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Peter S. Ray, Alan Robinson, and Ying Lin

Abstract

During the Taiwan Area Mesoscale Experiment (TAMEX), three Doppler radars complemented enhanced surface and upper-air observations. The focus of the experiment was to better understand the interaction of the terrain with precipitation systems in the production of the important heavy rainfall. The intensive operational period (IOP) number 8 extended from 1400 IST (local standard time) 7 June 1987 until 0800 LST 9 June 1987. During this time, a mesoscale convective system (MCS) formed in the Straits of Taiwan and moved inland. It was interrogated by many observing instruments, including three Doppler radars, over a 6-h period. During this time the front moved through the radar network. The front was shallow and the precipitation widespread, both ahead of and behind the front. The front was only 1.6-km deep over a distance of 100 km.

Using velocity-azimuth display (VAD) data, a portion of the frontogenetic function was computed during the times the front was in the vicinity of the radar. The increase in both convergence and deformation contributed to large values of the frontogenetic function.

Dynamic retrieval was also attempted on the data during the time when the front was most favorably located for analysis. The results are very similar to what has been observed both for tropical squall lines and for midlatitude squall lines.

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Alan Shapiro, Paul Robinson, Joshua Wurman, and Jidong Gao

Abstract

An approximate (rapid scan) dynamical model for single-Doppler retrieval of the vector wind field is investigated. This approximate model is based on the Lagrangian form of the radial component of the equation of motion and is valid for retrieval time windows that are smaller than the effective timescale of the flow but larger than the product of the effective timescale and (nondimensional) relative error in the radial wind observations. The retrieval was tested with data gathered by two Doppler-on-Wheels mobile Doppler research radars of a cold front on 16 June 2000 near Grandfield, Oklahoma. Experiments focused on the impact of time resolution and the utility of a background constraint obtained from a volume velocity processing (VVP)-like estimate of the wind field. Retrieval error statistics were substantially improved as the volume scan intervals decreased from 5 min [characterizing the current Weather Surveillance Radar-1988 Doppler (WSR-88D) scan rates] down to 1 min. Use of the background constraint also improved the results, with superior results obtained in the high temporal resolution experiments when the background constraint was selectively imposed.

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