Climatology of O/N₂ Variations at Low- and Mid-Latitudes during Solar Cycles 23 and 24

Abstract

We present a study concerning the thermospheric O/N2 variations for the period 2002 to 2020, using the measurements of global ultraviolet imager (GUVI) onboard TIMED satellite. In this regard, monthly averaged O/N2 was computed—using the five quietest days of the month—at low- and mid-latitudes. To find the longitudinal dependence of thermospheric variations, the analysis is further extended to different longitudinal sectors, namely Asia, Africa, and America. We found that the latitudinal and longitudinal O/N2 variations follow the solar activity. These variations, during a high solar activity in northern winter, are found to be always much greater than southern winter and northern summer. The latitudinal and longitudinal variations of O/N2 at low- and mid-latitudes in December solstice are observed to be higher than June solstice counterparts in the northern hemisphere. We also computed the amplitudes of annual and semiannual variations using the bandpass filters. The former variations of O/N2 for low-latitudes do not follow the solar activity in the southern hemisphere. Moreover, these variations are stronger for mid-latitudes as compared with low-latitude regions. Similarly, the annual variations in Asian and African sectors of southern hemisphere do not follow the solar cycle (SC) trends. In the northern hemisphere, the variations are stronger during a solar maximum than in the southern counterpart. The observed semiannual variations are in-phase for both hemispheres; moreover, the corresponding amplitude remains almost the same at low- and mid-latitudes, while the semiannual variations for low-latitudes, and corresponding longitudinal regions, are stronger during a high solar activity. These variations, for mid-latitudes, in African, northern Asian, and southern American sectors do not follow the SC activity.

Keywords

• O/N₂
• annual variations
• semiannual variations
• thermospheric composition