Physics – Plasma Physics
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996jgr...101.7817p&link_type=abstract
Journal of Geophysical Research, Volume 101, Issue A4, p. 7817-7828
Physics
Plasma Physics
75
Magnetospheric Physics: Current Systems, Magnetospheric Physics: Magnetopause, Cusp, And Boundary Layers, Magnetospheric Physics: Solar Wind/Magnetosphere Interactions, Space Plasma Physics: Magnetic Reconnection
Scientific paper
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 and 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.
Paschmann Goetz
Phan Tai-Duc
Sonnerup Bengt U. Ö.
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