Sporadic E-like Topside Layer Driven by Wind Shear in the Martian Ionosphere

Ionospheric plasma density disturbances significantly affect radio wave propagation, impacting communication and planetary exploration. At Earth, sporadic E layers (Es) are commonly observed. They are characterized by thin, high-density plasma structures in the E-region ionosphere, primarily formed by electromagnetic forces induced by horizontal wind shears. Similar sharp vertical electron density changes have also been observed in the topside of the Martian ionosphere by missions like Mars Global Surveyor, Mars Express, and Mars Atmosphere and Volatile EvolutioN. Recent studies suggest that such structures observed on Mars can be attributed to a sporadic E-like mechanism induced by magnetic shear, which can be referred to as Es-like structures. While wind shear theoretically contributes to such events, no observational evidence currently reports wind shear as an explanation for these density gradients on Mars. In this study, we report a novel observation of an Es-like topside layer in the Martian ionosphere, characterized by both density layer and rift (an abrupt depletion in density), where wind and magnetic shear are simultaneously observed. Statistical analysis of 305 orbits with wind speed observations revealed wind shear is observed in nine Es-like events, primarily occurring in strong crustal magnetic field regions. Simulations suggest that the observed rift and layer can be explained either by "wind shear" or by "wind and magnetic shear" under strong crustal magnetic field. This study provides new observations of Es-like events on Mars and serves as a credible candidate for the contribution of wind shear to the formation of an Es-like topside layer.