<P> Here, it is φ latitude, λ longitude, and t time, ω the angular frequency of one year, ω the angular frequency of one solar day, and τ = ω t + λ the local time . t = June 21 is the date of northern summer solstice, and τ = 15: 00 is the local time of maximum diurnal temperature . </P> <P> The first term in (3) on the right is the global mean of the exospheric temperature (of the order of 1000 K). The second term (with P = 0.5 (3 sin (φ) − 1)) represents the heat surplus at lower latitudes and a corresponding heat deficit at higher latitudes (Fig . 2a). A thermal wind system develops with wind toward the poles in the upper level and wind away from the poles in the lower level . The coefficient ΔT ≈ 0.004 is small because Joule heating in the aurora regions compensates that heat surplus even during quiet magnetospheric conditions . During disturbed conditions, however, that term becomes dominant, changing sign so that now heat surplus is transported from the poles to the equator . The third term (with P = sin φ) represents heat surplus on the summer hemisphere and is responsible for the transport of excess heat from the summer into the winter hemisphere (Fig . 2b). Its relative amplitude is of the order ΔT ≃ 0.13 . The fourth term (with P (φ) = cos φ) is the dominant diurnal wave (the tidal mode (1, − 2)). It is responsible for the transport of excess heat from the daytime hemisphere into the nighttime hemisphere (Fig . 2d). Its relative amplitude is ΔT ≃ 0.15, thus on the order of 150 K. Additional terms (e.g., semiannual, semidiurnal terms and higher order terms) must be added to eq. (3). However, they are of minor importance . Corresponding sums can be developed for density, pressure, and the various gas constituents . </P> <P> In contrast to solar XUV radiation, magnetospheric disturbances, indicated on the ground by geomagnetic variations, show an unpredictable impulsive character, from short periodic disturbances of the order of hours to long - standing giant storms of several days' duration . The reaction of the thermosphere to a large magnetospheric storm is called thermospheric storm . Since the heat input into the thermosphere occurs at high latitudes (mainly into the auroral regions), the heat transport represented by the term P in eq. (3) is reversed . In addition, due to the impulsive form of the disturbance, higher - order terms are generated which, however, possess short decay times and thus quickly disappear . The sum of these modes determines the "travel time" of the disturbance to the lower latitudes, and thus the response time of the thermosphere with respect to the magnetospheric disturbance . Important for the development of an ionospheric storm is the increase of the ratio N / O during a thermospheric storm at middle and higher latitude . An increase of N increases the loss process of the ionospheric plasma and causes therefore a decrease of the electron density within the ionospheric F - layer (negative ionospheric storm). </P>

Why is the mesosphere cold and the thermosphere hot