Contribution of chemical processes to infrared emissions from nitric oxide in the thermosphere

Abstract

AbstractInfrared emissions from nitric oxide (NO) are the dominant source of radiative cooling between 120 and 200 km and play an important role in determining the energy budget of the Earth's upper atmosphere. The emission arises as a consequence of producing vibrationally excited NO, either by collisions with energetic atomic oxygen or via the reaction of atomic nitrogen with molecular oxygen. The latter process is a potentially important source of cooling, as it can excite the higher vibrational levels (v ≥ 2) of nitric oxide, resulting in the emission of multiple photons. This chemiluminescent emission has been modeled by calculating the level populations of NO(v ≤ 10) considering production from the reaction of N(2D) and N(4S) with O2, along with interlevel cascade due to radiative deexcitation and collisional quenching. We integrate this model into the NCAR TIE‐GCM (Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model) to calculate the contribution of chemiluminescence to infrared emissions from NO in the thermosphere. For day 80 of 2003, it is shown that chemiluminescence accounts for 15–30% of the total column emissions from NO in the sunlit thermosphere between ±50° latitude. More than 60% of the chemiluminescence is produced from v ≥ 3, indicating that these vibrational levels are an important source of thermospheric cooling. Model calculations of the first overtone emission (Δv = 2) are shown to be in agreement with measurements by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS‐1A) experiment. A computationally inexpensive parameterization which calculates the chemiluminescence from v ≤ 10 within 5% of the full calculation is also presented.