青藏高原大气水汽探测误差及其成因

Systematic errors in the precipitable water vapor measurements over the Tibetan Plateau and its causes

中文关键词:  大气可降水量（PW）， 探空仪， 地基全球定位系统， 系统性误差， 青藏高原

英文关键词:Precipitable water vapor (PW), Radiosonde, Ground based GPS, Systematic error, Tibetan Plateau

中文摘要:

      青藏高原大气水汽分布对区域天气气候有很大影响，其探测资料的可靠性备受关注。以地基全球定位系统(GPS)遥感的大气可降水量为对比参照，分析了1999—2008年拉萨和2003年那曲探空观测大气可降水量的误差及其原因。结果表明，近10年拉萨站探空观测的可降水量比GPS遥感的可降水量明显偏小，偏小程度随使用不同的探空仪而异。GZZ-2型机械探空仪和GTS-1型电子探空仪多年平均的大气可降水量相对偏差分别为8.8%和4.4%，随机误差分别为19.8%和13.3%。近10年大气可降水量探测偏差具有减少的趋势，从12.7%减少至2.4%，主要是由探空仪性能改进所致。分析发现青藏高原大气可降水量探测偏差具有明显的日变化，12时（世界时）比00时大。拉萨站GZZ-2型和GTS-1型探空仪在12时多年平均的大气可降水量探测偏差分别为15.8%和8.3%，00时分别为1.6%和0.5%。那曲站GZZ 2型探空仪在12和00时的大气可降水量探测偏差分别为12.4%和0.3%。大气可降水量探测偏差还具有季节变化，夏季大，冬季小。对大气可降水量探测偏差日变化和季节变化的成因分析表明，12时气温比00时气温高以及夏季比冬季气温高是造成大气可降水量探测偏差日变化和季节变化的重要原因。

英文摘要:

      The distribution of the precipitable water vapor (PW) over the Tibetan Plateau has an important impact on the regional weather and climate. The reliability of PW measurements is of concern. The characteristics of the systematic and random errors of the radiosonde (RS) PW data in comparison with ground based GPS measurements at Lhasa during the period from 1999－2008 and at Naqu in 2003 are studied. The results show that the RS_PW is significant dryer than the GPS_PW at Lhasa in recent 10 years. Different types of humidity sensor show a different magnitude of the dry bias of PW. The GZZ 2 (goldbeater's skin hygrometer) and the GTS-1 (carbon hygristor) have the relative mean dry bias of 8.8% and 4.4%, respectively, and have the relative mean random errors of 19.8% and 13.3%, respectively. The relative PW difference is apparently reduced in recent 10 years, from 12.7% to 2.4%. The main reason is that high performance humidity sensors (GTS-1) have been introduced. The variation characteristics of the RS_PW dry bias are also investigated. The results show that the RS_PW dry bias exhibited pronounced diurnal and annual variations. The dry bias of the RS_PW is much larger at 12:00 UTC than that at 00:00 UTC and larger in summer than that in winter. The GZZ-2 and the GTS-1 have the relative mean PW bias of 15.8% and 8.3%, respectively, at 12:00 UTC at Lhasa. The GZZ-2 and the GTS-1 have the relative mean PW bias of 1.6% and 0.5%, respectively, at 00:00 UTC at Lhasa. The GZZ-2 has the relative mean PW bias of 12.4% and 0.3% at 12:00 and 00:00 UTC respectively. The causes of diurnal and annual variation of the RS_PW dry bias are analysed. It can be seen that the diurnal variations of the RS_PW dry bias are significant mainly because the air temperature is higher at 12:00 UTC than that at 00:00 UTC. The annual variations of the RS_PW dry bias are pronounced mainly because the air temperature is higher in summer than that in winter.