Characteristics of the double layer associated with terrestrial bow shock by THEMIS observation

This study presents observation and detailed analysis on the double layers (DLs) in the ramp and the foreshock contacting with the foot of the terrestrial bow shock by THEMIS on September 14, 2008 under enhanced dynamic pressure in the solar wind. The results reveal that: (1) The time duration of the double layers is mainly 3-8 ms, and their max parallel electric field is minus 10-40 mV/m. (2) On assuming a propagation speed at the ion acoustic speed (gv (s)), their spatial scale is estimated to be 0.3-1.15 km (about 75-200 lambda (D) ). (3) The net potential drop of DLs is estimated to be 5-32 V. (4) The DLs in the ramp and the foreshock contacting to the foot of the bow shock is current-carrying as a result of development and evolution of nonlinear phase of instability in the self-consistent current-carrying plasma. The DLs may play an important role in strong turbulence in the foreshock contacting with the foot of the bow shock.