하계 동한난류 경로 변동에 따른 동해남부 해역의 냉수대 발생 특성

Abstract

Using the long-term water temperature and velocity data, the characteristics of cold-pool occurrence by region of the East Sea were identified, and the correlation between the appearance of the cold-pool in the southern coast of the East Sea according to the path change of the EKWC northward along the East Sea was analyzed. First, based on previous research papers dealing with the occurrence of cold-pool and long-term water temperature observation data from the National Institute of Fisheries Science, the frequency of occurrence of cold-pool along the East Sea was identified. The frequency of occurrence of cold-pool was the highest at 45% in the coastal waters of Ulgi in August in the summer. Next, Gampo (33%) and Busan (22%) showed a higher frequency of occurrence of cold-pool in the southern part of the East Sea, located south of Homigot, than in other coastal areas. The water temperature and the horizontal and vertical structures of currents were compared and analyzed according to the presence or absence of cold-pool along the Ulgi coast. As a result of analyzing the characteristics of the vertical distribution of water temperature, the water temperature stratification in the coastal area is formed in the shallow water during the cold-pool. On the other hand, in the case of non-occurrence of the cold-pool, the interval of isothermal lines along the coast is widely distributed. EKWC, which flows northward along the southern coast of the East Sea, passes 36.5°N and changes its path. EKWC main pathway variations can be divided into three categories. The first is the case of EKWC northward adjacent to the coast (On-coastal), the second is the case of EKWC northward along the 129.7°E line about 40 km away from the Hupo coast (Normal), and the third is the case of EKWC northward along the outer sea away from the coast (off-coastal). The probability of cold-pool occurrence according to the three paths of EKWC was 22% when on-coastal, 0% when normal, and 91%. Correlation was identified through spectral analysis using TWC transport, water temperature, and long-term fluctuation indexes, ONI and PDO data. As a result of the Coherence of ONI and PDO, which are long-term fluctuation indices, they show a high correlation in a long-term period of more than 3 years. In the Coherence results of ONI and water temperature, no correlation was found. However, as a result of comparing the time series data, the water temperature along the East Sea decreased during the period when the ONI was high, and as the ONI rapidly decreased, the water temperature in the entire East Sea increased from the following year. Rapid changes in ONI were found to affect the water temperature distribution in the East Sea. In the result of Coherence analysis of PDO and TWC transport, the Coherence value was 0.7 in the period of 0.8 to 1.2 years, showing high correlation. In addition, the correlation was relatively high even in the long period of 5 years or more. As a result of comparative analysis of time series data of PDO and TWC transport, it was found that there was a negative correlation between the two factors. The Coherence of PDO and Ulgi water temperature shows a correlation of 0.6 in a 1.2-year cycle, and there are no other highly correlated cycles. In the short-period component, the Coherence between TWC transport and water temperature in the coastal waters of Ulgi is high, ranging from 0.6 to 0.75. Therefore, it can be seen that there is a mutual correlation between the amount of TWC transport and the water temperature of Ulgi in relation to the occurrence of the cold-pool. It was found that the change in the path of the EKWC northward from the Hupo coast and the change in the intensity of the current were highly correlated with the occurrence of the cold-pool in the Ulgi coast. Therefore, the correlation between the flow characteristics of each station (H-01 to H-10) of the Hupo line and the water temperature along the coast of Ulgi was analyzed. The Coherence of the 4-month cycle, which coincides with the occurrence cycle of the cold-pool, is higher than 0.7 in coastal waters (H-01 to H-03), and the Coherence is lower than 0.5 in the open waters (H-06 to H-10). As such, it was found that there was a high correlation between the occurrence of cold-pool along the Ulgi coast and the flow change characteristics at the station close to the Hupo coast.