Temperature In Lower Thermosphere Research Articles

The thermosphere in motion

Analysis of rocket-borne mass spectrometric thermospheric measurements of major and minor neutral species by coupled multicomponent equations of motion reveals the lower thermosphere to be in a nonequilibrium state. The individual species motion and thermal diffusion are significant factors in (1) the theoretical calculations of self-consistent species distributions and velocities for almost all atmospheric species and (2) the determination of lower-thermospheric temperatures from individual species profiles. The theoretical approach and the results of rocket probe analyses with regard to thermospheric species distributions, temperatures, and vertical velocities are presented.

On the semiannual variation of the upper atmosphere

The effects of the seasonal variations of the dynamical properties of the lower thermosphere at and below 120 km, like the dissociation of molecular oxygen, the turbopause levels of different constituents and the temperature on the semiannual variation (SAV) in the upper atmosphere on the basis of steady state models have been studied. It is concluded that the seasonal variations in the mass density and temperature in the lower thermosphere as adopted from the US Standard Atmosphere Supplements (1966) in conjunction with the observed dissociation ratio (O/O 2) do not yield the observed semiannual amplitude (SAA) (maximum value in equinoctial months/minimum value in solstitial months) in the upper atmosphere. However, if one adopts on the basis of observations a SAA of about 1.25 in density and temperature in the lower thermosphere, the observed SAA at 190 km can be theoretically reproduced, but only if the ratio (O/O 2 in solstitial months/O/O 2 in equinoctial months) has a value of about 4 or if the number density of atomic oxygen in solstitial months is greater by a factor of about 1.7 than that in equinoctial months, at 120 km. Under the ideal condition of no seasonal variation in the lower thermospheric temperature, the observed SAA at 190 km can be theoretically reproduced if the above said ratio of 4 is reduced to 0.8. It is concluded that the SAV of the dissociation ratio at 120 km exists in phase or out of phase with that of the atmospheric density depending on whether the SAA in the temperature is less or greater than about 1.1 at 120 km. The increase of the SAA within the solar cycle, when the solar activity changes from 80 to 150 F -units can be explained if the dissociation increases more rapidly with solar activity in equinoctial months as compared to that in solstitial months. At altitudes where helium predominates, the observed SAA indicates that the turbopause levels of helium lie at about 100 km in winter, 102 km in equinox, and 104 km in summer.