THEMIS observations of the dayside traveling compression region and flows surrounding flux transfer events

Abstract

We present multipoint observations of Flux Transfer Events (FTEs) by the THEMIS spacecraft in a string‐of‐pearls configuration, at the near‐equatorial magnetopause. Common characteristics from a number of cases, examined at various local times, are exemplified here by a case study of FTE trains observed in the pre‐noon sector, on Aug. 18, 2007. We show that the magneto‐pause‐normal flow velocity is consistently towards and away from the magnetopause on the inbound and outbound transit of the FTE, on all spacecraft sufficiently away from the magnetopause. The velocity just outside the FTE at the time of closest proximity to the FTE core is opposite to the FTE direction of motion even when the FTE moves in the same direction as the adjacent sheath. The total pressure inside and just outside the FTE is consistently larger than expected from pressure balance at a nominal (unperturbed) magnetopause and therefore the result of local compression by the passing FTE. The multi‐spacecraft observation enables the reconstruction of the Dayside Traveling Compression Region (DTCR), whose result is consistent with previous theoretical results. Semi‐periodic compressional velocity oscillations were observed and are likely driven by nearby occurrences of FTE trains, implying recurrent reconnection with a similar periodicity.