To better understand ultra-high-altitude climate characteristics and their changes, an automatic weather station was installed on August 4, 2005 on the Mt. Xixiabangma Dasuopu glacier (28°23.04′N, 85°43.72′E, 6900 m a.s.l.) in the middle of the Himalayas. Mountain weather conditions were observed continuously and automatically. This paper is the first to publish meteorological data for a whole year for a high-elevation region, and analyze wind direction, wind speed, air temperature, air pressure and humidity. Analysis of the observation data reveals that this region was strongly influenced by the westerly jet from October 10, 2005 to April 21, 2006 and by the Indian monsoon from May to September. The seasonal transitions of the westerly jet were characterized by changes in meteorological elements. In winter, influenced by the westerly jet, the wind speed in the study region was very high and fluctuated violently, gale days were frequent, temperature and air pressure fluctuated dramatically, the diurnal range of temperature decreased and the diurnal range of air pressure increased, relative humidity and specific humidity declined sharply, and air was dry. In summer, influenced by the Indian monsoon, the relative humidity and specific humidity were high. In addition, we analyzed reanalysis data for the location of the automatic weather station. The results confirmed that this region was strongly affected by the westerly jet from October 10, 2005 to April 21, 2006 and the observations that the seasonal transitions of the westerly jet were characterized by changes in meteorological elements.
Analysis of daily precipitation samples for stable oxygen isotopes (δ18O) collected at the Shiquanhe and Gêrzê (Gaize, Gertse) stations in the Ngari (Ali) region on the western Tibetan Plateau indicates that air temperature affects the δ18O variations in precipitation at these stations. In summer, Shiquanhe and Gêrzê show strongly similar trends in precipitation δ18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ18O values in precipitation during the active monsoon period, resulting from the southwest monsoon (the summer phase of the Indian monsoon). However, during the break monsoon period (during the summer rainy season, when the monsoon circulation is disrupted), δ18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ18O strengthen during the non-monsoon period (January―June, and October―December) due to continental air masses and the westerlies. In addition, evaporation also influences the δ18O variations in precipitation. The observed temporal and spatial variations of δ18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.
Seasonal δ 18O variation in water on the southeast Tibetan Plateau has been studied, showing the consistent variation pattern of δ 18O with altitude indicative of relevant atmospheric circulation processes. Study shows a similar variation pattern of fixed-site river water δ 18O with that of the precipitation δ 18O in southeast Tibet. δ 18O in regional rivers in southeast Tibet demonstrates a gradual depletion with increasing altitude, though the rates vary seasonally. The most depleted river 18O occurs during the monsoon period, with the lowest δ 18O/altitude lapse rate. The river 18O during the westerly period is also depleted, together with low δ 18O/altitude lapse rate. The pre-monsoon rivers witness the most enriched 18O with least significant correlation coefficient with the linear regression, whilst the postmonsoon rivers witness the largest δ 18O/altitude lapse rate. Different coherence of seasonal δ 18O variation with the altitude effect is attributed to different moisture supplies. Though sampling numbers vary with seasons, the δ 18O-H linear correlation coefficients all reach the 0.05 confidence level, thus witnessing the variation features of δ 18O in seasonal river water due to the influence of atmospheric general circulation and land surface processes revealed from the altitudinal lapse rates.
YANG XiaoXinXU BaiQingYANG WeiQU DongMeiLIN Ping-Nan
根据青藏高原上建立的TORP(Tibetan Observation and Research Platform)平台的28个站点获取的降水δ18O的研究,探讨了季风期河水δ18O的海拔递减率,也讨论了全年河水δ18O的高程效应.研究发现,青藏高原内部降水δ18O广泛受到不同水汽来源的影响.印度季风对青藏高原降水及河水δ18O的组成起着重要作用.总体而言,受季风影响地区水体中δ18O比西风影响区的水体δ18O更贫化,反映了西南来的海洋水汽在长途传输和随喜马拉雅山爬升过程使δ18O逐步贫化.由于季风环流对高原南部气候的控制,季风期河水δ18O随海拔的递减率更大.综合考虑季风期和非季风期河水δ18O的高程效应发现,其河水δ18O的海拔递减率大于不考虑季风期河水同位素组成的海拔递减率.因为青藏高原上河水和降水的高程效应是季风和非季风期水汽共同作用的结果,因此在利用稳定氧同位素恢复古高度时,需要考虑季风期高原水体中δ18O的组成和高程效应.
