Ionospheric response to an interplanetary shock passage at Mars

We analyze multipoint observations from the Mars Express and MAVEN spacecraft to determine the response time scale of the Martian upper ionosphere to an interplanetary shock passage on 2 February 2017. The interplanetary shock was measured by MAVEN located well upstream from the Martian bow shock. The interplanetary shock passage is characterized by an extremely sharp jump in the solar wind dynamic pressure and magnetic field magnitude within 1 s. Meanwhile, the MARSIS instrument on board Mars Express, located in the dayside upper ionosphere, detected an exceptionally abrupt and large enhancement in the local magnetic field magnitude 1 min after the shock passage at MAVEN. The observed time lag is roughly consistent with the expected propagation time of a compressional pressure pulse from the bow shock to the upper ionosphere. Furthermore, MARSIS remote soundings indicate the formation of highly irregular structures in the topside ionosphere below Mars Express shortly after the local magnetic field enhancement. These observations demonstrate that the Martian ionosphere responds quickly to an interplanetary shock with time scales determined primarily by propagation of the pressure enhancement information.