Modelling Regional Scale Surface Energy Exchanges And Cbl Growth In A Heterogeneous, Urban-Rural Landscape

Over the last decade, simple models of theconvective boundary layer (CBL) have beensuggested as an approach to inferring regionallyaveraged land-air exchanges of heat, water and tracegases, because the properties of the CBL respond toan average of the underlying small-scaleheterogeneity. This paper explores the use of anintegral CBL method to infer regionally averagedfluxes in a landscape that has at least three majorsources of heterogeneity – irrigated andnon-irrigated rural land use and a large urban area(Sacramento region, California).The first part of the paper assesses the validity ofthe simple slab model of the CBL – this isintegrated forwards in time using local-scalemeasured heat and water vapour fluxes, to predictmixed-layer depth, temperature and humidity. Of thefour different CBL growth schemes used, the Tennekesand Driedonks model is found to give the bestperformance. Evaluation of the model performancewith different weightings of heat and water vapourfluxes based on the land use characteristics in theregion suggest that the source area for theboundary-layer sonde measurements is larger thanphysically-based estimates would suggest.Finally, measured time series of potentialtemperature are used to infer regionally averagedsensible heat fluxes using an integral CBL (ICBL)method. These ICBL fluxes are compared with thosemeasured at the local scale over the three land usetypes that comprise the region of interest. They arefound to be closest to the heat fluxes calculated byappropriately weighting the measured heat fluxes inthe source area calculated for the ICBL. We concludethat the integral CBL budget method providesadequate estimates of regionally-averaged surfaceheat fluxes in a landscape that is characterised bysurface types with distinctly different surfaceenergy budgets.     

Influence of Thermal Effects on the Wind Field Within the Urban Environment

Micrometeorological conditions in the vicinity of urban buildings strongly influence the requirements that are imposed on building heating and cooling. The goal of the present study, carried out within the Advance Tools for Rational Energy Use towards Sustainability (ATREUS) European research network, is the evaluation of the wind field around buildings with walls heated by solar radiation. Two computational fluid dynamics (CFD) codes were validated against extensive wind-tunnel observations to assess the influence of thermal effects on model performance. The code selected from this validation was used to simulate the wind and temperature fields for a summer day in a specific region of the city of Lisbon. For this study, the meteorological data produced by a non-hydrostatic mesoscale atmospheric model (MM5) were used as boundary conditions for a CFD code, which was further applied to analyze the effects of local roughness elements and thermodynamic conditions on the air flow around buildings. The CFD modelling can also provide the inflow parameters for a Heating, Ventilation and Air Conditioning (HVAC) system, used to evaluate the building energy budgets and to predict performance of the air-conditioning system. The main finding of the present three-dimensional analyses is that thermal forcing associated with the heating of buildings can significantly modify local properties of the air flow.     

Relationship of surface heat flux to microscale temperature variations: Application to boreas

The surface heat flux is normally parameterized in terms of the difference between the air temperature and the surface radiative temperature, or equivalently, the temperature computed from the surface energy balance. In this note, the relationship between the heat flux and the air-surface temperature difference is shown to be sensitive to the microscale variability of the surface radiation temperature caused by differences between the well-ventilated tree tops and less ventilated ground surface. This conclusion is based on surface and aircraft data collected during the Boreal Ecosystem-Atmosphere Study (BOREAS). For this case, the heat flux cannot be predicted by adjusting the thermal roughness height. As an alternative, the aerodynamic temperature can be related to a weighted average of the surface radtation temperature analogous to application of a simple canopy model. Here, the total heat flux is the sum of the heat fluxes from each individual surface type weighted by the area-fractional coverage.Part of this work was carried out in the Dept. of Earth and Atmospheric Sciences, St. Louis University and the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research.Part of this work was carried out in the Mesoscale and Microscale Meteorology Division of the National Center for Atmospheric Research.     

不同压力下部分饱和砂岩纵波衰减的理论及实验研究

深入了解不同压力、频率、流体含量和流体分布对岩石中弹性波传播特性的影响,对指导油气勘探开发具有重要意义.不同尺度下的波致流效应,是声波传播过程中产生速度频散和衰减的重要原因.本文以不同压力下水饱和区域改进的骨架模量为纽带,建立了联合介观尺度斑块饱和效应与微观尺度喷射流效应的部分饱和岩石声学理论模型.开展针对性声学实验,根据不同压力下部分饱和砂岩纵波速度测量数据,确定理论模型中的相关参数,从而实现对不同压力下部分饱和岩石纵波衰减的定量表征.在此基础上,通过理论与实验测量的纵波衰减的对比,分析不同压力、含水饱和度以及频率对岩石纵波衰减的影响.研究结果表明,在较低压力,较高含水饱和度以及较高频段,喷射流效应较强,因此新建模型计算的衰减明显大于斑块饱和模型的衰减.由于新建模型体现了斑块饱和效应与喷射流效应的综合影响,相比于斑块饱和模型,新建模型计算的部分饱和岩石的纵波衰减更接近于实测衰减,但受到岩石自身因素影响,新建模型计算的衰减仍略小于实测衰减.     

一个描述小尺度深凹地形大气边界层的数值模式及数值模拟试验

文中针对小尺度深凹地形（深凹露天矿）的特点,建立了一个高分辨率的、三维非静力的大气边界层数值模式,模式中采用能量（E-ε）闭合方案。利用该模式对小尺度深凹地形边界层的三维结构进行了较充分的研究,并且有选择地对影响边界层结构的因子进行了数值试验。     

海门一次F1级龙卷的多普勒天气雷达特征分析

用多普勒天气雷达、常规观测和地面加密观测资料对2011年7月13日发生在江苏南通海门市树勋镇的龙卷风过程进行了详细分析。得出:较长时间的不稳定层结的存在,较低的抬升凝结高度,较强的水平和垂直风切变以及地面干线的存在为龙卷风的发生发展提供很好的动力条件;底层冷空气的切入,较强的风切变易使单体发展更加旺盛。强回波中心高度和垂直积分液态含水量的下降,径向速度风场中气旋性涡旋的迅速发展是对龙卷风提前警戒的很好指标。龙卷风进行过程中,此系统为低位质心的对流系统,产生的天气是龙卷,伴随大风,与冰雹的高位质心对流系统有明显的区别。中气旋高度,最大切变高度的骤降,中气旋尺度的急剧收缩预示着龙卷的发生,为我们今后的龙卷风预警提供有利的参考。     

Three-dimensional Nonhydrostatic Numerical Simulation for the PBL of Open-pit Mine

A high-resolution,nonhydrostatic, three-dimensionalplanetary boundary-layer (PBL) model wasestablished considering the characteristic features of an open-pit mine, which is only (2 km × 2 km) wide and more than 100 m deep. The (E-) closure schemes was used in the model. Physical processes such as shortwave radiation of the sun and its uneven distribution on the ground,longwave radiation of earth-atmosphere systems, sensible heat and latent heat and heat flowing into the substrate of the earth, were involved in the model. Using this model PBL structures over this kind of microscale concave terrain (an open-pit mine) were fully studied and numerical experiments on the effects of parameters including H, depth of the mine, , slope angle of the mine, u, incidcent airflow velocity, and P, indicating shear of the initial velocity, on the PBL were also made. Finally, the evolution process of the PBL was simulated. The results showed that a characteristic and major feature of the PBL is re-circulation, which is greatly influenced by the topography of the mine and the meteorolgical conditions therein. Thermal and mechanical forcing play different but important roles in the evolution process of the PBL.