Predicting extreme rainfall over eastern Asia by using complex networks

A climate network of extreme rainfall over eastern Asia is constructed for the period of 1971-2000, employing the tools of complex networks and a measure of nonlinear correlation called event synchronization （ES）. Using this network, we predict the extreme rainfall for several cases without delay and with n-day delay （1 ≤ n ≤ 10）. The prediction accuracy can reach 58% without delay, 21% with 1-day delay, and 12% with n-day delay （2 ≤ n ≤ 10）. The results reveal that the prediction accuracy is low in years of a weak east Asia summer monsoon （EASM） or 1 year later and high in years of a strong EASM or 1 year later. Furthermore, the prediction accuracy is higher due to the many more links that represent correlations between different grid points and a higher extreme rainfall rate during strong EASM years.     

基于游程理论和两变量联合分布的中国西南地区干旱特征研究

基于中国西南地区(四川省、云南省、贵州省和重庆市)89个站点1961—2010年的逐月标准化降水指数序列,利用游程理论和Copula函数分析了这一地区不同等级和不同历时干旱的出现概率及重现期特征.结果表明:西南地区的干旱事件多为历时小于4个月、强度小于3的干旱事件;月内轻旱、月内中旱、季内特旱和跨季特旱的概率较大.干旱历时小于3个月和干旱强度为中旱以下的干旱类型多出现在西南地区的东部和西部,而干旱历时大于3个月和干旱强度为重旱以上的干旱类型多出现在西南地区中部.西南地区东部和西部的重现期大于中部地区,且随着干旱历时和干旱强度的增大,重现期空间差异越明显.而且,各气候态下相同干旱类型的概率差值不大,概率波动范围为±0.05,即随着时间推移,各干旱类型出现的概率均未出现较大幅度的变化.     

Objective identification research on cold vortex and mid-summer rainy periods in Northeast China

Considering the differences between the Northeast China Cold Vortex(CV) and the Mid-Summer(MS) rainy period and their corresponding atmospheric circulations are comprehensively analyzed, and the objective identification methods of defining the annual beginning and ending dates of Northeast China CV and MS rainy periods are developed respectively.The annual beginning date of the CV(MS) rainy period is as follows. In a period from April to August, if daily regional mean precipitation ryi is larger than yearly regional mean precipitation R(or 2R) on a certain day, the station precipitation rs is larger than the station yearly mean precipitation r(or 2 r) in at least 50% of stations in Northeast China, and this condition is satisfied in the following 2(7) days, then this date is defined as the beginning date of the CV(MS) rainy period.While the definition of the ending date of the MS rainy period shows the opposite process to its beginning date. With this objective identification method, the multi-year average(1981–2010) beginning date of the CV rainy period is May 3, the beginning date of the MS rainy period is June 27, the ending day of the CV rainy period is defined as the day before the beginning date of the MS rainy period, and the ending date of the MS rainy period is August 29. Meanwhile, corresponding anomaly analysis at a 500-h Pa geopotential height, 850-h Pa wind, Omega and relative humidity fields all show that the definitions of the average beginning and ending dates of the CV and MS rainy periods have a certain circulation meaning.Furthermore, the daily evolution of the CV index, meridional and zonal wind index, etc. all show that these objectively defined beginning and ending dates of the CV and MS rainy periods have climate significance.