TY - JOUR

T1 - IN-SITU OBSERVATIONS OF MAGNETOTAIL RECONNECTION PRIOR TO THE ONSET OF A SMALL SUBSTORM

AU - Sergeev, V.A.

AU - ANGELOPOULOS, V.

AU - MITCHELL, DG

AU - RUSSELL, CT

PY - 1995/10/1

Y1 - 1995/10/1

N2 - On April 15, 1979 at 0645 UT, several minutes prior to the expansion phase onset of a weak substorm, the ISEE 1 and 2 spacecraft were located 16 R(E) downtail and close to local midnight. The two spacecraft were on opposite sides of the current sheet, allowing us to better constrain the possible interpretations of the available plasma, magnetic field, and energetic particle data. Plasma sheet acceleration occurring earthward of the spacecraft was evident in the energetic particle data 2-3 min before the first ground-based signatures of substorm onset. The ensuing magnetic field and particle changes are consistent with an X-type neutral line moving tailward of ISEE 1 and 2 with an apparent speed of similar to 30 km/s, while the plasma sheet thickness decreased to a minimum of less than 0.2 R(E). Although the substorm effects at geosynchronous altitude and on the ground were weak, the reconnection rate was locally quite intense (>1 mV/m) and produced earthward bursty bulk flows of peak velocity >600 km/s. Ion velocity-space distributions confirm that the flows are indeed convective flows of a single-ion population and not counterstreaming beams, as is often the case at the plasma sheet boundary. The fast tailward flows observed at the initial stage of reconnection were localized to a thin layer surrounding the neutral sheet. The magnitude of the current disruption and the region 1 sense field-aligned currents associated with reconnection were sufficiently large to explain the intensity of the substorm current wedge, as inferred from ground magnetometers.

AB - On April 15, 1979 at 0645 UT, several minutes prior to the expansion phase onset of a weak substorm, the ISEE 1 and 2 spacecraft were located 16 R(E) downtail and close to local midnight. The two spacecraft were on opposite sides of the current sheet, allowing us to better constrain the possible interpretations of the available plasma, magnetic field, and energetic particle data. Plasma sheet acceleration occurring earthward of the spacecraft was evident in the energetic particle data 2-3 min before the first ground-based signatures of substorm onset. The ensuing magnetic field and particle changes are consistent with an X-type neutral line moving tailward of ISEE 1 and 2 with an apparent speed of similar to 30 km/s, while the plasma sheet thickness decreased to a minimum of less than 0.2 R(E). Although the substorm effects at geosynchronous altitude and on the ground were weak, the reconnection rate was locally quite intense (>1 mV/m) and produced earthward bursty bulk flows of peak velocity >600 km/s. Ion velocity-space distributions confirm that the flows are indeed convective flows of a single-ion population and not counterstreaming beams, as is often the case at the plasma sheet boundary. The fast tailward flows observed at the initial stage of reconnection were localized to a thin layer surrounding the neutral sheet. The magnitude of the current disruption and the region 1 sense field-aligned currents associated with reconnection were sufficiently large to explain the intensity of the substorm current wedge, as inferred from ground magnetometers.

KW - PLASMA SHEET BOUNDARY

KW - ENERGETIC ION ANISOTROPIES

KW - GEOMAGNETIC TAIL

KW - MAGNETIC-FIELD

KW - CURRENT WEDGE

KW - GROWTH-PHASE

KW - MARCH 22

KW - DYNAMICS

KW - CDAW-6

KW - FLOWS

U2 - 10.1029/95JA01471

DO - 10.1029/95JA01471

M3 - статья

VL - 100

SP - 19121

EP - 19133

JO - Journal of Geophysical Research: Biogeosciences

JF - Journal of Geophysical Research: Biogeosciences

SN - 0148-0227

IS - A10

ER -