利用水汽总量资料诊断入梅时间的方法

The Method of Diagnosing the Onset of Meiyu Based on the Moisture Data

  • 摘要: 梅雨期是江淮流域从春季到夏季一个重要的过渡时期。传统诊断入梅的方法主要根据雨日和温度及副热带高压位置等来确定。由于雨日的不连续, 天气形势的多变, 常会引起诊断入梅日期的分歧。利用长江三角洲地区地基GPS网所反演的连续的大气水汽总量 (GPS/PWV) 资料详细分析了长江三角洲地区2002—2005年入梅情况, 发现GPS/PWV资料可以反映出入梅前后大气中水汽发生显著季节性跳跃的特征, 总结出利用大气中水汽变化特征来诊断入梅时间的方法 (PWV方法)。采用1980—2000年的历史探空资料计算的大气水汽总量 (PWV) 资料, 对该方法进行了检验:21年中有13年的入梅日期与历史上传统方法诊断的入梅日期相吻合; 对两种方法诊断的入梅日期相差较大的3年的入梅情况进行的分析表明, PWV方法诊断出的入梅日比原定入梅日更合理。该方法在2006年入梅诊断的应用也得到验证。

     

    Abstract: Meiyu is an important transition period from spring to summer in the Huaihe and Yangtze River Reaches. The traditional methods to diagnose the onset of Meiyu are mainly based on rainy days, temperatures and position of subtropical high, etc. But because of the discontinuous rainy days and variable synoptic background, the traditional methods can't reach consistent results to the onset of Meiyu in many years. A new method is introduced to diagnose the onset of Meiyu using moisture. Characteristics of moisture variation during Meiyu season in recent four years are analyzed based on the precipitable water vapor data from GPS Meteorological Network (thereafter as GPS/PWV) in the Yangtze River Delta. It is founded that the GPS/PWV changes significantly on the beginning of Meiyu, which shows a seasonal change of moisture. The following three indexes of GPS/PWV are concluded to diagnose the onset of Meiyu:Everyday average and five-day average of GPS/PWV ascend to more than 40 mm; five-day average of GPS/PWV is stably under 40 mm before the onset of Meiyu, occasionally over 40 mm, after the onset of Meiyu, five-day average is stably over 40 mm, occasionally under 40 mm; the difference of five-day average shows a peak more than 20 mm at about the onset of Meiyu.If the three requirements are met by the GPS/PWV variation, it can be considered as the onset of Meiyu. This method is tested by PWV from 1980 to 2000 based on radiosonde sounding data. Results show that the onset days of Meiyu diagnosed by new method are more reasonable than those by traditional methods; the seasonal transformation can be better illustrated by the moisture data. This method is also successfully applied to diagnose the onset of Meiyu in 2006. The onset day of Meiyu in 2006 over the lower reaches of the Yangtze River issued by different observatories is different, such as 13—14 and 22 of June. Through analysis of GPS/PWV data from June to July, June 22 is more reasonable as the onset day of Meiyu in 2006.In addition, analysis shows the increasing of water vapor is directly led to by north-moving of subtropical high, which is advantageous to the establishment of Meiyu front.

     

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