서울 기상 관측소(서울시 종로구 송월동, 37˚34'N, 126˚57'E, 이하 송월)의 일 최저기온과 결빙 자료, 그리고 인근인 한강 관측소(37˚30'N, 126˚57'E, 이하 한강)의 결빙 자료를 사용하여, 1907-2006년(100년) 동안 한국 서울에서의 결빙기후의 장기 변동을 조사하였다. 송월의 결빙은 옥외 노장의 물이 동결하는 현상으로 정의하였고, 이곳에서 6 km 떨어진 한강의 결빙은 한강 대교 남단에서 2번째와 4번째 교각의 상류 100 m 부근이 완전히 얼었을 때로 정의한다. 평균 첫 결빙일은 송월이 10월 28일, 한강이 12월 28일이며, 각각 0.78 days decade-1와 3.47 days decade-1로 점차 늦어지는 추세를 나타냈다. 평균 연 결빙 일수는 송월이 159.06일, 한강이 50.33일이며, 각각 2.01 days decade-1와 5.24 days decade-1로 감소하는 추세를 보였다. 특히, 1950년대 후반을 기점으로 변화율이 급변하였는데, 한강에서 100년 동안 발생한 7번의 무결빙해(1960, 1971, 1972, 1978, 1988, 1991, and 2006)도 모두 1950년대 이후에 발생하였다. 송월과 한강에서 첫 결빙일의 일 최저기온은 평균적으로 각각 0.55˚C와 -12.22˚C이다. 영하의 일 최저기온이 송월은 6.43일, 한강은 8.94일 지속되고 난 뒤 첫 결빙이 발생하였다. 송월과 한강의 연 최저기온에 대해서 첫 결빙일은 양의 상관을 보였고, 결빙 일수는 음의 상관을 보였다. 이러한 결과는 결빙기후의 변화가 기후변화의 일환으로 나타나는 기온변화와 유관함을 보였다. 향후 더 넓은 지역에서 다양한 추가 연구를 실시함으로써, 지속적으로 결빙기후를 주시하고자 한다.

In 2007, just after the recession of the Changma, anomalously long rainy period (from July 30 to August 15) occurred in Korea. To identify the cause of the sustained rainy period, we performed synoptic analysis and the associated air motions. The behavior of each air parcel trajectory associated with atmospheric motion was then investigated. As a result, three particular phenomena occurring at latitudes lower than 40˚N were discovered. First, a mass of relatively cold air, referred to as E, made a deep intrusion from 20˚N to 60˚N. Second, this intrusion was accompanied by another mass of air called dE. It was colder and drier than E and originated from the mid-troposphere over the tropical ocean. Third, dE and E rotated clockwise three times over a period of 17 days over the Northwestern Pacific and blocked the westerly waves imbedded in the zonal flow from propagating. Two additional phenomena were observed at latitudes higher than 40˚N. First, the cold core system, while approaching from the west with low geopotential values at its center, was stagnated over Shanxi China. It enhanced the northward intrusion of dE and E, and then diminished. The subsequent low system showed similar evolution as the first one. Second, a warm core anticyclone was formed over Lake Baikal, blocking the westerlies for 13 days and contributed to the persistent northward incursion of warm moist air. Moreover, a horizontally extended intrusion of upper level clouds from the tropics to 50˚N, which may be interpreted as a tropical plume, was found around the end of the period (from August 12 to 15, 2007) with successive tropical nights over Korea.

The relationship between two interannual climate variabilities and the frequency of tropical cyclone (TC) that landed over the Korean Peninsula (KP) has investigated for the period of 1951-2004. In the analysis of the relationship between KP-landfall TC frequency and the ENSO phase, most TCs of C-14 (TCs that do not pass through mainland China before landing the KP) and C-23 (TCs that pass through mainland China before landing the KP) tended to more land in the warm phase than normal and cold phases. However, TC intensity at landfall was stronger in the cold and normal phases. In the analysis of the relationship between KP-landfall TC frequency and Arctic Oscillation (AO) phase, the TCs of C-14 tended to more land in the positive (POS) phase of AO and the negative (NEG) phase of AO for C-23. It was found that AO index was negatively correlated with the Niño-3.4 index. And then the TCs of C-14 landed more frequently over the KP in the AO POS - Niño-3.4 NEG phases and in the AO NEG - Niño-3.4 POS phases for the TCs of C-23.