Heavy Rainfall Events Lasting 18 Days from July 31 to August 17, 1998, over Korea

The 18-day continuous heavy rainfall occurrence from July 31 to August 17, 1998, over southern Korea is investigated to understand the synoptic-scale characteristics and development mechanisms of the long-lasting heavy rainfall. An elongated monsoon front is maintained over central China throughout the Korean Peninsula for about 20 days under strong summer time baroclinic development between the continental polar lows north of Korea and the northwestward extended Northwestern Pacific high. The remarkable features of the synoptic-scale environment that resulted in heavy rainfall events are the quasi-stationary location of the upper-level jet and the low-level jets. Further, there is a sufficient moisture supply from the low-level jets that are intensified by the typhoons in landfall on southern China and over the East China Sea. The daily heavy-rainfall event over southern Korea is strongly tied to the intensity and the north-south oscillation of the upper-level jet that locates just to the north of the heavy-rainfall area, as well as the diabatic heating process that well corresponds to the upward motion in the area of the heavy rainfall according to the solution of the Sawyer-Eliassen equation. The periods of 2-3 days and 1 day appearing in the variations of 200 hPa v-component wind and u-component wind, respectively, correspond well to those of about 2 days and 1 day appearing in the spectrum of hourly rainfall data. The 1 day period in the variation of 200 hPa v-wind fields demonstrates that the heavy rainfall over Korea was enhanced by the secondary circulation around the upper-level jet. The period also appears approximately in the variations of heat source, moisture sink, and vertical motion over Korea.

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