Steady reconnection during intervals of northward IMF: Implications for magnetosheath properties

Details Steady reconnection during intervals of northward IMF: Implications for magnetosheath properties Steady reconnection during intervals of northward IMF: Implications for magnetosheath properties

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.1458p&link_type=abstract

Journal of Geophysical Research, Volume 108, Issue A12, pp. SMP 18-1, CiteID 1458, DOI 10.1029/2003JA009979

Physics

Plasma Physics

5

Space Plasma Physics: Magnetic Reconnection, Magnetospheric Physics: Magnetosheath, Magnetospheric Physics: Magnetopause, Cusp, And Boundary Layers, Magnetospheric Physics: Magnetotail Boundary Layers, Magnetospheric Physics: Solar Wind/Magnetosphere Interactions

Scientific paper

This study examines the location of the reconnection site on the magnetopause for conditions of northward interplanetary magnetic field (IMF) and its implications for properties of the magnetosheath. Ion distribution functions from the Toroidal Imaging Mass Angle Spectrometer (TIMAS) instrument on board the Polar spacecraft during passes through the dayside cusp region when the IMF was steady and northward are used. Cutoff velocities are determined from these distributions and the distance from the Polar spacecraft to the site of reconnection is estimated. A magnetospheric magnetic field model is used to map these determined distances to a location on the magnetopause where reconnection is believed to have occurred. Nearly all of these reconnection sites lie in places where the magnetosheath flow is estimated to be super-Alfvénic (using hydrodynamic theory and an analytic magnetosheath magnetic field model). However, there exist strict constraints on the speed of the ambient magnetosheath flow at the reconnection site, in order for this particular type of particle distribution to have been observed by TIMAS. Different physical models are discussed, including the possibility of nonstationary reconnection sites and the existence of a plasma depletion layer which significantly increases the magnetosheath Alfvén speed close to the magnetopause. From the observations and mapped reconnection locations, we estimate statistically how much the average ion density must decrease (and the magnetic field must increase) in the plasma depletion layer to be consistent with the cusp region observations. The resulting range of values is consistent with the theoretical estimates of Zwan and Wolf [1976] (k >= 2).

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