Green Simulation Co.

Cutral-Có, Argentina

Green Simulation Co.

Cutral-Có, Argentina

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Cha Y.,National Typhoon Center Korea Meteorological Administration | Kim H.-D.,Keimyung University | Kang S.-D.,Green Simulation Co.
Theoretical and Applied Climatology | Year: 2015

In the present study, the fact that strong positive correlations have existed between East Asian summer monsoons (EASMs) and western North Pacific tropical cyclone (TC) genesis frequency over the last 37 years was found. To figure out the cause of these correlations, 7 years (positive East Asian summer monsoon index (EASMI) phase) that have the highest values and 7 years (negative EASMI phase) that have the lowest values in the normalized EASM index were selected and the differences in averages between the two phases were analyzed. In the positive EASMI phase, TCs mainly occurred in the northwestern waters of the tropical and subtropical western North Pacific and showed a tendency to move from the far eastern waters of the Philippines, pass the East China Sea, and move northward toward Korea and Japan. On the 500 hPa streamline, whereas anomalous anticyclones developed in the East Asia middle-latitude region, anomalous cyclones developed in the tropical and subtropical western North Pacific. Therefore, in this phase, whereas EASMs were weakened, western North Pacific summer monsoons (WNPSMs) were strengthened so that some more TCs could occur. In addition, in the case of the East China Sea and the southern waters of Japan located between the two anomalous pressure systems, TCs could move some more toward the East Asia middle-latitude region in this phase. According to an analysis of the 850 hPa relative vorticity, negative anomalies were strengthened in the East Asia middle-latitude region while positive anomalies were strengthened in the region south to 25 N. Therefore, in the positive EASMI phase, whereas EASMs were weakened, WNPSMs were strengthened so that some more TCs could occur. According to an analysis of the 850 and 200 hPa horizontal divergence, whereas anomalous downward flows were strengthened in the East Asia middle-latitude region, anomalous upward flows were strengthened in the tropical and subtropical western North Pacific. According to an analysis of 200–850 hPa vertical wind shear and 600 hPa relative humidity, negative anomalies and positive anomalies were strengthened in the tropical and subtropical western North Pacific, respectively, to provide good atmospheric environments in which some more TCs could occur in the positive EASMI phase. According to an analysis of sea surface temperatures (SST) too, whereas cold SST anomalies were strengthened in the East Asia middle-latitude region, warm SST anomalies were strengthened in the tropical and subtropical western North Pacific to provide good marine environments in which some more TCs could occur in the positive EASMI phase. © 2015 Springer-Verlag Wien


Choi K.-S.,National Institute of Meteorological Research Jeju Korea | Kim H.-D.,Keimyung University | Kang S.-D.,Green Simulation Co.
International Journal of Climatology | Year: 2015

In this study, the variations of Australian summer monsoons (AUSMs) over the last 30 years (1983-2012) were examined. The analysis period for a total of 30 years was divided into 15 years for 1983-1997 (8397) and 15 years for 1998-2012 (9812) to analyse interdecadal variations of AUSMs. The AUSM index (AUSMI) generally showed negative values in the 8397 period while showing positive values in the 9812 period, indicating that clear interdecadal variations exist in the AUSMI over the last 30 years. Recently, AUSMs have been trending towards being reinforced. The precipitable water averaged in the area for defining the AUSMI has also shown a tendency to increase, until recently, along with the characteristics of interdecadal variations. To examine the cause of the recent reinforcement of AUSMs, differences in 850 hPa stream flows between the average of the 9812 period and the average of the 8397 period were analysed. Anomalous cyclones were located in the west of Australia and the South China Sea, and anomalous anticyclones existed in the central and eastern Pacific in both hemispheres. Because of these patterns of anomalous pressure systems, anomalous equatorial easterlies (anomalous trade winds) were reinforced. The 200 hPa stream flows showed patterns opposite to those of the pressure systems shown by 850 hPa stream flows. Because of these patterns of anomalous pressure systems, anomalous equatorial westerlies were reinforced. These results mean that the Walker circulations - in which air currents ascend in the northern region of Australia and the Maritime Continent and descend in the equatorial central Pacific - were reinforced further in the 9812 period. These changes may be related to the interdecadal changes in the Pacific Ocean, including the Pacific Decadal Oscillation and El Niño-Southern Oscillation. © 2015 Royal Meteorological Society.


Choi K.-S.,National Institute of Meteorological Research | Kim H.-D.,Keimyung University | Kang S.-D.,Green Simulation Co. | Shim C.-S.,Korea Environment Institute
Theoretical and Applied Climatology | Year: 2015

This study analyzed the frequency of tropical cyclones (TCs) that occurred in each month of July to September, which is when most TCs occur during a year, in the western North Pacific for the last 20 years. Since the mid-1990s, the TC genesis frequency has tended to decrease during July to August but to increase during September. Therefore, the time series of the TC genesis frequency during July to August was analyzed. The average TC genesis frequency during July to August was 10TCs. Until 2006, a greater number of years had a TC genesis frequency more than 10TCs; however, from 2006, a greater number of years had a TC genesis frequency less than 10TCs. To determine why the TC genesis frequency showed this change in the mid-2000s, the difference between the average of July and August 2007 to 2014 (0714) and that of July and August 1995 to 2006 (9506) was analyzed. With regard to the TC genesis frequency, TCs occurred largely in the eastern sea of the Philippines during 0714 and in the distant eastern sea of the Philippines during 9506. With regard to the TC passage frequency, TCs came ashore at the southeastern area of China via the South China Sea from the Philippines during 0714 and tended to go north toward Korea and Japan through the East China Sea from the distant eastern sea of the Philippines during 9506. The cause of the differences in TC tracks between the two periods was verified through an analysis of the 850- and 500-hPa streamlines. During 0714, anomalous anticyclonic circulations were strengthened in most areas of the western North Pacific. Therefore, the TC genesis frequency during 0714 was lower than that during 9506 in the tropical and subtropical western North Pacific; in particular, in this area, anomalous easterlies were strengthened, which caused TCs to go toward the southeastern area of China. © 2015 Springer-Verlag Wien


Choi K.-S.,National Institute of Meteorological Research | Cha Y.,National Typhoon Center | Kim H.-D.,Keimyung University | Kang S.-D.,Green Simulation Co.
Climate Dynamics | Year: 2015

This study analyzed the correlation between tropical cyclone (TC) frequency and the Western North Pacific monsoon index (WNPMI), which have both been influential in East Asia’s mid-latitude regions during the summer season over the past 37 years (1977–2013). A high positive correlation existed between these two variables, which was not reduced even if El Niño-Southern Oscillation (ENSO) years were excluded. To determine the cause of this positive correlation, the highest (positive WNPMI phase) and lowest WNPMIs (negative WNPMI phase) during a nine-year period were selected to analyze the mean difference between them, excluding ENSO years. In the positive WNPMI phase, TCs were mainly generated in the eastern seas of the tropical and subtropical western North Pacific, passing through the East China Sea and moving northward toward Korea and Japan. In the negative phase, TCs were mainly generated in the western seas of the tropical and subtropical western North Pacific, passing through the South China Sea and moving westward toward China’s southern regions. Therefore, TC intensity in the positive phase was stronger due to the acquisition of sufficient energy from the sea while moving a long distance up to East Asia’s mid-latitude. Additionally, TCs occurred more in the positive phase. Regarding the difference of the two phases between the 850 and 500-hPa streamlines, anomalous cyclones were strengthened in the tropical and subtropical western North Pacific, whereas anomalous anticyclones were strengthened in East Asia’s mid-latitude regions. Due to these two anomalous pressure systems, anomalous southeasterlies developed in East Asia’s mid-latitude regions, which played a role in the anomalous steering flows that moved TCs into these regions. Furthermore, due to the anomalous cyclones that developed in the tropical and subtropical western North Pacific, more TCs could be generated in the positive phase. Both the lower and upper tropospheric layers had warm anomalies in most regions of the Western North Pacific, while relative humidity in the middle tropospheric layer showed a positive anomaly in the tropical and subtropical western North Pacific, which provided a better environment to strengthen TC intensity in the positive WNPMI phase. Furthermore, a negative anomaly was manifested not only in the tropical and subtropical western North Pacific, but also in East Asia’s mid-latitude regions, with 200–850-hPa vertical wind shear, while a warm sea surface temperature anomaly was shown in East Asia’s mid-latitude seas, which further strengthened TC intensity in the positive phase. The analysis on the global-scale atmospheric circulations showed that converged air in the lower layer of the subtropical western Pacific during the positive phase diverged in the upper layer, which moved westward and converged in the upper layer of the equatorial Indian Ocean and then diverged in its lower layer. © 2015 Springer-Verlag Berlin Heidelberg


Choi J.-W.,National Institute of Meteorological Research | Cha Y.,National Typhoon Center | Kim H.-D.,Keimyung University | Kang S.-D.,Green Simulation Co.
Advances in Meteorology | Year: 2016

This study obtained the latitude where tropical cyclones (TCs) show maximum intensity and applied statistical change-point analysis on the time series data of the average annual values. The analysis results found that the latitude of the TC maximum intensity increased from 1999. To investigate the reason behind this phenomenon, the difference of the average latitude between 1999 and 2013 and the average between 1977 and 1998 was analyzed. In a difference of 500 hPa streamline between the two periods, anomalous anticyclonic circulations were strong in 30°-50°N, while anomalous monsoon trough was located in the north of South China Sea. This anomalous monsoon trough was extended eastward to 145°E. Middle-latitude region in East Asia is affected by the anomalous southeasterlies due to these anomalous anticyclonic circulations and anomalous monsoon trough. These anomalous southeasterlies play a role of anomalous steering flows that make the TCs heading toward region in East Asia middle latitude. As a result, TCs during 1999-2013 had higher latitude of the maximum intensity compared to the TCs during 1977-1998. © 2016 Jae-Won Choi et al.


Choi J.-W.,National Institute of Meteorological Research | Cha Y.,National Typhoon Center | Kim H.-D.,Keimyung University | Kang S.-D.,Green Simulation Co.
Advances in Meteorology | Year: 2016

The present study analyzed the interdecadal variation by applying the statistical change-point analysis to the frequency of the tropical cyclone (TC) that landed in the Korean Peninsula (KP) for the recent 54 years (1951 to 2004) and performed cluster classification of the Korea-landfall TC tracks using a Fuzzy Clustering Method (FCM). First, in the interdecadal variation analysis, frequency of TC that landed in the KP was largely categorized into three periods: high frequency period from 1951 to 1965, low frequency period from 1966 to 1985, and high frequency period from 1986 to 2004. The cluster analysis result of the Korea-landfall TC tracks produced the optimum number of clusters as four. In more detail, Cluster A refers to a pattern of landing in the southern coast in the KP starting from East China Sea followed by heading north while Cluster B refers to a pattern of landing in the west coast of the Korean Peninsula, also starting from East China Sea followed by heading north. Cluster C refers to a pattern of landing in the southern region of the west coast in the KP moving from mainland China while Cluster D refers to a pattern of landing in the mid-north region of the west coast in the Korean Peninsula, also moving from mainland China. Copyright © 2016 Jae-Won Choi et al.

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