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

摘要

The cold ions (energy less than several tens of electronvolts) flowing out from thepolar ionosphere, called the polar wind, are an important source of plasmafor the magnetosphere. The main source of energy driving the polar wind issolar illumination, which therefore has a large influence on the outflow.Observations have shown that solar illumination creates roughly two distinctregimes where the outflow from a sunlit ionosphere is higher than that from adark one. The transition between both regimes is at a solar zenith anglelarger than 90°. The rotation of the Earth and its orbit around theSun causes the magnetic polar cap to move into and out of the sunlight. Inthis paper we use a simple set-up to study qualitatively the effects of thesevariations in solar illumination of the polar cap on the ion flux from thewhole polar cap. We find that this flux exhibits diurnal and seasonalvariations even when combining the flux from both hemispheres. In additionthere are asymmetries between the outflows from the Northern Hemisphere andthe Southern Hemisphere.