共查询到17条相似文献，搜索用时 954 毫秒
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基于2007年7月青海祁连站的野外加密探空资料,结合高分辨率的三维边界层模式,模拟研究了青藏高原东北边坡复杂地形条件下,边界层对流引起的干动力过程对该地区地形重力波产生及传播的影响机理。结果表明:在不同的背景场强迫下,高原东北边坡复杂地形上空对流和重力波的空间结构存在较大差异。当背景风向与山体垂直时,随着风速增加,山脊背风坡混合层顶附近大气不稳定能量加强,激发了下游区域较强的重力波信号,此时对流线组织性增强、重力波波列较长,高水汽含量的空气被波峰传输到较高的高度,为对流云发展提供了有利条件;当背景风向与山脊走向平行时,山顶上空对流发展旺盛,山脊背风坡混合层顶大气状态较稳定,激发的地形重力波信号较弱且波列较短,整个混合层顶附近水汽较少,对流云形成条件减弱;当背景大气浮力频率减小时,整个区域上空对流发展更加旺盛但组织性减弱,背风坡下游重力波向上传输的距离减小,信号不显著,混合层顶附近水汽分布均匀且变化幅度较小,有利于层状云发展。 相似文献
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本文给出了热带地区大气边界层顶的垂直速度,并以此对积云对流加热进行了参数化。用垂直二层楼式讨论了在积云对流加热作用下赤道波的线性稳定性性质。结果表明,在加热强度因子η=O(1)的情况下,由波动自身在大气低层的辐散辐合进行参数化的积云对流加热仅仅引起波动的频率修正,它对波动的不稳定增长率没有贡献;而由边界层旋转抽吸进行参数化的积云对流加热可直接引起波动的不稳定增长。当η>0.5时,由边界层旋转抽吸进行参数化的积云对流加热便使赤道波出现不稳定增长;重力型波动均存在有限波长的最大增长率;Rossby型波动的不稳定增长率远较重力型波动大。此外,由边界层旋转抽吸进行参数化的积云对流加热也会引起波动的频率修正。在此修正下,Kelvin波成为频散波. 相似文献
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《高原气象》2017,(2)
藏东南地区是青藏高原山地复杂下垫面的典型代表,其边界层大气过程异常复杂,给数值模拟和预报带来较大困难。大气边界层参数化方案的选取关系到能否正确模拟和预报局地大气过程。本研究采用中尺度模式WRF(Weather Research and Forecasting Model)对藏东南林芝地区对流和稳定边界层大气过程进行模拟,与2013年夏季"藏东南地区复杂下垫面地气交换观测实验"资料对比,研究ACM2,Boulac,M YJ,QNSE和YSU5种边界层参数化方案在青藏高原复杂下垫面的适用性。结果表明:对于水汽混合比垂直结构的模拟,Boulac和MYJ方案分别在模拟对流边界层和稳定边界层时能力最优。ACM 2方案最适宜藏东南复杂下垫面条件下的位温和风速垂直分布的模拟。各边界层参数化方案模拟对流边界层高度均较实际观测偏低,其中,QNSE方案模拟的边界层高度最接近观测。同一种边界层参数化方案对于夜间稳定边界层和正午对流边界层的模拟能力也不相同。该地区边界层风场受地形影响显著,风速较小,模拟的近地层风场较观测偏弱,MYJ和QNSE方案对近地层风场的模拟效果较好。 相似文献
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非均匀层结大气中的重力惯性波及其激发对流的物理机制 总被引：6，自引：0，他引：6
本文用WKBJ方法求解Boussinesq近似下的重力波方程,导出非均匀层结大气中重力惯性内波的一个守恒波作用量(称为广义波作用量)。根据广义波作用量守恒原理,着重讨论了重力惯性内波在发展过程中尺度变化的规律;在适当的条件下,重力波随着其尺度的变化而可能崩溃(或破碎),从而激发对流的发展。 相似文献
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将模式NP-89的陆面过程参数化方法应用到北京大学的三维复杂地形中尺度数值模式中, 得到了一个较理想的三维陆面过程及边界层模式, 利用这个改进的三维模式对20 km×20 km范围的山丘地形的陆面过程及边界层特征进行了数值模拟。模拟结果表明, 由于地形阻挡所造成山后的湍流较山前强, 进而造成近地面温度梯度和感热支出小, 最终造成山后的温度比山前的温度明显偏高; 而且随着山高的增加, 这种现象更加明显, 即该模式对山丘地形条件下的陆面过程和大气边界层特征具有较强的模拟能力; 模拟结果合理, 对研究过山气流形成机制、起伏地形大气边界层物理特征和污染物的扩散具有理论和应用价值。 相似文献
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Impact of the Diurnal Cycle of the Atmospheric Boundary Layer on Wind-Turbine Wakes: A Numerical Modelling Study 总被引：1，自引：1，他引：0
The wake characteristics of a wind turbine for different regimes occurring throughout the diurnal cycle are investigated systematically by means of large-eddy simulation. Idealized diurnal cycle simulations of the atmospheric boundary layer are performed with the geophysical flow solver EULAG over both homogeneous and heterogeneous terrain. Under homogeneous conditions, the diurnal cycle significantly affects the low-level wind shear and atmospheric turbulence. A strong vertical wind shear and veering with height occur in the nocturnal stable boundary layer and in the morning boundary layer, whereas atmospheric turbulence is much larger in the convective boundary layer and in the evening boundary layer. The increased shear under heterogeneous conditions changes these wind characteristics, counteracting the formation of the night-time Ekman spiral. The convective, stable, evening, and morning regimes of the atmospheric boundary layer over a homogeneous surface as well as the convective and stable regimes over a heterogeneous surface are used to study the flow in a wind-turbine wake. Synchronized turbulent inflow data from the idealized atmospheric boundary-layer simulations with periodic horizontal boundary conditions are applied to the wind-turbine simulations with open streamwise boundary conditions. The resulting wake is strongly influenced by the stability of the atmosphere. In both cases, the flow in the wake recovers more rapidly under convective conditions during the day than under stable conditions at night. The simulated wakes produced for the night-time situation completely differ between heterogeneous and homogeneous surface conditions. The wake characteristics of the transitional periods are influenced by the flow regime prior to the transition. Furthermore, there are different wake deflections over the height of the rotor, which reflect the incoming wind direction. 相似文献
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利用 1 998年第 2次青藏高原野外试验中的多普勒声雷达探测、低空探测观测以及卫星观测资料对高原大气边界层内的对流现象进行分析研究。声雷达探测到了高原边界层内有强烈的对流活动。这种对流泡中心的垂直速度可超过 1m/s,并存在尺度为 1个多小时的周期性 ,表现为中小尺度的有组织的湍流活动。高原边界层强对流得以发展和维持的物理机制是 :强辐射加热、复杂的地形地貌形成的下垫面不均一性造成边界层斜压性、边界层内的平流活动等 ,这些现象都有利于对流的发展。在这些条件的作用下 ,边界层内可以产生一系列有组织的强湍流大涡旋活动 ,这些大涡旋形成的热泡在向上发展的过程中有的能够发生合并 ,变得更大也更为猛烈 ,达到凝结高度以上可形成对流云 ,并发生充分的对流混合。成云过程凝结潜热释放更有利于对流运动进一步发展 ,使对流云逐步发展成更大的对流云团 ,从而产生卫星云图中显示的云团发展过程。 相似文献
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Large-Eddy Simulation of stable boundary layers (SBLs) has been considered particularly difficult, indeed perhaps impossible with present computational resources. Here we present a new series of successful simulations of SBLs over uniform, flat terrain, using an approach previously successful for neutral and convective conditions, and showing that essentially the same model can handle all three main dry types of atmospheric boundary layer. We consider both technical requirements for successful and accurate SBL simulations and the observed characteristics of the simulated SBL. We discuss the evolution (in some cases to quasi-steady states) and compare with theory and experimental data. Effects of static-stability on the flow are analyzed using one-point and two-point statistics. Results show the development of a shear-driven SBL, with little sign of distinctively wavelike motions. The flow statistics are found to be consistent with local scaling, and that framework is used to compare with other data and theoretical models. 相似文献
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Large-eddy simulations of the effects of hilly terrain on the convective boundary layer 总被引：1，自引：1，他引：1
Large-eddy simulations of the convective boundary layer are compared over hilly versus flat surfaces. Moderate values for the height and horizontal spacing of the hills were selected. Thermally-direct hill-valley circulations are induced by the uneven terrain, accounting for a significant fraction of the resolved energy in the boundary-layer eddies. The probability of upward eddy motion reaches up to 70% over the hilltops and down to 15% over the valleys. Above-average values of both subgrid scale turbulent kinetic energy and upward eddy heat transport are found above the higher terrain. Horizontal spectra of vertical motion are strongly biased toward the horizontal scales of the terrain. Vertical profiles of atmospheric variables obtained by horizontal averaging, however, exhibit no significant differences between hilly and flat terrain simulations. 相似文献
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Arctic outbreaks over the Canadian Western Plains during the late spring period frequently take the form of a cold east-northeasterly flow over a warmer, sloping surface. A mesoscale numerical model is developed in an attempt to simulate such circulations. Following Lavoie (1972) the atmospheric structure of the cold air mass is represented by three layers: a constant flux layer in contact with the earth's surface, a well-mixed planetary boundary layer capped by an inversion, and a deep stratum of overlying stable air. Averaging the set of governing primitive equations through the depth of the mixed layer yields predictive equations for the horizontal wind components, potential temperature, specific humidity, and the height of the inversion. Time-dependent calculations are limited to this layer by parameterizing the interactions between the mixed layer and both the underlying and overlying layers. Precipitation from limited convective clouds, and latent heat within the layer are included in terms of mesoscale variables.A 47.6-km by 47.6-km grid mesh of 1369 points covering the Canadian Prairie Provinces is used to represent the variables. The governing equations are solved numerically with terrain influences, surface roughness, temperature variations, and moisture fluxes allowed to perturb the mixed layer from its initial conditions until resultant mesoscale boundary-layer weather patterns evolve.The mean spring topographic precipitation pattern is successfully reproduced by the simulated late spring upslope flow with limited convective precipitation. Mesoscale planetary boundary-layer weather patterns appear to exert a dominant control over the location and intensity of perturbations in the spring precipitation pattern. The elimination of surface heating significantly reduces the area and intensity of precipitation. A case study based on observed initial conditions showed that the model could reproduce a persistent limited convective precipitation pattern maintained by upslope flow and that a low-level trough exerts a marked influence on the location and the intensity of the precipitation. 相似文献
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Analytical solutions of convective waves in the convective boundary layer (CBL) were obtained with two-layer linearized atmospheric
equations including Rayleigh friction, which represents the turbulent viscosity in the lower CBL. The analytical model shows
that the interaction between the convection in the lower layer and gravity waves in the upper layer is one of the causes for
the formation of convective bands. The flow and temperature fields obtained by the analytical model present the main characteristics
of convective bands found in field observations. We have also investigated the influences of atmospheric conditions on the
characteristics of the bands. Results accord with previous knowledge about these phenomena. 相似文献
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This paper reviews the main theoretical progress of mesoscale weather dynamics since 2003, including： （1） The dynamic mechanisms of balanced and unbalanced flow are applied to study the genesis and development problems of mesoscale circulation. The symmetric instability and transverse-wave instability are analyzed in line and vortex atmosphere convection, and further research has been done on nonlinear convective symmetric instability. The interaction between forced convection and unstable convection and the wave characteristics of mesoscale motion are also discussed. （2） Intermediate atmosphere dynamic boundary layer models are developed. The complicated nonlinear interaction is analyzed theoretically between the atmospheric boundary layer and the free atmosphere. The structure of the topography boundary layer, atmospheric frontogenesis, the structure and circulation of the low-level front and other boundary layer dynamic problems are discussed. （3） The formation and development of meso-β-scale rainstorms under the background of the East-Asia atmosphere circulation are diagnosed with the variation of MPV （moist potential vorticity） anomalies. And some physical vectors are modified and applied in the moist atmosphere. 相似文献