• 제목/요약/키워드: Atmospheric boundary

검색결과 448건 처리시간 0.034초

월령 연안지역 대기경계층의 유동특성과 대기 안정성에 대한 고찰 (Estimation on The Atmospheric Stability and Flow Characteristics of Planetary Boundary Layer in Wolryong Coastal Region)

  • 정태윤;임희창;김현구;장문석
    • 한국환경과학회지
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    • 제18권8호
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    • pp.857-865
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    • 2009
  • The physical properties of an atmospheric boundary layer in Wolryong, a west coastal region of Jeju, South Korea, in terms of the atmospheric stability and roughness length, is important and relevant to both engineers and scientists. The study is aiming to understand the atmospheric stability around this region and its effect on the roughness length. We calculate the Monin-Obukhov length(L) against 3 typical regions of the atmospheric condition - unstable regime (-5$-0.2{\leq}H/L{\leq}0.2$) and stable regime (0.2

Response of Ecosystem Carbon and Water Vapor Exchanges in Evolving Nocturnal Low-Level Jets

  • Hong, Jin-Kyu;Mathieu, Nathalie;Strachan, Ian B.;Pattey, Elizabeth;Leclerc, Monique Y.
    • Asian Journal of Atmospheric Environment
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    • 제6권3호
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    • pp.222-233
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    • 2012
  • The nocturnal low-level jet makes a significant impact on carbon and water exchanges and turbulent mixing processes in the atmospheric boundary layer. This study reports a case study of nocturnal surface fluxes such as $CO_2$ and water vapor in the surface layer observed at a flat and homogeneous site in the presence of low-level jets (LLJs). In particular, it documents the temporal evolution of the overlying jets and the coincident response of surface fluxes. The present study highlights several factors linking the evolution of low-level jets to surface fluxes: 1) wavelet analysis shows that turbulent fluxes have similar time scales with temporal scale of LLJ evolution; 2) turbulent mixing is enhanced during the transition period of low-level jets; and 3) $CO_2$, water vapor and heat show dissimilarity from momentum during the period. We also found that LLJ activity is related not only to turbulent motions but also to the divergence of mean flow. An examination of scalar profiles and turbulence data reveal that LLJs transport $CO_2$ and water vapor by advection in the stable boundary layer, suggesting that surface fluxes obtained from the micrometeorological method such as nocturnal boundary layer budget technique should carefully interpreted in the presence of LLJs.

An Algorithm to Determine Aerosol Extinction Below Cirrus Cloud from Mie-LIDAR Signals

  • Wang, Zhenzhu;Wu, Decheng;Liu, Dong;Zhou, Jun
    • Journal of the Optical Society of Korea
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    • 제14권4호
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    • pp.444-450
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    • 2010
  • The traditional approach to inverting aerosol extinction makes use of the assumption of a constant LIDAR ratio in the entire Mie-LIDAR signal profile using the Fernald method. For the large uncertainty in the cloud optical depth caused by the assumed constant LIDAR ratio, an not negligible error of the retrieved aerosol extinction below the cloud will be caused in the backward integration of the Fernald method. A new algorithm to determine aerosol extinction below a cirrus cloud from Mie-LIDAR signals, based on a new cloud boundary detection method and a Mie-LIDAR signal modification method, combined with the backward integration of the Fernald method is developed. The result shows that the cloud boundary detection method is reliable, and the aerosol extinction below the cirrus cloud found by inverting from the modified signal is more efficacious than the one from the measured signal including the cloud-layer. The error due to modification is less than 10% taken in our present example.

언덕지형을 지나는 유동에 관한 연구 (Wind Flow over Hilly Terrain)

  • 임희창;김현구;이정묵;경남호
    • 한국대기환경학회지
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    • 제12권4호
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    • pp.459-472
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    • 1996
  • An experimental investigation on the wind flow over smooth bell-shaped two-dimensional hills with hill slopes (the ratio of height to half width) of 0.3 and 0.5 is performed in an atmospheric boundary-layer wind tunnel. Two categories of the models are used in the present investigation; six two-dimensional single-hills, and four continuous double-hills. The measurements of the flow field and surface static-pressure distribution are carried out over the Reynolds number (based on the hill height) of 1.9 $\times 10^4, 3.3 \times 10^4, and 5.6 \times 10^4$. The velocity profiles and turbulence characteristics are measured by the pitot-tube and X-type hot-wire anemometer, respectively. The undisturbed boundary-layer profile on the bottom surface of the wind tunnel is reasonably consistent with the power-law profile with $\alpha = 7.0 (1/\alpha$ is the power-law exponent) and shows good spanwise uniformities. The profiles of turbulent intensity are found to be consistent along the centerline of the wind tunnel. The measured non-dimensional speed-up profiles at the hill crest show good agreements with the predictions of Jackson and Hunt's linear theory. The flow separation occurs in the hill slope of 0.5, and the oil-ink dot method is used to find the reattachment points in the leeside of the hill. The measured reattachment points are compared with the numerical predictions. Comparisons of the mean velocity profiles and surface pressure distributions between the numerical predictions and the experimental results show good agreements.

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Impact of boundary layer simulation on predicting radioactive pollutant dispersion: A case study for HANARO research reactor using the WRF-MMIF-CALPUFF modeling system

  • Lim, Kyo-Sun Sunny;Lim, Jong-Myung;Lee, Jiwoo;Shin, Hyeyum Hailey
    • Nuclear Engineering and Technology
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    • 제53권1호
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    • pp.244-252
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    • 2021
  • Wind plays an important role in cases of unexpected radioactive pollutant dispersion, deciding distribution and concentration of the leaked substance. The accurate prediction of wind has been challenging in numerical weather prediction models, especially near the surface because of the complex interaction between turbulent flow and topographic effect. In this study, we investigated the characteristics of atmospheric dispersion of radioactive material (i.e. 137Cs) according to the simulated boundary layer around the HANARO research nuclear reactor in Korea using the Weather Research and Forecasting (WRF)-Mesoscale Model Interface (MMIF)-California Puff (CALPUFF) model system. We examined the impacts of orographic drag on wind field, stability calculation methods, and planetary boundary layer parameterizations on the dispersion of radioactive material under a radioactive leaking scenario. We found that inclusion of the orographic drag effect in the WRF model improved the wind prediction most significantly over the complex terrain area, leading the model system to estimate the radioactive concentration near the reactor more conservatively. We also emphasized the importance of the stability calculation method and employing the skillful boundary layer parameterization to ensure more accurate low atmospheric conditions, in order to simulate more feasible spatial distribution of the radioactive dispersion in leaking scenarios.

최악의 대기 조건 하의 공기조력 비행선 운전 (Aeroassisted Orbital Maneuvering in a Worst-Case Atmosphere)

  • 이병수
    • 제어로봇시스템학회논문지
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    • 제6권10호
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    • pp.936-941
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    • 2000
  • Advanced space transportation systems, such as the National Aerospace Plane or an Orbital Transfer Vehicle, have atmospheric maneuvering capabilities. For such vehicles the use of aeroassisted orbital transfer from a high Earth orbit to a low Earth orbit, with unpowered flight in the atmosphere, has the potential for significant fuel savings compared to exoatmospheric Hohmann transfer. However, to exploit the fuel savings that can be achieved by using the Earths atmosphere to reduce the vehicles energy, a guidance law is required, and it must be able to handle large unpredictable fluctuations in atmospheric density, on the order of ${\pm}$50% relative to the 1962 US Standard Atmosphere. In this paper aeroassisted orbital transfer is considered as a differential game, with Nature controlling the atmosphere density to yield a worst case (min-max fuel required) atmosphere, from which the guaranteed playable set boundary are achieved. Inside the playable set, it is guaranteed that the vehicle achieves the optimal atmospheric exit condition for the minimum fuel consumption regardless of the atmospheric density variations.

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대구상공에서의 대기 오염 물질 확산에 관한 연구 (A Study on the Diffusion of Atmospheric Pollutants over Taegu)

  • 윤일희;민경덕;박동재
    • 한국환경과학회지
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    • 제3권3호
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    • pp.241-252
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    • 1994
  • Meteorological parameters In the atmospheric boundary layer and the vertical and horizontal dispersion parameters were determined by analyzing the data obtained by the special upper-air observations of one clear day for each season from October 1991 to August 1992. The concentration of the aklospheric pollutants over Taegu was analyzed by using the application of the Gaussian diffusion model. In the diurnal variation of diffusion of atmospheric pollutants, vertical diffusion due to turbulence is active in daytime while horizontal diffusion due to wind is active in nighttime. The mean concentration of pollutants in the side of downwind is higher during the daytime than the nighttime. Thus, the height of the mixed-layer at the nighttime considered as the most important parameter of the mean concentration of pollutants. In the seasonal variation of diffusion of atmospheric pollutants, vertical diffusion due to strong solar radiation is active in summer case day, and horizontal diffusion due to strong wind is active in winter case day. In winter case day, the mean concentration of pollutants in the side of downwind is maximum in the daytime. However, in summer case day, that is maximum in the nighttime.

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