An Improved Terminal Winds Analysis Technique

An important element of the FAA Integrated Terminal Weather System (ITWS) is the Terminal Winds gridded wind analysis. This product was originally developed to feed into air traffic automation systems that need wind information to compute time of flight. Operational usage at three ITWS demonstration system sites have shown that the use by TRACON supervisors to optimize aircraft merging and sequencing also provides a substantial delay reduction benefit, for example $20-$30 million per year in New York. The Terminal Winds product was the first operational weather analysis system to employ a true multi-Doppler analysis, using both the FAA Terminal Doppler Weather Radar (TDWR) and the NWS Next Generation radar (NEXRAD or WSR-88D). Terminal Winds also uses ground station data and reports of winds from commercial aircraft, as well as wind forecasts from NWS numerical models. The analysis technique used was developed specifically for this application.

The initial Terminal Winds product does not provide all the capabilities that the National Air System needs. In particular, the Doppler radar data are not fully exploited on days, such as in the winter, when data are sparse, but the winds are known to be relatively uniform. The current Doppler data processing can lead to significant errors in the wind estimates during severe vertical shear events that are the high benefit situations at coastal airports such as New York. Also, the prediction of storm growth and decay needs information on surface wind convergence, which is best computed directly from the observations, not by a simple differencing of grid point values. A new analysis technique, that extends the original, has been developed to alleviate these shortcomings. This technique is outlined and its performance compared to the initial Terminal Winds analysis.