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\begin{document}

\title{Long-term Trends in the Upper atmosphere using the incoherent scatter
radar observations over Arecibo}



\author[1]{Selvaraj Dharmalingam}%
\author[2]{Michael P. Sulzer}%
\author[3]{Shun-Rong Zhang}%
\author[4]{Christiano Garnett Marques Brum}%
\author[2]{Nestor Aponte}%
\affil[1]{Arecibo Observatory / UCF}%
\affil[2]{Arecibo Observatory}%
\affil[3]{MIT Haystack Observatory}%
\affil[4]{Arecibo Observatory/University of Central Florida}%


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  \date{June 16, 2024}


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\begin{abstract}
Upper atmospheric long-term trends could be examined in the ion
temperatures (\$T\_i\$) at the ionospheric F-region altitudes by the
close coupling between neutrals and ions. We have analyzed the \$T\_i\$
data sets of Arecibo Observatory (AO) incoherent scatter radar
(18\textbackslash{}textdegree20'N, 66\textbackslash{}textdegree45'W)
from 1985 to 2019, to examine the long-term trends of the ion
temperature as a function of height from \$\textbackslash{}sim\$140 km
to \$\textbackslash{}sim\$677 km. For this, the responses of \$T\_i\$ to
solar and geomagnetic activities have been taken into account as
forcings of the \$T\_i\$ behavior as well the annual and semi-annual
oscillations. By removing the known forcing that govern the Ti behavior
by the difference between the \$T\_i\$ data and a climatological model,
our results indicate that the upper atmosphere/ionosphere over Arecibo
is cooling over the 35 years studied. Around 350 km, our findings also
show that the rate of cooling over Arecibo is lower than previously
reported for high latitudes, suggesting a latitudinal dependency. These
cooling trends are believed to be the result of increasing green house
gases, but the observed cooling trends exceed the magnitude of the
cooling expected from green house gases. We have made an attempt to find
the additional driver for observed cooling trends by linking the these
upper atmospheric trends to lower atmospheric weather phenomena. We
found that gravity waves in the lower atmosphere associated with
terrestrial weather phenomena might be contributing to the observed
cooling trends in the upper atmosphere.%
\end{abstract}%



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