Reconnection Energization of Electrons, Dual Lobe Reconnection, and the Formation of the Cold Dense Plasmasheet "

James McFadden (SSL)

Cluster observations show that electron energization associated with reconnection at the dayside magnetopause are consistent with a simple picture of the reconnection geometry. Reconnection flows at the high shear magnetopause provide velocity kicks of twice the Hoffmann-Teller velocity. In addition, electrons will interact with an ambipolar field at the front of the magnetosheath ion expansion into the magnetosphere. These two acceleration mechanisms appear to be adequate to explain the observed heated electrons on newly reconnected dayside field lines.

Cluster high latitude observations provide evidence that dual lobe reconnection, which forms closed magnetic flux tubes, is common during northward IMF. A simple explanation for this unexpected phenomena is presented. Lobe reconnection requires a plasma depletion layer so the magnetosheath flow is sub-Alfvenic. The depletion layer initially forms at the sub-solar region after the field line has draped, and spreads toward both lobes simultaneously. Sub-solar draping assures that the magnetic shear in both lobes is about the same leading to nearly identical conditions in both hemispheres. Reconnection will not be simultaneous, but is favored to occur in both hemispheres due to similar conditions.

Dual lobe reconnection results in the formation of closed flux tubes with trapped magnetosheath plasma that move tailward due to the interchange instability. This plasma eventually forms the Cold Dense Plasma Sheet. What has not been appreciated is that the dual injection of ions at both lobe reconnection sites produces velocity dispersed ion signatures (VDIS) that remain as the flux tubes move around the magnetospheric flanks. Observations suggest that many VDIS events observed by other spacecraft away from the cusp are actually cusp injections with bounce-drift producing complex, overlapping VDIS signatures.