AOSC Departmental Seminar
April 7, 2016

The Impact of GPS Radio Occultation Data on the Prediction of Tropical Cyclogenesis

William Kuo
University Corporation for Atmospheric Research

Accurate prediction of tropical cyclogenesis by global models has been a significant challenge, largely because of the lack of observations over the tropical oceans. One important observing system that can provide valuable data over the tropical oceans is the GPS radio occultation (RO) technique. In this study we present a detailed analysis of the impact of the GPS 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. Nuri is a challenging case, as operational models did not predict its formation. 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.