TY - JOUR
T1 - Observations of two complete substorm cycles during the Cassini Earth swing-by
T2 - Cassini magnetometer data in a global context
AU - Khan, H.
AU - Cowley, S. W.H.
AU - Kolesnikova, E.
AU - Lester, M.
AU - Brittnacher, M. J.
AU - Hughes, T. J.
AU - Hughes, W. J.
AU - Kurth, W. S.
AU - McComas, D. J.
AU - Newitt, L.
AU - Owen, C. J.
AU - Reeves, G. D.
AU - Singer, H. J.
AU - Smith, C. W.
AU - Southwood, D. J.
AU - Watermann, J. F.
PY - 2001/12/1
Y1 - 2001/12/1
N2 - During the Earth swing-by of the Cassini spacecraft, a worldwide program of data-gathering was undertaken to define the prevailing interplanetary and geophysical conditions. This included observations of the interplanetary medium, outer magnetosphere, geostationary orbit, UV aurora, geomagnetic disturbance, and ionospheric flow. These data show that during the Cassini outbound passage through the geomagnetic tail the magnetosphere underwent two complete "classic" substorm cycles. The global data are used to set the Cassini data into a context which allows a much fuller interpretation. The pass took place through the dawn tail, where previous Geotail observations indicate that the plasma sheet usually remains 'stationary' at expansion phase onset. Reconnection and plasmoid formation are typically dusk and midnight phenomena. The Cassini observations nevertheless show a marked response of the plasma sheet both to the growth phase (thinning), and expansion phase onset (expansion without heating). Subsequent impulsive expansion of the substorm into the Cassini sector, however, resulted in the prompt appearance of reconnection-related phenomena (earthward flowing plasma and strongly disturbed fields), though the spacecraft footprint remained poleward of the intense UV auroras. Due to continuing strong southward-directed IMF during the expansion phases, a quasi-equilibrium appears to have formed between dayside and near-Earth nightside reconnection for ∼30 min after onset. Auroral zone recovery began about ∼10 min after a northward turn of the interplanetary magnetic field (IMF) to nearer-zero values in each case. A net closure of open flux then ensued, leading to deflation of the tail lobe field, 'dipolarization' of the near-Earth tail plasma sheet field, simultaneous reduction in the earthward plasma sheet flow and the flow in the nightside ionosphere, and displacement of the ground-based disturbance to high latitudes.
AB - During the Earth swing-by of the Cassini spacecraft, a worldwide program of data-gathering was undertaken to define the prevailing interplanetary and geophysical conditions. This included observations of the interplanetary medium, outer magnetosphere, geostationary orbit, UV aurora, geomagnetic disturbance, and ionospheric flow. These data show that during the Cassini outbound passage through the geomagnetic tail the magnetosphere underwent two complete "classic" substorm cycles. The global data are used to set the Cassini data into a context which allows a much fuller interpretation. The pass took place through the dawn tail, where previous Geotail observations indicate that the plasma sheet usually remains 'stationary' at expansion phase onset. Reconnection and plasmoid formation are typically dusk and midnight phenomena. The Cassini observations nevertheless show a marked response of the plasma sheet both to the growth phase (thinning), and expansion phase onset (expansion without heating). Subsequent impulsive expansion of the substorm into the Cassini sector, however, resulted in the prompt appearance of reconnection-related phenomena (earthward flowing plasma and strongly disturbed fields), though the spacecraft footprint remained poleward of the intense UV auroras. Due to continuing strong southward-directed IMF during the expansion phases, a quasi-equilibrium appears to have formed between dayside and near-Earth nightside reconnection for ∼30 min after onset. Auroral zone recovery began about ∼10 min after a northward turn of the interplanetary magnetic field (IMF) to nearer-zero values in each case. A net closure of open flux then ensued, leading to deflation of the tail lobe field, 'dipolarization' of the near-Earth tail plasma sheet field, simultaneous reduction in the earthward plasma sheet flow and the flow in the nightside ionosphere, and displacement of the ground-based disturbance to high latitudes.
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U2 - 10.1029/2001ja900049
DO - 10.1029/2001ja900049
M3 - Article
AN - SCOPUS:39449092720
SN - 2169-9402
VL - 106
SP - 30141
EP - 30175
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - A12
M1 - 2001JA900049
ER -