Comparing NOAA-12 and Radiosonde Atmospheric Sounding Profiles for Mesoscale Weather Model Initialization

ABSTRACT Mesoscale meteorological models such as the MM5 model from NCAR utilize atmospheric sounding data from radiosondes to initialize numerical computations. Radiosondes are released twice daily from manned land-based weather stations, commonly located near population centers. Over remote land and oceanic regions, modellers commonly resort to previous 6 hour model predictions for initial conditions. As an alternative, satellite derived atmospheric soundings provide continuous spatial coverage at regular intervals irrespective of geographical location. With the recent installation of a remote sensing station at the Hong Kong University of Science & Technology for L-band polar orbiting satellites, comparison studies between radiosonde and satellite derived atmospheric soundings have been initiated. Microwave and infrared emission measurements from the NOAA-12 polar orbiting satellite were processed with a TOVS (Tiros Operational Vertical Sounder) retrieval software package developed by the University of Wisconsin to derive temperature, dew point, wind direction and speed. Comparisons were conducted when both soundings were within 60 km ground distance and 1 hour of release from each other. Vertical profiles were constructed for 9 standard atmospheric levels from radiosonde and TOVS soundings over the South China Sea region, between January 16 - May 11, 1995. Wind speed profiles were consistently biased from the associated radiosonde profiles. Interestingly, the profiles maintained a similar shape throughout the vertical domain. A preliminary examination of the MM5 model sensitivity to the identified offset will also be presented.