometers measurements provide scant evidence that several terajoules of electromagnetic energy was deposited in the mid-latitude ionosphere. We provide examples of these main-phase phenomena observed during the superstorms of March 1991, April 2000 and October 2003 and discuss some implications for the equations of state used to describe the transport of ring-current plasma.
SM12B-05 11:30h
Storm-time Global Evolution of the Inner Magnetospheric Proton Distributions: an Empirical Approach Applied to the April 21-24th 2001 Storm
The empirical approach in global modelling the proton distributions of the inner magnetosphere [Orsini et al., 2004] is here applied for a detailed analysis of the April 21-24th 2001 storm. This method based on comparison of the Milillo et al. [2001] model with local proton spectra, results as a simple and powerful tool for inner magnetospheric studies. In this work we use the LANL proton spectra and other available data in order to obtain the time evolving model parameters. By applying these parameters to the Milillo et al. [2001] empirical model we can derive the global evolving proton distributions. The macroscopic physical features and their developments on a global scale are analysed in terms of magnetic pressure, electric potential, equatorial current and total energy. Then, we compare both the model parameters and the derived quantities (related to the ring current) with the geomagnetic indexes as well as with the solar wind data. Finally, the presented results are discussed in the light of energetic neutral atom data from IMAGE.
SM12B-06 11:45h
Particle Transport From the Plasma Sheet to the Ring Current Region and Ring Current Development Under the Influence of Substorm-Associated Electric Fields
The coupling between plasma populations, namely, the ring current and the plasma sheet, is analyzed in the frame of study on the storm-time ring current response and development under the influence of substorm-associated electric fields. We model the proposed periods of April-June 2001 and April 2002 storm. We trace particles with arbitrary pitch angles numerically in the drift approximation. Tracing is performed in different realistic time-dependent magnetic and electric field models. Substorm-associated electric field is given by Gaussian pulse with azimuthal field component propagating inward with a velocity dependent on radial distance. The magnetic field from this pulse is calculated by Faraday's law. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during storm events. The obtained model Dst index, energy density and particle flux maps are then compared to ground-based and satellite observations such as ground-based magnetic field and IMAGE, LANL, CLUSTER particle measurements. The role of substorm-associated fields in the energization of the plasma sheet particles to higher energies (more than 100 keV) and their transport inward to closed drift shells is closely studied.
SM12B-07 12:00h
Simultaneous Observations of ULF Waves in the Magnetosphere, Ionosphere and on the Ground
External solar wind sources transfer energy, either directly or indirectly, into the Earth's dayside magnetosphere to drive ultra-low frequency (ULF) waves in the Pc3-5 (1-100mHz) band. The wavelength of these waves is of the same order as the scale size of the magnetospheric cavity and consequently ULF wave energy is generally observed as standing wave resonances, either Alfven mode field line resonances or fast mode cavity/waveguide resonances. The ULF wave spectra seen by ground magnetometers contains information relating to the properties of the wave source and the magnetosphere and ionosphere regions and associated boundaries through which wave energy must travel to reach the ground. This study tracks individual daytime Pc3-5 wave trains, seen in the outer magnetosphere at geostationary orbit in September 2003 by magnetometers onboard the GOES 8 and 9 satellites (195 and 205 degrees west longitude), down through the ionosphere where they are observed by the Tasmanian TIGER SuperDARN HF radar, and to the ground where they are observed by the ground magnetometer at Macquarie Island. Of particular interest is a comparison of wave amplitudes seen in the magnetosphere, ionosphere and on the ground. Ionospheric ULF wave azimuthal wave numbers are known to differ from those measured on the ground due to spatial integration. Wave numbers in the magnetosphere, ionosphere and on the ground will be compared, and other wave properties observed simultaneous between the three regions, including travel time, phase and polarization characteristics will be discussed. This provides new knowledge on the transfer of ULF wave energy from the magnetosphere to the ground.