LAUSR

Multipoint observations from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on board Mars Express and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission reveal a dynamic response of the Martian ionosphere to abrupt variations in the upstream solar wind plasma. On 2 February 2017, MAVEN, located upstream from the Martian bow shock, encountered a CIR-related interplanetary shock with a sudden enhancement in the dynamic pressure. MARSIS, operating in the upper ionosphere at ∼478 km altitudes and ∼78∘ solar zenith angles, observed a sharp increase in the local magnetic field magnitude ∼1 min after the shock passage at MAVEN. The time lag is roughly consistent with the expected propagation time of a pressure pulse from the bow shock to the upper ionosphere at the fast magnetosonic speed. Subsequently, remote soundings recorded disturbed signatures of the topside ionosphere below Mars Express.