On the distribution of relative humidity in cirrus clouds

[摘要] We have analysed relative humidity statistics from measurements incirrus clouds taken unintentionally during the Measurement of OZone byAirbus In-service airCraft project (MOZAIC). The shapes of thein-cloud humidity distributions change from nearly symmetric inrelatively warm cirrus (warmer than −40°C) to considerablypositively skew (i.e. towards high humidities) in colder clouds.These results are in agreement to findings obtained recently fromthe INterhemispheric differences in Cirrus properties fromAnthropogenic emissions (INCA) campaign (Ovarlez et al., 2002). Weinterprete the temperature dependence of the shapes of the humiditydistributions as an effect of the length of time a cirrus cloudneeds from formation to a mature equilibrium stage, where thehumidity is close to saturation. The duration of this transitionalperiod increases with decreasing temperature. Hence cold cirrusclouds are more often met in the transitional stage than warmclouds.

[学科分类] 大气科学