연구보고서
- 저자
- 오지현 박사
- 작성일
- 2017.07.04
- 조회
- 303
- 요약
- 목차
The East Asian Summer Monsoon (EASM) is characterized by a distinct rainy spell that lasts for several weeks. A zonally elongated rain band during the rainy period migrates northward from the Yangtze River valley in China to Korea. The rainy season, called “Changma” in Korea, “Meiyu” in China, and “Baiu” in Japan, is vital to water management in populous East Asian countries. In particular, the rainfall amount during Changma accounts for 30% of the total annual precipitation in Korea. Therefore, it is critical to predict the onset of the rainy season for the effective planing regarding water storage and supply over the East Asian region.
The Boreal Summer Intraseasonal Oscillation (BSISO) is one of important sources of EASM variability, and affects the onset of summer monsoon precipitation. In order to support the protection of lives and property in the APEC countries from natural atmospheric hazards, the APEC Climate Center (APCC) has disseminated BSISO forecast based on BSISO indices since 2013. This study aims to advance our understanding of BSISO and facilitate the application of BSISO forecast by investigating climatological aspects of BSISO and its features, which modulate the rainfall and atmospheric circulation over East Asia. Commonality and dissimilarity between BSISO1 and BSISO2 are mainly discussed.
Phase 4 of BSISO1 and phase 6 of BSISO2 are closely related to an increase in rainfall amounts over East Asia based on observed precipitation data, spanning from 1981 to 2010. During these two phases, both BSISO1 and BSISO2 accompany low-level anticyclonic circulation over the Philippine Sea, supplying moisture to East Asia. It is shown that the Philippine Sea anticyclone during phase 4 of BSISO1 is associated with a teleconnection pattern extending from the western tropical Pacific to North America, which is revealed in the composite of the geopotential height at 500hPa. However, the Philippine Sea anticyclone for phase 6 of BSISO2,
is only pronounced over the East Asia region as a part of the meridional tripole pattern. The difference in the large-scale spatial pattern between phase 4 of BSISO1 and phase 6 of BSISO2, is attributed to the different horizontal distribution of convective heating anomalies.
In addition, dissimilarity in vertical circulation is remarkable between phase 4 of BSISO1 and phase 6 of BSISO2. While the zonal vertical circulation is dominant for phase 4 of BSISO1, the meridional vertical circulation is salient for phase 6 of BSISO2.
The relationship between Changma onset and the occurrence of phase 4 (6) of BSISO1 (2) from 1981 to 2016 is further investigated. 5 out of 36 cases of Changma onset occur in phase 4 of BSISO1, whereas 8 out 36 cases of Changma onset concur with phase 6 of BSISO2. Intriguingly, the Changma onset is concurrent with phase 4 of BSISO1 in the ensuing summer of El Nino. Based on analysis of 30 years of BSISO indices, it is found that a monthly variation of BSISO phase exists. The amplitude of BSISO2 phase 6 is at its maximum in June, in conjunction with an onset of rainy season in East Asia.
BSISO events for the last 30 years are categorized into propagating cases and non-propagating cases in this study by applying objective criteria based on previous studies. As a result, the average duration of each event is approximately 10 days, and each event tends to propagate through 3 successive phases on average, maintaining its amplitude greater than unity. Also BSISO2 has the most propagating events in June, which could be related to the development of EASM rainfall.