Extended Abstract (2.6M)P1.50
Large-scale organization of tropical convection in two-dimensional explicit numerical simulations
Wojciech W. Grabowski, NCAR, Boulder, CO; and M. W. Moncrieff
This paper will discuss results from idealized 2D (x-z) cloud-resolving simulations in which a periodic global-scale horizontal domain is used (20,000 km) and a horizontally homogeneous SST is assumed. These simulations are relevant to the issue of large-scale organization of convection in the tropics and the coupling between convection and the large-scale dynamics. Two sets of simulations were performed, one with the prescribed radiative cooling and the second one which applied a radiation transfer model to include interactions between radiation and moisture. Simulations with prescribed radiation feature mesoscale convective systems with horizontal scales of several hundred kilometers moving east-to-west with speeds similar to the mean wind, and envelopes of convection with a horizontal extent of a few thousand kilometers and propagating west-to-east. The propagation speed of the large-scale envelopes compares well with the phase velocities of convectively coupled Kelvin waves observed in the equatorial waveguide. Convective momentum transport and the impact of convective systems on temperature and moisture near the surface are key processes responsible for the large-scale organization of convection. Interactive radiation modifies this picture by adding yet another mechanism of convection organization: long-lived mesoscale convective systems tend to occur within the ascending branches of a weak overturning circulation of a few thousand kilometers in scale. These circulations are steered by the mean wind and are a manifestation of the large-scale baroclinic response to horizontal gradients of radiative heating established between the moist and dry regions. Sensitivity tests, including various radiation transfer models, various microphysical parameterizations, and a sheared environment, demonstrate the robustness of these results.
Poster Session 1, Tropical Cyclones, Large-scale Dynamics and Convection
Monday, 29 April 2002, 11:00 AM-12:30 PM
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