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The statistical change-point analysis demonstrates that there is a climate regime shift in the April mean precipitation in Korea in 1981. The April mean precipitation in the years post-1981 showed a distinct decrease compared to the years pre-1981. This phenomenon was also noticed in China and Japan, excluding south China. One of the major causes for this decrease in April mean precipitation was the increased snow depth in the mid-latitude regions of continental East Asia. This resulted in a strengthened cold and dry anticyclone anomaly over continental East Asia and a relatively weakened subtropical anticyclone anomaly over the western North Pacific, thus forcing a continuation of the typical winter pressure pattern of “high-West and low-East” in East Asia in April. The strengthened northerly anomaly from this zonal pressure pattern anomaly played a significant role in restricting the northern movement of the subtropical anticyclone and preventing the inflow of warm and humid air into Korea.

This study assessed drought conditions in northern China and Mongolian areas using the Palmer drought severity index (PDSI). Droughts in this area were intensified throughout all seasons. In particular, this intensifying trend was pronounced in the summer and autumn. In the summer, the PDSI showed an overall increase from the early 1990s to the late 1990s, and then, it rapidly decreased after the late 1990s. Therefore, this study focused on summer droughts and analysed mean differences before the late 1990s (9098) and after the late 1990s (9905). Regarding differences in 850 hPa stream flows between the two periods, anomalous anticyclonic circulations were strengthened in northern China and Mongolia that showed strong negative anomalies in the PDSI. These anomalous anticyclones were formed as a positive North Atlantic Oscillation pattern formed in the European region spread eastward in the form of wave trains. The anomalous anticyclones formed in northern China and Mongolia led to reduced total cloud cover. As a result, this region exhibited high sensible heat net fluxes. Consequently, warm and dry anticyclones may have recently been strengthened in this region, thereby intensifying droughts. As this shows, recently strengthened warm and dry anticyclones in northern China and Mongolia were associated with recently reduced snow depths in this region during the preceding spring. In recent years, the frequency of Asian dust has also increased due to warm and dry air conditions.

This study examined the relationship between the western North Pacific monsoon (WNPM) and the tropical cyclone (TC) activity over western North Pacific during the summer (June to August) in a period from 1977 to 2013. According to the western North Pacific monsoon index (WNPMI), 10 years with high indices (referred to as the positive WNPMI phase) and 10 years with low indices (referred to as the negative WNPMI phase) were chosen. TCs frequently formed in the southeast quadrant of the subtropical western North Pacific in the positive WNPMI phase, and in the northwest quadrant in the negative phase. With respect to the TC track, TCs tended to move northward from the distant sea off the east coast of the Philippines towards Korea and Japan past the East China Sea in the positive WNPMI phase, whereas the characteristic pattern of the negative phase was the TC movement from the Philippines to southern China and the Indochinese peninsula over the South China Sea. As for the TC intensity, the TCs were stronger in the positive WNPMI phase than in the negative WNPMI phase. The anomalous cyclonic circulations in the south of the 30°N signified strong convection, causing the high TC genesis frequency in the positive WNPMI phase. In addition, the East China Sea, Korea and Japan were shown to be influenced by the anomalous southeasterly, which contributed as the anomalous steering flows and was favourable for the TCs to move into these regions in the positive WNPMI phase. Meanwhile, the positive anomaly of 600 hPa relative humidity and sea surface temperature as well as the negative anomaly of vertical wind shear presented in most regions of the subtropical western North Pacific, creating an environment that facilitated the generation of TCs in the positive WNPMI phase.

This study analyzes the characteristics of Western North Pacific (WNP) tropical cyclone (TC) activity and large-scale environments according to the Western Pacific (WP) teleconnection pattern in summer. In the positive WP phase, an anomalous cyclone and an anomalous anticyclone develop in the low and middle latitudes of the East Asia, respectively. As a result, southeasterlies are reinforced in the northeast area of the East Asia including Korea and Japan which facilitates the movement of TC to this area, whereas northwesterlies are reinforced in the southwest area of the East Asia including South China and Indochina Peninsula which blocks the movement of TC to this area. Due to the spatial distribution of this reinforced pressure system, TCs develop, move, and turn more to the northeast of WNP than those in the negative WP phase. Consequently, the characteristics of this TC activity in the positive WP phase are associated with the location of upper tropospheric jet further to the northeast. Meanwhile, TCs in the negative WP phase mainly move to the west from Philippines toward south China and Indochina Peninsula. Furthermore, due to the terrain effect caused by the high passage frequency of TCs in the mainland China, the intensity of TCs are weaker than those in the positive WP phase.Key words:Western Pacific teleconnection pattern, Tropical cyclone, Large-scale environments, East Asia, Upper tropospheric jet

This study analyzed the climate regime shift using statistical change-point analysis on the time-series tropical cyclone (TC) frequency that affected Japan in July to September. The result showed that there was a significant change in 1995 and since then, it showed a trend of rapidly decreasing frequency. To determine the reason for this, differences between 1995 to 2012 (9512) period and 1978 to 1994 (7894) period were analayzed. First, regarding TC genesis, TCs during the 9512 period showed a characteristic of genesis from the southeast quadrant of the tropical and subtropical western North Pacific and TCs during the 7894 period showed their genesis from the northwest quadrant. Regarding a TC track, TCs in the 7894 period had a strong trend of moving from the far east sea of the Philippines via the East China Sea to the mid-latitude region in East Asia while TCs in the 9512 period showed a trend of moving from the Philippines toward the southern part of China westward. Thus, TC intensity in the 7894 period, which can absorb sufficient energy from the sea as they moved a long distance over the sea, was stronger than that of 9512. Large-scale environments were analyzed to determine the cause of such difference in TC activity occurred between two periods. During the 9512 period, anomalous cold and dry anticyclones were developed strongly in the East Asia continent. As a result, Korea and Japan were affected by the anomalous northerlies thereby preventing TCs in this period from moving toward the mid-latitude region in East Asia. Instead, anomalous easterlies (anomalous trade wind) were developed in the tropical western Pacific so that a high passage frequency from the Philippine to the south China region along the anomalous steering flows was revealed. The characteristics of the anomalous cold and dry anticyclone developed in the East Asia continent were also confirmed by the analysis of air temperature, relative humidity and sensible heat net flux showing that most regions in East Asia had negative values.

This study analyzes the correlation between Western Pacific (WP) teleconnection pattern index (WPI) in April during 1954-2008 and rainfall amounts in the same month. Based on the results, it is identified that there have been strong positive correlations between central China, Korea and the southwestern part of Japan in the East Asian region. Through differences between 10 positive WP years and 10 negative WP years selected from the April WPI excluding ENSO years, it is found that rainfall amounts increase in April of positive WP years due to the following characteristics. Increases in rainfall amounts are evident in the East Asian middle latitudinal region where the positive correlation between the two variables is the highest and this is because anomalous southwesterlies are strengthened in the East Asian middle latitudinal region due to the spatial pattern of a south-low-north-high anomalous pressure system centered on this region that is made by anomalous anticyclones centered on the southeastern side of the region and other anomalous anticyclones centered on the northeastern side of the region. In addition, anomalous westerlies (jet) are strengthen in the upper troposphere of the East Asian middle latitudinal region and as a result, anomalous upward flows are strengthened in this region and thus anomalous warm air temperatures are formed in the entire level of the troposphere in the region. In addition to atmospheric environments, anomalous warm sea surface temperatures are formed in the seas in the East Asian middle latitudinal region to help the rainfall amount increases in the East Asian middle latitudinal region.

This study analyzed a correlation between South China Sea summer (June to September) monsoon (SCSSM) and the ENSO for the last 32 years (1979 to 2010). There was a correlation that the higher (lower) the SST in the Nino-3.4 region was, the weaker (stronger) the SCSSM intensity was. To identify the reason for this correlation, a difference of means between 8 El Nino years and 8 La Nina years (June to September).The analysis on the difference between two groups with respect to the 850 hPa stream flows showed that there were anomalous huge cyclones in the subtropical Pacific in the both hemispheres so that cold and dry anomalous northerlies were strengthened in the South China Sea relatively while anomalous westerlies were strengthened from the Maritime Continent to the off the coast of Chile. The analysis on the difference between two groups with respect to the 200 hPa stream flows showed that the opposite anomalous pressure system pattern to that in the 850 hPa stream flows were shown. In the subtropical Pacific of the both hemispheres, anomalous anticyclones existed so that anomalous easterlies were strengthened from the Maritime Continent to the equatorial central Pacific. Considering the anomalous atmospheric circulations in the upper and lower layers of the troposphere, upward airflows from the equatorial central and eastern Pacific were downward in the South China Sea and the Maritime Continent, which was a structure of anomalous atmospheric circulations. This means that the Walker Circulation was weakened and it was a typical structure of atmospheric circulations revealed in El Nino years.

This study was conducted to examine the correlation between the South Asian High (SAH) shift and the summer (June–August) rainfall variability in Korea over the course of 45 years (1958–2002). It is found that the shift in the west–east direction is closely related to the summer rainfall variability in Korea. The atmospheric circulations in the east shift years showed that at 850 hPa, an intensification of the western North Pacific subtropical high allowed a sufficient amount of warm and humid air to be supplied to the lower atmosphere near Korea. On the other hand at 200 hPa, the SAH expanded toward the east, near the southern part of Korea, causing the intensification of the northwesterlies, and this allowed the supply of cold and dry air to the upper atmosphere near Korea. Meanwhile, in the latitudinal zone in which Korea is located, there were anomalous upward flows with warm and humid characteristics in the lower atmosphere and anomalous downward flows with cold and dry characteristics in the upper atmosphere. As such, the cold and warm air masses present in the upper and lower atmosphere near Korea led to thermal instability, and this was analyzed to be a major factor that could potentially increase the amount rainfall in Korea in summer in the east shift years. Moreover, a warm SST anomaly was formed in the mid-latitude zones of East Asia, and it heated the lower troposphere, thereby intensifying the thermal instability even further. Furthermore, TCs frequently had an impact on Korea in the east shift years, and were another factor that caused the increased rainfall in summer.

Regarding the tropical cyclone (TC) genesis frequency, TCs between 1999 and 2013 were generated more frequently in the northwest waters of the tropical- and subtropical western North Pacific than TCs between 1977 and 1998. TCs over the period from 1977-1998 showed a northward track trend generated mostly from the distant sea in east of the Philippines via the mainland of the Philippines and the South China Sea to the west toward Indochina or from the distant sea in east of the Philippines to the distance sea in east of Japan. TCS over the period from 1999-2013 showed a northward shift pattern to the mid-latitude region mostly in East Asia. Therefore, TCs over the period from 1999-2013 tended to move to much higher latitudes than TCs over the period from 1977-1998, which also resulted in the high possibility of maximum TC intensity occurred in higher latitudes during the former period than the latter period. In the difference of 500 hPa streamline between two periods, the anomalous anticyclonic circulations were strengthened in whereas the anomalous monsoon trough was placed in north of the South China Sea, which was extended to the east up to . The mid-latitude in East Asia is affected by the anomalous southeasterlies due to the above anomalous anticyclonic circulations and anomalous monsoon trough. The anomalous southeasterlies play a role in anomalous steering flows that directed TCs to the mid-latitude regions in East Asia, which made the latitudes of the maximum intensities in TCs over the period from 1999 - 2013 further to the north than those in TCs over the period from 1977-1998.

In this study, 690 meteorological disasters that are recorded on the Disaster Yearbook from NEMA (the National Emergency Management Agency) from 1979 to 2013 have been analyzed to investigate the frequency and damage and to evaluate the influence of meteorological disasters on the Korean economy. As a result, the total damage has so far reached the 28 trillion won, and 19.7 disasters has been occurred and brought 804 billion won damages on average. 41.9 percent of meteorological disasters have been occurred in the 1980s and 19.3 percent in the 2000s, but the corresponding damage cost was opposite: 11.4 percent in the 1980s and 60.6 percent in the 2000s. This result means meteorological disasters are becoming larger. 45.5 percent of the meteorological disasters have been found in summer season which is intensively affected by heavy rains and typhoons. The Disaster Yearbook from NEMA classifies the cause of meteorological disasters into 31 cases, and most of disasters are a single phenomenon (94.9%) than a complex phenomenon (5.1%). It was confirmed that the meteorological disaster trend has been changed in that heavy rain has appeared consistently every year, and the number of typhoons has been decreased compared to the 1980s. Heavy rain took the highest portion (37.8 percent) of total disasters and followed by typhoons (8.7 percent), but the amount of damages of meteorological disasters is more related to typhoons (45.6 percent) than heavy rains (35.4 percent). Both of them accounts for 81 percent of the total damage. Therefore, it is necessary to build intensive prevention measures for two phenomena. The highest loss, approximately 0.9% of GDP, was taken place in 1987. Categorically, typhoon RUSA brought 0.68 percent of GDP loss in 2002 and heavy rains caused 0.45 percent of GDP loss in 1987. This result means that if a high impact meteorological disaster occurs, the ripple effect is enormous as socioeconomic.

This study analyzed the change in tropical cyclone (TC) activity according to the fluctuation in July-to-September average North Pacific Oscillation index (NPOI) and its underlying large-scale environment during the last 37 years from 1977 to 2013. For this purpose, seven years with highest index NPOI value (positive NPOI phase) and another seven years with lowest NPOI index value (negative NPOI phase) among the 37 years were selected as sample after excluding the ENSO years.During the positive NPOI phase, TCs were created in the east of tropical and subtropical western North Pacific and moved to the west from the Philippines toward the southern region in China or toward far eastern sea of Japan. Meanwhile, during the negative NPOI phase, TCs tended to proceed to the north toward Korea or Japan passing East China Sea from the eastern sea of the Philippines. As a result, also in the TC recurvature, TCs in positive NPOI phase showed a tendency of recurving toward more eastern direction compared to TCs in negative NPOI phase. Hence, TC intensity was stronger in negative NPOI phase which allowed more time for obtaining energy from the ocean.

In this study, the correlation between the frequency of summer tropical cyclones (TC) affecting areas around Korea over the last 37 years and the western North Pacific monsoon index (WNPMI) was analyzed. A clear positive correlation existed between the two variables, and this high positive correlation remained unchanged even when excluding El Nio-Southern Oscillation (ENSO) years. To investigate the causes of the positive correlation between these two variables, ENSO years were excluded, after which the 8 years with the highest WNPMI (positive WNPMI phase) and the 8 years with the lowest WNPMI (negative WNPMI phase) were selected, and the average difference between the two phases was analyzed. In the positive WNPMI phase, TCs usually occurred in the eastern waters of the tropical and subtropical western North Pacific, and tended to pass the East China Sea on their way north toward Korea and Japan. In the negative WNPMI phase, TCs usually occurred in the western waters of the tropical and subtropical western North Pacific, and tended to pass the South China Sea on their way west toward the southeastern Chinese coast and the Indochina peninsula. Therefore, TC intensity was higher in the positive WNPMI phase, during which TCs are able to gain sufficient energy from the sea while moving a long distance to areas nearby Korea. TCs also tended to occur more often in the positive WNPMI phase. In the difference between the two phases regarding 850 and 500 hPa streamline, anomalous cyclones were reinforced in the tropical and subtropical western North Pacific, while anomalous anticyclones were reinforced in mid-latitude East Asian areas. Due to these two anomalous pressure systems, anomalous southeasterlies developed in areas near Korea, with these anomalous southeasterlies playing the role of anomalous steering flows making the TCs head toward areas near Korea. Also, due to the anomalous cyclones developed in the tropical and subtropical western North Pacific, more TCs could occur in the positive WNPMI phase.

The onset, retreat, and precipitation of the Korean summer rainy season (Changma) significantly affect human health and daily lives as well as domestic industry and economy. To increase revenue during Changma period, retail industry has tried to develop various weather marketing strategies on a regional basis. This study investigated the impact of Changma on the retail sales in Jeju. During Changma in Jeju in 2014, the temperature has dropped by 2.3°C, from 26.2°C to 23.9°C while the precipitation has significantly increased from 115.3mm to 441.5mm compared to last year. Due to these weather characteristics of Changma, large retailers in Seogwipo city have seen a high increase in sales of umbrellas, raincoats, and rain boots by 250-400 percent, but a decrease in sales of air conditioners by 15 percent. This results from more frequent rainfall and cool weather compared to the previous year. However, opposite results were found regarding traditional markets in Jeju. Depending on industrial structures in each region, the identical weather phenomenon have different impacts on the number of visitors to the markets. In other words, the impact of Changma on local retail sales is influenced by multiple local factors including demographic composition and industrial structure in the regional economy.

By performing a statistical change-point analysis of activities of the tropical cyclones (TCs) that have affected Korea (K-TCs), it was found that there was a significant change between 1983 and 1984. During the period of 1984–2004 (P2), more TCs migrated toward the west, recurved in the southwest, and affected Korea, compared to the period of 1965–1983 (P1). These changes for P2 were related to the southwestward expansion of the subtropical western Pacific high (SWPH) and, simultaneously, elongation of its elliptical shape toward Korea. Because of these changes, the central pressure and lifetime of K-TC during P2 were deeper and longer, respectively, than figures for P1. This stronger K-TC intensity for P2 was related to the more southwestward genesis due to the southwestward expansion of the SWPH. The weaker vertical wind shear environment during P2 was more favorable for K-TC to maintain a strong intensity in the mid-latitudes of East Asia.

This study investigated a drought prediction method on the basis of similarity of spatiotemporal patterns of past droughts in Korea. The method was implemented in the following steps: First, drought areas in Korea were divided into four drought subregions by means of hierarchical clustering analysis. Second, spatiotemporal drought statistics for each subregion for the period from 1926 to 2008 were established. Temporal statistics involve the drought onset, end dates, duration, and regional drought intensities, measured by the Effective Drought Index (EDI). These statistics were collected over the four subregions, and spatial patterns of drought were examined. Third, the analogous drought events that had spatiotemporal patterns similar to those of the current or subject drought were selected. Fourth, the progress of the subject drought and the selected drought were compared. Finally, the progress pattern of the subject drought was predicted on the basis of the hypothesis that it will progress in a way similar to the selected analogous case. We applied this predicted method to several previous drought cases and evaluated the prediction efficiency. The results showed that this method was efficient in predicting droughts for about 1 year.

This study is carried out in order to bridge the gap to understand the relationships between South Asian and East Asian monsoon systems by comparing the summer (June-September) precipitation of Nepal and South Korea. Summer monsoon precipitation data from Nepal and South Korea during 30 years (1981-2010) are used in this research to investigate the association. NCEP/NCAR reanalysis data are also used to see the nature of large scale phenomena. Statistical applications are used to analyze these data. The analyzed results show that summer monsoon precipitation is higher over Nepal (1513.98 ± 159.29 mm y -1 ) than that of South Korea (907.80 ± 204.71 mm y -1 ) and the wettest period in both the countries is July. However, the coefficient of variation shows that amplitude of interannual variation of summer monsoon over South Korea (22.55%) is larger in comparison to that of Nepal (10.52%). Summer monsoon precipitation of Nepal is found to be significantly correlated to that of South Korea with a correlation coefficient of 0.52 (99% confidence level). Large-scale circulations are studied to further investigate the relationship between the two countries. wind and specific humidity at 850 hPa show a strong westerly from Arabian Sea to BOB and from BOB, wind moves towards Nepal in a northwestward direction during the positive rainfall years. In case of East Asia, strong northward displacement of wind can be observed from Pacific to South Korea and strong anticyclone over the northwestern Pacific Ocean. However, during the negative rainfall years, in the South Asian region we can find weak westerly from the Arabian Sea to BOB, wind is blowing in a southerly direction from Nepal and Bangladesh to BOB.

We found that, in 1984, there was a climate regime shift in April mean precipitation in Gwangju of Jeollanam-do province, Korea using a statistical change-point analysis. During the period of post-1984(1985-2013), the April mean precipitation in the years post-1984 showed a distinct decrease, compared to the pre-1984 period(1954-1984). This regime shift was also observed in China and Japan, excluding southern China. One of the major causes for the decreasing April mean precipitation during the recent three decades was the increased snow depth in the mid-latitude regions of continental East Asia. The increased snow depth resulted in strengthened cold and dry anticyclone anomaly over continental East Asia and a relatively weakened subtropical anticyclone anomaly over the western North Pacific. The anomalous synoptic conditious supported a continuation of the typical winter pressure pattern of 'high-West and low-East' over East Asia in April. The intensified northerly winds from this zonal pressure pattern anomaly played a significant role in restricting the northern movement of the subtropical anticyclone and there by preventing the inflow of warm and humid air into Korea.

This study has analyzed the concentration variation of four air pollutants (, , CO, and ) during the typhoon periods over 10 years (2002~2011). In this study, 10 typhoon events which had rainfalls in Korean Peninsula were selected during the study period. The analysis was performed using the observation data of both the air pollutants and rainfall. In order to examine and compare the concentrations of the air pollutants between normal periods and typhoon periods, we have obtained monthly average concentrations from July to September and daily average concentrations during typhoon periods. For the period from July to September, 34% of the total rainfalls can be explained by typhoons, and the concentration of air pollutants during the typhoon period was lower than the normal period. In addition, the concentration variations of the pollutants during the typhoon period were analyzed according to two categories: differences in the concentrations between the day before and the day of the typhoon (Case 1) and between the day before and after the typhoon (Case 2). The results indicated that the reduction rate of , , CO, and was 30.1%, 17.9%, 11.6%, 9.7% (Case 1) and 22.8%, 21.0%, 9.0%, 8.0% (Case 2), respectively. This result suggested that air quality was significantly improved during the typhoon period than after the typhoon period by the rainfall.

This study identified the causes of the nonoccurrence of tropical cyclones (TCs) in August 2014 by examining large-scale environments. First, over the previous 30 years, the TC genesis frequency in August showed an overall statistically significant decline. In the tropical and subtropical western Pacific, the outgoing longwave radiation anomaly index also exhibited an overall increase until recently. Regarding precipitable water and precipitation, an analysis was performed on the difference between the mean values for August 2014 and the mean values for August over the previous 30 years. As a result, while convective activities were suppressed in the tropical and subtropical western Pacific, convective activities were strong in the mid-latitudes of East Asia. This indicates that while the western North Pacific summer monsoon was weakened in August 2014, the East Asian summer monsoon was strengthened. The weakening of the western North Pacific summer monsoon may have made it difficult for TCs to occur. An analysis of 850 hPa and 500 hPa stream flows showed the strengthening of anomalous huge anticyclonic circulations in the tropical and subtropical western Pacific, whereas anomalously cyclonic circulations were reinforced in the mid-latitudes of East Asia. This was associated with the result that the western North Pacific subtropical high (WNPSH) showed further westward and southward expansion in August 2014 compared to the climatological mean WNPSH. Therefore, TCs were unlikely to occur in the tropical and subtropical western Pacific, but anomalous cold northerlies and anomalous warm southerlies converged in the Japanese Islands after originating in China’s central region and passing the East China Sea. Therefore, a favorable environment for the occurrence of precipitation had been formed.

We analyzed the changes in precipitation and drought climatology over East Asia by global warming using the daily precipitation data from 14 coupled atmosphere-ocean general circulation model simulations under the Special Report on Emission Scenarios (SRES) A1B scenario at the end of the twenty-first century. The models were consistent in predicting an increase in the mean precipitation over East Asia. However, the increase was less significant in Southeast Asia, and was accompanied by even larger increase in precipitation variability. This predicted precipitation climatology was translated into a change in drought climatology using the effective drought index (EDI). According to the increased precipitation, East Asia tends to be wetter with a decreased frequency and duration of drought. However, because of the enhanced precipitation variability, extreme droughts are predicted to be more frequent, especially over Southeast Asia.

Correlation between the frequency of summer tropical cyclones (TCs) affecting Korea and the East Asian summer monsoon index (EASMI) was analyzed over the last 37 years. A clear positive correlation existed between the two variables, and this high positive correlation remained unchanged even when excluding El Nino-Southern Oscillation (ENSO) years. To investigate the causes of the positive correlation between the two variables in non-ENSO years, after the 8 years with the highest EASMI (high EASMI years) and the 8 years with the lowest EASMI (low EASMI years) were selected, and the average difference between the two phases was analyzed. In high EASMI years, in the difference between the two phases regarding 850 and 500 hPa streamline, anomalous cyclones were reinforced in the tropical and subtropical western North Pacific, while anomalous anticyclones were reinforced in mid-latitude East Asian areas. Due to these two anomalous pressure systems, anomalous southeasterlies developed near Korea, with these anomalous southeasterlies playing the role of anomalous steering flows making the TCs head toward areas near Korea. In addition, a monsoon trough strengthened more eastward, and TCs in high EASMI years occurred more in east ward over the western North Pacific.

This study found that there is a significant negative correlation between summer drought in Korea, China and Japan and the frequency of tropical cyclone (TC) in the subtropical western North Pacific (SWNP) using effective drought index (EDI). The frequency of TCs that affect Korea is low (high) in a year of summer drought (non-drought). As a case study, in 1994 when there is extremely severe summer drought in Korea, there was high frequency of TCs while in 2003 when there was least severe summer drought, the frequency of TCs is the lowest. Changes in the anomalous secondary circulation, namely anomalous upward (downward) flow in the SWNP and anomalous downward (upward) flow in the mid-latitudes of East Asia, are one of the causes of drought (non-drought).