A GPS MET SOUNDING THROUGH AN INTENSE UPPER-LEVEL FRONT/

A Global Positioning System Meteorology (GPS/MET) proof-of-concept exp eriment became a reality on 3 April 1995. A small satellite carrying a modified GPS receiver was launched into earth orbit to demonstrate th e feasibility of active limb sounding of the earth's neutral atmospher e and ionosphere using the radio occultation method. On 22 October 199 5, a GPS/MET occultation took place over northeastern China where a de nse network of radiosonde observations was available within an hour of the occultation. The GPS/MET refractivity profile shows an inflection , and the corresponding temperature retrieval displays a sharp tempera ture inversion around 310 mb. Subjective analyses based on radiosonde observations indicate that the GPS/MET occultation went through a stro ng upper-level front. In this paper, the GPS/MET sounding is compared with nearby radiosonde observations to assess its accuracy and ability to resolve a strong mesoscale feature. The inflection in the refracti vity profile and the sharp frontal inversion seen in the GPS/MET sound ing were verified closely by a radiosonde located about 150 km to the east of the GPS/MET occultation site. A similar frontal structure was also found in other nearby radiosonde observations. These results show ed that high-quality GPS/MET radio occultation data can be obtained ev en when the occultation goes through a sharp temperature gradient asso ciated with an upper-level front.