| The solar wind interaction with Mars has been studied extensively through satellite observations and numerical models. From these studies it is well known that Mars lacks a global dipole field nonetheless presents a significant ionospheric obstacle to the solar wind. Moreover, the presence of strong crustal magnetic sources makes the interaction spatially and temporally variable as the planet rotates on its axis and causes local transient particle events. In data from the Mars Global Surveyor orbiter's Electron Reflectometer (MGS/ER) instrument, we discover a new local event of particle enhancements: A seasonal, nighttime clustering of electron flux enhancements at low-energy levels is observed over a localized geographical region in the southern hemisphere of Mars. This enhancement phenomenon is interpreted as the transportation of photoelectrons above the crustal magnetic sources on the dayside to the magnetotail on the nightside of Mars along the lines of the reconnected Interplanetary Magnetic Field (IMF). In order to explain the origin of this phenomenon, a semi-empirical-analytical model is developed to describe the magnetic field configuration of the Martian solar wind interaction. In this model, crustal fields are represented by spherical harmonic expansion, and the perturbed solar wind field is derived from the deviation of a proton flow around a conducting spherical obstacle. Overall magnetic field is obtained from the vector superposition of the crustal fields and perturbed solar wind field. Results of this semi-empirical-analytical model account for the observed electron enhancements. Furthermore, the primary conclusions of this model are validated by simulations obtained from a self-consistent Magnetohydrodynamic model, allowing for a more accurate and reliable description of the exact nature of the Martian solar wind interaction. |
