11A.2
Atmospheric vortex structures retrieved from single-Doppler radar observations. Part I: The Generalized VTD (GVTD) technique
Wen-Chau Lee, NCAR, Boulder, CO; and B. J. D. Jou
The primary circulations of tropical cyclones (TCs) and tornados can be derived from single Doppler radar observations using the Ground-Based Velocity Track Display (GBVTD) algorithms. The GBVTD algorithm has limitations in four areas: (a) the unresolved cross-beam mean wind, (b) geometric distortion of the retrieved asymmetric wind fields, (c) limited analysis domain, and (d) unable to separate the asymmetric tangential and radial winds. This paper presents the Generalized VTD (GVTD) technique providing a generalized formulation of the VTD-family of techniques and eliminating the first three limitations inherent in the GBVTD technique. This GVTD algorithm transforms the representation of a vortex from traditional Vd into a new variable, VdD/RT, where D is the range of each gate and RT is the range of the vortex center. In this new paradigm, VdD/RT links to the TC circulation in the vortex-centered, linear coordinates (θ) rather than in a radar-centered, nonlinear coordinates (ψ) used in the GBVTD. Key vortex kinematic structures (e.g., mean flow, axisymmetric tangential wind, etc) possess different signatures in the VdD/RT space that in fact simplify the interpretation of radar signature as well as eliminates the geometric distortion inherent in the Vd display, a significant improvement in diagnosing vortex structures in both operation and research. The advantages of using VdD/RT are illustrated using analytical TCs and the properties are compared with GBVTD. Although the GVTD equations are more complicated than the GBVTD equations, GVTD certainly has advantages over GBVTD in this idealized study. In particular, the constant mean wind signature in the GVTD framework is a set of parallel lines that can be easily identified in the VdD/RT display. In Part II of the paper (Lee, Jou, Lee, and Zhao), an automated procedure to identify the mean wind vector from the VdD/RT display of an atmospheric vortex will be presented.
Oral presentation is preferred. Please arrange the Part II paper following this paper in the same session.
Session 11A, Severe Weather and Mesoscale Meteorology I (Parallel with 11B)
Thursday, 9 August 2007, 4:00 PM-6:00 PM, Hall A
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