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广东省前汛期暴雨与500 hPa关键区准双周振荡
Variations of Torrential Rain in First Rainy Season in Guangdong Province and Its Relationships with the Biweekly Oscillation of 500 hPa Key Region
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摘要: 采用小波分析、功率谱和交叉谱分析、Lanczos滤波等方法探讨了1961—2008年广东省前汛期暴雨的变化及与影响广东省前汛期降水的500 hPa关键区准双周振荡的关系。结果表明：20世纪90年代以来，广东省6月发生暴雨的日数明显增多, 强度增强；但90年代后期以来，前汛期暴雨的总日数却减少；前汛期暴雨总日数具有较明显的准6~7年周期振荡。广东省前汛期暴雨量占总降水量的37.7%，它与总降水量呈显著正相关。广东省前汛期降水与500 hPa关键区在大多数年份均存在显著的准单周、准双周振荡。虽然它们也存在30~60 d振荡，但不显著。500 hPa关键区与广东省前汛期降水在准双周振荡尺度上关系最密切，振荡超前或滞后的时间差在2 d之内。统计近48年4—6月500 hPa关键区准双周振荡波谷前后3 d (个别4 d) 广东省暴雨出现的概率为79%。采用典型个例的合成分析，得到500 hPa关键区准双周振荡波谷附近有、无暴雨出现的大气环流场演变具有明显差异，可为广东省前汛期暴雨的中期预报提供参考。
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关键词:
- 前汛期暴雨;
- 500 hPa关键区;
- 准双周振荡;
- 中期预报
Abstract: In order to improve medium range prediction of torrential rain in Guangdong Province, the variation characteristics of the torrential rain in first rainy season and their relationships with biweekly oscillation of a key region at 500 hPa geopotential height are investigated with wavelet analysis, power spectrum analysis, cross spectrum analysis and Lanczos filter using the daily precipitation data of 86 stations and rainfall regimes, and NCEP/NCAR daily data for the last 48 years of 1961-2008. The results show that torrential rain during June has increased in both the number of days and intensity since the 1990s, but the total number of torrential rain days for the season has decreased since the end of the 1990s, exhibiting significant quasi periodic oscillations of 6—7 years. The storm rainfall accounts for 37.7% of total rainfall during Guangdong first rainy season, and is significantly positive correlated to the total rainfall. The area (20°-30°N, 102.5°-120°E) with 500 hPa geopotential height is significantly negative correlated with the daily precipitation during April-June in Guangdong, named as the 500 hPa key region. The daily precipitation during April-June in Guangdong and 500 hPa key region exhibit significant quasi weekly (5—9 days) and quasi bi weekly (10-20 days) oscillations but less significant 30—60 days oscillations. The relation between 500 hPa key region and the daily precipitation during April—June in Guangdong Province in the quasi biweekly oscillation scale is most close connected, and the lead or lag time of oscillation is within 2 days. From April to June over the 48 years, the probability of torrential rain is 79% within three or four days (in fewer cases) before or after the valleys of the quasi biweekly oscillations in the 500 hPa key region. The characteristics of atmospheric circulation with or without torrential rain in Guangdong Province for quasi biweekly oscillatory valleys of 500 hPa key region are analyzed with the composite analysis of typical examples. When the torrential rain happens near the valleys, the cold air moves southward by significantly enhanced trough over East Asian, meanwhile, trough over the Bay of Bengal significantly deepens and widens, and torrential rain in Guangdong Province are caused by the interaction between north cold air and southwest warm and moist air brought by strong southwest flow from the Bay of Bengal. When no torrential rain happens near the valleys, the cold air acts northward, no significantly transfer of water vapor moisture transport from the Bay of Bengal, Guangdong Province is controlled by strong southwesterly at the verge of subtropical high and is located in the divergent region of moisture flux, the rainfall is weaker. All these are not conducive to the occurrence of rainfall, especially torrential rain. Therefore, the significant difference between the circulation fields can be used as reference for medium range forecast of torrential rain in Guangdong Province. -
图 1 1961-2008年4-6月广东省暴雨日数 (a) 及4-6月暴雨量占总降水量的百分比 (b)
Fig. 1 The number of Guangdong torrential rain day during April-June (a) and the percentage of storm rainfall accounting for total rainfall during April-June (b) from 1961 to 2008
图 2 1961-2008年4-6月广东省暴雨总日数的变化 (a) 及其墨西哥帽小波分析 (b) 与小波功率谱 (c)
(图a中实横线代表广东省4-6月暴雨总日数的历年平均值:17.3d, 虚线为高斯九点平滑滤波；图b中阴影区表示达到0.10显著性水平的区域，两边的交叉区域表示边界效应的影响域)
Fig. 2 The number of Guangdong torrential rain day during April-June from 1961 to 2008(a) with its Mexican wavelet analysis (b) and its global wavelet power spectrum (c)
(the horizontal solid line stands for 17.3 days, the mean days of Guangdong torrential rain during April-June from 1961 to 2008, and dashed line stands for smoothed filtered by 9 points Gaussian smoothing in Fig.2a; the shaded areas represent regions with significance level of 0.10 and the cross hatched regions on both ends indicate the areas with boundary effects in Fig.2b)
图 3 1961-2008年4-6月广东省86站平均逐日降水与500hPa高度场逐年相关系数的多年平均分布
(浅色阴影:通过0.05显著性水平检验；深色阴影:通过0.01显著性水平检验；矩形区:本文定义的500hPa关键区)
Fig. 3 The distribution of mean correlation coefficient between daily Guangdong rainfall averaged by 86 stations and geopotental height field at 500 hPa during April-June from 1961 to 2008
(the light and deep shaded area stands for passing the significance level of 0.05 and 0.01, respectively; the rectangular area is 500 hPa key region defined in this paper)
图 4 1961-2008年4-6月逐日降水与500hPa关键区的凝聚谱值与0.05显著性水平谱值之比 (阴影区为比值≥1的区域，表示通过0.05显著性水平检验)(a) 及落后时间长度 (b)
Fig. 4 The ratio of the coherence spectrum of the daily precipitation and index of 500 hPa key region to the spectrum with 0.05 significance level (shaded areas with the ratio≥1 passes the significance level of 0.05)(a) and their lag-temporal spectrum (b) during April-June from 1961 to 2008
图 5 2000年3-7月500hPa关键区位势高度逐日距平 (a) 与广东省86站平均逐日降水 (b) 及其经10~20d滤波的低频分量
(图中粗虚线为10~20d滤波；图a中水平细虚线表示10~20d低频序列的1倍标准差，数字1~5表示准双周振荡的5个不同位相)
Fig. 5 The daily anomaly of 500 hPa key region index (a) and daily mean rainfall of Guangdong (b) with their10-20-day Lanczos filter during March-July iN2000
(the thick dashed line is for 10-20-day Lanczos filter; the thin dashed horizontal line denotes one standard deviation of the10-20-day oscillation, and number1-5 represent the five different phases of the10-20-day oscillation in Fig.5a)
图 6 500hPa关键区准双周振荡低频波谷附近有暴雨的500hPa高度场 (单位:dagpm) 与850hPa风场位相1~4的合成场分布
Fig. 6 The composition of 500 hPa geopotential height field (unit:dagpm) and 850 hPa wind field for Phase 1-4 with the torrential rain in first rainy season in Guangdong associated with the quasi-biweekly oscillatory valleys of the 500 hPa key region index
图 7 500hPa关键区准双周振荡低频波谷附近有、无暴雨的850hPa水汽输送 (矢量，单位:kg·hPa-1·m-1·s-1) 及水汽通量散度 (等值线，单位:10-7kg·hPa-1·m-2·s-1)1~4个位相的合成场分布
Fig. 7 The composition of 850hPa moisture flux (vectors, unit:kg·hPa-1·m-1·s-1) and moisture flux divergence (isolines, unit:10-7kg·hPa-1·m-2·s-1) for Phase 1-4 with or without the torrential rain in first rainy season in Guangdong associated with the quasi-biweekly oscillatory valleys of the 500 hPa key region inde
表 1 1961-2008年4-6月逐日降水功率谱分析得到的5d以上主要周期
Table 1 The main period above5days of the daily precipitation during April-June from 1961 to2008 in Guangdong by Fourier power spectra analysis
表 2 1961-2008年4-6月逐日500hPa关键区功率谱分析得到的5d以上主要周期
Table 2 The main period above 5 days of the daily 500 hPa key region duringApril-June from 1961 to 2008 in Guangdong by Fourier power spectra analysis
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