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.

Reconstruction and Application of the Monthly Western Pacific Subtropical High Indices

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

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

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

    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

    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)

    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)

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

    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131318212764565351523827
    强度指数 重建2726343238128119991161067147
    脊线指数 重建151515171822262926232017
    西伸脊点 重建158139145134140132136137134124131139
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    Table  2  Maximum and minimum of the monthly WPSH indices from 1951 to 2010

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    Table  3  3 Correlation coefficients of two series of the monthly WPSH indices from 1951 to 2010

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    Table  4  Correlation coefficients among the reconstructed monthly WPSH indices

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