Observations of 4.26 μm CO₂ Auroral Emissions From AIRS Nadir Sounder Measurements

Abstract

The Atmospheric Infrared Sounder (AIRS) instrument onboard the NASA Aqua satellite is used to observe aurora associated with the CO2 4.26 μm emission. These observations are due to non‐local thermodynamic equilibrium (NLTE) resulting from the vibrational excitation of CO2, which arises in the process of auroral energetic particle precipitation, as opposed to the dayside NLTE occurring due to solar radiation. The observations are confirmed to be associated with aurora using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) limb measurements and the SuperMAG Electrojet (SME) index. The high spectral resolution and low noise associated with the AIRS instrument allows for the emission spectrum to be calculated and confirmed to arise from CO2. Our new NLTE index values derived from AIRS provide the ability to globally measure auroral events associated with CO2 with a spatial resolution on the order of ∼13.5 km.