HR: 0800h
AN: SM31B-0410    [Abstracts]
TI: Reconnection Tailward of the Cusp Under Negative IMF Bz Conditions
AU: * Farrugia, C J
EM: charlie.farrugia@unh.edu
AF: Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 United States
AU: Sandholt, P
EM: p.e.sandholt@fys.uio.no
AF: Department of Physics, University of Oslo, OSLO, 0105 Norway
AB: In the recent statistical work of Twitty et al. (2004) based on Cluster observations in the high- and mid-altitude cusp at near-noon local times (MLT), the prevalent opinion that lobe reconnection is exclusively a northward IMF (B_z > 0) phenomenon is given further support. Contrary to this view, we present a case of lobe reconnection during a steady south-easterly IMF (B_z = -5 nT, IMF clock angle = 115°) midway through the passage at Earth of an interplanetary magnetic cloud on April 17, 1999. Robust signatures of lobe reconnection are present in particle data obtained from Polar/HYDRA during an overflight of the southern polar cusp at 08-09 MLT in the form of an inverse energy-versus-latitude dispersion of precipitating ions. From the ground magnetometer records of the Svalbard stations of the IMAGE chain we infer the presence of a long series of pulsed ionospheric flows (PIFs) in both the merging and lobe convection cells in the northern hemisphere. These data provide strong evidence for the occurrence of (pulsed) lobe reconnection during this interval of steady southeast IMF. The interplanetary conditions included a dominant IMF B_y component of 20 nT, a low proton plasma beta (< 0.1) and a low Alfven Mach number (~3) near the center of the cloud. We speculate that these conditions may give rise to a plasma depletion layer next to the high-latitude magnetopause, a circumstance which favors lobe reconnection.
Twitty, C. et al., Geophys. Res. lett., 31, L19808, 2004. This work is supported by a grant in NASA's SEC-GI Program
DE: 2111 Ejecta, driver gases, and magnetic clouds
DE: 2455 Particle precipitation
DE: 2463 Plasma convection (2760)
DE: 2706 Cusp
DE: 2723 Magnetic reconnection (7526, 7835)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005