共查询到18条相似文献，搜索用时 140 毫秒
1.
本文利用高分辨率中尺度WRF模式,通过改变边界层参数化方案进行多组试验,评估该模式对美国北部森林地区边界层结构的模拟能力,同时比较了五种不同边界层参数化方案模拟得出的边界层热力和动力结构.结果表明：除个别方案外,配合不同边界层方案的WRF模式都能成功模拟出白天对流边界层强湍流混合特征和夜间稳定边界层内强逆温、逆湿和低空急流等热力和动力结构.非局地YSU、ACM2方案在白天表现出强的湍流混合和卷夹,相比于局地MYJ、UW方案,模拟的对流边界层温度更高、湿度更低、混合层高度更高、感热通量更大,更接近实际观测,这表明在不稳定层结下考虑非局地大涡输送更为合理,但局地方案在风速和风向的预报上存在一定优势.TEMF方案得到的白天局地湍流混合强度为所有方案中最弱,混合层难以发展,无法体现对流边界层内气象要素垂直分布均匀的特点.对于夜间稳定边界层的模拟,不同参数化方案之间的差异较小,但是YSU方案在一定程度上高估了机械湍流,导致局地湍流混合偏强,从而影响了其对稳定边界层的模拟能力. 相似文献
2.
森林冠层上下湍流谱结构和耗散率 总被引：3，自引：1，他引：2
利用新型三维超声风速 /温度仪 ,根据在长白山原始森林冠层上下两个高度上测量的湍流资料 ,采用涡动相关法计算和分析了森林冠层上下湍流谱的结构、局地各向同性和耗散率 .结果表明 ,在惯性副区 ,归一化湍流谱遵从 - 23的指数规律 ;在森林冠层上 ,尽管谱的形状与均匀表面的一致 ,但是 ,大气湍流是非各向同性的 ;而在森林冠层内则是近似各向同性的 ;森林冠层上下湍流能量和热量耗散率比典型草原和牧场的结果大 ,揭示了森林粗糙表面在湍流输送过程中的动力扰动和对大涡的破碎作用 相似文献
3.
《中国科学:地球科学》2015,(6)
通过对青藏高原东南缘大理2008年3~8月大样本边界层铁塔观测系统超声和梯度资料、风廓线雷达和GPS探空资料的综合分析,研究发现高原东南缘湍能分量(湍流动能、切变项和浮力项)强弱依赖于下垫面植被的变化状况,且与局地稳定度特征及其动力、热力条件存在显著关系.近地层处于中性层结时,机械湍流较强,湍流动能主要贡献来源于切变项;当不稳定层结时大气湍流运动则以热力湍流为主,即浮力项较强,切变项较弱;在稳定层结时湍流发展呈间歇性特征,其中浮力项与切变项亦较弱,且湍流动能显著小于中性和不稳定状态.研究亦发现春季位于青藏高原大地形南坡的林芝站浮力项贡献显著大于高原大地形东南缘大理站,这反映了青藏高原南坡强对流活动过程中热力湍流的重要贡献,但位于高原东南缘山谷起伏、复杂地形区域的大理站近地层的机械湍流却显著大于高原南坡林芝站;从湍流-对流运动不同尺度相互作用视角,研究发现高原东南缘午时对流边界层CBL(Convective Boundary Layer)顶高可达1500~2500 m,边界层湍流动能、切变项、浮力项与对流边界层顶高、局地垂直运动均呈显著相关,且白天地面感热通量或浮力项的热力湍流作用对CBL发展高度亦有明显影响,而机械湍流的剪切作用影响却相对小;另外,近地层切变项机械湍流输送对垂直运动影响显著,尤其午前其对垂直运动影响高度可达2500~3000 m;春、夏季浮力项、切变项与垂直运动相关的日变化峰值均为大气层结显著不稳定阶段,尤其夏季层结不稳定背景下浮力项午后对垂直运动贡献显著.本文研究结论揭示出高原东南缘对流活动的湍能源驱动特征及其两者的相互作用. 相似文献
4.
研究新一代中尺度气象模式WRF中两种大气边界层方案(MYJ,YSU)对沈阳冬季大气边界层结构模拟的影响,重点分析温度层结、低层风场、边界层高度等对污染物扩散有重要影响的气象要素.和观测数据的比对表明WRF基本能够模拟出温度风速的日变化特征,但模拟风速偏大.YSU方案由于模拟的边界层顶卷挟和边界层内混合作用较强,夜间接地逆温强度低于MYJ方案,逆温维持时间比MYJ方案短4小时,同时模拟边界层高度也高于MYJ方案,有利于污染物垂直扩散.边界层高度的3种计算方法中,湍流动能方法计算的边界层高度最高,Richardson数方法次之,位温方法得到的高度最低.Richardson数方法对临界值的选取较敏感. 相似文献
5.
利用中尺度气象数值模式（Weather Research and Forecasting Model,WRF）模拟风场,结合兰州大学半干旱气候与环境观测站（Semi-Arid Climate and Environment Observatory of Lanzhou University,SACOL）湍流观测资料,分析了黄土高原复杂地形上稳定边界层低空急流对近地层湍流活动的影响.黄土高原复杂地形上稳定边界层低空急流的形成与地形作用引发的局地环流有关.低空急流对近地层湍流活动有强烈影响,剪切作用使小尺度湍涡活动加剧,湍动能增大,同时非平稳运动被压制.低空急流发生时,观测数据有87.3%是弱稳定情形（梯度理查森数小于0.25）;而无低空急流时,对应时段的观测表明65.4%属于强稳定层结（梯度理查森数大于0.3）,非平稳运动造成湍流功率谱在低频端迅速增大.与无低空急流和弱低空急流情形相比,强低空急流发生时,近地层湍动能增大1倍,湍动能在垂直方向上的传递增大1个量级,且方向向下,约为-3 × 10-3 m3·s-3,湍流在上层产生并向下传递. 相似文献
6.
《中国科学:地球科学》2020,(6)
植被是重要的城市地表覆盖类型之一,它通过蒸散降温和阻挡强冷空气,对城市风温湿大气微环境和污染物扩散特征会产生显著影响.准确预测植被环境流动和标量输运特性,理解植被与大气之间湍流交换过程,对城市环境改善具有重要意义.文章建立和发展了适用于森林植被环境湍流流动和标量场演化仿真计算的大涡模拟方法,将中尺度气象预报模式与微尺度精细大涡模拟方法耦合,利用地表能量平衡关系考虑大气辐射等多物理过程,研究了典型天气条件下复杂森林下垫面大气流动问题.通过考察不同大气稳定度条件下森林植被环境流动发现,在不稳定和稳定大气情况,浮力分别起到增强和抑制大气湍流混合作用,风切变也相应减小和增加.在北京奥林匹克森林公园的多尺度模拟试验中,通过与外场观测结果比较,文章验证了耦合模型可以较好地模拟城市复杂地表上空风速、温度和相对湿度的日变化.尤其是对于风场的模拟,耦合方案明显优于传统中尺度数值模拟,这主要是由于耦合方案既考虑了外部中尺度流动的影响,又通过降尺度方法可以精细分辨城市非均匀地表粗糙元素分布,从而较为精确的复现了城市粗糙子层内复杂大气流动和湍流通量输运. 相似文献
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首次用验证时间序列中是否存在动力非平稳性的一种简单图示方法——space time index法来分析大气边界层湍流的动力平稳性特征.本文以取自淮河流域和威斯康星森林下垫面条件下的三维高精度风速和温度、湿度湍流脉动资料对大气边界层湍流的平稳性特征进行了分析.结果表明space time index方法能有效地检验大气边界层湍流信号中是否存在动力平稳性.另外,均匀下垫面条件（水稻田）及复杂下垫面条件（森林）下的大气边界层湍流信号中几乎都存在动力非平稳性,大气湍流动力学非平稳性可能是边界层湍流信号相当普遍具有的一种特性.大气边界层湍流中的间歇性和相干结构使得其非平稳性图形的特征不同于一般时间序列非平稳性图形的“V”型特征;森林下垫面条件下的湍流信号比相对均匀下垫面（水稻田）下的湍流信号更有组织性,相干结构更强. 相似文献
8.
利用WRF模式中5种常用边界层参数化方案(ACM2、YSU、BouLac、MYJ和MYNN2.5)及美国能源部大气辐射观测试验(ARM)寿县综合观测数据(2008年8—12月),对比分析了晴天及阴天条件下,不同参数化方案对典型农田下垫面气象要素及边界层结构的模拟效果,结果表明:(1)模式对于云层状况的模拟,非局地方案ACM2和YSU方案优于局地方案.(2)对于近地层气象要素,晴天和阴天条件下均是ACM2方案对于2 m温度和比湿的模拟效果最好,MYJ方案对于风向风速的模拟效果最好.(3)对于位温及比湿垂直廓线的模拟,晴天和阴天条件下均是非局地方案(ACM2和YSU)对白天的模拟效果优于局地方案;ACM2方案对夜间弱稳定层结和逆湿结构的模拟最优;(4)对于风速垂直廓线的模拟,白天不稳定条件下,晴天条件MYJ方案最优,阴天MYNN2.5方案的模拟效果最好;夜间弱稳定条件下,晴天条件ACM2方案与观测值之间的偏差最小,阴天YSU方案模拟效果最好;(5)总体而言,在对典型农田下垫面进行模拟时,晴天和阴天条件下均是ACM2方案更具优势. 相似文献
9.
为了揭示黄土高原复杂地形条件下湍流涡旋的分布特征,提高湍流观测的精度,湍流的各态历经性研究随即成为实验研究的首要问题.文章利用甘肃省平凉市白庙塬地形条件下单点湍流观测的结果,对比分析并揭示了从稳定层结到不稳定层结,除小于10min尺度的湍流易于满足各态历经性外,地形易造成周期性存在的大尺度湍流相干结构.与平坦下垫面湍流相比,塬区10~40min的大尺度湍流定常性更好,也易于满足各态历经性.在极不稳定层结条件下,风速较小,并具有明显的大尺度周期性波动,同时伴随平稳的增温趋势,因此造成大尺度风速湍流和温度湍流都较易于满足各态历经性;但在极稳定层结条件下,湍流间歇性则造成大尺度风速和温度波动的非周期性较强,湍流不易于满足各态历经性. 相似文献
10.
藏南羊卓雍错湖面大气湍流特征观测分析 总被引：2，自引：1，他引：1
湍流运动是大气边界层的本质特征,是地表与大气之间能量和物质交换的主要方式.本文利用2016和2017年4-10月藏南羊卓雍错湖泊涡动观测资料,分析了湖面大气湍流方差和湍流特征量的统计和变化特征.结果表明：（1）不稳定层结下,三维风速分量和超声虚温、水汽密度、CO2密度的无量纲标准差随稳定度变化符合Monin-Obukhov相似理论的"1/3"或"-1/3"次幂律,垂直风速的拟合效果最好;稳定层结下,除CO2密度无量纲标准差与稳定度无明显关系外,其他量基本上满足相似性规律;中性条件下,以上物理量的无量纲标准差分别趋近常数：3.57、3.93、0.77、20.91、6.35和11.96.（2）水平方向平均湍流强度（0.60和0.58）大于垂直方向（0.13）,三维方向湍流强度与平均风速的变化呈显著负相关,相关系数分别为-0.39、-0.42和-0.34.（3）湖面湍流动能随风速呈线性增长,增长率达0.45 m/s;近中性层结时湍流动能最大,层结越稳定或不稳定湍流动能均减小.（4）湖泊下午到傍晚动量输送较强,13：00-22：30时间段平均动量通量达0.091 kg/（m·s2）;热量输送以潜热为主,潜热通量日平均值（77.3 W/m2）是感热通量（14.6 W/m2）的5.3倍,感热和潜热通量日变化峰值分别出现在5：30（22.4 W/m2）和16：00（106.6 W/m2）. 相似文献
11.
Vegetation constitutes one of the fundamental types of land use on Earth. The presence of trees in urban areas can decrease local winds and exchange sensible and latent heat with the surrounding environments, thus exerting notable influences on the urban microenvironment. A better understanding of the turbulent transfer of momentum and scalars around vegetation canopy could significantly contribute to improvement of the urban environment. This work develops a large-eddy simulation(LES) method that is applicable to model the flow and scalar transport over the forest canopy. We study the atmospheric flow over complex forested areas under typical weather conditions by coupling LES to the mesoscale model. Models of radiation and energy balance have been developed with explicit treatment of the vegetation canopy. By examining the flow over a forest canopy under a range of stability conditions, we found that buoyancy enhances or suppresses turbulent mixing in unstable or stable atmosphere respectively, with decreasing or increasing wind shear, respectively. From the multiscale modeling of the Beijing Olympic Forest Park, the present coupling scheme proves to better resolve the diurnal variations in wind speed,temperature, and relative humidity over complex urban terrains. The coupling scheme is superior to the traditional mesoscale model in terms of wind field simulation. This is mainly because the coupling scheme not only takes the influences of external mesoscale flow into consideration, but also resolves the heterogeneous urban surface at a fine scale by downscaling, thus better reproducing the complex flow and turbulent transport in the urban roughness sublayer. 相似文献
12.
Local flow properties and regional weather or climate are strongly affected by land‐atmosphere interactions of momentum and scalars within the daytime convective boundary layer (CBL). In this study, we investigate the impact of green space scale on the daytime atmospheric boundary layer (ABL) over a synthetic urban domain using a recently developed large‐eddy simulation‐land surface model (LES–LSM) framework. With the use of realistic soundings as initial conditions, a series of numerical experiments over synthetic urban surfaces with varied scale of vegetated area is performed. Simulated micrometeorological properties, surface fluxes, basic CBL characteristics, and cloud distribution are analysed. The results show reference‐level air potential temperature and specific humidity as well as surface fluxes over green space are significantly affected by the scale of green space in the urban domain. The surface organization due to vegetated area scale also has impacts on horizontally averaged scalar and momentum profiles; however, the magnitude in this study is smaller than the results of a previous study using a set of offline surface fluxes as the lower boundary condition for LES. In addition, even though this study only performs a daytime diurnal cycle, the impact of green space scale on cloud distribution in simulations is significant. The cases with more organized green space yield lower‐elevated cumulus cloud and larger‐cloud cover fraction, which impacts the energy budget at the top of boundary layer and, in turn, could lead to additional surface cooling with respect to longer‐term weather and climate. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
13.
Annual fluxes of canopy‐level heat, water vapour and carbon dioxide were measured using eddy covariance both above the aspen overstory (Populus tremuloides Michx.) and hazelnut understory (Corylus cornuta Marsh.) of a boreal aspen forest (53·629 °N 106·200 °W). Partitioning of the fluxes between overstory and understory components allowed the calculation of canopy conductance to water vapour for both species. On a seasonal basis, the canopy conductance of the aspen accounted for 70% of the surface conductance, with the latter a strong function of the forest's leaf area index. On a half‐hour basis, the canopy conductance of both species decreased non‐linearly as the leaf‐surface saturation deficits increased, and was best parameterized and showed similar sensitivities to a modified form of the Ball–Berry–Woodrow index, where relative humidity was replaced with the reciprocal of the saturation deficit. The negative feedback between the forest evaporation and the saturation deficit in the convective boundary layer varied from weak when the forest was at full leaf to strong when the forest was developing or loosing leaves. The coupling between the air at the leaf surface and the convective boundary layer also varied seasonally, with coupling decreasing with increasing leaf area. Compared with coniferous boreal forests, the seasonal changes in leaf area had a unique impact on vegetation–atmosphere interactions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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15.
F. Holwerda R. Burkard W. Eugster F. N. Scatena A. G. C. A. Meesters L. A. Bruijnzeel 《水文研究》2006,20(13):2669-2692
The deposition of fog to a wind‐exposed 3 m tall Puerto Rican cloud forest at 1010 m elevation was studied using the water budget and eddy covariance methods. Fog deposition was calculated from the water budget as throughfall plus stemflow plus interception loss minus rainfall corrected for wind‐induced loss and effect of slope. The eddy covariance method was used to calculate the turbulent liquid cloud water flux from instantaneous turbulent deviations of the surface‐normal wind component and cloud liquid water content as measured at 4 m above the forest canopy. Fog deposition rates according to the water budget under rain‐free conditions (0·11 ± 0·05 mm h?1) and rainy conditions (0·24 ± 0·13 mm h?1) were about three to six times the eddy‐covariance‐based estimate (0·04 ± 0·002 mm h?1). Under rain‐free conditions, water‐budget‐based fog deposition rates were positively correlated with horizontal fluxes of liquid cloud water (as calculated from wind speed and liquid water content data). Under rainy conditions, the correlation became very poor, presumably because of errors in the corrected rainfall amounts and very high spatial variability in throughfall. It was demonstrated that the turbulent liquid cloud water fluxes as measured at 4 m above the forest could be only ～40% of the fluxes at the canopy level itself due to condensation of moisture in air moving upslope. Other factors, which may have contributed to the discrepancy in results obtained with the two methods, were related to effects of footprint mismatch and methodological problems with rainfall measurements under the prevailing windy conditions. Best estimates of annual fog deposition amounted to ～770 mm year?1 for the summit cloud forest just below the ridge top (according to the water budget method) and ～785 mm year?1 for the cloud forest on the lower windward slope (using the eddy‐covariance‐based deposition rate corrected for estimated vertical flux divergence). Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
16.
A model of the wave and current boundary‐layer structure was developed using the k–ε turbulent closure model. The finite‐difference method was used to solve the governing equations. Vertical logarithmic grids and equal time steps were adopted. The following modelled simulations were obtained: (1) vertical profiles of wave velocity amplitude, eddy viscosity coefficient and turbulent kinetic energy with waves only; (2) vertical profiles of wave velocity amplitude, mean current velocity, eddy viscosity coefficient and turbulent kinetic energy with waves having a following current. To test the validity and the rationality of the present model, vertical profiles of modelled wave velocity amplitude and mean velocity were compared with corresponding experimental results available in the literature. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
17.
大量近地层观测试验表明,利用涡动相关法观测的湍流通量小于近地层可利用能量,即近地层能量是不闭合的,这种不闭合度一般为20%甚至更高.而陆面过程模式是基于地气间能量平衡建立,并且模式中的湍流边界层参数化方案通常根据实际观测的湍流通量来确定,因此能量不闭合必将对陆面过程模式造成一定的影响.本文利用2007年春季SACOL站的近地层观测资料,依据能量守恒将能量不闭合中的残余能量通过波文比分配到观测的湍流通量中,即修正涡动相关法观测的湍流通量使得近地层能量达到平衡;之后分别利用观测和修正的湍流通量,建立了能量不闭合和闭合情形下的湍流参数化方案,借助陆面过程模式SHAW,通过数值模拟和对比分析方法考察近地层能量闭合度对陆面过程模式的影响.研究结果表明近地层能量闭合对陆面过程模式有显著的影响:在陆面过程数值模拟中,当应用近地层能量不闭合的湍流通量形成的湍流参数化方案时,陆面过程模式会明显高估地表长波辐射及土壤温度;但当应用修正湍流通量使得近地层能量达到闭合形成的湍流参数化方案后,在不改变任何地表土壤物理生化属性的情况下,陆面过程模式能较好地模拟地表长波辐射和土壤温度. 相似文献
18.
《Journal of Hydrology》2002,255(1-4):212-233
Forest soils are often covered with a litter that influences the rate of mass and energy transfer between the soil and the air above, thereby modifying the temperature and moisture fields in the soil. The presence of a litter should therefore be accounted for in forest SVAT models, especially when long-term simulations are to be performed. A heat and moisture litter model has been developed by adding two dynamical equations to a force-restore type soil model. The experimental data used for the model validation was collected in a pine forest canopy in the South-West of France, that was part of the Euroflux network. The model is tested and validated over a two-year period. It is shown to provide a fairly good simulation of soil and litter moisture, soil and litter temperature and turbulent fluxes measured above the forest floor. It is also shown that simulations without the litter layer are unable to reproduce all these variables simultaneously. We then perform a sensitivity analysis to the parameters whose values are either uncertain or likely to be variable in time and space, such as the litter thickness, the rainfall fraction intercepted by the litter or the maximum value of the surface resistance. A threshold value of the litter moisture used in the surface resistance parameterisation turns out to be the most critical parameter. Further work is needed to investigate the possible relationships between the various parameters describing the litter, but the present litter model can already be used in combination with other forest SVAT models. 相似文献