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Journal Article

The interannual variability of east asian winter monsoon and its relation to the summer monsoon


Graf,  Hans-F.
MPI for Meteorology, Max Planck Society;

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Chen, W., Graf, H.-F., & Ronghui, H. (2000). The interannual variability of east asian winter monsoon and its relation to the summer monsoon. Advances in Atmospheric Sciences, 17, 48-60. doi:10.1007/s00376-000-0042-5.

Cite as: https://hdl.handle.net/21.11116/0000-0005-7595-F
The interannual variability of East Asian winter monsoon (EAWM) is studied based on a mon-
soon intensity index with the data from the NCEP/NCAR reanalysis for the period of 1968-
1997. The results show that both the regional Hadley Circulation along the East Asian coast and
the Walker Circulation over equatorial latitudes are more intense in a strong monsoon winter
than in a weak monsoon winter. This difference corresponds to the shift of major tropical con-
vection centres. In a strong monsoon winter the convection is much enhanced over the maritime
continent and reduced over the central Pacific, the situation is reverse in a weak monsoon win-
ter. These anomalous heat source distributions force opposite phases of the PNA pattern. It is
suggested that the barotropic instability of the extratropical zonal flow, which is associated with
the interannual variation of EAWM, is important for the propagation of stationary waves along
the route of the PNA pattern. There also seems to be a stationary wave originating over the trop-
ical western Pacific which propagates eastward and reaches the central and eastern Pacific dur-
ing strong monsoon winters. '

The lag-correlations between the EAWM intensity index and tropical Pacific sea surface tem-
perature anomaly (SSTA) indicate that the interannual variability of EAWM is mainly influ-
enced by the SST As over the tropical Pacific of the preceding summer. These SST As disappear
in the following spring. Generally a cool (warm) sea surface temperature in the tropical central
and eastern Pacific corresponds to a strong (weak) EAWM. Thus the processes of tropical
ocean-atmosphere interactions are suggested to be the dominant mechanism which influence
the interannual variations of EAWM. However, the instability processes at midlatitudes can
also cause anomalous winter monsoon, such as the 76/77 and 78/79 winter. On the other hand,
the SSTA in the South China Sea has been shown to be influenced mainly by the EAWM and
may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China
confirm that an anomalous East Asian summer monsoon is closely related to the preceding