单个掩星事件湿度场资料同化实验

Assimilated Test of Humidity Field in Single Occultation Event

将一个掩星事件反演的湿度场数据同化入WRFDA系统。同化后,在850 hPa和500 hPa高度上掩星事件点附近的西北侧和200 hPa上的东南侧温度增高,850 hPa和500 hPa高度上掩星事件点的东南侧和200 hPa上的西北侧温度降低。水汽混合比在各层的正增长均位于掩星事件点的西北侧,负增长位于东南侧。温度和水汽混合比的正、负增长区以掩星事件点为中心呈准对称分布。气压在各个模式层上减小,平均偏差极值为0.5 hPa,位于近地面附近,减幅随着高度的增加而单调递减。温度和水汽混合比的正负增长在300 hPa上下均有,但温度的变幅极值区主要集中在300 hPa附近,极值达2 K以上。水汽混合比的调整主要出现在30 km以下的高空,其最大值2.2×10-3kg·kg-1在近地面(47.5°N,72.5°E)附近,随着距离的增加而递减。此次单个掩星事件湿度场的同化不仅改善了沿天山一带的降水量预报效果,并且有效降低了青藏高原北坡的虚假降水量,缩小了虚假降水落区范围。

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 wetPrfC003. 2009. 145. 00. 32. G070001. 0002nc 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 307pieces 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 and500 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 below30 km. The maximum value（ 2. 2 × 10- 3kg·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.