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Long‐term behaviour of precipitating tropical cloud systems: A numerical study
Author(s) -
Grabowski Wojciech W.,
Moncrieff Mitchell W.,
Kiehl Jeffrey T.
Publication year - 1996
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712253302
Subject(s) - atmospheric sciences , cirrus , environmental science , convection , atmosphere (unit) , climatology , radiative transfer , cloud forcing , precipitation , mesoscale meteorology , meteorology , radiative forcing , geology , physics , aerosol , quantum mechanics
Results of a 24‐day, two‐dimensional integration of tropical cloud systems forced by large‐scale ascent, surface fluxes and radiation in a typical sheared tropical environment are presented. A non‐hydrostatic, cloud‐resolving numerical model containing sophisticated microphysical parametrizations as well as turbulence, surface flux and short/long‐wave radiative representations was used. A predominant cloud‐system hierarchy was identified: fast westward‐moving mesoscale convective systems, producing extensive cirrus anvils and a strong radiative effect; and slow‐moving regions of enhanced precipitation, causing a significant modification of the fast‐moving cloudsystem behaviour on the time‐scale of about one day. The experimental set‐up was similar to that used by Sui et al. The demonstrated episodic convective activity and the fundamental role of organized deep convection by and large agrees with their analysis. However, despite many similarities, the results for the mean thermodynamic statistical equilibrium are dramatically different: a warm and humid regime, as opposed to the cold and dry regime of Sui et al. High relative humidities and very high upper‐tropospheric cirrus cloud amount led to a strong greenhouse effect with low outgoing long‐wave radiation at the top of the atmosphere (120–150 W m −2 ). At the same time, these clouds screened the ocean surface from the solar radiation and caused very low solar radiation absorption at the surface (only about 30 W m −2 when averaged over a diurnal cycle). The surface net cloud forcing was very large, about −200 W m −2 which is in accord with earlier findings of Ramanathan and Collins. The above numbers should be considered as an upper limit of effects of deep convection on radiative fluxes in the tropics because of the warm and moist regime demonstrated in the experiment.