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Seoul, South Korea

Choi K.-S.,National Typhoon Center | Moon I.-J.,Jeju National University
Natural Hazards | Year: 2012

This study investigated the annual frequencies of tropical cyclones (TCs) that affected Korea during summer (June-September) over the last 60 years. Using a statistical change-point analysis, we found that significant regime shifts occurred in 1999 and 2005, as well as in the mid-1960s and mid-1980s. Focusing on the recent TC activities, this study analyzed the differences between the high-frequency period from 1999 to 2004 (P1) and the low-frequency period from 2005 to 2010 (P2). The analysis reveals that TCs during P2 tended to occur, move, and recurve farther to the west in the western North Pacific (WNP). This is because the WNP high expanded farther to the west during P2 compared to P1; as a result, more TCs made landfall on the west coast of the Korean peninsula (KP) during P2. In contrast, during P1, TCs tended to make landfall more frequently on the south coast of the KP. This implies that the recent TC tracks landing on the KP shifted gradually to the northwest. The analysis of streamlines at 500 hPa show that an anomalous northerly strengthened in the KP due to the formation of an anomalous anticyclone and an anomalous cyclone to the west and east of the KP, respectively. These anomalies played a role in blocking TCs from moving to the KP. At 850 hPa, the anomalous anticyclonic circulation was strengthened in most of WNP. This circulation formed an unfavorable environment for TC genesis, reducing the TC genesis frequency during P2. We verified this low convective activity in the WNP during P2 by analyzing the outgoing longwave radiation, vertical wind shear, and sea surface temperature. © 2012 Springer Science+Business Media B.V. Source

Choi J.-W.,National Institute of Meteorological Science | Cha Y.,National Typhoon Center
Dynamics of Atmospheres and Oceans | Year: 2016

This study has developed the index for diagnosis on possibility that tropical cyclones (TCs) affect Korean Peninsula. This index is closely related to the strength of the western North Pacific subtropical high (WNPSH), which is calculated as a difference in meridional wind between at the highest correlation area (around Korean Peninsula) and at the lowest correlation area (sea southeast of Japan) through a correlation analysis between TC frequency that affects Korean Peninsula and 500 hPa meridional wind. In low frequency years that selected from Korea affecting TC index, anomalous northeasterly is strengthened from Korea to the South China Sea because the center of anomalous anticyclonic circulation is located to northwest of Korean Peninsula. Thus, TCs tend to move westward from the sea east of the Philippines to the mainland China. On the other hand, in high frequency years, anomalous southwesterly serves as steering flow that more TCs move toward Korean Peninsula because the center of anomalous anticyclonic circulation is located to sea east of Japan. Consequently, this study suggests that if this index is calculated using real time 500 hPa meridional winds that forecasted by dynamic models during the movement of TCs, the possibility that TCs approach Korean Peninsula can be diagnosed in real time. © 2016 Elsevier B.V. Source

Choi K.-S.,National Typhoon Center | Wu C.-C.,National Taiwan University | Wang Y.,University of Hawaii at Manoa
Asia-Pacific Journal of Atmospheric Sciences | Year: 2011

The effect of ENSO on landfalling tropical cyclones (TCs) over the Korean Peninsula is examined. It is found that although the landfalling frequency does not show any statistically significant difference among ENSO phases, the landfalling tracks are shifted northward in response to the decrease in Niño-3.4 index. In the neutral ENSO phase, many TCs pass through mainland China before landfalling over the Korean Peninsula due to the westward expansion of the western North Pacific subtropical high. Therefore, the landfalling TC intensity over the Korean Peninsula in the neutral phase is similar to that in the La Niña phase because more than half of those TCs made landfall over mainland China. However, it is found that the preceding winter ENSO phases are not related to the landfalling TC activity over the Korean Peninsula during summer. © The Korean Meteorological Society and Springer 2011. Source

Kang K.,National Typhoon Center | Kim S.,Weather Information Service Engine Institute
Ocean Engineering | Year: 2015

Wave propagation conditions and wave-tide interactions are studied in a tide-dominant bay area during a strong storm event with a speed of 15-20 ms-1 during the study period of March 3-8, 2007. The study area is Kyunggi Bay, which is a large estuarine system in the west coast of Korea, a well-known macrotidal area. To investigate wave-tide interactions, a series of numerical experiments were designed to determine significant factors that contribute to wave height deformation and periodic wave-height modulations during a strong passing storm. The findings suggest that the periodically occurring wave height modulations at onshore and near coastal areas are mainly caused by the water depth changes by tide, which means that more wave energy can propagate into the coastal area increasing the wave height. The wave propagation was changed by tide, and the peak wave period was increased during the flood and decreased during the ebb tide. Although the effect was relatively weak, the tidal current also contributed to the increase and decrease of wave height during the flood and the ebb. It is worth noting that the wind was not a factor of periodic wave-height modulations, but it played a role in increasing the wave height. © 2015 Elsevier Ltd. All rights reserved. Source

Kim D.-W.,National Institute of Meteorological Research | Choi K.-S.,National Typhoon Center | Byun H.-R.,Pukyong National University
Climate Dynamics | Year: 2012

This study compares the impacts of El Niño Modoki and El Niño on precipitation over Korea during the boreal winters from 1954 to 2009. Precipitation in Korea tends to be equal to or greater than the normal level during an El Niño Modoki winter, whereas there is no significant change during an El Niño winter. Greater than normal precipitation during El Niño Modoki was also found over the lower reaches of the Yangtze River, China and much of southern Japan. The latitudes of these regions are 5-10° further north than in southern China, where precipitation increases during El Niño. The following two anomalous atmospheric circulations were found to be causes that led to different precipitation distributions over East Asia. First, an atmospheric wave train in the lower troposphere, which propagated from the central tropical Pacific (cyclonic) through the southern Philippine Sea (anticyclonic) to East Asia (cyclonic), reached the southern China and northern Philippine Sea during El Niño, whereas it reached Korea and southern Japan during El Niño Modoki. Second, an anomalous local meridional circulation, which consists of air sinking in the tropics, flowing poleward in the lower troposphere, and rising in the subtropics, developed between the southern Philippine Sea and northern Philippine Sea during El Niño. During El Niño Modoki, however, this circulation expanded further to the north and was formed between the southern Philippine Sea and regions of Korea and southern Japan. © 2011 Springer-Verlag. Source

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