Another useful product that is based on the velocity is the Velocity Azimuth Display. We will discuss the theory behind this product in a future lecture. For now, let's just consider what the velocity field would look like for a uniform westerly wind blowing across the region sampled by our radar. Looking to the north, we would get zero radial velocity since the wind direction would be perpendicular to the orientation of the radar beam. Looking to the east, we would get the maximum receding flow. As we scanned toward south, the radial velocity would again decrease to zero. From south to west, the radial velocity would increase to a maximum inbound pointing due west. From west to north, the velocity values would decrease back to zero.

Now, if we considered a particular range circle centered on the radar and plotted the value of the velocity as a function of azimuth, we would get a perfect sine wave. This type of figure is a Velocity Azimuth Display (VAD). The best fit sine wave through a set of velocity values displayed in this manner will give the best estimate of the mean wind over the region between the radar and the range ring chosen for the VAD. The closer the velocity values are to the best fit sine wave, the more meaningful the mean wind estimate. The reliability of the mean wind estimate is usually stated in terms of the root-mean-square (RMS) of the distances between the sine wave and the data points along the velocity (y) axis.

Since a radar beam gains altitude with range, one can construct a vertical profile of mean wind estimates by using rings at different ranges or by using the same range, but higher elevation PPIs. This is done to create the Vertical Wind Profile (VWP) product. The colors used to plot the wind profile indicate the RMS value of the mean wind estimate. Since the WSR-88D collects data every 5 or 6 minutes in precipitation mode, a time series of vertical wind profiles can be created. This type of information can be used to help indentify wind shear changes in the environment of storms or the strength of the low-level jet.