Interdecadal variability of summer rainfall in the late 1990s in the Korea and north China region

  • Increase of summer rainfall in the Korea and North China region in the late 1990s
  • Association with the La Niña pattern and reinforcement of the Walker circulation
  • Reinforcementoflocal Hadley circulation

This study analyzed the trend of increasing summer (June to August) rainfall in the Korea and North China region (35°–40°N, 110°–130°E) in the late 1990s. In order to investigate the causes of the increase in summer rainfall since 1998 in the Korea and North China region, we analyzed the differences in summer averages between 1998–2012 and 1981–1997. The analysis of the 850 hPa stream flows showed that the anomalous huge anticyclonic circulations were reinforced in the North Pacific and eastern Australia. In both hemispheres, the anomalous easterlies (anomalous trade winds) were reinforced from the equatorial central Pacific to the tropical western Pacific by the anomalous circulations, which was an anomalous circulation pattern that appeared in the La Niña years. As for the 200 hPa stream flows, the anomalous huge cyclonic circulations were also reinforced in both the South Pacific and North Pacific. These two anomalous circulations reinforced the anomalous westerlies in the equatorial central and western Pacific, leading to the increase in summer rainfall in the Korea and North China region beginning in the late 1990s that was associated with the La Niña pattern, which was connected to reinforcement in the Walker circulation. Recently in East Asia, the local Hadley circulation has been reinforced to induce upward flows in the equatorial western Pacific and mid-latitude region of East Asia that have descended in the subtropical western Pacific.

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