Colorado State University Tropical Weather and Climate Research

Research

GVTD

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Are the asymmetric dynamics of Hurricane Michael (2018) polygonal eyewall consistent with vortex Rossby wave (VRW) theory?

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Group Members: Ting-Yu Cha , Michael M. Bell , Alex DesRosiers

While polygonal eyewall shapes have been seen in previous hurricanes, the corresponding evolution of wind asymmetries has never been quantitatively deduced due to limitations from previous observations. Here we show the first observational evidence of the evolving wind field of a polygonal eyewall during RI to Category 5 intensity by deducing the winds at 5-minute intervals from single-Doppler Next Generation Weather Radar (NEXRAD) observations. The single Doppler radar analysis shows that the propagation speeds of different VRWs are consistent with linear wave theory.

How do the asymmetric processes impact Hurricane Matthew's (2016) Eyewall replacement cycle?

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Group Members: Ting-Yu Cha , Michael M. Bell , Alex DesRosiers

Hurricane Matthew was observed by the NEXRAD KAMX, KMLB, and KJAX polarimetric radars and NOAA P-3 airborne radar when it approached the southeastern United States during an ERC event. The radar observations indicate that Matthew's primary eyewall was replaced with a weaker outer eyewall, but unlike a classic ERC, Matthew did not reintensify after the inner eyewall disappeared. The single-Doppler analyses indicate that the inner eyewall decayed a few hours after the P-3 flight, while the outer eyewall contracted but did not reintensify and the asymmetries increased episodically. The analysis suggests that the resilient outer eyewall was influenced by both environmental vertical wind shear and an internal vortex Rossby wave damping mechanism during the ERC evolution.

What are the pros and cons of using single Doppler radar technique (GVTD) and pseudo-dual Doppler airborne retrievals for studying advantages and disadvantages of each technique for studying tropical cyclone structure?

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Group Members: Ting-Yu Cha , Michael M. Bell

In this study, a comparison between the two techniques shows that the axisymmetric tangential winds are generally comparable between the two techniques after the improvements to Generalized Velocity Track Display (GVTD) retrievals. Fourier decomposition of asymmetric kinematic and convective structure shows more discrepancies due to spatial and temporal aliasing in the retrievals. Complementary information can be retrieved from both single and multiple Doppler retrievals.