HR: 16:20h
AN: SM14A-02 INVITED     [Abstracts]
TI: Difficulties in Constraining Substorm Models
AU: * McPherron, R L
EM: rmcpherron@igpp.ucla.edu
AF: Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, CA 90095-1567 United States
AU: * McPherron, R L
EM: rmcpherron@igpp.ucla.edu
AF: Department of Earth and Space Sciences, University of California Los Angeles, Los Angeles, CA 90095-1567 United States
AB: An outstanding controversy of substorm physics is the nature of the process responsible for initiation of the onset of the expansion phase of a substorm. The near-Earth neutral line model (NRNL) postulates that this process is magnetic reconnection at some location beyond 15 Re in the tail. A variety of other models postulate that the actual onset begins in the near geosynchronous region (8-10 Re) and is caused by processes other than reconnection. The THEMIS mission is designed to resolve this controversy by aligning spacecraft in the radial direction at three different distances in the tail. Accurate timing obtained with both satellite and ground measurements will be used to determine the initial direction of propagation of disturbances in the tail and hence the location of the onset. In this paper we will review a variety of difficulties likely to be encountered in carrying out this project. Among these are the following. Simulations suggest that the onset of magnetic reconnection and the subsequent flow channels are remarkably complex. There is no need for flows to be aligned along the tail axis. Earthward flows can be reflected and carry northward field tailward. Almost all substorms have multiple onsets that are often referred to as pseudo breakups, main onsets, intensifications, and poleward boundary intensifications. It is frequently difficult to determine which of the activations the main onset is. It is easy to argue that the main onset has been misidentified and consequently the presumed "cause" is actually an "effect". The cadence of measurements is usually too low to resolve the direction of propagation. The probability of proper alignment when a substorm occurs is likely to be low. These difficulties and others will be discussed in this presentation.
DE: 7900 SPACE WEATHER
DE: 7954 Magnetic storms (2788)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005