Parameterization of solar heating by the near IR CO 2 bands in the mesosphere

Abstract

Absorption of solar energy by CO 2 bands at wavelengths shorter than 5 μm provides a secondary source of heating in the mesosphere. This source is essential between 65 and 85 km where it can exceed 1 K/day and contribute up to 30 % to the total solar heating, provided the mesospheric ozone heating has a local minimum in this region. A proper calculation of the solar heating in the near-infrared CO 2 bands involves consideration of complicated NLTE processes in the CO 2 molecule. This circumstance and the relatively small energy effect account for the absence of parameterizations for the near-infrared CO 2 solar heating in the mesosphere suitable for use in GCMs. In this paper we present what we believe is the first such parameterization. It has been developed for use in GCMs as a daytime correction to the 15 μm CO 2 band cooling previously parameterized only for nighttime conditions. At any given height level this parameterization has an explicit dependence on both the volume mixing ratio of CO 2 at the altitude in question and the CO 2 column density along the solar radiation path. Dependence on a variety of other parameters is quite complicated but of less importance and has been taken into account through statistics. The accuracy of the parameterization is examined for a wide variety of atmospheric conditions. Between 70 and 80 km, where the near-infrared CO 2 solar heating is of the most importance, the error of daily averaged values of this heating does not generally exceed 0.1 K/day or less than 10 %.