Long-Term Trends in the Upper atmosphere using the observations of Incoherent Scatter Radar over Arecibo

An increase in greenhouse gases in the lower atmosphere by anthropogenic/natural activity leads to a change in the energy budget of the earth's atmosphere in long-term. In the upper atmosphere, a cooling trend is expected theoretically due to an increase in greenhouse gases. Long-term trends could be examined in the temperature of the ions (T i) at the ionospheric F-region by the close coupling between neutrals and ions. We have analyzed the Ti data sets of Arecibo Observatory (AO) incoherent scatter radar (18o20'N, 66o45'W) from 1981 to 2019, to examine the long-term trends of the ion temperature as a function of height from ~140 km to ~677 km over Arecibo. These long-term trends are examined in relation to the solar flux of F10.7 (flux at 10.7 cm) and Ap index for the understanding of the influence of solar flux and geomagnetic activity on temperature trends of the F-region. The results indicate that the upper atmosphere/ionosphere over Arecibo is cooling over a period of time. In most of the upper atmosphere, the rate of cooling over Arecibo is relatively lower than High-latitudes upto ~500 km. Above ~500 km, cooling trends are increasing rapidly. There is a latitudinal dependency, that will be discussed.