Use of Mid-Level Model Wind Data and VAD Winds to Improve WSR-88D Velocity Dealiasing

In 2012, the Radar Operations Center began to use the two-dimensional velocity dealiasing algorithm (2DVDA) as its primary dealiasing tool. One of the 2DVDA’s strengths is its ability to retain a historical background wind field to assist with dealiasing. From its initial deployment to the most recent software release in 2016-17 (Build 17), the 2DVDA has relied on this internal field rather than on external model data or the external velocity azimuth display (VAD) algorithm. However, during quiescent periods at mid-latitudes, when one weather system has moved out of radar coverage and new echoes are entering the area of coverage from the opposite side of the radar, the lack of recent historical background wind information can lead to incorrect dealiasing of the new echoes. In this paper, we show results of modifications to the 2DVDA to correct this type of error. These modifications include increased usage of external model data and the creation of an internally derived VAD-type of analysis of the geostrophic flow or “free atmospheric wind” (FAW), computed between three and nine kilometers above ground level (AGL) in addition to and separate from the internal VAD. This FAW computation is used as a quality check for both the external model data and the historical background wind and limits the use of model data to prevent aberrations from negatively impacting the dealiasing solution.