INVESTIGATION OF THE HOT FLOW ANOMALY STRUCTURE

  1. Space Research Institute (IKI)

The aim of this study was to investigate the structure of the Hot Flow Anomaly detected by Interball-Tail
on 96/03/14 near Earth’s bow shock. The work is based on data acquired by ion spectrometer SKA-1, electron
spectrometer ELECTRON, and magnetometer MIF-3. The orientation of interplanetary current sheet that
caused formation of HFA was found with use of these data. Several characteristic regions within the HFA
were identified from dynamic spectra of electrons and ions. Using the geometry of the bow shock it was found
from the data, that electric field on both sides of the current sheet is directed towards the current sheet. This
corresponds to previous ideas on the reason of HFA’s formation. It is known that ions reflected by bow shock
are injected back into the current sheet that leads to instability and formation of an HFA. We estimated the
velocity of the HFA’s motion along the bow shock front and transverse dimension of HFA. Analysis of plasma
velocities estimated mean velocity of HFA; we found that HFA was expanding sideways from the current sheet.
The reason of this expansion was found by the comparison of internal and external pressures. Detailed analysis
of the ion velocity distributions within HFA showed that it has complicated structure and consists of two parts.
It was also shown that part of HFA has sunward directed velocity indicative to convective structure of the
HFA. Analysis of magnetic field and ion velocity distributions allowed us to locate the source of thermal and
convective energy.