Comparison of a photochemical model with observations of mesospheric hydroxyl and ozone

Abstract

We present a comparison of a photochemical model with mesospheric hydroxyl (OH) data from the Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) and mesospheric ozone (O 3) data from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER). Although SHIMMER and SABER do not measure the atmosphere coincidently, by sampling the photochemical model at the appropriate local time of each measurement, an effective concurrent test of mesospheric odd oxygen and odd hydrogen theory can be achieved. Consistent with previous, more limited analyses of SHIMMER data, we find no evidence of a systematic model overprediction of mesospheric OH. However, at 80 km, the standard chemical scheme shows a model deficit in the morning hours and a dramatic model excess in the late afternoon. Using a higher rate coefficient for the H + O 2 + M → HO 2 + M reaction ameliorates this problem. Such a higher rate is consistent with the only reported laboratory measurements at the low temperatures appropriate to the mesosphere. Regarding the SABER ozone, the model significantly underpredicts the data. Some of this could be explained by a previously reported, systematic high bias to the SABER ozone, and comparisons of our model with Microwave Limb Sounder data support that suggestion. Nonetheless, a persistent model ozone deficit remains. Since the model agreement with SHIMMER OH is generally very good, this model ozone deficit is unlikely to be due to a mischaracterization of mesospheric HOx. Key Points Comprehensive comparison of a model with both OH and ozone Key chemical rates should be remeasured at mesospheric temperatures Model underpredicts ozone, but OH comparison is good. © 2012 American Geophysical Union. All Rights Reserved.