关键词: GPS, 掩星资料, 水汽通量, 同化技术, 降水

Abstract: A selected Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) event point was assimilated into the Advanced Weather Research and Forecast Model (WRF) Data Assimilation (DA) system. Analyses with and without single Wet Profile COSMIC occultation event were compared with each other. Zonal mean temperature, humidity and surface pressure differences between the GPS analyses and NOGPS analyses were examined. Particular case of occultation event wetPrf_C003.2009.145.00.32.G07_0001.0002_nc at 47.648°N and 73.830°E occurred at 00:32 o’clock, May 25th, 2009, used in this study, contained 400 pieces of records, in which 7 pieces were uncompleted, 85 pieces failed to pass the quality control procedure, and 307 were assimilated to the initial field. The wellobserved 393 pieces of records were distributed in the altitude range from 0.7 km to 31.4 km, latitude range from 47.399 34°N to 48.179 68°N, and longitude range from 73.669 02°E to 74.264 92°E. The typical duration of an occultation event was 3 minutes. Although only 307 pieces out of 400 items of the single point were ingested and water vapor was not directly related to wind, the assimilation did lead to an improvement of wind and temperature as well as the pressure analysis through internal model dynamic adjustment. Temperature was increased near the occultation event on the northwest side at 850 hPa and 500 hPa and on the southeast side at 200 hPa, but the temperature was decreased on the southeast side at 850 hPa and 500 hPa and on the northwest side at 200 hPa. The positive increment of water vapor mixing ratio occurred on the northwest side at all the levels, and the negative one on the southeast side. Both the positive and negative increments of temperature and water vapor mixing ratio were distributed around the occultation point in a quasisymmetry way. The increase and decrease of temperature occurred on both sides of 300 hPa level, but basically around the occultation point, and the increase and decrease of the water vapor mixing ratio occurred mainly at an altitude below 30 km. The maximum value (2.2×10^-3 kg•kg^-1) occurred near ground (47.5°N, 72.5°E). The DA of the single wet profile of GPS occultation point did contribute not only the improvement of prediction level of rainfall along the Tianshan Mountains, but also the reduction of false precipitation in the north piedmont of the Qinghai-Tibetan Plateau.

Key words: GPS, occultation data, water vapor flux, assimilation, precipitation