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In-Hye Lee Young-Hee Lee Jinkyu Hong 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(3):281-291
Canopy turbulence plays an important role in mass and energy exchanges at the canopy-atmosphere interface. Despite extensive studies on canopy turbulence over a flat terrain, less attention has been given to canopy turbulence in a complex terrain. The purpose of this study is to scrutinize characteristics of canopy turbulence in roughness sublayer over a hilly forest terrain. We investigated basic turbulence statistics, conditionally sampled statistics, and turbulence spectrum in terms of different atmospheric stabilities, wind direction and vertical structures of momentum fluxes. Similarly to canopy turbulence over a homogeneous terrain, turbulence statistics showed coherent structure. Both quadrant and spectrum analysis corroborated the role of intermittent and energetic eddies with length scale of the order of canopy height, regardless of wind direction except for shift of peak in vertical wind spectrum to relatively high frequency in the down-valley wind. However, the magnitude of the momentum correlation coefficient in a neutral condition was smaller than typical value over a flat terrain. Further scrutiny manifested that, in the up-valley flow, temperature skewness was larger and the contribution of ejection to both momentum and heat fluxes was larger compared to the downvalley flow, indicating that thermal instability and weaker wind shear in up-valley flow asymmetrically affect turbulent transport within the canopy. 相似文献
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Ocean Science Journal - This study examines the different effects of high and low freshwater discharge on the water physical structure of the water column and plankton community in a tide-dominated... 相似文献
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We analyzed wind profiler data collected over Ulsan airport during the period from 2008 to 2009 to examine the characteristics of low level jets (LLJs). The Ulsan airport is located within the narrow valley with north-south axis. The frequency analysis results indicates that the nearly 19% of the total nocturnal periods have the presence of jets and LLJ occurrence rate is high in winter (32%) and low in summer (10%). The mode in the wind speed histogram is 4?C6 m s?1. A majority of jet occurs below 100 m (about 77.8 m) above ground. The predominant wind direction of jet is northerly. In order to examine the favorable conditions for LLJ formation of Ulsan airport, we investigated temperature difference between valley and plain at the surface and synoptic wind direction and speed at 850 hPa. Our results show that air temperature in the valley is lower than over the plain during the nighttime, indicating the existence of thermal forcing for along-valley wind. Under a significant temperature difference along the valley, westerly wind speed at 850 hPa is slightly weaker on LLJs event night than no event night, indicating weaker north-south large-scale pressure gradient on LLJ event night. The magnitude of northerly wind at 850 hPa is much stronger on event night than no event night, implying higher downward transfer of northerly wind on event night. Our findings suggest that jet formation over Ulsan airport is related to the strong northerly wind at 850 hPa in the presence of thermal forcing due to temperature contrast between valley and plain. 相似文献
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Hyerin Kim Sung-Hyun Cho Dongguen Lee Youn-Young Jung Young-Hee Kim Dong-Chan Koh Jeonghoon Lee 《Environmental Earth Sciences》2017,76(2):82
For water resources management, many studies for investigating flow paths from rainfall to subsurface have been conducted for last half century. A hydrograph separation based on end member mixing was carried out to evaluate the importance of the hydrological pathways providing the main sources of a small granitic watershed, Dorim-cheon, Seoul. An analysis of chloride, oxygen-18 and deuterium isotopes from precipitation and stream water during three storms was conducted with high-resolution data using 129 samples. Stream water, collected in advance of rain event, was assumed as a pre-event water (baseflow) component according to its dry condition and isotopic values compared with the values of different time periods. The contribution from vadose water was ignored due to the thin soil layer covering the study area. Using a two-component mixing model, hydrograph separation of the stream water in Dorim-cheon was conducted based on weighted mean values of rain water and pre-event water component with the high-resolution datasets. As a result of the analysis with water isotopes, contribution of groundwater was dominant during the entire study period (73–74%) except of instant dominance of rainfall at the earliest period. Using chloride as a tracer for hydrograph separation, a significant difference for the amount of pre-event water contribution was identified. This might be caused by the large variation of chloride concentration during the rain event and the end member determination. 相似文献
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The 2018 Winter Olympic and Paralympic Games will be held in Pyeongchang, Korea, during February and March. We examined the near surface winds and wind gusts along the sloping surface at two outdoor venues in Pyeongchang during February and March using surface wind data. The outdoor venues are located in a complex, mountainous terrain, and hence the near-surface winds form intricate patterns due to the interplay between large-scale and locally forced winds. During February and March, the dominant wind at the ridge level is westerly; however, a significant wind direction change is observed along the sloping surface at the venues. The winds on the sloping surface are also influenced by thermal forcing,showing increased upslope flow during daytime. When neutral air flows over the hill, the windward and leeward flows show a significantly different behavior. A higher correlation of the wind speed between upper-and lower-level stations is shown in the windward region compared with the leeward region. The strong synoptic wind, small width of the ridge, and steep leeward ridge slope angle provide favorable conditions for flow separation at the leeward foot of the ridge. The gust factor increases with decreasing surface elevation and is larger during daytime than nighttime. A significantly large gust factor is also observed in the leeward region. 相似文献
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Young-Hee Lee Hee-Jeong Lim Kazuhito Ichii Yingnian Li 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(5):561-570
The Tibetan plateau plays an important role in energy and carbon cycles by providing an elevated heat source and by storing a large amount of soil carbon due to low temperature. The main vegetation of the plateau is alpine grassland. This study evaluates performance of Community Land Model 3.5 with carbon and nitrogen cycles (CLM3.5CN) over a alpine grassland in the Tibetan plateau in terms of energy and carbon fluxes in conditions of reasonable phenology and initial carbon pool comparable to observations. Comparison between model and observation shows following features. The model captures the magnitude of maximum leaf area index (LAI) but underestimats leaf mass. Net ecosystem exchange (NEE) is significantly underestimated during the growing season and soil temperature is also underestimated throughout a year with higher negative bias in winter than in other seasons. In order to examine the cause of the model deficiencies, we design four sensitivity tests: seasonal mulch; shallow rooting depth; reduction of critical soil moisture to limit the decomposition rate; smaller specific leaf area (SLA). Considering seasonal mulch improves the negative bias of soil temperature during dormant season has little effect on the NEE during the growing seasson. Underestimation of NEE during the growing season is partly due to underestimated decomposition rate which results from underestimated soil temperature and deep root placement in the soil column. Underestimation of latent heat flux during summer is partly due to use of large SLA in the model. Other deficiencies are also discussed. 相似文献
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