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Characteristic large-scale circulation pattern of the persistent droughts of Northeast Asia from premonsoon season to monsoon season

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Authors
박종서
Advisor
임규호
Major
자연과학대학 지구환경과학부
Issue Date
2014-02
Publisher
서울대학교 대학원
Keywords
western North Pacific subtropical highdroughtEast Asian Westerly Jet Indexpremonsoonpersistent feature
Description
학위논문 (박사)-- 서울대학교 대학원 : 지구환경과학부, 2014. 2. 임규호.
Abstract
Characteristic patterns of atmospheric circulation anomalies over the
northeast Asian region in the dry and wet premonsoon seasons have been
analyzed. The relationship between these patterns in the premonsoon season and
the precipitation anomalies in the monsoon season has been also investigated.
Since this study focuses on dry premonsoon season, features of anomalous
large-scale atmospheric circulations during springtime droughts that occurred
over the northeast Asia are revealed. The Palmer drought severity index is used
in order to define drought years. In drought years, the anomalous circulation over
the northeast Asia exhibits the weakened northward flow from the western North
Pacific, and the position of the East Asian westerly Jet (EAWJ) maximum core at
300hPa is shifted southward. Thus, the rainfall band is moved southward, and the
associated precipitation is suppressed over Korea, Japan, and southeastern China
during spring droughts. The Sea Surface Temperature (SST) anomalies and
outgoing longwave radiation anomalies, which show a north–south dipole pattern
between the Philippines and the northeast Asian region, support these dry
conditions through the Hadley circulation. The anomalously warm SSTs in the
western North Pacific seem to play an important role in the atmospheric
circulation associated with persistent northeast Asian droughts
The persistent features of extreme precipitation over the northeast Asia from
premonsoon season to monsoon season are found. In order to understand some
characteristics of the circulation anomalies associated with persistent features of
extreme precipitation, six dry cases and six wet cases in the premonsoon season
are selected. Both of the extreme conditions are nearly persistent in each case. As
mentioned in spring drought analysis, the weakened western North Pacific
subtropical high (WNPSH) and the southward-shifted EAWJ are predominant
for dry cases. For wet cases, the strengthening of WNPSH, the northward-shifted
EAWJ in spring, and southward-shifted EAWJ in summer are apparent. However,
dry cases are associated with the warm SST anomalies of the western North
pacific, whereas wet cases are related to the warm SST anomalies of the Indian
Ocean and Bay of Bengal. The dependency of extreme precipitation on this SST
anomaly pattern is supported through numerical experiments. Based on the
observational analysis and model experiments, the main connection system
between extreme precipitation such as drought and SST is the anomalous
cyclonic circulation over the western North Pacific.
Language
English
URI
https://hdl.handle.net/10371/121195
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College of Natural Sciences (자연과학대학)Dept. of Earth and Environmental Sciences (지구환경과학부)Theses (Ph.D. / Sc.D._지구환경과학부)
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