An observational study of the energetics and dynamical aspects of GATE cloud clusters Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m613n1108

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  • Thermodynamical and dynamical aspects of tropical cloud clusters are studied using data from the GARP Atlantic Tropical Experiment (GATE). The data set used in this study is a three-dimensional gridded set of upper-air analyses constructed by Ooyama and Chu (Hurricane Research Division, AOML/NOAA and SSEC-University of Wisconsin) for wind data and Esbensen (Oregon State University) for thermodynamic data. The energy and momentum budgets are estimated on the scale of large cloud clusters. A strong upper-tropospheric heat source and middle-tropospheric drying are characteristic features of the mature stage of the observed cloud clusters. The heat source, moisture sink and the virtual heat flux for cloud clusters are larger than the corresponding quantities from GATE easterly-wave composites. The surface precipitation estimates produced from the vertically integrated moisture budget are consistent with direct observations. From the momentum budget study, the following conclusions are drawn concerning the cumulus momentum effects. In the growing stage, the mesoscale and cumulus scale effect tends to: 1) provide a vertically integrated net sink for westerly momentum around the cluster center; 2) induce a convergent circulation in the lower layer. In the mature stage, the effects are to: 1) induce a divergent circulation in the upper layer and maintain a vorticity couplet pattern; 2) maintain a weak convergent circulation in the lower layer; and 3) cause a relatively weak easterly acceleration in the upper layer at the center. A hypothesis is postulated to illustrate the convective dynamical effects. A simple barotropic non-divergent model was constructed to investigate the large-scale response to the hypothesized cumulus momentum forcing similar to that found in the GATE cloud-cluster momentum budget. The numerical results show that the cumulus momentum forcing is a plausible kinetic energy source for the mesoscale wavenumber spectrum. The sporadic nature of the convective mass flux does not have a significant effect on the large-scale dynamical response for physically realistic parameters in a barotropic non-divergent dynamical system.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-05-09T16:19:01Z (GMT) No. of bitstreams: 1 WangJoughTai1987.pdf: 3306838 bytes, checksum: 530ae11a392e66209037449d302869b6 (MD5)
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