Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 5 2006 10.5194/acpd-6-10773-2006 http://www.atmos-chem-phys-discuss.net/6/10773/2006/ http://www.atmos-chem-phys-discuss.net/6/10773/2006/acpd-6-10773-2006.html http://www.atmos-chem-phys-discuss.net/6/10773/2006/acpd-6-10773-2006.pdf 10773 10809 2006-10-24 The role of the retention coefficient for the scavenging and redistribution of highly soluble trace gases by deep convective cloud systems: model sensitivity studies M. Salzmann M. G. Lawrence V. T. J. Phillips L. J. Donner Max-Planck-Institute for Chemistry, Department of Atmospheric Chemistry, PO Box 3060, 55020 Mainz, Germany Geophysical Fluid Dynamics Laboratory, NOAA, Princeton University, PO Box 308, Princeton, NJ 08542, USA The role of the retention coefficient (i.e. the fraction of a dissolved trace gas which is retained in hydrometeors during freezing) for the scavenging and redistribution of highly soluble trace gases by deep convective cloud systems is investigated using a modified version of the Weather Research and Forecasting (WRF) model. Results from cloud system resolving model runs (in which deep convection is initiated by small random perturbations in association with so-called "large scale forcings (LSF)") for a tropical oceanic (TOGA COARE) and a mid-latitude continental case (ARM) are compared to two runs in which bubbles are used to initiate deep convection (STERAO, ARM). In the LSF runs scavenging is found to almost entirely prevent a highly soluble tracer initially located in the lowest 1.5 km of the troposphere from reaching the upper troposphere, independent of the retention coefficient. The release of gases from freezing hydrometeors leads to mixing ratio increases in the upper troposphere comparable to those calculated for insoluble trace gases only in runs in which bubbles are used to initiate deep convection. This result indicates that previous cloud resolving model studies using bubbles to initiate deep convection may possibly have over-estimated the influence of the retention coefficient on the vertical transport of highly soluble tracers. The retention coefficient is, however, found to play an important role for the scavenging and redistribution of highly soluble trace gases with a (chemical) source in the free troposphere and also for trace gases for which even relatively inefficient transport may be important.