The inclusion of GPS limb sounding data into NCEP's global data assimilation system

Global Positioning System (GPS) radio occultation data are examined using a ray tracing algorithm for potential incorporation in the National Centers for Environmental Prediction's (NCEP's) Spectral Statistical Interpolation (SSI) analysis system. First the observed bending angle is statistically compared with the simulated one. The investigation demonstrates that the simulated bending angle from the global analysis agrees well with the observed angle between the altitude of 7km and 35km. Next two case studies on super refraction are presented. The result suggests that the limb sounding technique often can only be applied above a certain critical altitude (200m-800m) where the near surface inversion is typically found in moist regions. Experiments are then performed examining the impact of the data on analyses. The experiments show that the analysis procedure works properly and fits the observations reasonably. These results validate the reliability of the radio occultation data and the applicability of the assimilation procedure. However, while significant improvement on cost performance has been achieved for the ray tracing algorithm, considerable further effort (at least 2 orders of magnitude improvement is speed) is required to make the operational use of this data computationally feasible. Takayuki Matsumara, John C. Derber, James G. Yoe, Francois Vandenberghe, Xiaolei Zou. "June 1999." System requirements: Adobe Acrobat Reader. Includes bibliographical references (pages 25-26). 1999 NWS (National Weather Service) NCEP (National Centers for Environmental Prediction) Library Public Domain 2285