Thermospheric Nitric Oxide Cooling Responses to the 14 December 2020 Solar Eclipse

Abstract

The behaviors of the nitric oxide (NO) cooling in the lower thermosphere during the 14 December 2020 solar eclipse are studied using Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements and WACCM‐X simulations. We found that NO cooling rate decreases during the solar eclipse in both SABER measurements and WACCM‐X simulations. The maximum decrease of the NO cooling is 40% in SABER measurements and 25% in WACCM‐X simulations. The NO cooling process is initiated almost entirely through the collisions with atomic oxygen (O) which depends linearly on NO and O densities and non‐linearly on the neutral temperature. During the eclipse, the NO concentration and temperature decreases are larger than that of O concentration. Consequently, the eclipse‐time NO concentration and temperature decreases are the major drivers of the NO cooling rate decrease. The decreases of the temperature and the NO concentration contribute comparably to the eclipse‐time NO cooling rate decrease.

Nitric Oxide Concentration: A New Data Set Derived From SABER Measurements

“…The storm time NO concentration variation matches the MLT temperature variations discussed in (Wang et al., 2021). Moreover, since the NO concentration is quasi‐linearly related to the NO cooling (Wang, Yu, et al., 2022), understanding the storm‐time NO concentration behavior can provide insight into the NO cooling variation during geomagnetic storms.…”

“…The NO infrared cooling in the 5.3 μm band regulates the upper atmosphere thermal structure and energy balance (Mlynczak et al, 2003(Mlynczak et al, , 2005. NO emissions, as a "natural thermosphere thermostat," exhibit significant variations on both short timescales (geomagnetic storms and solar eclipses) (Lu et al, 2010;Mlynczak et al, 2003;Wang, Yu, et al, 2022) and long timescales (11-year solar cycle) (Knipp et al, 2017;Mlynczak et al, 2014), and dominates thermospheric radiative cooling processes, particularly above 125 km. While there are extensive studies focused on the NO infrared cooling responses to geomagnetic storms (e.g., Bharti et al, 2018;Dobbin et al, 2006;Knipp et al, 2013Knipp et al, , 2017Lei et al, 2011Lei et al, , 2012Li et al, 2019;Lu et al, 2010;Mlynczak et al, 2003Mlynczak et al, , 2005Sheng et al, 2017;Zhang et al, 2014) using both numerical simulations and SABER observations, there have been fewer investigations into the behavior of NO concentration on both short and long timescales, due to limited data availability.…”