Tropical Cyclone Kinetic Energy and Structure Evolution in the HWRF Model

Tropical cyclones exhibit significant variability in their structure, especially in terms of size and asymmetric structures. These variations can influence subsequent storm evolution as well as the environmental impacts and play an important role in forecasting. This study uses the Hurricane Weather Research and Forecasting (HWRF) model to investigate the horizontal and vertical structure of tropical cyclones. Five real data HWRF model simulations from the 2005 Atlantic tropical cyclone season (two of Hurricanes Emily and Wilma, and one of Hurricane Katrina) are used. A simplified version of the HWRF without ocean coupling was utilized for this study.

Horizontal structure is investigated via several methods: the decomposition of the integrated kinetic energy field into wavenumber space, composite analysis of the wind and precipitation rate fields, and azimuthal wavenumber decomposition of the tangential wind and precipitation rate fields. Specific focus is given to the asymmetric structures forced by storm environmental factors including storm motion, shear, and the relative orientation of the shear to the storm motion vectors. Previous studies have indicated that asymmetries can also occur due to the excitation of vortex Rossby waves that propagate on the vorticity gradient associated with the primary vortex circulation. An analysis of the vortex Rossby wave contribution to storm azimuthal wavenumber-2 asymmetries is completed using a spatial and temporal spectral decomposition of the vorticity field. The vortex Rossby wave forced asymmetries are compared to the synoptic forced asymmetries to determine their relative importance and predictability.

The views, opinions, and findings contained in this manuscript are those of the authors and should not be construed as an official National Oceanic and Atmospheric Administration or U.S. government position, policy, or decision.