P13A.10 A new formulation of dual-Doppler analysis for convective flows

Thursday, 9 August 2007
Halls C & D (Cairns Convention Center)
Corey K. Potvin, Univ. of Oklahoma, Norman, OK; and A. M. Shapiro and J. Gao

A major challenge in dual-Doppler analysis is accurate retrieval of the vertical velocity field, especially in the presence of severe convection. Doppler wind observations usually contain little information about the vertical component of the flow due to the shallowness of radar beam elevation angles. Improvements gained by imposing mass continuity as a constraint can be limited by large errors in the specified vertical velocity boundary conditions as well as accumulation of error due to inaccurate horizontal divergence estimates. Recent work (e.g. Mewes and Shapiro 2002) has shown that using the vertical vorticity equation as an additional constraint can further improve vertical velocity retrievals, especially for quicker volume scan periods.

In this study, mass continuity, the anelastic vertical vorticity equation, and smoothness are imposed as weak constraints in a dual-Doppler analysis system. The technique is tested with idealized winds from a translating 3-D Beltrami flow, for which velocity divergence and vertical vorticity tendency are identically zero. In some experiments, error is added to the wind field in order to evaluate the technique's performance when observations do not exactly fit the model. The sensitivity of the retrieved wind field, particularly the vertical component, to the emulated radar scanning strategy, observing resolution and model constraint weights is explored. The subsequent sensitivity of parcel trajectory analyses to the above conditions is also examined.

In the future, the retrieval technique will be applied to an Advanced Regional Prediction System (ARPS) high-resolution tornado dataset in order to assess its performance for wind fields which are more representative of those observed near supercells and tornadoes. Ultimately, the technique will be tested using real observations.

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