共查询到20条相似文献，搜索用时 46 毫秒
1.
V. K. Makin 《Boundary-Layer Meteorology》2008,129(3):469-478
A simple model of the atmospheric boundary layer over the ocean where the swell impact on the atmosphere is explicitly accounted
for is suggested. The model is based on Ekman’s equations, where the stress in the wave boundary layer is split into two parts:
the turbulent and wave-induced stress. The turbulent stress is parameterized traditionally via the eddy viscosity proportional
to the generalized mixing length. The wave-induced stress directed upward (from swell to the atmosphere) is parameterized
using the formalism of the wind-over-waves coupling theory. The model can be seen as an extension of the model by Kudryavtsev
and Makin (J Phys Oceanogr 34:934–949, 2004) to the scale of the entire atmospheric boundary layer by including the Coriolis force into the momentum conservation
equation and generalizing the definition of the mixing length. The regime of low winds for swell propagating along the wind
direction is studied. It is shown that the impact of swell on the atmosphere is governed mainly by the swell parameter—the
coupling parameter that is the product of the swell steepness and the growth rate coefficient. When the coupling parameter
drops below − 1 the impact of swell becomes significant and affects the entire atmospheric boundary layer. The turbulent stress
is enhanced near the surface as compared to the no-swell case, and becomes negative above the height of the inner region.
The wind profile is characterized by a positive gradient near the surface and a negative gradient above the height of the
inner region forming a characteristic bump at the height of the inner region. Results of the model agree at least qualitatively
with observations performed in the atmosphere in presence of swell. 相似文献
2.
Abstract Winter operation of an acoustic sounder at Calgary, Alberta, has led to some unique observations during Chinook periods. Acoustic backscatter records obtained in these periods reveal an identifiable pattern of events in the atmospheric boundary layer. Descending turbulent structures are observed in pre‐Chinook conditions; the arrival of these structures near ground is associated with the onset of ground‐level warming. When ground‐level temperatures have risen to near 0°C, a deep (200–500 m thick) characteristic region of turbulence is generated in the boundary layer. The correlation of these features with surface wind and temperature data is discussed. 相似文献
3.
R.L. Raddatz 《大气与海洋》2013,51(4):399-419
Abstract This paper describes a 1‐D agroclimatic model of the atmosphere/crop‐soil interface. Vertical profiles of wind, potential temperature and water vapour are constructed twice daily for the overnight‐low and maximum temperature times by combining 1200 and 0000 UTC upper‐air standard‐level grid‐point data with climatological observations. The vertical structure of the atmospheric boundary layer has a surface constant‐flux layer that is usually topped by a mixed layer by day but not at night. The crop‐soil boundary layer consists of a shallow top‐zone and a growing root‐zone. Vegetation cover and root depth depend upon crop type and phenological stage. Water‐balance accounting tracks the moisture contents of both the top‐ and root‐zones. Evapotranspiration or the vertical flux of water vapour in the atmospheric boundary layer is tied to the evolution of the crop‐soil boundary layer. The model was calibrated using field data from the Regional Evaporation Study's primary site in an agricultural area of central Saskatchewan. The evolution of 1991's wheat‐soil boundary layer from the crop's heading to ripe stages was then successfully simulated at two additional sites in the same geographical area. 相似文献
4.
Yves Delage 《Boundary-Layer Meteorology》1988,43(4):365-381
Two formulations of the stable atmospheric boundary layer are proposed for use in weather forecasting or climate models. They feature the log-linear profile near the surface, but are free from the associated critical Richardson number. The diffusion coefficients in the Ekman layer are a natural extension of the surface layer. They are locally determined using wind shear in one case and turbulent kinetic energy in the other. The parameterizations are tested in a one-dimensional model simulating the evolution of the nocturnal boundary layer with and without radiative cooling. Both formulations give very similar results, except near the top of the boundary layer where the transition to the free atmosphere is smoother with the wind shear formulation. A distinctive feature of these schemes is that they retain their simulating skill when resolution is reduced. This is verified for a wide range of situations. In practice, this means that there is no need for a large-scale model to have a level below 50 m or so. 相似文献
5.
利用中尺度数值模式WRF v3.8中的YSU、MYJ、QNSE、ACM2、UW、GBM、Boulac七种不同边界层参数化方案,采用高分辨率（1.33 km）数值试验的方法研究了不同边界层方案对模拟台风“莫兰蒂”（1614）登陆减弱阶段的移动路径、强度、结构、降水量、近地层有关物理量场分布等方面的影响,结果表明:（1）“莫兰蒂”台风登陆减弱阶段,不同边界层方案对台风路径、强度、降水量模拟影响显著,24 h内模拟台风路径、最低气压、最大风速及24 h累积降水量极值的最大差异分别达80 km、11 hPa、27 m s?1及241 mm;（2）Boulac方案模拟台风路径与实况最为接近,GBM、YSU和MYJ方案分别次之,ACM2和UW方案再次之,而QNSE方案最差;UW和QNSE方案模拟的最低气压以及MYJ和QNSE方案模拟的最大风速与观测最为接近;不同边界层方案均模拟出台风登陆阶段最低气压逐渐升高以及其升高速率在台风登陆后大于登陆前的特征,这与实况一致,但台风登陆前各方案模拟最低气压升高速度均大于实况,而台风登陆后却又不及实况;（3）Boulac方案模拟的24 h降水分布、强降水落区、结构、强度和各量级降水TS评分均最优,MYJ方案次之;而QNSE、UW和ACM2方案雨带向西北方向推进过快,各量级降水TS评分均较差;（4）综合台风路径、强度和降水模拟,Boulac和MYJ方案相对最优,其中Boulac方案在台风路径和降水模拟上更优,而MYJ方案在台风强度模拟上更优;YSU和GBM方案次之,而QNSE、UW和ACM2方案相对较差;（5）不同边界层方案计算的近地层潜热通量、感热通量显著不同,进而影响台风路径、强度、降水量模拟存在显著差异。比较而言,QNSE方案潜热通量相对异常偏高,MYJ和Boulac方案量值适中,其余方案相对偏低;QNSE方案感热通量相对略偏高,MYJ方案适中,其他方案则相对显著偏低;（6）不同边界层方案模拟降水区边界层热、动力结构显著不同,其中Boulac方案具有较明显优势,尤其是对日间边界层结构的模拟。 相似文献
6.
Abstract Airborne measurements in the atmospheric boundary layer (ABL) above the marginal ice zone (MIZ) on the Newfoundland Shelf reveal strong lateral variations in mean wind, temperature and the vertical fluxes of heat and momentum under conditions of cold, off‐ice wind. Flux measurements in (and near) the surface layer indicate that the neutral 10‐m drag coefficient depends on ice concentration, ranging from 2 × 10‐3 at 10% coverage to 5 × 10‐3 at 90%. Furthermore, cross‐ice‐edge transects consistently show increasing wind speed, temperature and heat flux in the off‐ice direction, but the momentum flux may either increase or decrease, depending on the relative importance of surface buoyancy flux and roughness. For the conditions encountered in this experiment, it appears surface wave maturity does not have a significant influence on the drag coefficient in fetch‐limited regimes near the ice edge. 相似文献
7.
In this study the role of atmospheric boundary layer schemes in climate models is investigated. Including a boundary layer scheme in an Earth system model of intermediate complexity (EMIC) produces only minor differences in the estimated global distribution of sensible and latent heat fluxes over land (upto about 15% of the net radiation at the surface). However, neglecting of boundary layer processes, such as the development of a well-mixed layer over land or the impact of stability on the exchange coefficient in the surface layer, leads to erroneous surface temperatures, especially in convective conditions with low wind speeds. As these conditions occur frequently, introducing a boundary layer scheme in an EMIC gives reductions in June-July-August averaged surface temperature of 1–2 °C in wet areas, to 5–7 °C in desert areas. Even a relatively simple boundary layer scheme provides reasonable estimates of the surface fluxes and surface temperatures. Detailed schemes that solve explicitly the turbulent fluxes within the boundary layer are only required when vertical profiles of potential temperature are needed. 相似文献
8.
基于大气化学模式WRF/Chem采用4种边界层方案（YSU,BL,MYJ和MYN3）模拟2015年全年天津地区细颗粒物质量浓度演变趋势,分析不同边界层方案对天津地区PM2.5质量浓度模拟和预报的影响,并构建多种边界层方案的集合预报产品,以期提高天津地区PM2.5质量浓度预报效果。结果表明:大气化学模式的4种边界层方案在空气质量模拟中均有较好的适用性,PM2.5模拟值与观测值相关系数达到0.76左右,晴空和大风天气BL方案表现较优,阴天和小风天气YSU和MYJ方案表现优于其他两种方案,综合所有过程没有任何单一方案具有显著优势。基于上述原因,该文开展多种边界层方案的天津空气质量集合预报试验,经过对2015年全年模拟值分析,多边界层方案和多气溶胶机制扰动的集合预报可以减小PM2.5质量浓度预报的相对误差和均方根误差,降低重污染天气预报的漏报率,提升空气质量等级预报能力,在计算资源得到保证的基础上,是一种可以提升数值模式PM2.5质量浓度预报能力的有效手段。 相似文献
9.
WRF模式对福建沿海风电场风速预测的效果分析 总被引：2，自引：1，他引：1
在WRF模式中选取不同的边界层、近地面层以及陆面过程参数化方案,设计了4种不同物理过程参数化方案,组合模拟福建沿海某测风塔站2010年1月1—11日和7月1—11日的逐时风速,将数值模拟结果和同期测风塔观测数据进行对比,以寻求最佳参数化方案。经分析比较,采用MYJ边界层方案,Monin-Obukhov近地面层方案以及Noah陆面过程方案的方案2模拟效果最好。使用该方案对2010年1月和7月的风速进行模拟,按不同风速级别分别对数值模拟结果进行对比分析,结果表明:方案2对6~15m/s风速模拟的平均相对误差在20%左右,能够满足风电预测的精度需求;而对0~6m/s风速模拟的误差相对较大,这可能是由于模式地形分辨率不够精细以及风塔所处海陆交界处的特殊位置,使低风速容易受地面扰动以及海陆气流影响所致。 相似文献
10.
Abstract The relationships between monthly anomalies of sea surface temperature (SST) and monthly anomalies of several surface wind parameters are examined using ten years of data from the mid‐latitude North Pacific Ocean. The wind parameters involve both u3 * and curl τ, where u* is the atmospheric friction velocity and τ the surface stress. These quantities are calculated from surface wind components analysed on synoptic (6‐hourly) maps. In order to examine the effect of synoptic disturbances, the time series of surface wind components at each grid point is high‐pass filtered (passing periods less than 10 days) and the above wind parameters are calculated from both filtered and unfiltered wind components. Two statistically significant relationships are found between monthly anomalies of SST and those of the various wind parameters. The first is a large coherent negative correlation between monthly anomalies of u3 * calculated from the high‐pass filtered wind components and month‐to‐month changes in the SST anomalies in the Central Pacific. This relationship is attributed to the production of turbulent vertical mixing in the ocean by synoptic disturbances in the atmosphere. The second relationship is a large positive correlation between curl τ calculated from the unfiltered wind components and SST anomaly changes in the Eastern Pacific. This relationship, which is opposite to that expected from Ekman pumping, is attributed to a negative association between the wind stress curl and the meridional advection of heat by the eastern boundary current system. It is shown that these atmospheric forcing mechanisms explain up to 10 per cent of the variance of monthly SST anomalies in a large part of the mid‐latitude North Pacific Ocean. This amount is in addition to, but certainly less than, that which can be explained by anomalous horizontal advection through statistical relationships with sea‐level pressure anomalies (Davis, 1976). 相似文献
11.
Abstract The effects of small‐scale surface inhomogeneities on the turbulence structure in the convective boundary layer are investigated using a high‐resolution large‐eddy simulation model. Surface heat flux variations are sinusoidal and two‐dimensional, dividing the total domain into a checkerboard‐like pattern of surface hot spots with a 500‐m wavelength in the x and y directions, or 1/4 of the domain size. The selected wind speeds were 1 and 4 m s‐l, respectively. As a comparison, a simulation of the turbulence structure was performed over a homogeneous surface. When the wind speed is light, surface heat flux variations influence the horizontally averaged turbulence statistics, including the higher moments despite the small characteristic length of the surface perturbation. Stronger mean wind speeds weaken the effects of inhomogeneous surface conditions on the turbulence structure in the convective boundary layer. Results from conditional sampling show that when the mean wind speed is small, weak mean circulations occur, with updraft branches above the high heat flux regions and down‐draft branches above the low heat flux regions. The inhomogeneous surface induces significant differences in the turbulence statistics between the high and low heat flux regions. However, the effect of the surface perturbations weaken rapidly when the mean wind speed increases. This research has implications in the explanation of the large‐scale variability commonly encountered in aircraft observations of atmospheric turbulence. 相似文献
12.
WRF模式对青藏高原那曲地区大气边界层模拟适用性研究 总被引：2，自引：0，他引：2
采用WRF（Weather Research and Forecasting）模式4种边界层参数化方案对青藏高原那曲地区边界层特征进行了数值模拟,并利用"第三次青藏高原大气科学试验"在青藏高原那曲地区5个站点的观测资料对模拟结果进行验证,分析不同参数化方案在那曲地区的适用性。研究表明,YSU、MYJ、ACM2和BouLac方案对2 m气温和地表温度的模拟偏低。BouLac方案模拟的地表温度偏差较小。通过对能量平衡各分量的对比分析发现,温度模拟偏低可能是向下长波辐射模拟偏低以及感热通量和潜热通量交换过强导致的。对于边界层风、位温和相对湿度垂直结构的模拟,局地方案的模拟效果均优于非局地方案。BouLac方案对那曲地区近地层温度、边界层内位温和相对湿度的垂直分布模拟效果较好。 相似文献
13.
G.S. Strong 《大气与海洋》2013,51(1):29-63
Abstract Diurnal changes in the local atmospheric moisture budget over the Canadian Prairies are computed using sequential radiosonde soundings from the 1991 Regional Evaporation Study (RES‐91). Previous attempts to estimate evapotranspiration with radiosonde data have used either similarity theory or a moisture budget, but have been confined to the boundary layer in either case. These studies, as well as semi‐empiric operational techniques which use surface‐based data, exclude the effects of moisture advection and energy exchanges between the boundary layer and the free atmosphere, assuming negligible effects on evapotranspiration. The moisture budget method adopted here includes horizontal advection explicitly, and treats vertical fluxes implicitly through a total tropospheric moisture budget. Comparison of the evapotranspiration estimates with those of other techniques are positive only when results are averaged over several days to weeks. While the advection estimates are a major source of error for the “daily” estimates in this particular study, it is shown that neither advection nor moisture flux through the boundary layer can be ignored in estimating daily evapotranspiration, regardless of the technique used. The results also suggest that evapotranspiration is more variable on a daily basis than other techniques have indicated. With an improved synoptic database now available for advection estimates, the moisture budget technique may provide an excellent ground‐truth method for fine‐tuning techniques for remote sensing of evapotranspiration, and could lead to improved parametrization schemes for both NWP models and GCMs. 相似文献
14.
Abstract Cloud‐motion winds measured from organized and disorganized cumulus cloud fields are compared with winds measured at collocated buoys in the northeast Pacific Ocean. Findings suggest that an automated tracking algorithm using GOES satellite imagery can measure cloud‐level winds at these latitudes. Comparisons with buoy wind measurements show that the influence of boundary‐layer stability should be included in estimates of surface winds from cloud‐motion data. 相似文献
15.
A Comparative Study and Evaluation of Mixing-Height Estimation Based on Sodar-RASS, Ceilometer Data and Numerical Model Simulations 总被引：1，自引：1，他引：0
C. G. Helmis G. Sgouros M. Tombrou K. Sch?fer C. Münkel E. Bossioli A. Dandou 《Boundary-Layer Meteorology》2012,143(3):507-526
The unmanned aerial system SUMO (Small Unmanned Meteorological Observer) has been used for the observation of the structure and behaviour of the atmospheric boundary layer above the Advent Valley, Svalbard during a two-week period in early spring 2009. Temperature, humidity and wind profiles measured by the SUMO system have been compared with measurements of a small tethered balloon system that was operated simultaneously. It is shown that both systems complement each other. Above 200?m, the SUMO system outperforms the tethered balloon in terms of flexibility and the ability to penetrate strong inversion layers of the Arctic boundary layer. Below that level, the tethered balloon system provides atmospheric profiles with higher accuracy, mainly due to its ability to operate at very low vertical velocities. For the observational period, a numerical mesoscale model has been run at high resolution and evaluated with SUMO profiles reaching up to a height of 1500?m above the ground. The sensitivity to the choice of atmospheric boundary-layer schemes and horizontal resolution has been investigated. A new scheme especially suited for stable conditions slightly improves the temperature forecast in stable conditions, although all schemes show a warm bias close to the surface and a cold bias above the atmospheric boundary layer. During one cold and cloudless night, the SUMO system could be operated nearly continuously (every 30?C45?minutes). This allowed for a detailed case study addressing the structure and behaviour of the air column within and above Advent Valley and its interaction with the local topography. The SUMO measurements in conjunction with a 10-m meteorological mast enabled the identification of a very stable nocturnal surface layer adjacent to the valley bottom, a stable air column in the valley and a strong inversion layer above the summit height. The results indicate the presence of inertial-gravity waves during the night, a feature not captured by the model. 相似文献
16.
V. P. Yushkov 《Russian Meteorology and Hydrology》2013,38(12):818-827
The wind speed shear in the case of stable stratification in the linear part of the profile spreading high above the surface layer of constant flows is studied using the data of long-term sodar measurements in the atmospheric boundary layer. The wind speed shear in this part remains almost invariable during several hours at the significant change in parameters of the Monin-Obukhov theory. The length of this linear part can be associated with the layer of the critical Richardson number. In the case of the pronounced temperature inversion (with the positive gradient of more than 1°C per 100 m), the wind speed profile is close to the linear function in the most part of the nocturnal mixing layer. Proposed is a scale characterizing the height of the surface layer of constant flows. 相似文献
17.
H. Linné B. Hennemuth J. Bösenberg K. Ertel 《Theoretical and Applied Climatology》2007,87(1-4):201-211
Summary Water vapour flux profiles in the atmospheric boundary layer have been derived from measurements of water vapour density fluctuations
by a ground-based Differential Absorption Lidar (DIAL) and of vertical wind fluctuations by a ground-based Doppler lidar.
The data were collected during the field experiment LITFASS-2003 in May/June 2003 in the area of Lindenberg, Germany. The
eddy-correlation method was applied, and error estimates of ±50 W/m2 for latent heat flux were found. Since the sampling error dominates the overall measurement accuracy, time intervals between
60 and 120 min were required for a reliable flux calculation, depending on wind speed. Rather large errors may occur with
low wind speed because the diurnal cycle restricts the useful interval length. In the lower height range, these measurements
are compared with DIAL/radar-RASS fluxes. The agreement is good when comparing covariance and error values. The lidar flux
profiles are well complemented by tower measurements at 50 and 90 m above ground and by area-averaged near surface fluxes
from a network of micrometeorological stations. Water vapour flux profiles in the convective boundary layer exhibit different
structures mainly depending on the magnitude of the entrainment flux. In situations with dry air above the boundary layer
a positive entrainment flux is observed which can even exceed the surface flux. Flux profiles which linearly increase from
the surface to the top of the boundary layer are observed as well as profiles which decrease in the lower part and increase
in the upper part of the boundary layer. In situations with humid air above the boundary layer the entrainment flux is about
zero in the upper part of the boundary layer and the profiles in most cases show a linear decrease. 相似文献
18.
利用WRF-Chem模式,采用3种边界层参数化方案 (YSU, MYJ和ACM2),针对1个晴空、静稳日 (2013年8月26日20:00—27日20:00(北京时)) 进行模拟,着重分析不同边界层参数化方案对夜间残留层形成及日出前后O3浓度垂直分布形式的模拟效果,并与固城站地面及垂直同步观测资料进行对比。结果表明:3种边界层参数化方案均能够模拟出温度及风速的区域分布形式以及风温垂直结构的变化特征;相比之下,MYJ方案模拟的夜间边界层高度较YSU方案和ACM2方案明显偏高,该对比结果可能是导致近地面污染物浓度模拟差异的重要原因;在夜间稳定层结至日出后稳定状态打破的边界层结构演变过程中,采用YSU方案和ACM2方案模拟的温度和风速垂直扩线形式与观测结果更为接近;同样采用非局地闭合的YSU方案和同时考虑局地和非局地闭合的ACM2方案,对于边界层高度内O3浓度垂直分布形式的模拟效果具有明显优势。 相似文献
19.
Richard A. Dobbins 《Boundary-Layer Meteorology》1977,11(1):39-54
Data from low-level soundings over Cambridge, U.S.A. were selected on the basis of an Ekman-like variation of the wind vector with altitude combined with evidence of a barotropic atmosphere. The method of geostrophic departure was used to determine the shear-stress distribution. The analysis yields the dimensionless properties of the barotropic Ekman layer under neutral and stable stratification. Some important results include: the geostrophic drag coefficient displays no dependence on the degree of static stability; the dimensionless height of the boundary layer decreases with increasing stability in agreement with the prediction of Zilitinkevich; the properties of the urban surface layer, where the roughness elements are multistory buildings, show no dependence on atmospheric stability under the moderate wind conditions which display the Ekman-like wind profile; and the directions of the horizontal shear stress and the vertical derivative of the velocity vector usually tend to be parallel only near the surface layer. Values of the two constants of the Rossby number similarity theory are found for the neutral barotropic Ekman layer at a surface Rossby number equal to 2 × 105. The implications of the work with respect to wind-tunnel simulation of the flow over models of urban areas are discussed. 相似文献
20.
根据2017、2019年7月塔克拉玛干沙漠腹地GPS探空和地面观测数据,利用位温廓线法等方法,对比分析了沙漠腹地夏季晴天和沙尘暴天气大气边界层结构变化特征。结果表明：晴天和沙尘暴天气大气边界层结构特征显著不同。晴天大气边界层各气象要素垂直分布较为均一,白天对流边界层深厚,高度接近5 km,夜间稳定边界层一般在500 m左右。沙尘暴天气边界层内位温和比湿垂直变化较小,风速较大,可达24.0 m/s,其白天对流边界层在1.5 km左右,夜间稳定边界层在1 km左右。晴天辐射强烈,地表升温迅速,湍流旺盛,是形成晴天深厚对流边界层的主要因素。大尺度天气系统冷平流的动力条件,以及云和沙尘减弱了到达地表的辐射强度是形成沙尘暴天气独特的大气边界层结构的主要因素。 相似文献