Transport of radon-222 and methyl iodide by deep convection in the GFDL Global Atmospheric Model AM2

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Read Full Article (file size: 2471828 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D17303, doi:10.1029/2006JD007548, 2007 Transport of radon-222 and methyl iodide by deep convection in the GFDL Global Atmospheric Model AM2 Leo J. Donner Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, New Jersey, USA Larry W. Horowitz Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, New Jersey, USA Arlene M. Fiore Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, New Jersey, USA Charles J. Seman Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, New Jersey, USA Donald R. Blake University of California, Irvine, California, USA Nicola J. Blake University of California, Irvine, California, USA Abstract Transport of radon-222 and methyl iodide by deep convection is analyzed in the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model 2 (AM2) using two parameterizations for deep convection. One of these parameterizations represents deep convection as an ensemble of entraining plumes; the other represents deep convection as an ensemble of entraining plumes with associated mesoscale updrafts and downdrafts. Although precipitation patterns are generally similar in AM2 with both parameterizations, the deep convective mass fluxes are more than three times larger in the middle- to upper troposphere for the parameterization consisting only of entraining plumes, but do not extend across the tropopause, unlike the parameterization including mesoscale circulations. The differences in mass fluxes result mainly from a different partitioning between convective and stratiform precipitation; the parameterization including mesoscale circulations detrains considerably more water vapor in the middle troposphere and is associated with more stratiform rain. The distributions of both radon-222 and methyl iodide reflect the different mass fluxes. Relative to observations (limited by infrequent spatial and temporal sampling), AM2 tends to simulate lower concentrations of radon-222 and methyl iodide in the planetary boundary layer, producing a negative model bias through much of the troposphere, with both cumulus parameterizations. The shapes of the observed profiles suggest that the larger deep convective mass fluxes and associated transport in the parameterization lacking a mesoscale component are less realistic. Received 23 May 2006; accepted 10 July 2007; published 12 September 2007. Keywords: Convection; transport; general circulation. Index Terms: 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 3314 Atmospheric Processes: Convective processes; 3319 Atmospheric Processes: General circulation (1223); 3337 Atmospheric Processes: Global climate models (1626, 4928). Read Full Article (file size: 2471828 bytes) Cited by Citation: Donner, L. J., L. W. Horowitz, A. M. Fiore, C. J. Seman, D. R. Blake, and N. J. Blake (2007), Transport of radon-222 and methyl iodide by deep convection in the GFDL Global Atmospheric Model AM2, J. Geophys. Res., 112, D17303, doi:10.1029/2006JD007548. Copyright 2007 by the American Geophysical Union.

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