To improve understanding of the characteristics of large-scale environments associated with summer monsoon precipitation in Korea. we have constructed an index to measure the Changma using area-averaged and period-averaged Climate Prediction Center merged analysis precipitation over Korea during the years 1979-2001. Strong and weak Changma years are defined as years in which the precipitation anomaly is over +/-0.5sigma. The domain and period for this analysis are selected over the Korean peninsula (31.25-41.25 degreesN, 123.75-131.25 degreesE) from late June to late July. In strong Changma years, strong upper level divergence occurs near the Korean peninsula, located at the entrance of the mid-latitude jet core, leading to low pressure in the lower layer. Between strong and weak Changma years, 850 hPa southwesterly flows are significant throughout the East China Sea and southern Japan. Clear differences exist between strong and weak Changma years. Weak Changma is well correlated with a weak Pacific high, as seen in the changes in sea-level pressure and 500 hPa geopotential height, and wind speed in the lower level jet. Strong Changma is well correlated with strong migratory highs in northern parts of the Korean peninsula. It is shown that the long-term changes in summer monsoon rainfall, such as those between the two climate regimes of 1979-92 and 1993-2001. are characterized by a shift of maximum rainfall periods from late July to mid August. Copyright (C) 2005 Royal Meteorological Society.
