Bremen 2017 – wissenschaftliches Programm

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EP: Fachverband Extraterrestrische Physik

EP 13: Erdnaher Weltraum

EP 13.4: Hauptvortrag

Donnerstag, 16. März 2017, 17:30–18:00, GW2 B2880

Magnetospheric current systems during magnetic storms — •Hermann Lühr — Deutsches GeoForschungsZentrum GFZ, Potsdam

During times of enhanced energy and momentum transfer from the solar wind into the magnetosphere the magnetopause is typically displaced inward and the ring current is enhanced. Commonly the Dst index is used as an indicator for storm intensity. But recent observations provide evidence for deficiencies of the Dst index with respect to ring current strength. During the storm main phase an azimuthal asymmetry of the disturbance level appears, larger deflections on the duskside than on the dawnside. This is traditionally attributed to the formation of a partial ring current in the evening sector. However, in-situ current density measurements of the ring current region reveal strongest currents in the post-midnight sector. For reconciling the near-Earth recordings with observations in the magnetosphere an additional storm-time current system is proposed. A possible configuration includes generators in the equatorial plane close to the low-latitude boundary layer both on the dawn and duskside. They drive field-aligned currents (FACs) into the ionosphere on the prenoon and afternoon sides. Currents are routed along the electrojets on both sides, and leave the ionosphere as FACs on the nightside for closing the circuit. The distribution of current between the two hemispheres depends on local season.