Impacts of reconnaissance flight data on numerical simulation of tropical cyclones over South China Sea

Abstract

In 2011, the Hong Kong Observatory (HKO) and the Government Flying Service (GFS) of the Hong Kong Government conducted reconnaissance data collection flights for two tropical cyclones over the South China Sea. It was the first time in the region that flight measurements of this kind had been carried out specifically for tropical cyclones. Horizontal wind velocity components, temperature and relative humidity at selected flight levels were recorded at the temporal resolution of 20 times per second to delineate the wind flow and other meteorological conditions. They were found to be consistent with other synoptic station data sparsely located over the sea areas, as well as in good agreement with the ocean surface wind data from the satellite microwave scatterometer. In this study, aircraft measurements for the two tropical cyclones in 2011 and one in July2009 were assimilated into the HKO mesoscale Non-Hydrostatic Model (NHM) using its three-dimensional variational data assimilation (3DVAR) to investigate the impact of the data on the model analysis and forecast. Model sensitivity experiments with and without the flight measurements were conducted. The flight observations were found to improve model analysis and forecasts of wind circulation, temperature and humidity in the vicinity of the tropical cyclones. Improvement in track forecast was obtained although an insignificant effect was seen in predicting the central pressure of the storms. The inclusion of flight measurements also improved the forecast of the surface wind distribution and precipitation associated with the tropical cyclones.