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서경환(Kyong-Hwan Seo),최진호(Jin-Ho Choi) 한국기상학회 2022 대기 Vol.32 No.1
This study evaluates the economic values for the several first precipitation events during Changma period. The selected three years are 2015, 2019, and 2020, where average precipitation amounts across the 58 Korean stations are 12.8, 20.1 and 13.3 mm, respectively. The four categories are used to assess the values including air quality improvement, water resource acquisition/accumulation, drought mitigation, and forest fire prevention/recovery. Economic values for these three years are estimated 50~150 billion won. Among the four factors considered, the effect of air quality improvement is most highly valued, amounting to 70 to 90% of the total economic values. Wet decomposition of air pollution (PM<SUB>10</SUB>, NO₂, CO, and SO₂) is the primary reason. The next valuable element is water resource acquisition, which is estimated 9~15 billion won. Effects of drought mitigation and fire prevention are deemed relatively small. This study is the first to estimate the value of the precipitation events during Changma onset. An analysis for more Changma years will be performed to achieve a more reliable estimate.
서경환(Kyong-Hwan Seo),손준혁(Jun-Hyeok Son),이준이(June-Yi Lee) 한국기상학회 2011 대기 Vol.21 No.1
This study revisits the definition of Changma, which is the major rainy season in Korea and corresponds to a regional component of the East Asian summer monsoon system. In spite of several decades of researches on Changma, questions still remain on many aspects of Changma that include its proper definition, determination of its onset and retreat, and relevant large-scale dynamical and thermodynamical features. Therefore, this study clarifies the definition of Changma (which is a starting point for the study of interannual and interdecadal variability) using a basic concept of air mass and front by calculating equivalent potential temperature (θ<SUB>e</SUB>) that considers air temperature and humidity simultaneously. A negative peak in the meridional gradient of this quantity signifies the approximate location of Changma front. This front has previously been recognized as the boundary between the tropical North Pacific air mass and cold Okhotsk sea air mass. However, this study identifies three more important air masses affecting Changma: the tropical monsoon air mass related to the intertropical convergence zone over Southeast Asia and South China Sea, the tropical continental air mass over North China, and intermittently polar continental air mass. The variations of these five air masses lead to complicated evolution of Changma and modulate intensity, onset and withdrawal dates, and duration of Changma on the interannual time scale. Importantly, use of θ<SUB>e</SUB>, 500-h㎩ geopotential height and 200 h㎩ zonal wind fields for determining Changma onset and withdrawal dates results in a significant increase (up to ~57%) in the hindcast skill compared to a previous study.
이규환(Gyu-Hwan Lee),서경환(Kyong-Hwan Seo) 한국기상학회 2008 대기 Vol.18 No.4
The hourly precipitation data from 1973 to 2007 observed at 60 weather stations over Korea are used to characterize the diulllal and semidiulllal cycles ortotal precipitation amount, intensity and frequency and examine their spatial patterns and interannual variations. The results show that the diurnal eycle peaks in the morning (03-09LST) and the semidiumal cycle peaks in the late afternoon (16-20LST). It is found that the spatial variations of the peak phase of diulllal or semidiumal eycle relative to their corresponding seasonal mean cycle are considerably small (large) for total precipitation amount and intensity (frequency, respectively) in both winter and summer seasons. Also, the diumal phase variations for individual years relative to the seasonal mean precipitation show the significant interannual variability with dominant periods of 2-5 years for all three clements of precipitation and the slightly decreasing trend in total precipitation amount and intensity. To compare the relative contributions of frequency and intensity to the diurnal and semidiurnal cycles (and their sum) of total precipitation amount, the percentage variance of each cycle of precipitation amount explained by frequency is estimated. The fractional variance accounted for by precipitation intensity is greater than that of frequency for these three cycles. All above analyses suggest that intensity plays a more important role than frequency in the diurnal variations of total precipitation amount.
여름철 계절내 진동에 의한 대기 와도의 연직 구조: 순압성 또는 경압성?
송은지(Eun-Ji Song),서경환(Kyong-Hwan Seo) 한국기상학회 2012 대기 Vol.22 No.2
This study investigates the reason why the barotropic vorticity structure prevails vertically in response to the enhanced convection associated with the boreal summer intraseasonal oscillation over the central Indian Ocean. The relative vorticity tendency analysis for a 2.5-layer simplified model demonstrates that the barotopic vorticity structure is predominant due to the following two factors: 1) vertical easterly shear on the meridional gradient of barotropic divergence (which induces generation of barotropic vorticity twice larger than that of baroclinic vorticity); and 2) vertical easterly shear on the meridional gradient of baroclinic divergence (which appears only in relation to the generation of barotropic vorticity). The percentage of contribution by each term to barotropic and baroclinic vorticity tendency equations is presented.
자기조직화지도(Self-Organizing Map)를 이용한 최근 우리나라 여름철 극한온도 특성 분류
임원일(Won-Il Lim),서경환(Kyong-Hwan Seo) 한국기상학회 2018 대기 Vol.28 No.3
This study investigates the characteristic spatial patterns and dynamic processes associated with the summertime extreme temperature events in South Korea during the last 20 years (1995~2014) using Self-Organizing Map (SOM). The classified SOM patterns commonly have high temperature and anticyclonic circulation anomalies over South Korea. The two major teleconnection patterns are identified: one is from the subtropical western North Pacific (WNP) affecting to the north and the other is from the North Atlantic (NA) affecting downstream region. The meridional teleconnection pattern is related to the forcing of positive sea surface temperature (SST) anomaly over the WNP. The northward propagating Rossby wave generates the East Asia-Pacific (EAP) pattern to form an anticyclonic circulation anomaly over South Korea. On the other hand, NA SST anomalies generate an eastward Rossby wave train across the Eurasian continent, leading to the development of an anticyclonic circulation anomaly over South Korea. The EAP pattern occurs more frequently in July and August, whereas the midlatitude teleconnection pattern associated with NA SST anomalies develops more frequently in early summer (June).