A study of infrared diabatic forcing of ice clouds in the tropical atmosphere

[1] The diabatic exchange occurring in the atmosphere and within ice cloud layers in tropical standard conditions is investigated. The crossover from the spectral region in which the cloud's layer experiences a net emission ( roughly the far infrared) to the region in which it experiences net absorption ( window) does not significantly depend on the ice amount, but appears strictly connected with cloud's height and atmospheric temperature structure. For a fixed atmosphere, the cloud's internal structure of radiative heating and cooling is highly dependent on cloud trasmissivity. The energy absorbed by ice crystals at the base of a cirrus is different from that absorbed by the air molecules occupying the same layer and the effects of scattering are quantified and compared to particle's emission. Simulations have been done in case of spherical and hexagonal column-shaped ice particles. Small differences are obtained in the integrated quantities due to compensating effects which appear fairly unimportant when compared to uncertainties caused by our inadequate knowledge of some of the main properties of ice clouds, such as ice amount and effective radius. Of larger magnitude are variations in layer's absorbed flux due to changes in the water vapor concentration.