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

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. Plain Language Summary The aurora are caused by energetic particle precipitation into Earth's atmosphere due to energy buildup and release in Earth's magnetic field from interaction with the solar wind. These energetic particles smash into Earth's atmosphere with high energy, and react with atoms and molecules in the atmosphere. There are many types of emissions of light that are associated with Earth's aurora. One of these emissions is the infrared emission centered near 4.26 μm associated with excited CO2 molecules. When CO2 is vibrationally excited through an exchange of energy with an N2 molecule excited by auroral particles, the CO2 molecule eventually relaxes from this state and releases a photon near 4.26 μm. This research presents a satellite observation from NASA's AIRS instrument allowing for the CO2 auroral emission to be viewed and mapped from space. Key Points A carbon dioxide infrared emission at 4.26 microns associated with the aurora is observed by the Atmospheric Infrared Sounder (AIRS) instrument A new non‐local thermodynamic equilibrium index provides a quantitative measure of the carbon dioxide auroral‐associated emission The AIRS auroral observations are confirmed by simultaneous Sounding of the Atmosphere using Broadband Emission Radiometry measurements and the SuperMAG Electrojet index