Predicting the Genesis of Typhoon Nuri (2008): Impact of GPS Radio Occultation Data
In this study we present a detailed analysis of the impact of GPS radio occultation (RO) data on the prediction of Typhoon Nuri (2008), which was observed during the field phase of T-PARC (THORPEX Pacific Asia Regional Campaign) over the western North Pacific. Typhoon Nuri was declared a tropical storm at 1800 UTC 16 August 2008, and its incipient disturbance can be tracked more than ten days prior to tropical storm formation. Nuri is a challenging case for numerical model prediction. The NCEP GFS model failed to predict the storm in operation. The WRF model, initialized with either the NCEP or ECMWF global analysis, also failed to predict its genesis. However, with the assimilation of GPS RO soundings obtained from COSMIC and other missions, using a two-dimensional observation operator, the moisture analysis was substantially improved. This enhanced moisture analysis led to a more accurate prediction of the convection associated with the incipient disturbance, which developed into a robust mid-level vortex. This mid-level vortex was responsible for the subsequent formation of Nuri through its interaction with convective and boundary layer processes. Without the assimilation of GPS RO data, the convection was suppressed and the mid-level vortex did not develop, and the model failed to predict the genesis of Nuri. Further experiments on nine additional typhoons over the western North Pacific between 2008-2010 showed that the assimilation of GPS RO data substantially improved the model’s ability to forecast tropical cyclogenesis.