No abstract

This study shows that the Pacific‐Japan (PJ) teleconnection pattern has a significant influence on tropical cyclone (TC) activities over the western North Pacific (WNP) during the boreal summer (July, August, and September). During positive (negative) PJ phase, TCs form at a more northward (southward) location, recurve at a more northeastward (southwestward) location, and frequently pass over the northeast Asian (southeast Asian) region, including Korea and Japan (South China Sea and southern China). In particular, this difference in the TC track between the two phases is observed as a dipole‐like pattern between the regions of Southeast and Northeast Asia. The TC characteristics during the positive PJ phase are caused by the following two stronger atmospheric circulations over the WNP: an anticyclonic circulation centered to the east of Japan and a cyclonic circulation centered to the east of Taiwan. The southeasterly between these two circulations serves as steering flow that TCs move northward toward Korea and Japan from the northeast of the Philippines. Conversely, TCs during the negative PJ phase mainly move westward toward the South China Sea and southern China by the easterly from a stronger anticyclonic circulation centered to the east of Taiwan. As a result of this feature of TC track during the negative PJ phase, TC lifetime is shorter and TC intensity is weaker.

The climatological characteristics of drought in South Korea were investigated using daily precipitation data for 1777-2008. The effective drought index was used to quantify the drought intensity. As a result, five characteristics were discovered. First, South Korea can be divided into four drought subregions (the central, southern, and east coastal regions and Jeju Island) using hierarchical cluster analysis. Second, a map for longterm drought conditions in the four subregions is created that allows identification of the spatiotemporal distribution of droughts for the 231 yr at a glance. Third, droughts in South Korea have time scales that depend on the onset season. Spring (March-May) droughts tend to be short (#200 days) because the summer (June-September) rainy season follows. Summer droughts tend to be long (.200 days) because the dry season (October-February) follows. In the dry season, droughts tend to be sustained or become severe rather than being initiated or relieved. Fourth, 5-, 14-, 34-, and 115-yr drought cycles were identified by spectral analysis. The 5-yr cycle was dominant in all of the regions, the 14-yr cycle was observed over the southern and east coastal regions, and the 34-yr cycle was observed over the central region. Fifth, the most extreme drought occurred in 1897-1903 (return period: 233 yr) and was associated with the 115-yr drought cycle. After this drought, severe droughts (return period of .10 yr) occurred in they were caused by the consecutive shortage of summer rainfall for two or more years.

No abstract

This study shows that the frequency of summer tropical cyclones (TCs) in the areas of Japan, Korea, and Taiwan (JKT), which are located in the middle latitudes of East Asia, has a positive correlation with the Arctic Oscillation (AO) occurring during the preceding spring, while summer TC frequency in the Philippines (PH), located in the low latitudes, has a negative correlation with the AO of the preceding spring. During a positive AO phase, when the anomalous anticyclone forms over the mid-latitudes of East Asia, other anomalous cyclones develop not only in the high latitudes but also in the low latitudes from the preceding spring to the summer months. With this change, while southeasterlies in the JKT area derived from the mid-latitude anticyclone plays a role in steering TCs toward this area, northwesterlies strengthened in the PH area by the low-latitude cyclone plays a role in preventing TC movement toward this area. In addition, because of this pressure systems developed during this AO phase, TCs occur, move, and recurve in further northeastern part of the western North Pacific than they do during a negative AO phase.