青藏高原地区大气红外探测器(AIRS)资料质量检验及揭示的上对流层水汽特征

Validation and Characteristics of Upper Tropospheric Water Vapor over the Tibetan Plateau from AIRS Satellite Retrieval

上对流层水汽（UTWV）是大气中最重要的温室气体,对全球气候变暖有重要贡献;而青藏高原被认为是UTWV进入平流层的重要通道,在平流层-对流层水汽交换及平流层水汽变化中扮演着重要角色。首先利用高原探空站资料对大气红外探测器（AIRS）反演的水汽数据在高原地区的质量进行了检验,发现AIRS反演的水汽数据与探空实测数据是相当一致的。其中全年和夏半年AIRS的可信度较好,而冬半年,尤其是上对流层AIRS水汽可信度相对较低,但在缺乏高精密数据时仍部分可用。利用AIRS资料对青藏高原地区UTWV季节变化特征进行了分析,结果表明,高原冬季偏干,而夏季显著偏湿,并且空间分布具有明显的不均匀性。经验正交函数（EOF）分析显示,夏季高原UTWV主要存在三种空间分布型,即全区一致型,高原东西偶极型和南北带状偶极型。一致型分布具有明显的季节变化,而偶极型则以季节内振荡为主。在此基础上,重点研究夏半年高原地区UTWV季节内振荡特征,结果表明,UTWV季节内振荡的显著周期位于10～20天和30～60天。前者主要表现为纬向东传,并且可以越过高原进入我国江淮流域上空;而后者主要向南移动,基本表现为高原局地振荡。最后,进一步探讨了高原UTWV季节内振荡的可能机制,结果表明,高原地区UTWV的低频变化主要与高原热状况、南亚高压活动及其与二者相耦合的对流活动有关。

Upper Tropospheric Water Vapor （UTWV） is a key greenhouse gas which exerts a major influence on the energy balance of the earth- atmosphere system. The Tibetan Plateau （TP） is believed as an important channel by which UTWV enters into the stratosphere, and accordingly plays an important role in exchange over the upper troposphere and the lower stratosphere （UTLS） as well as distribution of stratospheric water vapor. Radiosonde measurements over the TP are used to validate measurements of water vapor column mixing ratio from the Atmospheric Infrared Sounder （AIRS） satellite instrument. In general, AIRS reproduces the observations of water vapor with good fidelity. The all-year and summer AIRS data have good confidence, while the winter AIRS, especially in the upper troposphere, have worse confidence but still are usable in lack of data with high spatial and temporal resolution. A climatology from AIRS indicates that the TP in winter is extremely dry while remarkably wet in summer, and the spatial distributions of UTWV over it are characterized by asymmetry. The empirical orthogonal function （EOF） analysis shows that the summer UTWV over the TP has three modes in spatial distribution as follows： monopole with the same anomalous signs in the whole TP, west - east dipole with the reverse signs in western and eastern TP, and south- north dipole with the reverse signs in southern and northern TP. The monopole exhibits seasonal variations, while the dipoles oscillate on intraseasonal scale. Based on the above results, the intraseasonal oscillations （ISOs） of the summer UTWV are investigated. It is found that intraseasonal cycles of UTWV over the TP have periods of 10 - 20 days and 30 - 60 days. The former moves eastwards and arrives over the Yangtze River - Huanghe River valleys. The latter propagates southwards but oscillates just inside the TP. In addition, the possible mechanism influencing the ISOs of UTWV over the TP is further discussed. The data show that the ISOs of UTWV over the TP are closely related to heating in the TP, activities of South Asian high, and coupling convection.