Redistribution of trace gases by convective clouds - mixed-phase processes

[摘要] The efficiency of gas transport to the free and upper troposphere inconvective clouds is investigated in an axisymmetric dynamic cloud model withdetailed microphysics. In particular, we examine the sensitivity of gas transport to the treatment of gas uptake by different ice hydrometeors. Twoparameters are used to describe this uptake. The gas retention coefficientdefines the fraction of dissolved gas that is retained in an ice particle upon freezing, which includes also the riming process. We also define a gasburial efficiency defining the amount of gas entrapped in ice crystals growing by vapour diffusion. Model calculations are performed for continentaland maritime clouds using a complete range of gas solubilities, retention coefficients and burial efficiencies. The results show that the magnitude ofthe gas retention coefficient is much more important for gas transport in maritime clouds than in continental clouds. The cause of this difference liesin the different microphysical processes dominating the formation and evolution of hydrometeors in the two cloud types. For highly soluble gases,the amount of gas transported to the free troposphere in maritime clouds falls approximately linearly by a factor of 12 as the retention coefficientis varied between 0 and 1. Gas transport is relatively insensitive to the magnitude of the gas burial efficiency. However, the burial efficiencystrongly controls the concentration of trace gases inside anvil ice crystals,which subsequently form cirrus clouds.

[学科分类] 大气科学