Long-term Trends in the Upper atmosphere using the observations of Incoherent Scatter Radar at Arecibo Observatory

Several studies on long-term trend using the ion temperature in ionospheric F-region are made in high-latitude stations using Incoherent Scatter Radar (ISR) measurements. Those observed trends indicate the upper atmospheric cooling. Those studies reported that those have strong dependency on magnetic latitude for the altitudes above −275 km. Given the advantage of high sensitivity of Arecibo Observatory's ISR and its location at geomagnetic latitude (29°N), it is very much interesting to examine the long-term trends of the ion temperatures (T
i
) for the altitudes above −275 km. We have analyzed T
i
data sets of ISR from 1985 to 2015, to examine the long-term trends of the ion temperature as function of altitude from ~122 km to ~700 km over Arecibo (18.3°N). These long-term trends are examined in relation to solar flux of F
10.7
(flux at 10.7 cm) and A
p
index for the understanding of influence of solar flux and geomagnetic activity on temperature trends of the F-region. These results will be discussed to understand the effects of solar activity and geomagnetic activity.