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

AbstractFuture 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.