This study examines the overall changes in the characteristics of winter cold surges over Korea for the period 1979-2014 using ERA-Interim reanalysis data and the relationship between these cold surges with large-scale climate variability. The cold surge is defined based on the synoptic criteria such as the strengthening of the Siberian high and the subsequent abrupt surface temperature drop within 2 days. Using the dynamical indices of cold surges developed by Park et al. (2015), cold surges over Korea were classified into three types according to their dynamical origins: wave type, blocking type, and local type. The wave type cold surge is associated with a southeastward expansion of the Siberian High and a northerly wind, which is caused by growing baroclinic waves. The blocking type cold surge is associated with a southward expansion of the Siberian High originated in the Arctic and a northeasterly wind, which is caused by subarctic blocking and deepening of the East Asian coastal trough. The local type is associated with fast traveling

upper-level waves.

For 36 winters (1979-2014), the detected 278 cold surges were classified into the 3 major types, resulting in 144 (51.8%), 109 (39.2%) and 24 (9%) cases under wave, blocking, and local type cold surges, respectively. Compared with wave or local type cold surges, blocking type cold surges exhibit a longer duration and stronger intensity. Examination of the long-term change in cold surge occurrences shows different interdecadal and intraseasonal variations among the 3 types. The number of total cold surge days decreased slightly corresponding to the warming trend over Korea due to climate change, while blocking type cold surge days increased despite the warming trend, especially in December. Moreover, the blocking type tends to occur more frequently with a longer duration and stronger intensity, which leads to exceptional extreme cold winter. The number of blocking type cold surge days is strongly correlated with the monthly mean air temperature, with a correlation coefficient of -0.79.

The wave type cold surge displays no association with the phase of large-scale climate indices, while the blocking type cold surge has a dependency with respect to the Arctic Oscillation (AO), Western Pacific (WP) pattern, El Nino/Southern Oscillation (ENSO), Pacific North America (PNA) pattern and Pacific Decadal Oscillation (PDO). It is further found that the occurrence of these cold surges is

more likely when the AO, WP, ENSO is in its negative phase and/or the PNA and PDO is in its positive phase, which are enhanced the East Asian monsoon circulation. Cold surges of different dynamic origins may have different interdecadal variation, so it is important to investigate long-term variation of total occurrences as well as for the different types. Therefore decadal changes in cold surge characteristics over Korea are analyzed. Power spectrum analysis of temperature reveals that the low-frequency variabilities with a period longer than 10 days are significantly enhanced, while the high-frequency variabilities with a period shorter than 10 days are weakened in the 2000s. This corresponds to the result that cold surges were stronger and lasted longer during the 2000s compared to those that occurred in the 1990s. The more frequent strong and long-lasting cold surge occurrences in the 2000s are strongly associated with the more frequent strong negative phase of AO and WP, which shows an in-phase relationship with East Asia Winter Monsoon circulation.

1. 서론

2. 자료 및 분석 방법

2.1 자료

2.2 한파의 정의

2.3 한파 형태의 분류

3. 한반도 한파의 시·공간적 특성

3.1 한파의 종관적 특징

3.2 한파 발생의 계절내 특성

3.3 한파 발생에 영향을 미치는 기후인자 분석

3.4 한파 발생의 장주기 변동성

4. 결론 및 토의

REFERENCE