Mars has a complex magnetic topology where crustal magnetic fields can interact with the solar wind magnetic field to form magnetic cusps. On the nightside, solar wind electron precipitation can produce enhanced ionization at cusps while closed field regions adjacent to cusps can be devoid of significant ionization. Using an electron transport model, we calculate the spatial structure of the nightside ionosphere of Mars using Mars Global Surveyor electron measurements as input. We find that localized regions of enhanced ionospheric density can occur at magnetic cusps adjacent to low density regions. Under this configuration, thermospheric winds can drive ionospheric electrojets. Collisional ions move in the direction of the neutral winds while magnetized electrons move perpendicular to the wind direction. This difference in motion drives currents and can lead to charge accumulation at the edges of regions of enhanced ionization. Polarization fields drive secondary currents which can reinforce the primary currents leading to electrojet formation. We estimate the magnitude of these electrojets and show that their magnetic perturbations can be detectable from both orbiting spacecraft and the surface. The magnitude of the electrojets can vary on diurnal and annual time scales as the strength and direction of the winds vary. These electrojets may lead to localized Joule heating, and closure of these currents may require field-aligned currents which may play a role in high altitude acceleration processes.
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机译：火星具有复杂的磁拓扑，地壳磁场可以与太阳风磁场相互作用形成磁尖。在夜晚，太阳风的电子沉淀会在尖端产生增强的电离作用，而靠近尖端的封闭电场区域可能不会产生明显的电离作用。使用电子传输模型，我们使用Mars Global Surveyor电子测量值作为输入来计算火星夜间电离层的空间结构。我们发现电离层密度增加的局部区域可能出现在与低密度区域相邻的磁性尖端处。在这种配置下，热层风可以驱动电离层电喷流。碰撞离子沿中性风的方向运动，而磁化电子垂直于风向运动。这种运动差异会驱动电流，并可能导致电荷在电离增强区域的边缘积累。极化场驱动次级电流，次级电流可以增强初级电流，从而形成电喷流。我们估计了这些电喷的强度，并表明它们的磁扰动可以从轨道飞行器和地表中检测到。随着风的强度和方向的变化，电喷的强度会在昼夜和年度尺度上变化。这些电喷可能导致局部的焦耳热，并且关闭这些电流可能需要场对准的电流，这可能在高海拔加速过程中起作用。
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