Three‐Dimensional Modeling of the O2(1∆) Dayglow: Dependence on Ozone and Temperatures.

Future space missions dedicated to measuring CO2 on a global scale can make advantageous use of the O2 band at 1.27 μm to retrieve the air column. The 1.27 μm band is close to the CO2 absorption bands at 1.6 and 2.0 μm, which allows a better transfer of the aerosol properties than with the usual O2 band at 0.76 μm. However, the 1.27 μm band is polluted by the spontaneous dayglow of the excited state O2 (1∆), which must be removed from the observed signal. We investigate here our quantitative understanding of the O2(1∆) dayglow with a chemistry‐transport model. We show that the previously reported −13% deficit in O2(1∆) dayglow calculated with the same model is essentially due a −20% to −30% ozone deficit between 45 and 60 km. We find that this ozone deficit is due to excessively high temperatures (+15 K) of the meteorological analyses used to drive the model in the mesosphere. The use of lower analyzed temperatures (ERA5), in better agreement with the observations, slows down the hydrogen‐catalyzed and Chapman ozone loss cycles. This effect leads to an almost total elimination of the ozone and O2(1∆) deficits in the lower mesosphere. Once integrated vertically to simulate a nadir measurement, the deficit in modeled O2(1∆) brightness is reduced to −4.2 ± 2.8%. This illustrates the need for accurate mesospheric temperatures for a priori estimations of the O2(1∆) brightness in algorithms using the 1.27 μm band. Plain Language Summary: Future space missions dedicated to measuring CO2 in the atmosphere can make advantageous use of the O2 absorption band at 1.27 μm. Indeed, the 1.27 μm band is close to the wavelengths where CO2 absorbs the solar radiation, which allows more precise calculations. However, the 1.27 μm band is polluted by the spontaneous infrared emission of O2 in its excited state called O2(1∆), which occurs in the upper atmosphere and must be removed from the observed signal. We investigate here our understanding of the O2(1∆) emission with a chemistry‐transport model. When compared to observations, there is a −13% deficit in O2(1∆) in our model. We find that this deficit is due to excessively high temperatures (+15 K) used in the calculations. The use of temperatures more in line with the observations slows down the ozone‐destroying chemical cycles, which leads to an almost total elimination of the O2(1∆) deficit. Once integrated vertically to simulate a satellite measurement, the deficit in modeled O2(1∆) brightness is reduced to −4.2 ± 2.8%. This illustrates the need for accurate temperatures in the middle atmosphere for a reliable prediction of the O2(1∆) emission occurring in the 1.27 μm band. Key Points: Three‐dimensional simulations of the O2(1∆) dayglow at 1.27 μm are compared to satellite dataThe model and observations show that O3 and O2(1∆) near the stratopause and in the lower mesosphere are anti‐correlated with temperatureThe O2(1∆) brightness at 1.27 μm calculated with reanalyzed temperatures is on average −4.2 ± 2.8% lower than the observations [ABSTRACT FROM AUTHOR]