Substorms, Aurorae, and Ion Outflows II
Presiding: S A Fuselier, Lockheed Martin Advanced Technology Center; W R Paterson, Hampton University
SM51B-01 08:30h
Growth Phase Current Sheet and Substorm Processes
We present POLAR observation of a substorm event from growth phase to substorm expansion. We also make use of the particle pressure computed from HYDRA data along the POLAR orbit to model the 3D structure of the current sheet in the near-Earth region (~ 8-10 RE) during the growth phase. We will also show the magnetic field fluctuations associated with the substorm activity. In particular, we find that the substorm turbulence activity consists of fluctuations with period of about 60 seconds (in the Pi 2 range) to waves with period of a few seconds, consistent with previous observations by AMPTE/CCE and Geotail. We will also show numerical solutions of kinetic ballooning modes for the modeled 3D equilibrium.
SM51B-02 08:45h
Plasma Sheet Expansion: Revisit
The present study observationally examines the expansion of the plasma sheet in the near-Earth magnetotail. Three possible explanations are tested with plasma and magnetic field measurements made by the Geotail satellite. Those explanations are (1) the filling of newly closed flux tube with fresh plasma, (2) the increase in the plasma-sheet plasma pressure on the arrival of the fast plasma flow, and (3) the decrease in the lobe magnetic pressure due to tail current disruption. The result will be addressed in terms of connection between near-Earth (tail current disruption) and mid-tail substorm (near-Earth reconnection) processes.
SM51B-03 09:00h
Multipoint Substorm Studies With the Present Fleet of Spacecraft
The time-sequence of events that occurs prior to onset is a matter of intense interest for determination of the physical mechanism that initiates substorms. The presently-available fleet of magnetospheric spacecraft including ACE, Cluster, Geotail, IMAGE, and Polar offers a capability for simultaneous observation of the tail plasma sheet at radial distances ≤10 RE and ~20 RE with concurrent imaging of auroral luminosities and of energetic neutral atoms from the inner magnetosphere. This combination of observations can provide insight, for examples, by identifying the position of onset with respect to the ring curent, or by searching for precursor beams in the middle magnetotail. In this report we discuss occurrences of substorms during fortuitous conjunctions of the above-mentioned spacecraft that may be good cases for global simulations. We also discuss difficulties associated with this methodology.
SM51B-04 09:15h
Combined in situ and remote sensing of ionospheric ion outflow
Images of charge-exchanged neutrals from ion outflow during a period of substorm recovery are supported by simultaneous in situ ion outflow measurements and images of the auroral oval. From this combination of remote sensing and in situ measurements, the ion outflow is shown to consist of ion conics that likely increase in energy as the conics rise out of the Earth's ionosphere. Above about 1.6 Earth Radii, the conic thermal energy is greater than 10 eV while at about 0.7 Earth Radii, it is below this value. This outflow occurs over the entire dayside auroral oval at high latitudes, even in the vicinity of the cusp, where the auroral emissions are relatively weak. Outflow on the nightside may be weaker than on the dayside and/or may have a different energy-altitude dependence.
SM51B-05 09:30h
The relationship between aurora and high-latitude ion upflow for May 2-5, 1998
Many previous studies have demonstrated the relationship between high-altitude energetic ion outflow and auroral processes. These studies typically relied on in-situ measurements made on a single spacecraft and so could not always observe the conditions that lead to the energization of the observed ions. Either enough time had passed so that one could suspect that local conditions had changed since the ions were energized or the observed ions convected across surrounding regions whose conditions were not observed at all. This problem can be overcome, to an extent, through the use of global auroral imaging. We apply this method to a statistical study of the first step in the ion outflow process (topside ion upflows) using DMSP drift meter data (~830 km) with Polar UVI auroral images providing a frame of reference. The resultant database allows us to investigate the relationship between auroral intensity/history/form/substorm-phase and the corresponding ionospheric upflow response. Its subsequent analysis, can be used to produce maps of O+ upflow at DMSP altitudes as a function of both global parameters like total energy deposition, and local parameters like the time history of specific discrete auroral features. We demonstrate our methodology by investigating a four day period (May 2-5, 1998) to look for correlations between auroral intensity and upflow observations (including parallel velocities and densities) from 4 DMSP satellites (F11, F12, F13, F14). More than 700 auroral images and over 226k DMSP observations are used. Correlations are investigated for auroral conditions near the footprint of the DMSP satellite, for global conditions along the satellite ground track, and for the time history of auroral activity along the ground track.
SM51B-06 09:45h
Modeling Ion Outflows Associated with Electromagnetic Ion Cyclotron Waves
Satellites in the auroral region often detect energetic heavy ion outflows together with electromagnetic ion cylotron wave activity (1-100Hz). Because the Poynting flux of the waves is into the ionosphere, the waves can energize the ions at lower altitude leading to ion outflow from the topside ionosphere. One difficulty with relating the ion outflows to the wave activity is the nonlocality of the heating process---much of the heating occurs between the ionosphere (where the ions originate) and the spacecraft. A common practice is to assume a heating rate based upon the spectrum observed by the satellite. However, nonlocal wave solutions suggest that propagation and dissipation of the wave spectrum depends sensitively on the heavy ion plasma profiles in the topside ionosphere as well as the collisional ionospheric model. Consequently, the heating rate is strongly dependent on the plasma density profile. Because the heating rate determines the plasma profiles and the plasma profiles determine the heating rate, it is necessary to account for the feedback in a self-consistent manner. We successively iterate (1) a wave propagation code based on background plasma profiles (which solves the full electromagnetic equations including a realistic ionospheric model) and (2) a Monte Carlo simulation code to obtain the ion profiles based on heating rates obtained from the results of the wave propagation code. The method converges rapidly to a stable state, and the results suggest that the temporal evolution of the plasma profiles may involve a two-step process where helium is first heated then oxygen.
http://w3.pppl.gov/~jrj/icw.html