S-Space College of Natural Sciences (자연과학대학) Dept. of Earth and Environmental Sciences (지구환경과학부) Theses (Master's Degree_지구환경과학부)
An Index for Classification of Cold Surge Types over East Asia and its Application to CMIP5 Results
- 자연과학대학 지구환경과학부
- Issue Date
- 서울대학교 대학원
- 학위논문 (석사)-- 서울대학교 대학원 : 지구환경과학부, 2015. 2. 허창회.
- The cold surges over East Asia can be classified into wave-train type and blocking type according to their dynamic feature. Two indices are introduced to classify the wave-train and blocking type cold surge in this study. The indices capture upper atmosphere pattern, wave-train and meridional dipole structure using potential temperature on 2 potential vorticity units (PVU) surface. The wave-train index (WI) is defined a difference of anomalous potential temperature on 2 PVU between western North Pacific and northeast china to capture the wave-train, trough-ridge pattern. The blocking index (BI) is defined a difference of anomalous potential temperature on 2 PVU between subarctic region and northeast china to capture blocking pattern, meridional potential temperature gradient reversal. The each cold surge classified by the index method have essential feature in observation. The wave-train type has baroclinic wave with southeastward Siberian high expansion and the blocking type has dipole structure indicating the subarctic blocking and deepening of East Asian coastal trough induces a southward expansion of the Siberian high. The blocking type cold surge is less frequent but stronger and longer than the wave-train type cold surge. In addition, we exclude the cold surge don’t have the wave-train and dipole structure.
The index method is applied to 13 CGCMs in CMIP5. In historical run the cold surges in 13 CGCMs is well classified into the wave-train and blocking type cold surge by the index method. Wave-train type has wave pattern, and blocking type has dipole pattern in historical run. However, many 13 CGCMs simulate the less occurrence of cold surge and stronger and longer in both types in historical run compared with observation results. In RCP8.5, the ensemble mean occurrence and intensity of both types decreases, and the duration increases in blocking type, decreases in wave-train type.