Signatures of equatorial midnight temperature maximum as observed from in situ and ground-based ionospheric measurements in the Indian sector

摘要

Results of a preliminary study carried out on the features of midnight temperature maximum (MTM) over the Indian sector as observed from the first in situ electron temperature variations of Indian SROSS C2 RPA data, the thermospheric night airglow intensities at 630 nm recorded from a subtropical Indian station Waltair (17.7°N, 83.3°E) and a colocated Digital Ionosonde data are reported. The electron temperatures indicate that during the summer solstice months of low solar activity periods, there was a significant temperature gradient from the equator toward the latitudes of Waltair (14–18° N) from 2200 to 2400 hours IST even in the topside F region. In contrast, during the winter solstice months, temperature contours do not show significant gradient around midnight, though isolated peaks are seen between 0100 and 0300 hours IST, i.e., delayed in time by a couple of hours, suggesting that the MTM is weaker. The MTM induced F layer descent at subtropical latitudes due to a probable neutral wind modification and consequent increase in 630 nm night airglow zenith intensity are studied to characterize the MTM induced ionospheric changes in terms of the starting time, velocity of F layer descent indicative of the strength of MTM, and the time at minimum height indicative of the time of cessation of MTM induced perturbation. The results are discussed in the light of earlier work and the current understanding of the origin of equatorial MTM.