Due to its interaction with the magnetic field of the Earth, the solar wind imparts a large amount of energy to the Earth’s atmosphere. This can result in intense ionospheric outflow. It contributes to atmospheric erosion, and these outflowing ions may also affect magnetospheric dynamics. The magnetic polar cap does not receive much of this energy, however, and thus the main source of energy there is solar illumination. Nonetheless it is an important region of ionospheric outflow. Because the Earth’s magnetic field at the polar caps is directly connected with the interplanetarymagnetic field, a steady but low-energy type of ion outflow occurs there, called the polar wind. Because of the low energy of the ions, the polar wind is very difficult to measure due to spacecraft charging. There is an alternative technique to measure the polar wind, exploiting the spacecraft charging. Another type of outflow that also commonly occurs in the magnetic polar cap is ion outflow above polar cap arcs. The ions are strongly accelerated in this process, yet this outflow has some similarities to polar wind outflow. Since it is such an important source of energy for outflow in the polar ionosphere, we will look in this presentation at the dependence of these ion outflow processes on solar illumination.
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