Probing the first few minutes of substorm expansion phase onset using ULF wave techniques
Abstract
With the successful launch of the THEMIS spacecraft, the expansion of the CARISMA magnetometer array, and the deployment of the THEMIS GBOs, there exist exceptional opportunities to study the initiation of ULF waves surrounding substorm onset during the first THEMIS tail season. In this talk, we outline a number of techniques with which to diagnose the nightside magnetosphere around expansion phase onset. We use ULF pulsations to determine magnetospheric characteristics using both Pi2 (40-150s period) and long-period Pi1 (1-40s period) waveforms and investigate their relationship to substorm expansion phase onset. We present case studies whereby a ULF wave detection algorithm based upon a discrete wavelet transform [ e.g., Nose et al., 1998] is used to determine the very first signatures of ULF wave activity observed subsequent to substorm onset. We compare these results to the optical onset location in the ionosphere and the in-situ location of ULF wave initiation using the THEMIS and GOES satellites. Finally, we compare the location of the optical and magnetic signatures in the ionsosphere with results from a simple substorm current wedge model [e.g., Cramoysan et al., 1995] that produces estimates of the locations of the upward and downward field aligned currents and the Westward electrojet during the first few minutes of expansion phase onset. We propose to use these techniques to produce a substorm onset database during the THEMIS era.
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.2545R