Plasma sheet dynamics observed by the Polar spacecraft in association with substorm onsets

P K Toivanen; D N Baker; W K Peterson; X Li; E F Donovan; A Viljanen; A Keiling; J R Wygant; C A Kletzing

doi:10.1029/2000JA003020

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Plasma sheet dynamics observed by the Polar spacecraft in association with substorm onsets

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Plasma sheet dynamics observed by the Polar spacecraft in association with substorm onsets

P K Toivanen, D N Baker, W K Peterson, X Li, E F Donovan, A Viljanen, A Keiling, J R Wygant and C A Kletzing

Journal of geophysical research. Space physics, Vol.106(A9), pp.19117-19130

09/01/2001

DOI: 10.1029/2000JA003020

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Abstract

We present observations of the Polar spacecraft of magnetospheric substorm signatures in the plasma sheet midway along auroral field lines between the ionosphere and the equatorial plasma sheet. On October 17, 1997, Polar was located in the onset meridian in conjunction with the Scandinavian magnetometer chain (International Monitor for Auroral Geomagnetic Effects; IMAGE). In addition, a geostationary spacecraft, LANL-97A, was located near the onset meridian. On August 29, 1997, Polar was magnetically conjugate to the Canadian magnetometer chain (Canadian Auroral Network for the OPEN Program Unified Study; CANOPUS) similar to 5 hours east of the onset meridian. In both cases, substorm activity was manifested as strong magnetic (20 nT) and electric (40 mV m(-1)) field variations with bursts of parallel Poynting flux (similar to 1 erg cm(-2) s(-1)), predominantly directed toward the ionosphere. In the first event Polar was located in the plasma sheet near the plasma sheet boundary, and the field variations were initiated at the ground onset. In the second event, Polar crossed the plasma sheet boundary to the tail lobes a few minutes prior to a local plasma sheet expansion. As Polar was engulfed by the plasma sheet, the field variations occurred in the previously quiet plasma sheet boundary. This coincided with the auroral bulge reaching the CANOPUS stations. We compare these two events and argue that the field variations were most probably signatures of the reconnection of open field lines and the subsequent enhanced earthward flows. Furthermore, weak flow bursts were observed at Polar in both events similar to9 min before the onset. in the first event, a gradual development toward a negative bay and a burst of Pi2 pulsations were associated with the flow bursts. We anticipate that these signatures, often described in terms of pseudo-breakups, were a precursor of the substorm onset, the initiation of the reconnection of closed field lines.

Physical Sciences

Astronomy & Astrophysics

Science & Technology

Details

Title: Subtitle: Plasma sheet dynamics observed by the Polar spacecraft in association with substorm onsets
Creators: P K Toivanen - University of Colorado System
D N Baker - University of Colorado Boulder
W K Peterson - Lockheed Martin
X Li
E F Donovan - University of Calgary
A Viljanen - Finnish Meteorological Institute
A Keiling - University of Minnesota
J R Wygant
C A Kletzing - University of Iowa, Physics and Astronomy
Resource Type: Journal article
Publication Details: Journal of geophysical research. Space physics, Vol.106(A9), pp.19117-19130
Publisher: Amer Geophysical Union
DOI: 10.1029/2000JA003020
ISSN: 2169-9380
eISSN: 2169-9402
Number of pages: 14
Language: English
Date published: 09/01/2001
Academic Unit: Physics and Astronomy
Record Identifier: 9984428802202771

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