Exploring MRMS Merger Options for Polarimetric Moments and Doppler Wind-Derived Products

The Multi-Radar, Multi-Sensor (MRMS) system is capable of producing three-dimensional grids of radar moments. Currently, the operational MRMS system produces a three-dimensional reflectivity grid as the base for derived products. Additionally created are two azimuthal shear products that are flattened onto two 3-km layers prior to merging. Merging of polarimetric moments and Doppler wind-derived azimuthal shear and divergence products to a three-dimensional grid would enhance the MRMS system and provide additional inputs for future algorithms and MRMS reanalysis efforts.

The merging of polarimetric moments can be especially difficult considering calibration differences between radars, artifacts that extend down-radial from precipitation, especially convective storms, and quality of the polarimetric moments in general (e.g., distance from radar). Azimuthal shear and divergence products derived from the Doppler velocity field pose an especially difficult problem. For example, mesocyclone Doppler velocity signatures produce artifacts just as a result of the employed technique’s math and the mesocyclone’s rotation; first, depending on the intensity of the rotation, a tri-pole of negative-postive-negative can appear in the azimuthal shear field; second, a quad-pole of 2 negative peaks and 2 positive peaks can appear in divergence field. In general, the negative peaks in the azimuthal shear field are artifacts of the method employed to derive the azimuthal shear and with the exception of the convergence along the rear-flank gust front, the divergence field values are all artifacts of the method.

This presentation will explore different settings for the merger software in creating merged versions of these products. Different merger methods, and variations of weightings for some of those methods, will be explored. The presentation will also explore whether producing derived, or quasi-derived, products at the single radar and merging those products is better than just merging all single-radar moments on the three-dimensional MRMS grid. For instance, would a mesocyclone identification algorithm that could stamp out azimuthal shear prior to merging be better than trying to use a three-dimensional grid of azimuthal shear in MRMS to identify mesocyclones?