• 대기
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• 제30권2호
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• pp.125-139
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• 2020

On 6 August 2018, heavy rainfall of daily precipitation of more than 200 mm occurred in the Yeong-dong coastal area, and especially, 1-hour precipitation of 93 mm (0251~0351 LST (local standard time) 6 August) at Gangneung station, ranked second in the history of meteorological survey of the station. In this study, this heavy rainfall case over the Gangneung area would be studied to investigate the process in which the heavy rainfall occurred. A developed ridge moved toward the Yeong-dong coastal area from the Maritime Province in Russia. The approaching of the ridge led to the northeasterly cold wind over the coastal region, causing the collision between the incoming northeasterly cold wind, and the humid and warm (convectively unstable) air located over the Yeong-dong area. This collision led to a strong convergence (maximum -206 × 10^-5 s^-1) at 925 hPa level over the vicinity of Gangneung at 0300 LST 6 August, resulting updraft of up to about 4.4 m s^-1 at 700 hPa level over the area. This strong updraft forced to lift rapidly the convectively unstable, warm and humid air layer, located over the vicinity of Gangneung, leading to the heavy rainfall (1-hour precipitation of 93 mm) over the area.

• Wind and Structures
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• 제15권4호
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• pp.331-343
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• 2012

Thunderstorm downbursts are responsible for numerous structural failures around the world. The wind characteristics in thunderstorm downbursts containing vortex rings differ with those in 'traditional' boundary layer winds (BLW). This paper initially performs an unsteady-state simulation of the flow structure in a downburst (modelled as a impinging jet with its diameter being $D_{jet}$) using a computational fluid dynamics (CFD) method, and then analyses the pressure distribution on a solar updraft tower (SUT) in the downburst. The pressure field shows agreement with other previous studies. An additional pair of low-pressure region and high-pressure region is observed due to a second vortex ring, besides a foregoing pair caused by a primary vortex ring. The evolutions of pressure coefficients at five orientations of two representative heights of the SUT in the downburst with time are investigated. Results show that pressure distribution changes over a wide range when the vortices are close to the SUT. Furthermore, the fluctuations of external static pressure distribution for the SUT case 1 (i.e., radial distance from a location to jet center x=$D_{jet}$) with height are more intense due to the down striking of the vortex flow compared to those for the SUT case 2 (x=$2D_{jet}$). The static wind loads at heights z/H higher than 0.3 will be negligible when the vortex ring is far away from the SUT. The inverted wind load cases will occur when vortex is passing through the SUT except on the side faces. This can induce complex dynamic response of the SUT.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.171.2-171.2
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• 2011

지속가능한 발전과 저탄소 녹색성장의 개념이 대두되면서 우리나라를 비롯한 주요 선진국은 자국의 화석연료 의존도를 낮추고 대체에너지로 환경친화적이며, 청정에너지로 각광받는 신 재생에너지의 활용에 경제적, 정책적 지원을 아끼지 않고 있는 실정이다. 실제로 유럽에서는 바이오매스의 일종인 우드칩을 활용한 가정용 보일러가 보급되고 있으며, 동남아시아에서는 열대식물을 이용한 저온열분해를 활용하여 바이오디젤을 생산하고 있다. 우리나라의 경우 대부분의 바이오매스는 발생되는 임야에서 재이용되거나 경제성이 있을 경우에 운송되어 재활용되고 있으며, 임부목과 같은 일부 바이오매스는 수익성이 없어 발생현지에 방치되는 경우도 있다. 본 연구에서 주목한 왕겨의 경우 미곡종합처리장에서 대량으로 발생되지만 그 활용도에 있어서 축적된 바이오에너지에 비해 에너지회수율이 저조하다고 할 수 있다. 왕겨는 임야에서 발생되는 폐목재나 다른 바이오매스에 비해 함유되어 있는 수분이 적고(12%), 휘발분의 함량이 많으며(58%), 고정탄소(17%), 회분(13%)로 열분해/가스화에 적용가능하다. 본 실험에서 생산된 합성가스의 활용방법으로는 보일러를 이용한 스팀 및 전력생산, 가스엔진을 이용한 전력생산, 폐열회수 등이 있으며 생산된 합성가스를 활용하기 위해서는 오염물질의 정제특성에 대한 연구가 선행되어야 한다. 따라서 본 연구에서는 합성가스 내에 존재하는 분진, 타르, HCl, HCN, $NH_3$의 제거효율을 조사하였다.

• 대기
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• 제23권3호
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• pp.293-305
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• 2013

대류가 유도하는 중규모 흐름에 미치는 비정역학 효과를 조사하기 위하여 기존의 무차원화된 정역학 모형을 바탕으로 무차원화된 비정역학 모형을 개발하였다. 모형을 검증하기 위하여 정역학 방정식 계의 해석해와 비정역학성이 아주 작은 경우의 수치 실험 결과를 비교하였고, 두 결과가 거의 같음을 확인하였다. 무차원화된 비정역학 모형을 이용하여 선형 계와 비선형 계에서 대류가 유도하는 중규모 흐름에 미치는 비정역학 효과를 조사하였다. 선형 계와 비선형 계 모두에서 비정역학성 인자가 작은 경우 열원 꼭대기 위에서 연직 방향으로, 비정역학성 인자가 상대적으로 큰 경우 주 상승 기류의 풍하측에서 수평 방향으로 상승 운동과 하강 운동이 교대하는 파동 형태의 섭동장이 나타났다. 풍하측에서 나타나는 상승 운동과 하강 운동을 분석하기 위하여 선형, 정상 상태, 비점성 흐름에 대한 Taylor-Goldstein 방정식을 구하였다. 주 상승기류의 풍하측에서 교대로 나타나는 상승 하강 기류세포는 전파파의 수평 방향 전파 성분과 에바네센트파, 즉 비정역학성 인자에 의해 결정되는 임계 파장보다 파장이 짧아 연직 방향으로 전파되지 못하고 수평 방향으로만 전파되는 중력파의 중첩으로 설명할 수 있다. 선형 계에 대한 수치 실험 결과에서 나타난 상승 하강 기류 세포의 수평 방향 길이는 선형 계에 대한 방정식에서 얻은 에바네센트 파의 임계 파장 길이의 절반과 일치하였으나, 약한 비선형 계에 대한 수치 실험 결과에서 나타난 상승 하강 기류 세포의 수평 방향 길이는 선형 계에 대한 방정식에서 얻은 에바네센트 파의 임계 파장 길이의 절반보다 다소 길었다. 주 상승 기류 지역 내에서 최대 상승 기류의 위치는 비선형성과 비정역학성 정도에 따라 다르게 나타났다.

• 대기
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• 제21권3호
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• pp.229-241
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• 2011

The continuous urbanizations by a rapid economic growth and a steady increase in population are expected to have a possible impact on meteorology in the downwind region. Long-term (1972~2007) trends of precipitation have been examined in the mid-Korean peninsula for the westerly condition only, along with the sensitivity simulations for a golden day (11 February 2009). During the long-term period, both precipitation amount (PA) and frequency (PF) in the downwind region (Chuncheon, Wonju, Hongcheon) of urban area significantly increased for the westerly and light precipitation ($PA{\leq}1mm\;d^{-1}$) cases, whereas PA and PF in the mountainous region (Daegwallyeong) decreased. The enhancement ratio of PA and PF for the downwind region vs. urban region remarkably increased, which implies a possible urbanization effect on downwind precipitation. In addition, the WRF simulation applied for one golden day demonstrates enhanced updraft and its associated convergence in the downwind area (about 60 km), leading to an increase in the cloud mixing ratio. The sensitivity experiments with the change in surface roughness demonstrates a slight increase in cloud water mixing ratio but a negligible effect on precipitation in the upwind region, whereas those with the change in heat source represents the distinctive convergence and its associated updraft in the downwind region but a decrease in liquid water, which may be attributable to the evaporation of cloud droplet by atmospheric heating induced by an increase in an anthropogenic heat. In spite of limitations in the observation-based analysis and one-day simulation, the current result could provide an evidence of the effect of urbanization on the light precipitation in the downwind region.

• 한국환경과학회지
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• 제30권12호
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• pp.1027-1039
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• 2021

In this study, we investigated the optimal meteorological conditions for cloud seeding using aircraft over the Korean Peninsula. The weather conditions were analyzed using various data sources such as a weather chart, upper air observation, aircraft observation, and a numerical model for cloud seeding experiments conducted from 2018 to 2019 by the National Institute of Meteorological Sciences, Korea Meteorological Administration. Cloud seeding experiments were performed in the seasons of autumn (37.0%) and winter (40.7%) in the West Sea and Gangwon-do. Silver iodide (70.4%) and calcium chloride (29.6%) were used as cloud seeding materials for the experiments. The cloud seeding experiments used silver iodide in cold clouds. Aircraft observation revealed relatively low temperatures, low liquid water content, and strong wind speeds in clouds with a weak updraft. In warm clouds, the cloud seeding experiments used calcium chloride. Observations included relatively high temperatures, high liquid water content, and weak wind speeds in clouds with a weak updraft. Based upon these results, we determined the comprehensive meteorological conditions for cloud seeding experiments using aircraft over the Korean Peninsula. The understanding of optimal weather conditions for cloud seeding gained from this study provide information critical for performing successful cloud seeding and rain enhancement.

• 대기
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• 제17권2호
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• pp.195-205
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• 2007

The influences of ice microphysical processes on urban heat island-induced convection and precipitation are numerically investigated using a cloud-resolving model (ARPS). Both warm- and cold-cloud simulations show that the downwind upward motion forced by specified low-level heating, which is regarded as representing an urban heat island, initiates moist convection and results in downwind precipitation. The surface precipitation in the cold-cloud simulation is produced earlier than that in the warm-cloud simulation. The maximum updraft is stronger in the cold-cloud simulation than in the warm-cloud simulation due to the latent heat release by freezing and deposition. The outflow formed in the boundary layer is cooler and propagates faster in the cold-cloud simulation due mainly to the additional cooling by the melting of falling hail particles. The removal of the specified low-level heating after the onset of surface precipitation results in cooler and faster propagating outflow in both the warm- and cold-cloud simulations.

• 한국환경과학회지
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• 제13권7호
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• pp.655-660
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• 2004

This paper demonstrates the numerical simulation of three dimensional flow pattern for vehicular exhaust dispersion in the street canyons. The wind flow around buildings in urban is computed by the SIMPLEST method. The convection-diffusion equation was used to compute the $NO_X$ concentration level near buildings. Details are given of important boundary conditions and turbulence quantities variations. The simple turbulence model was used for unisotropic viscous effect. A control-volume based finite-difference method with the upwind scheme is employed for discretization equation. The simple turbulence model applied in this study has been verified through comparison between predicted and measured data near buildings. By the predictive results, the updraft induced by the presence of high-rise buildings is important in the transport of street level pollutant out from the street canyons. Our suggestion for reducing ground level pollution is to have high-rise buildings constructed or to reduce the channelling effect of street canyons.

• 대한토목학회논문집
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• 제12권2호
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• pp.123-130
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• 1992

Geogakakos와 Bras의 일차원 지점 강수량 모형이 전주지점 호우모형으로 적합한지를 검토하였다. 구름 물리학을 토대로 한 이 모형의 기본변수는 운정의 압력, 평균 상승 기류 속도, 운저의 평균 운적직경의 역수값 등인데, 입력변수에 의하여 매개상수화 된다. 매개상수는 Hooke와 Jeeves의 직접 탐색 알고리즘에 의하여 평가되었다. 그 결과 계산 강우량과 실측 강우량과의 평균 자승 오차를 최소화 하는데 평균 상승 기류 속도와 운저 운적직경에 관계된 매개상수가 크게 기여하였다. 이러한 수치실험에서, 계산 총강우량과 실측 총강우량의 편차는 크지 않았으나 시간분포는 상당한 차이를 보였다.

• 한국대기환경학회지
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• 제27권4호
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• pp.416-425
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• 2011

To analyze the physical processes of sea-breeze development over a coastal urban area, numerical simulation for seabreeze (SB) and its frontogenesis was examined based on urbanized MM5 (uMM5) with urban canopy parameterization. On 6 August 2006, SB and its front were well developed in Busan under a weak offshore flow. As a result of wind vector, ZVB (Zero Velocity Boundary), potential temperature obtained the uMM5, at 0900 LST, SB advanced below 200 m height in the coastal areas and the internal boundary grew with the urban coastal region. At noon, the height of the SB head with updraft was approximately one and a half times (~600 m) higher than its depth in central urban. Applying the frontogenesis function, the SB structure for frontogenesis and frontolysis were complicated spatially; the dynamic effects of wind (i.e. convergence and tilting term) could play an important role in the growth of SB, especially the convergence effect.