Observational Tests of Tropical Cyclone Intensity Estimation Using GPS Radio Occultation Temperature Measurements

Although there has been great progress in the trajectory forecasting of tropical cyclones (TCs) in the past few years, little progress has been made to their intensity forecasting. Convective bursts, inside the eyewall of TCs, markedly affect the background thermal structure of the upper-troposphere lower-stratosphere (UTLS) region manifesting as temperature inversion layers at the outflow, superimposed on the ambient tropopause region. The temperature difference between the ocean surface and the outflow region defines a TC's thermodynamic efficiency, which is a direct analog of its intensity. The Global Positioning System radio occultation (GPSRO) observations offer us a unique opportunity to sense the vertical thermal structure of the eyewall with a vertical resolution reaching ~100 m., allowing us to identify the outflow altitude and its temperature. Collocated vertical temperature profiles from the European Center for Medium-range Weather Forecasts Re-Analysis Interim (ERA-Interim) are also obtained and compared against the GPSRO temperature profiles. The GPSRO observations, along with ocean surface temperatures from NASA Modern Era-Retrospective Analysis for Research and Applications (MERRA), made it possible to derive TC intensities using a simplified vortex TC model [Wong and Emanuel, 2007]. We analyzed 15 TC cases in 2006–2010, and our GPSRO-based TC intensity estimates are found to be quantitatively consistent with best-track values from the Joint Typhoon Warning Center (JTWC) within 1.2–9.0%. This suggests that GPSRO datasets can potentially augment current datasets in TC intensity forecasting, and provide accurate thermal information of a TCs' environment.