Journal
SURVEYS IN GEOPHYSICS
Volume 33, Issue 3-4, Pages 637-656Publisher
SPRINGER
DOI: 10.1007/s10712-011-9148-9
Keywords
Convection; Climate; Humidity; Diurnal cycle; Intraseasonal variability
Categories
Funding
- DOE Atmospheric System Research Program
- NASA Modeling and Analysis Program
- NASA Precipitation Measurement Missions
- NASA CloudSat/CALIPSO Mission
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Convective cloud variability on many times scales can be viewed as having three major components: a suppressed phase of shallow and congestus clouds, a disturbed phase of deep convective clouds, and a mature phase of transition to stratiform upper-level clouds. Cumulus parameterization development has focused primarily on the second phase until recently. Consequently, many parameterizations are not sufficiently sensitive to variations in tropospheric humidity. This shortcoming may affect global climate model simulations of climate sensitivity to external forcings, the continental diurnal cycle of clouds and precipitation, and intraseasonal precipitation variability. The lack of sensitivity can be traced in part to underestimated entrainment of environmental air into rising convective clouds and insufficient evaporation of rain into the environment. As a result, the parameterizations produce deep convection too easily while stabilizing the environment too quickly to allow the effects of convective mesoscale organization to occur. Recent versions of some models have increased their sensitivity to tropospheric humidity and improved some aspects of their variability, but a parameterization of mesoscale organization is still absent from most models. Evidence about the effect of these uncertainties on climate change projections suggests that climate modelers should make improved simulation of high and convective clouds as high a priority as better representations of low clouds.
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