Mid‐latitude thermospheric neutral kinetic temperatures, 1. Solar, geomagnetic, and long‐term effects

Abstract

The effects of solar activity and geomagnetic activity on the nighttime mid‐latitude thermosphere kinetic temperatures have been investigated by using measurements obtained from 1972 through 1979. This study has been made by using the kinetic neutral temperatures obtained from the Doppler widths of the [O I] 15867K (630 nm) emission at Fritz Peak Observatory, Colorado (39.87°N, 105.5°W). During the time span of the measurements solar activity, expressed as the 2.8‐GHz solar radio flux, varied nearly five‐fold, while the corresponding thermospheric temperature almost doubled. With these data a single variable simple power law relationship gives a high correlation with the temperature. A linear relationship between temperature changes and geomagnetic activity, expressed by the index Ap, has also been found. The residuals from the data and these relations show strong annual and semiannual components, with the former undistinguishable in phase with the annual variation of the solar declination angle. A comparison of these results with empirical models shows that most of the presently available empirical models do not adequately represent the observed dependence of temperature on solar activity, in particular during times of high solar activity. It is also found that on the basis of four parameters, namely solar activity, solar declination, geomagnetic activity, and a semiannual variation (and its associated phase), it is possible to obtain a better fit for our data than with the available empirical models.