Reconstruction and Application of the Monthly Western Pacific Subtropical High Indices

Liu Yunyun; Li Weijing; Ai Wanxiu; Li Qingquan

Vol.23, NO.4, 2012

Article Contents

Article Navigation > Journal of Applied Meteorological Science > 2012 > 23(4): 414-423

Liu Yunyun, Li Weijing, Ai Wanxiu, et al. Reconstruction and application of the monthly western pacific subtropical high indices. J Appl Meteor Sci, 2012, 23(4): 414-423.

Citation:

Liu Yunyun, Li Weijing, Ai Wanxiu, et al. Reconstruction and application of the monthly western pacific subtropical high indices. J Appl Meteor Sci, 2012, 23(4): 414-423.

Liu Yunyun, Li Weijing, Ai Wanxiu, et al. Reconstruction and application of the monthly western pacific subtropical high indices. J Appl Meteor Sci, 2012, 23(4): 414-423.

Citation:

Liu Yunyun, Li Weijing, Ai Wanxiu, et al. Reconstruction and application of the monthly western pacific subtropical high indices. J Appl Meteor Sci, 2012, 23(4): 414-423.

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Reconstruction and Application of the Monthly Western Pacific Subtropical High Indices

National Climate Center, Beijing 100081

Received Date: 2011-08-25
Rev Recd Date: 2012-04-20
Publish Date: 2012-08-31

Abstract

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.
- the Western Pacific Subtropical High;
- area index;
- intensity index;
- ridge line index;
- western boundary index

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References(19)

Figures and Tables

图 1 1971—2000年夏季北半球500 hPa高度场 (单位：dagpm)

(a) NCEP/NCAR再分析资料，(b) 国家气候中心业务资料

Fig. 1 500 hPa geopotential height for Northern Hemisphere in summer averaged from 1971 to 2000(unit:dagpm) (a) NCEP/NCAR reanalysis data, (b) service data from NCC

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Fig. 2 Time series of the monthly WPSH ridge line indices in July from 1951 to 2010

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Fig. 3 Distribution of precipitation percentage anomalies over China in July (a)1978, (b)1999

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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

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图 5 1971—2000年6—8月副高脊线指数与我国同期降水的相关分布

(阴影区为相关系数达到0.05显著性水平的区域)

Fig. 5 Correlation distributions between the WPSH ridge line indices and monthly precipitation anomalies over China in June, July and August, respectively

(shaded areas denote passing the test of 0.05 level)

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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)

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Fig. 7 Distribution of summer precipitation anomalies corresponding the nine-classification of the WPSH

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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
面积指数	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
强度指数	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
脊线指数	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
西伸脊点	业务	131	123	117	112	112	118	124	124	115	106	115	114

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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
副高指数极值	脊线指数最大值	重建	18	17	17	19	22	26	32	34	30	25	22	20
业务	脊线指数最大值	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
脊线指数最小值	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
西伸脊点最大值	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
西伸脊点最小值	业务	90	90	90	90	90	90	95	90	90	90	90	90

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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

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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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