Impacts of the Pacific Indian Ocean Temperature Anomaly Mode on Asian Climate Systems

Figure 7 shows the composite of 100 hPa geopotential height for positive and negative phases (1954, 1955, 1964, 1970, 1988, and 1996 with the composite index less than or equal to 2.5) of PIM. The South Asian high is weaker and stretches eastward and southward for the positive phase. In contrast, the South Asian high is stronger and stretches westward and northward for the negative case.

Figures 8(a) and 8(b), respectively, show the composites for positive and negative phases of PIM at 500 hPa. In the case of positive phase, the contour of 5860 gpm of the western Pacific subtropical high is shifted to the coast areas of Fujian Province. The contour of 5880 gpm is found over the western Pacific to the east of Taiwan. During the year of negative phase, the contour of 5860 gpm retreats to the east of Taiwan Island. We cannot find the contour of 5880 gpm. So the PIM can influence the intensity and the longitudinal position of the western end of the western Pacific subtropical high.

Fig. 7. The composite of 100 hPa geopotential height for positive (a) and negative (b) phases.
Fig. 8. The composite of 500 hPa geopotential height for positive (a) and negative (b) phases.
Fig. 9. The composite anomalies at 850 hPa for positive (a) and negative (b) phase.

The positive phase features the anomalous cross-equator southerlies from the eastern Indian Ocean to the western Pacific at 850hPa (Fig. 9(a)). Thus, the South Sea monsoon trough and ITCZ are enhanced. Anomalous northerlies are found over East China. It indicates weaker East Asian summer monsoon. The Indian southwest monsoon is also weaker. In the year of negative phase (Fig. 9(b)), anomalous westerlies occupy over the western Indian Ocean, which means the stronger southwest monsoon. The anomalous southerlies over East China express the stronger East Asia summer monsoon. The anomalous cross-equator northerlies lie from the eastern Indian Ocean to the western Pacific. So the South Sea monsoon trough and ITCZ are weakened.

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