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. / Graduation date: 1987
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29077 |
| Date | 21 November 1986 |
| Creators | Wang, Jough-tai |
| Contributors | Esbensen, Steven K. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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