The Magnetic Field Induced by the Solar Wind on the Dayside of Mars

The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on Mars Express can be used to measure the local magnetic field. The technique relies on the detection of the electron echoes. These are series of echoes that are equally spaced in time at the electron cyclotron period. The echoes are believed to be caused by the periodic return to the antenna of electrons that are accelerated during the sounder pulse by strong electric fields near the antenna. From the period of the echo, the magnetic field strength in the vicinity of the spacecraft can be computed. These scalar measurements are highly complementary to those obtained by the Mars Global Surveyor Magnetic Field Experiment (MAG/ER). The Cain et al. (2003) model is used for nightside magnetic field measurements where MARSIS data is from the dayside. The difference between the nightside and the dayside measurements is due to the electrical currents that flow in the dayside ionopause. An average magnetic field vector which is induced by the solar wind is calculated using a best-fit method for each periapsis pass. This result will contribute to the study of the Mars-solar wind interaction.