열대지역 단기 대기변동성이 지역 해양 및 동아시아 강수 변동성에 미치는 영향 연구: 모델링과 분석

Abstract

In this study, the effects of tropical high-frequency atmospheric variability on regional ocean and precipitation variability in East Asia were analyzed in two main categories. First, we analyzed the effect of high frequency atmospheric forcing (HFF) on El Niño Southern Oscillation (ENSO) through the MOM4 model experiment. Second, the effects of tropical atmospheric variability on precipitation variability in East Asia were analyzed on intraseasonal time scale using reanalysis data.

In the model experiment, the reanalysis data is divided into the entire period (Exp_CTL), years without El Niño or La Niña (Exp_Nor), years with El Niño (Exp_El), and years with La Niña (Exp_La). A total of four experiments were carried out by implementing HFF by randomly selecting from the divided years. As a result, ENSO development was simulated in Exp_CTL and Exp_El, but not in Exp_Nor and Exp_La. The simulated ENSO in the model experiment were similar in their characteristics to the observed data. We also found that the eastward propagating Kelvin wave, which induced by HFF plays important role in ENSO development. In addition, we defined Westerly Wind Event (WWE) and analyzed the differences for each experiment. We found that WWE in two experiments simulating ENSO occurred more frequently during SON than the other two experiments, with regional differences in the magnitude of variability.

On the other hand, we used ECMWF reanalysis data to analyze the intraseasonal precipitation variability in Korea during boreal summer (June-July-August). We used Empirical Orthogonal Function (EOF) analysis on Northeast Asia and reconstructed the Korean precipitation variability on intraseasonal timescales representing northward propagating intraseasonal oscillation from the tropics-to-subtropics. Then we calculate the correlation coefficient with total precipitation variability in Korea. As a result, the correlation coefficients change from year to year, and showed a tendency to decrease in recent years. Years when correlation coefficient is high (low) are characterized by early (late) start of rainy season, large (small) amount of total precipitation, and enhanced (reduced) precipitation variability on an intraseasonal timescale. In addition, the enhanced convective activity in the western tropical Pacific and the associated atmospheric conditions including weakening of the Western North Pacific Subtropical High (WNPSH) with its eastward shift and vertical shear of zonal wind affect to the characteristic change of intraseasonal precipitation variability in Korea.