Reconstruction and Application of the Monthly Western Pacific Subtropical High Indices
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摘要: 针对目前国家气候中心业务监测中使用的月时间尺度西太平洋副热带高压指数存在的问题,利用NCEP/NCAR月平均再分析资料,对西太平洋副热带高压面积指数、强度指数、脊线指数和西伸脊点4种指数重新进行定义和计算,重建了1951—2010年逐月历史时间序列。面积指数、强度指数采用真实的面积和体积进行定义和计算,脊线指数则同时利用500 hPa高度场和纬向风切变线进行定义,且不仅仅局限于588 dagpm等值线,充分考虑了西太平洋副热带地区高压系统对我国夏季降水的影响作用。选取其中两个相对独立的指数——脊线指数与西伸脊点,通过对这两个指数的9种组合类型的构建,最大程度上涵盖了我国东部夏季降水各种雨型的分布特征。Abstract: In order to solve the problems of the monthly Western Pacific Subtropical High (WPSH) indices used in National Climate Center (NCC) monitoring service, a series of the monthly WPSH indices, including the area index, intensity index, ridge line index and western boundary index, are redefined and reconstructed, on the basis of the monthly NCEP/NCAR reanalysis datasets from 1951 to 2010.The reconstructed area index is defined by the "real area" of the WPSH surrounded by the 588 dagpm contour over western Pacific, while the intensity index is the "volume" of the WPSH over 588 dagpm. The reconstructed western boundary index is defined as the minimal longitude degree of the 588 dagpm contour in the region between 90°E and 180°. When 588 dagpm contour disappears in some month, it is substituted by the maximum of this index in this month during 1951 to 2010. The definition of the reconstructed ridge line index has more adjustment. It is defined by the latitude position of the isoline where 500 hPa zonal wind u=0 and ∂u/∂y > 0 surrounded by 588 dagpm contour. When there is no 588 dagpm contour, the 584 dagpm contour is just considered in the definition. If even no 584 dagpm contour exists in some month, it is substituted by the minimum of this index in this month during 1951 to 2010. Both the 500 hPa geopotential height and 500 hPa zonal wind shear line are considered in the reconstructed ridge line index, and no more restricted by 588 dagpm contour, which takes full consideration of the impact of the WPSH system on the summer precipitation in East China.The reconstructed WPSH indices have enabled describing objectively characteristics of the WPSH's monthly change, and overcoming the defect of the excessive dependence of the WPSH indices using in NCC service on the data resolution. The significant correlation of the reconstructed ridge line index and the summer precipitation over the Yangtze River also confirms its rationality and objectivity. Finally, two kinds of relatively independent WPSH indices, the ridge line index and western ridge point index, are selected to combine nine classifications of WPSH, which correspond with all kinds of distributions of summer precipitation anomaly in East China at large. It provides a scientific basis to further understand the relation of the position anomaly of the WPSH and the summer main rainfall belt in East China.
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图 4 1971—2000年夏季副高脊线指数与我国夏季降水的相关分布
(阴影区为相关系数达到0.05显著性水平的区域) (a) 业务指数,(b) 重建指数
Fig. 4 Correlation distributions between the WPSH ridge line indices and summer precipitation anomalies over China from 1971 to 2000(shaded areas denote passing the test of 0.05 level)(a) service indices, (b) reconstructed indices
图 6 1951—2010年夏季副高脊线和西伸脊点距平组合的九分类图
(Ⅰ:偏北偏西;Ⅱ:偏北;Ⅲ:偏北偏东;Ⅳ:偏东;Ⅴ:偏南偏东;Ⅵ:偏南;Ⅶ:偏南偏西;Ⅷ:偏西;Ⅸ:正常)
Fig. 6 The nine classification chart according to the combination of the summer WPSH ridge line and west boundary indices from 1951 to 2010
(Ⅰ: northwest anomaly; Ⅱ: north anomaly; Ⅲ: northeast anomaly; Ⅳ: east anomaly; Ⅴ: southeast anomaly; Ⅵ: south anomaly; Ⅶ: southwest anomaly; Ⅷ:west anomaly; Ⅸ: normal)
表 1 1971—2000年1—12月平均副高指数
Table 1 The monthly Western Percific Subtropic High (WPSH) indices averaged from 1971 to 2000
副高指数 分类 1月 2月 3月 4月 5月 6月 7月 8月 9月 10月 11月 12月 面积指数 重建 13 13 18 21 27 64 56 53 51 52 38 27 业务 8 8 11 13 17 22 22 22 21 21 16 13 强度指数 重建 27 26 34 32 38 128 119 99 116 106 71 47 业务 14 14 19 22 29 45 40 38 39 38 29 23 脊线指数 重建 15 15 15 17 18 22 26 29 26 23 20 17 业务 13 13 13 14 15 21 25 27 25 21 19 16 西伸脊点 重建 158 139 145 134 140 132 136 137 134 124 131 139 业务 131 123 117 112 112 118 124 124 115 106 115 114 表 2 1951—2010年1—12月副高指数的最大值及最小值
Table 2 Maximum and minimum of the monthly WPSH indices from 1951 to 2010
副高指数极值 分类 1月 2月 3月 4月 5月 6月 7月 8月 9月 10月 11月 12月 脊线指数
最大值重建 18 17 17 19 22 26 32 34 30 25 22 20 业务 17 17 16 19 21 27 30 34 30 26 24 19 脊线指数
最小值重建 13 12 13 13 14 18 22 20 23 19 18 14 业务 11 11 10 10 12 17 21 20 17 18 15 13 西伸脊点
最大值重建 170 148 168 160 172 170 178 165 165 175 168 162 业务 155 155 155 166 149 140 160 153 160 150 150 150 西伸脊点
最小值重建 90 90 90 90 90 105 110 90 95 90 98 90 业务 90 90 90 90 90 90 95 90 90 90 90 90 表 3 1951—2010年两套副高指数的相关系数
Table 3 3 Correlation coefficients of two series of the monthly WPSH indices from 1951 to 2010
月份 面积指数 强度指数 脊线指数 西伸脊点 1月 0.74 0.83 0.54 0.69 2月 0.68 0.83 0.58 0.62 3月 0.70 0.80 0.40 0.62 4月 0.73 0.77 0.40 0.52 5月 0.65 0.68 0.57 0.47 6月 0.74 0.78 0.71 0.62 7月 0.74 0.84 0.33 0.50 8月 0.74 0.83 0.67 0.47 9月 0.70 0.79 0.76 0.47 10月 0.76 0.80 0.71 0.39 11月 0.76 0.77 0.60 0.50 12月 0.81 0.85 0.51 0.62 表 4 重建的副高指数间的相关系数
Table 4 Correlation coefficients among the reconstructed monthly WPSH indices
副高指数 面积指数 强度指数 脊线指数 西伸脊点 面积指数 1.00 0.97 0.38 -0.75 强度指数 1.00 0.36 -0.67 脊线指数 1.00 -0.16 西伸脊点 1.00 -
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