SIMPLE ADJOINT RETRIEVALS OF MICROBURST WINDS FROM SINGLE-DOPPLER RADAR DATA

Although the simple adjoint (SA) method for retrieving the low-altitude winds from single-Doppler scans was previously examined with the Phoenix II data collected for rather uniform wind fields on nonstorm days with aluminum chaff dispensed from an aircraft (to enhance the reflectivity), the method has not been tested with storm data for complex flow fields. To examine this problem, the SA method is further developed and tested with the Denver airport microburst data through a series of numerical experiments. In addition to the earlier upgrading of the SA method, three new objectives are fulfilled to improve the retrievals. In particular, it is found that by imposing a weak vorticity constraint, by using the previous time-level retrieval as the initial guess of the retrieval at the current time level, and finally by incorporating the surface anemometer data into the method, the averaged rms difference between the retrieved (from FL-2 radar) and dual-Doppler observed winds reduces from 3.87 to 2.89 m s(-1), then to 2.66 m s(-1), and finally to 2.55 m s(-1), while the averaged correlation coefficient increases from 88% to 94%, then to 95%, and finally to 96%. The surface anemometer data can make a significant improvement, especially when the retrieval purely based on radar data is relatively poor. Factors responsible for the retrieval error are also examined and discussed with physical interpretations.