Features of High-latitude MAgnetic Reconnection In sub-alfvenic Flow: Interball Tail observations On 29 May 1996

The Interball/Tail spacecraft crossed the high latitude magnetopause under northward IMF conditions on 29 May 1996, with local magnetic time and geomagnetic latitude MLT ~7.3 hours, GMLT ~65.4 degrees, respectively. Two interesting properties of observations are the existence of anomalously moving plasma within the magnetopause current layer, and sunward convection of the mantle plasma. Both plasma domains show two magnetosheath-type plasma components indicating ongoing reconnection. Tangential stress balance and sunward plasma flow at the magnetopause observed by Interball Tail indicated that reconnection was occurring at high latitudes poleward of the cusp. This is also confirmed by the sunward convection within the boundary layer. At these high latitudes, the gas dynamic model of the solar/magnetosphere interaction indicated that the flow should be super-alfvenic and reconnection site should have propagated tailward, while the spacecraft observed sub-alfvenic flow in the magnetosheath near the reconnection site. These observations suggest that the region of sub-alfvenic flow and stable, quasi-steady reconnection extends to very high latitudes under northward IMF conditions.