Cluster observations of "crater" flux transfer events at the dayside high-latitude magnetopause

Abstract

On 11 January 2002 Cluster detected two "crater"-like flux transfer event (FTE) signatures. The four spacecraft were in quasi-linear formation, spread over ∼2 RE in the magnetopause normal direction, and sample a range of distances from it. The observations occur near a southward turning of the IMF, but no solar wind pressure pulses are detected. Analysis reveals: (1) C3, closest to the magnetopause, made two transient excursions into the magnetosheath which bracket two "crater"-FTE signatures detected at the other three spacecraft; (2) magnetic field deflections observed at the other spacecraft do not match the magnetosheath field direction at C3; (3) these FTE signatures involve encounters with reconnected field lines and associated boundary layers lying just inside the magnetopause, including a "separatrix layer" of accelerated magnetosheath electrons and an injection of magnetosheath ions. Under the observed conditions, reconnected flux tubes created by a transient and localized patch of reconnection located nearer to the subsolar point, will move northward and duskward over Cluster, consistent with observations inside the magnetosphere. The FTE signatures arise from this transient inward motion of reconnection-associated boundary layers over the spacecraft. We postulate that the transient relocation of C3 into the magnetosheath is due to a region of eroded magnetic flux, lying in the wake of the recoiling FTE, which itself is driven duskward at some fraction of the magnetosheath flow speed. The FTEs pass northward of C3, but the eroded wake, which we term the "traveling magnetopause erosion region" (TMER), is located equatorward of the FTEs and moves duskward over C3. Copyright 2008 by the American Geophysical Union.