Spherical asymmetry in thermospheric magnetic storms |
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| Authors: | HG Mayr H Trinks |
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| Institution: | NASA/Goddard Space Flight Center, Laboratory for Planetary Atmospheres, Greenbelt, MD 20771, U.S.A. |
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| Abstract: | During moderate magnetic storms, changes in the neutral composition suggest that energy is deposited in the auroral zones. This results in thermal expansion (enhancement in N2, Ar) and consequent redistribution of the lighter species O and He such that their densities decrease at high latitudes and increase at low latitudes. From measurements obtained by the ESRO 4 gas analyzer during a major storm in late February 1973 (Kp = 7+) these typical high latitude characteristics were observed in the southern hemisphere and at certain longitudes to extend toward mid and low latitudes as far as ?20° invariant latitude. Further examination of these data for latitudes across the equator up to +20° latitude, however, shows evidence for an enhancement zone in He and O which is clearly displaced into the northern hemisphere thus suggesting a pronounced spherical asymmetry. Ground based observations on the state of the ionosphere between ±50° latitude confirm this asymmetry and suggest that the center of this enhancement zone occurs at about +15° invariant latitude. Adopting a suitable energy distribution in both hemispheres the magnetic storm response in the neutral composition is simulated with a circulation model. From this analysis it is concluded that for some longitudes a difference of a factor of two or more between the heating rates of the northern and southern hemispheres is required to match the ESRO-4 data. |
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