Papers on Magnetospheric Physics
Low-latitude dayside magnetopause and boundary layer for high magnetic shear: 2. Occurrence of magnetic reconnection
Article first published online: 20 SEP 2012
Copyright 1996 by the American Geophysical Union.
Journal of Geophysical Research: Space Physics (1978–2012)
Volume 101, Issue A4, pages 7817–7828, 1 April 1996
How to Cite
1996), Low-latitude dayside magnetopause and boundary layer for high magnetic shear: 2. Occurrence of magnetic reconnection, J. Geophys. Res., 101(A4), 7817–7828, doi:10.1029/95JA03751., , and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 6 DEC 1995
- Manuscript Received: 8 FEB 1995
Quantitative comparisons of the flow velocity change across the magnetopause (MP) with the prediction from local tangential stress balance in a one-dimensional time-stationary rotational discontinuity, that is, with the Walén relation, have been performed on 69 Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) low-latitude (<30°) dayside (0800–1600 LT) high-shear (>45°) MP crossings. It is found that in 61% of the crossings the observed flow changes agree with the prediction to better than 50%. No dependence of the occurrence of reconnection flows on local magnetic shear, local time/latitude, local tangential magnetosheath flow speed, and local magnetosheath Alfvén Mach number is found. We confirm an earlier result that the agreement with the Walén relation becomes worse with increasing magnetosheath plasma β (β is the ratio of plasma pressure to magnetic pressure) but find that the velocity change itself, predicted by the Walén relation, decreases with increasing β. Moreover, the motion and thickness of the boundary also depend on β: the higher the β value, the faster the speed and the smaller the thickness. These effects combine to make velocity changes in high β events more difficult to measure accurately, which may contribute to the poor agreement with the Walén relation in these events. The 42 events which exhibit plasma flows in reasonable agreement with the Walén relation include 21 cases where the flow direction is inconsistent with a single X line hinged at the subsolar point. The discrepancies between the former result arid dayside X line locations reported earlier may be due to a bias in selection of reconnection events in earlier studies. An average (dimensionless) reconnection rate that is substantially lower than 0.1 is inferred for the 42 events.