• dissipation region;
  • in situ observation;
  • magnetic reconnection

[1] Signatures of the dissipation region of collisionless magnetic reconnection are investigated by the Geotail spacecraft for the 15 May 2003 event. The energy dissipation in the rest frame of the electron's bulk flow is considered in an approximate form De*, which is validated by a particle-in-cell simulation. The dissipation measure is directly evaluated from the plasma moments, the electric field, and the magnetic field. UsingDe*, a compact dissipation region is successfully detected in the vicinity of the possible X-point in Geotail data. The dissipation rate is 45 pWm−3. The length of the dissipation region is estimated to 1–2diloc (local ion inertial length). The Lorentz work W, the work rate by Lorentz force to plasmas, is also introduced. It is positive over the reconnection region and it has a peak around the pileup region away from the X-point. These new measuresDe* and W provide useful information to understand the reconnection structure.