Articles | Volume 34, issue 11
Regular paper
07 Nov 2016
Regular paper |  | 07 Nov 2016

Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination

Lukas Maes, Romain Maggiolo, and Johan De Keyser

Abstract. The cold ions (energy less than several tens of electronvolts) flowing out from the polar ionosphere, called the polar wind, are an important source of plasma for the magnetosphere. The main source of energy driving the polar wind is solar illumination, which therefore has a large influence on the outflow. Observations have shown that solar illumination creates roughly two distinct regimes where the outflow from a sunlit ionosphere is higher than that from a dark one. The transition between both regimes is at a solar zenith angle larger than 90°. The rotation of the Earth and its orbit around the Sun causes the magnetic polar cap to move into and out of the sunlight. In this paper we use a simple set-up to study qualitatively the effects of these variations in solar illumination of the polar cap on the ion flux from the whole polar cap. We find that this flux exhibits diurnal and seasonal variations even when combining the flux from both hemispheres. In addition there are asymmetries between the outflows from the Northern Hemisphere and the Southern Hemisphere.

Short summary
Ion outflow from the ionospheric regions at the highest latitudes is mainly driven by solar illumination. It is an important factor affecting atmospheric escape and space weather. But this region rotates into and out of the sunlight on a daily and seasonal basis. This creates daily and seasonal variations in the outflow, even with both hemispheres combined. The north–south asymmetry in Earth's magnetic field causes extra variations and asymmetries. This was studied with a simple empirical model.