Analysis and forecasting of the low-level wind during the Sydney 2000 forecast demonstration project

During the Sydney 2000 Forecast Demonstration Project (FDP) a four-dimensional variational assimilation (4DVAR) scheme was run to analyze the low-level wind field with high spatial and temporal resolution. The 4DVAR scheme finds an optimal fit to the data and a background field under the constraints of a dry boundary layer model. During the FDP, the system assimilated data from two Doppler radars, a surface mesonet, and a boundary layer profiler, and provided low-level analyses every 10 min. After the FDP, a number of experiments have been performed to test the ability of the system to provide short-term forecasts (0-60 min) of the low-level wind and convergence. Herein, the performance of the system during the FDP and the forecast experiment's performed after the FDP are described. Two strong gust front cases and one sea-breeze case that occurred during the FDP are also examined. It is found that for the strong gust front cases, the numerical forecasts improve over persistence in the 1-h time frame, whereas for the slower-moving sea-breeze case, it is difficult to improve over a persistence forecast.