북극진동의 자기상관 특성 및 우리나라 장마 및 태풍과의 교차상관 특성 평가

Evaluation of autocorrelation characteristics of arctic oscillation and its cross-correlation to the monsoon and typhoon

Abstract

본 연구에서는 북극진동이 우리나라에 미치는 영향을 파악하고자 북극진동지수(AOI)와 북태평양에서 발생한 태풍의 개수 및 우리나라에 영향을 준 태풍의 개수, 또한 장마기간 중 총강수량 및 장마기간 중 강수일수와의 교차상관분석을 시도하였다. AOI 자료는 월단위 형태로 존재하나 교차 상관 분석에는 1월을 중심으로 한 평균 자료와 봄, 여름, 가을, 겨울의 계절자료를 이용하였다. 장마 특성 및 태풍 특성 자료는 모두 연 단위자료이다. 본 연구에서는 AOI 및 태풍, 장마 자료의 가용성을 고려하여 1961년에서 2016년 사이의 자료를 이용하였다. 본 연구에서의 결과를 종합해 보면, 북극진동은 우리나라의 장마 특성에 약한 수준이나 유의하게 영향을 미치고 있음을 확인할 수 있었다. 그러나 그 정도는 전체기간에 대해 일정하지 않으며 시기에 따라 크게 다른 것으로 나타난다. 예를 들어, 최근 10년간 북극진동이 장마에 미친 영향은 교차상관계수로 0.8 이상이다. 그러나 그 전 30년간은 통계학적으로 유의한 영향은 없었다. 이와는 반대로 북극진동이 우리나라에 영향을 준 태풍의 개수에 미치는 영향은 전체적으로는 유의하지 않은 것으로 나타난다. 공교롭게도 부분적으로 보면 이 역시 기간에 따라 유의한 영향과 유의하지 않은 영향이 반복적으로 교차하는 모습을 보인다. 즉, 기간에 따라 북극진동의 영향은 비정상적으로 크게 변동하는 모습을 보인다. 또한, 북극진동이 우리나라의 장마와 태풍에 미치는 영향이 과거 1960년대에서 2000년대까지 서로 교차되는 특성을 보여 왔다는 점에 주목할 필요가 있다. 그러나 공교롭게도 2010년대에 들어서면서 장마에의 영향과 태풍에의 영향이 둘 다 증가하는 형태로 바뀐 것으로 보인다.

This study investigated the effect of arctic oscillation by analyzing the cross-correlation characteristics between the arctic oscillation index (AOI) and the number of typhoons occurred in the North Pacific, the number of typhoons affecting South Korea, total rainfall amount and number of rainy days during the monsoon season in South Korea. For this analysis, the monthly AOI data were transformed into the average data about January and seasonal AOI data representing winter, spring, fall and winter. The typhoon data and monsoon data were all those collected annually. The data period for this analysis was determined to be from 1961 to 2016 by considering the data available. Based on this analysis, it was found that the arctic oscillation has a weak but statistically significant effect on the monsoon characteristics of South Korea. However, the level of effect was not consistent over the data period but varied significantly periodically. For example, the cross-correlation coefficient derived for the recent 10 years was estimated to be higher than 0.8, but was simply insignificant during the 30 years before the last decade. The overall effect of arctic oscillation on the occurrence of typhoon was found to be statistically insignificant, but was also fluctuating periodically to show somewhat significant effect. Finally, it should be mentioned that the effect of arctic oscillation on the typhoon and monsoon had been changing by turns from 1960s to 2000s. However, in the 2010s, it happened that the effect of arctic oscillation has become significant on both typhoon and monsoon in South Korea.

Fig. 1. Time series plot of monthly arctic oscillation Index (AOI(1)) and its 12-month moving average (AOI(12))

Fig. 2. Comparison of box plots of monthly AOI

Fig. 3. Time series of rainfall amount and rainy days during the monsoon in South Korea

Fig. 4. Time series of annual number of typhoons occurred in the North Pacific and annual number of typhoons affecting South Korea

Fig. 5. Comparison of 3-, 5-, 7- and 9-month-average AOI time series (averaging was done around January)

Fig. 6. Comparison of seasonal AOI time series

Fig. 7. Autocorrelation functions of monthly AOI and 12-month moving average AOI time series

Fig. 8. Autocorrelation functions of seasonal and average AOI time series

Fig. 9. Autocorrelation functions of rainfall amount and rainy days during the monsoon in South Korea

Fig. 10. Autocorrelation functions of the number of typhoons occurred in the North Pacific (Typhoon_NP) and the number of typhoons affecting South Korea (Typhoon_KR)

Fig. 11. Cross correlations between AOI and rainfall amount during the monsoon in South Korea

Fig. 12. Cross correlations between AOI and rainy days during the monsoon in South Korea

Fig. 13. Cross correlations between AOI and number of typhoons occurred in the North Pacific

Fig. 14. Cross correlations between AOI and number of typhoons affecting South Korea

Fig. 15. Cross correlations between average AOI and characteristics of monsoon and typhoon

Fig. 16. Cross correlations between seasonal AOI and characteristics of monsoon and typhoon

Table 1. Means and standard deviations of monthly AOI used in this study (1961~2016)

Table 2. Means and standard deviations of average and seasonal AOI data