Wednesday, 1 August 2001
Initialization of a hurricane vortex with single-Doppler radar data
A method for hurricane vortex initialization has been developed that utilizes the bounded derivative initialization (BDI) in conjunction with the vorticity method to accurately determine the hurricane vortex dynamic structure based on the single Doppler radar wind fields retrieved from the ground-based velocity track display (GBVTD) technique. The GBVTD technique retrieves the reliable rotational wind and vorticity of a tropical cyclone (TC) from single Doppler radar data. Based on the momentum conservation, the vorticity method derives the hurricane divergent wind/vertical velocity from the high temporal and spatial vorticity variations retrieved by GBVTD. The divergent wind field, inferred dynamically, is used in conjunction with the rotational wind observed from single Doppler radar data to determine the total wind field, including the vertical velocity in a hurricane vortex. BDI derives smooth initial fields that evolve smoothly on the advective timescale by requiring a number of time derivatives in the initial data order of unity. In this study, BDI is used to smoothly insert the three-dimensional hurricane wind fields into the environmental flow defined by the analysis/forecast fields output from larger scale models such as the Eta model. BDI provides an effective way to reduce the amplitude of fast waves generated by the inconsistent initial states between the derived three-dimensional vortex wind and the environmental Eta fields.