Approximation for the vibrational excitation of middle atmospheric NO by upwelling radiation.

A plane-parallel approximation using FASCODE to calculate upward and downward IR flux density and angle-averaged radiance is described and tested against results that account for planetary curvature. The method is further developed to calculate the excitation of NO(v = 1) due to absorption of upwelling radiation in the earth's atmosphere. The algorithm is applied to a standard set of atmospheric models, in addition to typical and extreme desert atmospheric models which are included to maximize the effect. The results of this work show that upwelling radiation typically contributes <2.5% to the total NO(v = 1) excitation in the midstratosphere rises to ~5% at 50 km and becomes increasingly significant at higher altitudes. It is shown that in the mesosphere excitation due to upwelling and solar radiation become important compared to the dominant processes, thermal collisions, and chemical excitation. An approximate technique utilizing meteorological data, namely, tropospheric temperature, pressure, and humidity profiles, is developed to estimate the excitation of NO(v = 1) in the middle atmosphere. This technique would facilitate the retrieval of the NO mixing ratio from earthlimb emission data, as might be obtained from a satellite-borne limb sounding experiment, since it could be used to approximate the contribution of upwelling radiation to the NO(v = 1) non-LTE vibrational temperature efficiently.