Alan Shapiro
School of Meteorology (SOM)
and Center for Analysis and Prediction of Storms (CAPS), University of
Oklahoma, Norman OK
&
Katharine M. Kanak
School of Meteorology,
University of Oklahoma, Norman OK
ABSTRACT
The rise of an isolated dry thermal bubble in a quiescent unstratified environment is a prototypical natural convective flow. This study considers the rise of an isolated dry thermal bubble of ellipsoidal shape (elliptical in both horizontal and vertical cross-sections). The azimuthal asymmetry of the bubble allows the vorticity tilting mechanism to operate without an environmental wind. The dry Boussinesq equations of motion are solved analytically as a Taylor series in time for the short-term behavior of the bubble (involving derivatives of up to the third-order in time). The analytic results are supplemented with numerical simulations to examine longer-term behavior. The first non-zero term in the Taylor expansion for the vertical vorticity is a third-order term, and appears as a four-leaf clover pattern with lobes of alternating sign. The horizontal flow associated with this vorticity pattern first appears as a sheared stagnation point-type flow, but eventually organizes into vertical vortices that fill the bubble. The vortices induce large structural changes to the bubble, and eventually reverse the sense of the azimuthal asymmetry.
All animations contain
sequences
in time of XY-plane contour fields chosen at the (increasing) heights
of
the levels of domain maximum vertical vorticity.
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Recently the work has been expanded by M.S. student Allison P.
Silveira. As part of her thesis work she carried out a suite of
experiments in which an ambient wind shear was added to the simulations
presented in Shapiro and Kanak 2002. She is currently preparing
an article for publication on her work.
Last updated: 12-05
