Colorado State University Tropical Weather and Climate Research

Research

Modeling

Check the publication list of the related research

How does CD influence TC intensification?

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Group Members: Eleanor Casas , Michael M. Bell

We developed a new, simplified conceptual model that relates TC boundary layer structural quantities---the maximum tangential wind, its radius, its height, its underlying vertical gradient, and its underlying drag coefficient---to the TC’s potential for further intensification. In addition, the new conceptual model is also able to be inverted and be used to retrieve values of interest, namely the drag coefficient under the maximum tangential wind.

Mechanisms Contributing to the Heavy Rainfall Associated with a Meiyu Front near Taiwan

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Group Members: Jennifer C. DeHart , Michael M. Bell

We are analyzing a WRF simulation of a Meiyu front event near Taiwan during June 2017. We objectively identify the Meiyu front through time in order to test the importance of several mechanisms in heavy rainfall production.

What separates developing and nondeveloping disturbances?

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Group Members: C. Chelsea Nam , Dandan Tao , Michael M. Bell

To be, or not to be, that is the question of tropical cyclogenesis. Only about 15-20 % of African Easterly Waves develop into tropical cyclones (TCs). A WRF ensemble was created with multiple TC simulations spanning the relevant parameter space for three variables; 1) the VWS magnitude, 2) the environmental humidity, and 3) the initial vortex intensity. Unmeasurable random perturbations result in widely diverging scenarios in TC genesis in moderately sheared and dry environments. Here we hypothesize that the combination of moderate shear and dry air makes an unstable condition for a vortex to intensify or decay, which implifies that TC genesis in such environments may be intrinsically unpredictable in deterministic sense. We are currently looking at the link between the deep convection and the realignment of mid-level and low-level vortices comparing the developing and non-developing ensemble members.

On the contributions of incipient vortex circulation and environmental moisture to tropical cyclone expansion

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Group Members: Jonathan Martinez , C. Chelsea Nam , Michael M. Bell

Idealized numerical simulations of tropical cyclones are created to investigate the relative contributions of incipient vortex circulation and environmental moisture to tropical cyclone expansion. The principal findings demonstrate that an initially large vortex can expand more quickly than its relatively smaller counterpart. Increasing the environmental moisture further promotes expansion but mostly expedites the intensification process. Differences in the amount and scale of outer-core convection are associated with varying the incipient vortex circulation, resulting in variable expansion rates. Note: This project was also funded by the National Science Foundation Bridge to the Doctorate Fellowship Award 004863-00003.

On the nature and evolution of asymmetric structures during tropical cyclone rapid intensification

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Group Members: Jonathan Martinez , Michael M. Bell

Do asymmetries facilitate or interfere with tropical cyclone (TC) intensification? An idealized, high-resolution simulation of a rapidly intensifying TC is examined to assess asymmetric contributions to the intensification process. Scale-dependent contributions to the azimuthal-mean PV tendency reveal positive contributions from asymmetries that vary throughout the intensification period. Note: This project was also funded by the National Science Foundation Bridge to the Doctorate Fellowship Award 004863-00003.