中文摘要：

中国探空系统的湿度传感器从59型探空仪的肠膜湿元件改为L波段电子探空仪的碳湿敏碳质电阻后,敏感度极大提高,滞后误差明显减小,但出现新的问题,即在中低空经常出现极度偏干的现象,而且偏干层的厚度很大.利用2008年12月-2009年11月中国91个L波段探空站的相对湿度观测数据,初步分析了L波段探空系统相对湿度观测异常偏干的问题,得到结论：L波段探空系统相对湿度观测在对流层中下层出现异常偏干的现象,不是个别现象,具有相当的普遍性,占整个观测的10％～20％,其中在中国西南和东部沿海地区出现的概率更高,可达20％～40％;并且主要出现在对流层中低层650～ 500hPa的高度上,起始高度可以到900hPa以下;该现象具有明显的季节变化特征,与中国东部地区雨带的移动有较好的对应关系,冬季主要出现在贵州、广西和广东等地区,春夏秋季节逐渐随着雨带北移,然后南撤.L波段探空系统相对湿度观测的异常偏干已经超过了大气中可能出现的自然异常,主要是湿度传感器的不良性能造成的问题,并与探空球上升过程中湿度传感器穿过的云型特点有关.这些异常偏干的相对湿度数据不是真实反应大气状态的错误数据,在使用过程中应采取有效措施克服.

英文摘要：

With the improvement of the Chinese radiosonde system,the goldbeater＇s skin used in Type 59 has been replaced by carbon hygristor which is used in an L-band radiosonde system.After the update,the sensitivity of the humidity sensor has been significantly enhanced and the lag error decreases obviously.However,a new problem is found：an abnormally dry phenomenon often happens in the middle and low troposphere,and the thickness of the abnormally dry layer is quite large.Preliminary analysis was done on this dry phenomenon which occurs in the observation of relative humidity by the L-band radiosonde by using radiosonde data from 91 radiosonde stations from December 2008 to November 2009.The conclusions are as follows.The phenomenon is not individual but is quite common,accounting for 10％ ～ 20％ of the radiosonde observation.The occurrence probability of the phenomenon is higher in the southwest area and the eastern coastal area where the proportion accounts for 20％ ～ 40％.The abnormally dry phenomenon mainly occurs in the low and middle troposphere from 650 to 500 hPa,sometimes under 900 hPa.There is an obvious seasonal change in this abnormally dry phenomenon,which is in accord with the shift of rain belts over eastern China.In winter the phenomenon mainly happens in Guizhou,Guangxi and Guangdong and gradually moves northward and southward with the rain belt shifting from spring to autumn.The extent of this abnormally dry phenomenon is more than the natural dryness which may happen in the atmosphere.It mainly attributes to the poor performance of the humidity sensor and also relates to the cloud type across which the radiosonde passes.The wrong data of abnormally dry relative humidity cannot represent the true state of the atmosphere and therefore some effective measures must be taken while using these data.