Current sheet profile and structure before and during the thinning of the magnetotail

Thinning of tail plasma sheet is associated with transfer of energy from the solar wind into the magnetosphere. Recently Saito et al. [2010,Geophys, Res. Lett.] studied this thinning feature of the near Earth plasma sheet using observations by five THEMIS spacecraft in formation flight, which reveals new information on the structure and temporal behavior during substorms. Using the data from the same event, we examine the latitudinal profiles of plasma and magnetic field measurements around the magnetic equator and discuss their physical implications. We found that the total pressure of the outer part of the tail current sheet exhibited a significant latitudinal gradient both before and during the thinning of the tail, while the total pressure gradient in the inner part of the tail behaved differently. Assuming a latitudinal MHD force balance, the analysis of the total pressure suggests that the inner tail flux tube has different geometry from the outer part and evolves in close association with the thinning of the geomagnetic tail.