THEMIS spacecraft and ground observations of Substorms in the Earth's Magnetotail

FTE Dynamics and Effects on Local and Remote Regions Near the Dayside Magnetopause Reconnection Layer

Abstract:
The Themis mission consists of five identical spacecraft (TH-A, B, C, D, E) that were launched on 17 February 2007 into a near-equatorial Earth orbit. The initial coast phase of the mission with all five probes in the same 1.07 by 15.4 RE configuration lasted until mid-September 2007. The maximum distance between the four leading probes during this string-of-pearl phase was often 1.5 RE or less and provides a unique opportunity to study spatio-temporal behavior of dayside magnetopause magnetic reconnection exhausts such as the dynamics of so-called Flux Transfer Events (FTEs) which are believed to be generated as the rate of reconnection changes.
Several near-simultaneous bipolar magnetic field signatures were observed by Themis on 8 June 2007 during an outbound postnoon magnetopause (MP) crossing in a string-of-pearl configuration. We interpret each as an FTE event. Whether observed in the magnetosheath or in the dayside magnetosphere, we show that each FTE event is unambiguously linked to the MP layer and the northward reconnection exhausts during these steady southward IMF conditions.
Unlike the other probes, TH-C observed a bifurcated MP current as it traversed the active MP layer. This MP crossing was also unique in that it lacked any clear bipolar signatures. A high-resolution BATSRUS MHD simulation (0.0626 RE) suggests that the bifurcation can be generated temporarily in the wake of a passing FTE.
The same MHD simulation suggests that all of the simultaneously observed FTE signatures can be explained in terms of a single flux rope within the active MP layer and its remote effects on the dayside magnetosphere and the magnetosheath adjacent to the MP. Cold ions in the dayside magnetosphere with characteristic time-of-flight energy dispersions are likely one such remote effect of the passing FTEs in the nearby MP layer as indicated by the generation of a standing wave train in the normal component of the simulated plasma velocity (VN) and corroborated by the observed VN.

THEMIS Mission, a miracle! (low cost and high science return)

Abstract:
THEMIS, an acronym for Time History of Events and Macroscale Interactions During Substorms and also represents the goddess of justice in Greek mythology, was successfully launched on 2/17/2007 the Cape Canaveral, Florida. It was the first time in NASA's history to launch five identical space probes with a single launch vehicle (Delta-II). The five space probes are placed in desired orbits to measure charged particles over a broad energy range, and electric and magnetic fields. Its primary science objective is to answer fundamental questions regarding the magnetospheric substorm instability, a dominant mechanism of transport and explosive release of solar wind energy within Geospace. It will also help to address the source populations of the radiation belt electrons and study the bow shock and magnetopause. In the presentation, I will describe some engineering challenges associated with THEMIS mission and some science high lights achieved and LASP's involvement in this great mission.