Changes in thermospheric composition inferred from twilight O+(2P) emission |
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| Authors: | JF Noxon RB Norton |
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| Institution: | Fritz Peak Observatory, Aeronomy Laboratory, NOAA, Boulder, CO 80303, U.S.A. |
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| Abstract: | Measurements of the twilight enhancement of airglow emission from O+(2P) near 7325 Å reveal major changes which accompany geomagnetic activity, no significant distance between evening and morning and an increase in brightness paralleling the approach to solar maximum. The principal source for O+(2P) is direct photoionization from O(3P) but at low solar activity there appears to be a contribution from another source in early twilight which may be local photoelectron ionization into O+(2P). The geomagnetic and solar effects appear to reflect changes in the O and N2 density in the thermosphere; ground based twilight measurements of O+ emissions thus provide a simple means for monitoring thermospheric structure from 300 km to ～ 500 km at solar minimum and to ～600 km at solar maximum. |
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