Bifurcated current sheets in Earth's plasmasheet: scale size and occurrence frequency

Details Bifurcated current sheets in Earth's plasmasheet: scale size and occurrence frequency Bifurcated current sheets in Earth's plasmasheet: scale size and occurrence frequency

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm14a..03t&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SM14A-03

Physics

2708 Current Systems (2409), 2744 Magnetotail, 2764 Plasma Sheet

Scientific paper

We present results of a global MHD simulation of the magnetosphere under input conditions reflecting the solar wind properties observed when a bifurcated current sheet was identified by the Cluster spacecraft in the plasmasheet on August 29, 2001. A local bifurcation of the current sheet within a few RE of Cluster's position is characterized by structure in J⊥ (current density), weak parallel flows, spatial scales ~3-5 RE in Y and Z, and clear magnetic linkage to a neutral line ~3 RE tailward of the downtail position of Cluster. At the downtail distance of Cluster, the bifurcation forms and then assumes a single-peak structure over time scales of minutes, in agreement with Cluster measurements. We use the simulation results and previously published case studies to formulate an algorithm that automatically identifies bifurcations. We apply the algorithm to Cluster magnetometer data for 1500 km (2001) and 5000 km (2002) spacecraft spacings. We find bifurcations ~25% of the time that Cluster is located in the current sheet for both separation distances, arguing that bifurcations are typically at least 1 RE in scale size. The bifurcations have qualitative current density and flow characteristics similar to those found in the MHD simulation. Scale size estimates from both the simulation and our statistical results give a full thickness of ~1-3 RE showing that the bifurcation occurs on the MHD scale. Local magnetic field and flow signatures for 2/3 of our events are consistent with nearby neutral line activity, but our events show no clear association with substorm onsets as detected in the AE index. We propose that bifurcated current sheets are formed at neutral lines of limited dawn-dusk extent.

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