Nitric Oxide in Climatological Global Energy Budget During 1982–2013

Over the past decades, temperature and density of the upper atmosphere show negative trends and this decrease of the upper atmospheric temperature is attributed to the declining neutral density. Specifically, nitric oxide (NO) and carbon dioxide (CO ₂ ) govern thermospheric cooling at 5.3 and 15 μm, respectively. While a lot of efforts have focused on the CO ₂ effects on the long-term trends, relatively less attention has been paid to the impacts by NO, which responds to solar and geomagnetic activities dynamically. In this study, we investigate the role of NO in climatological global energy budget for the recent three solar cycles using the Global Ionosphere-Thermosphere Model. From 1982 to 2013, the F10.7 and Ap indices showed a decadal decrease of ~8% and ~20%, respectively. By imposing temporal-varying F10.7 and Ap values in the simulations, we find a decadal change of −0.28 × 10 ¹¹  W or −17.3% in total NO cooling power, which agrees well with that (−0.34 × 10 ¹¹  W or −17.2%) from the empirical Thermosphere Climate Index derived from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry data. Neutral density decreases by 10–20% at 200–450 km and T _ex decreases by 25.3 K per decade. The deduced-decadal change of NO cooling reaches ~25% of that of total heating at ~130 km and its significance decreases with altitude.