Numerical modeling of the atmospheric boundary layer over a hilly landscape

Summary A model for calculating the wind, turbulent exchange coefficients and a modification of the initial temperature over a hilly terrain is described. The paper mainly deals with a numerical realization of the model equations. Some features of the splitting method are discussed in detail. A special version of the splitting method suitable for solving the atmospheric boundary layer is described.

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Резюме Оnuсывaеmся мо?rt;ель ?rt;ля рaсчеma скоросmu веmрa, козффцuенma mурбуленmно?rt;о обменa u uзмененuŭ нaчaльнoŭ mемnерamуры воз?rt;ухa нa?rt; холмuсmым рельефом. Основное внuмaнuе у?rt;еляеmся меmо?rt;aм чuсленно?rt;о рещенuя. Деmaльно рaссмamрывaюmся некоmорые злеменmы меmо?rt;a рaсщеnленuя. Прuво?rt;umся сnецеnленuя. Прuво?rt;umся сnецuaльнaя версuя меmо?rt;a рaсщеnленuя, у?rt;обнaя ?rt;ля uзученuя amмосферно?rt;о nо?rt;рaнuчно?rt;о слоя.

     

On spectral extinction of solar radiation within a tropical atmospheric boundary layer

Helicopter measurements of solar irradiance and meteorological data within the atmospheric boundary-layer were made in Lagos during February 1979. Filter samples of aerosols were collected both during flight in February 1979 and at ground level in December 1978. Profile data on spectral aerosol optical depth were obtained and, from these, the aerosol extinction coefficient at two wavelengths (0.5 and 0.88 m) were calculated. Precipitable water was low and was contained mainly within the 750 m layer above ground, suggesting the establishment of a deep unstable boundary layer. Calculated channel energy depletions by aerosols show that, within the first 750 m of the surface, the 0·88 m might be more efficient at attenuating solar energy than 0·5 m. The lagoon (maritime) aerosol sample indicated a more monodisperse size-distribution than the dusty harmattan aerosol sample.     

Effects of wind shear on the atmospheric convective boundary layer structure and evolution

The article reviews past accomplishments and recent advances in conceptual understanding, numerical simulation, and physical interpretation of the wind shear phenomena in the atmospheric convective boundary layer.     

The effect of turbulent flow structures on saltation sand transport in the atmospheric boundary layer

The effect of turbulent flow structures on saltation sand transport was studied during two convective storms in Niger, West Africa. Continuous, synchronous measurements of saltation fluxes and turbulent velocity fluctuations were made with a sampling frequency of 1 Hz. The shear stress production was determined from the vertical and streamwise velocity fluctuations. The greatest stress-bearing events were classified as turbulent structures, with sweep, ejection, inward interaction, and outward interaction described according to the quadrant technique. The classified turbulent structures accounted for 63·5 per cent of the average shear stress during the first storm, and 56·0 per cent during the second storm. The percentage of active time was only 20·6 per cent and 15·8 per cent, respectively. High saltation fluxes were associated with sweeps and outward interactions. These two structures contribute positively (sweeps) and negatively (outward interactions) to the shear stress, but have in common that the streamwise velocity component is higher than average. Therefore, the horizontal drag force seems primarily responsible for saltation sand transport, and not the shear stress. This was also reflected by the low correlation coefficients (r) between shear stress and saltation flux (0·12 and 0·14, respectively), while the correlation coefficients between the streamwise velocity component and saltation flux were much higher (0·65 and 0·57, respectively). © 1998 John Wiley & Sons, Ltd.     

Development and evaluation of airborne microwave refractometer for studies on atmospheric tropical boundary layer radiorefractive index

Observations of high-resolution data on radio refractivity were obtained by the airborne microwave refractometer over the Indian sub-continent (a tropical country) from 1971 to 1988. Detailed vertical and horizontal distributions of radio refractivity on a near-real-time basis in the atmospheric boundary layer were determined. Radiosonde observations cannot detect the thin refractivity gradients which characterize the propagation environment in this low-altitude region. This knowledge is required to design reliable and efficient communication systems for strategic, tactical and operational needs. However, the results demonstrate the layer structures and the variability of the boundary layer in time and space. The radio refractive effects on electromagnetic propagation and the future direction of radio refractivity fine-structure measurements are discussed.     

Differences in the concentrations of atmospheric trace gases in and above the tropical boundary layer

Weekly air samples were collected at Cape Kumakahi (0 km) and at nearby Mauna Loa Observatory (3.4 km) which is above the boundary layer. EC/GC and GC/FID techniques were used to measure CH₃I, CHCl₃, CO and CH₄, which are largely natural in origin, and C₂Cl₄, CCl₄, CH₃, CCl₃, CCl₃F (F-11), CCl₂F₂ (F-12), CHClF₂ (F-22) and C₂F₃Cl₃ (F-113), which are due to anthropogenic activities. It was found that all these gases are significantly (0.05) more abundant in the boundary layer than above it.     

An analytical model for the altitude variation of aerosol number densities in the coastal atmospheric boundary layer

A simplified one dimensional analytical model to describe the altitude variation of aerosol number densities in the atmospheric boundary layer during clear sky and calm/moderate wind conditions, over a plane terrain on the tropical seacoast, is developed. The analytical model is mainly defined by two parameters, the aerosol mixing height and the exponential rate of decrease above the mixing height. The effect of surface impaction is also taken into account in this model. It is seen that this parameter varies with season. By matching the analytical profile with the observed mean profile in each month, the surface source strength has been estimated. The seasonal and inter-annual variations of this parameter are studied.     

The diffusive boundary layer of sediments: oxygen microgradients over a microbial mat

Oxygen microelectrodes were used to analyze the distribution of the diffusive boundary layer (DBL) at the sediment-water interface in relation to surface topography and flow velocity. The sediment, collected from saline ponds, was covered by a microbial mat that had high oxygen consumption rate and well-defined surface structure. Diffusion through the DBL constituted an important rate limitation to the oxygen uptake of the sediment. The mean effective DBL thickness decreased from 0.59 to 0.16 mm as the flow velocity of the overlying water was increased from 0.3 to 7.7 cm s-1 (measured 1 cm above the mat). The oxygen uptake rate concurrently increased from 3.9 to 9.4 nmol cm-2 min-1. The effects of surface roughness and topography on the thickness and distribution of the DBL were studied by three-dimensional mapping of the sediment-water interface and the upper DBL boundary at 0.1-mm spatial resolution. The DBL boundary followed mat structures that had characteristic dimensions > 1/2 DBL thickness but the DBL had a dampened relief relative to the mat. The effective surface area of the sediment-water interface and of the upper DBL boundary were 31 and 14% larger, respectively, than a flat plane. Surface topography thereby increased the oxygen flux across the sediment-water interface by 49% relative to a one-dimensional diffusion flux calculated from the vertical oxygen microgradients.     

北京城市化对夏季大气边界层结构及降水的月平均影响

为克服针对一次或几次天气过程研究城市化对边界层结构及降水影响的局限性,尝试研究北京城市化对夏季大气边界层结构及降水的月平均影响,本文首先总结了2006年8月份的主要天气过程,分析了气象站观测的10 m高度风速、2 m高度气温、2 m高度比湿和24 h降水的月平均分布特征,然后利用WRF/Noah/UCM模拟系统,进行了该月30个个例的高分辨率数值模拟及检验分析,并通过多组不同城市化情景的敏感性试验对比分析了城市化对夏季大气边界层结构及降水的月平均影响.研究表明:本文所用对高分辨率数值模拟结果进行月平均的方法可以较合理地模拟出城市化对大气边界层结构及降水的影响,并再现观测到的各站风频差异.8月份,北京城市化对气温的影响高度白天约为800 m,近地面气温升高1℃以上;夜间约为200 m,对近地面气温的影响达到最大(1.4℃以上).白天,城市化使城市及下风向的一些区域风速略有减小;夜间,城市及周边区域200 m以下风速明显减小,且在100 m左右高度处风速减小最明显,减小达0.8 m/s以上.城市化白天使700 m以下比湿减小,近地面处减小达1.2g/kg以上,夜间使近地面空气比湿略有减小.城市化对城市区域平均降水量的影响随城市发展的不同阶段而不同.初步模拟分析表明, 北京城市化已使上风向区域以及城区三环以内降水量减少,海淀和昌平降水明显增加.     

Upward flux of RaB and RaC in the planetary boundary layer as controlled by atmospheric microstructure

Summary Vertical mixing and transport processes are studied, and their variation as influenced by atmospheric fine-structure conditions investigated, using data gathered from simultaneous measurements of RaB and RaC concentration in the ambient air at three mountain stations located close to each other horizontally, but at markedly differing levels (730, 1780 and 2960 m). RaB was used as a tracer on account of the high sensitivity to variations of vertical-mixing activity evidenced by RaB abundance figures. Strong inversions between 700 and 2500 m a.s.l. create a zero condition at the higher level, where only 0.1% of the low-level RaB reading obtains; active turbulent mixing, on the other hand, leads to nearly equal RaB readings at the two levels. The vertical gradient of concentration of RaB is used to compute mean vertical-mass-exchange coefficients; the latter are studied in their relation to atmospheric structure characteristics. Statistical studies indicate that the barring effect of inversions is related solely to the magnitude of the inverse temperature gradient. Problems of radioactive equilibrium RaB-RaC are discussed, and the significance of aerosol particle size taken into consideration.

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Zusammenfassung Simultane Messungen der RaB- und RaC-Konzentration der Luft an 3 Bergstationen von geringem horizontalem Abstand aber mit relativ grossen Höhenunterschieden (Stationsniveau rund: 700, 1800 und 3000 m a.s.l.) werden benutzt um die vertikalen Mischungs-und Transportvorgänge und ihre Abhängigkeit von der atmosphärischen Feinstruktur zu studieren. Die RaB-Konzentration der Luft reagiert nämlich sehr empfindlich auf Schwankungen der Austauschintensität. Im Falle einer kräftigen Inversion zwischen 700 und 2500 m a.s.l. fällt die RaB-Konzentration über dieses Höhenintervall hinweg auf 0,1% des Basiswertes ab, bei turbulentem Austausch herrscht fast Konzentrationsgleichheit. Aus den vertikalen RaB-Konzentrationsgradienten werden mittlere vertikale Austauschkoeffizienten berechnet und diese zur atmosphärischen Struktur in Beziehung gesetzt. Es zeigte sich dabei, dass die Sperrwirkung einer Inversion nur durch die Steilheit der Temperaturänderung im Inversionsbereich bedingt ist. Probleme des radioaktiven Gleichgewichts zwischen RaB und RaC werden diskutiert. Auch die Bedeutung der Aerosolpartikelgrösse wird mit in Betracht gezogen.

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Paper presented at the XIVth General Assembly of the IUGG, meeting of the ICACR, Luzern, October 1967. The work has been sponsored by European Research Office, US Army, and Department of Defence of FRG     

民航气象观测的中国中东部大气边界层廓线数据的评估与应用

本文从民航气象报告(AMDAR)数据库中提取了2008—2019年期间我国中东部18个机场飞机起飞和降落期间的大气边界层(ABL)廓线数据,并利用常规探空数据评估了不同季节和高度范围的AMDAR数据准确性及其随探空站与机场距离和飞行状态的变化.与常规探空数据相比,低层(P>850 hPa)的AMDAR温度和风分量的均方根误差(RMSE)均比较高层(850~500 hPa)小,且各高度层上的温度和风分量的RMSE都随间隔距离的增加而增大.相对而言,飞行状态对AMDAR数据准确性的影响很小.在间隔距离小于50 km且P>850 hPa高度层范围内,温度、纬向风和经向风的平均RMSE分别为0.68~0.83 K、1.48~1.62 m·s^-1和1.73~1.81 m·s^-1.相比于RMSE,对应的平均偏差都显著更小,且随间隔距离无明显变化.数据应用示例表明,AMDAR廓线数据由于其较高的时间分辨率,不仅可以反映ABL结构的日变化特征,还可用于研究ABL局地环流特征.基于18个机场AMDAR廓线数据分析发现,我国远内陆、干燥地区大气边界层高度(ABLH)具有较强的日变化,尤其是在春夏两季,而沿海和近内陆地区ABLH的日变化强度和季节差异都较小.

     

The groundwater–land-surface–atmosphere connection: Soil moisture effects on the atmospheric boundary layer in fully-coupled simulations

This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can simulate spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-h period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land-surface temperatures trigger shifts in wind behavior, such as during early morning surface heating.     

The vertical distribution characteristics of integral turbulence statistics in the atmospheric boundary layer over an urban area in Beijing

Turbulence data(2008–2012) from a 325 m meteorological tower in Beijing, which consisted of three layers(47,140, and 280 m), was used to analyze the vertical distribution characteristics of turbulent transfer over Beijing city according to similarity theory. The conclusions were as follows.(1) Normalized standard deviations of wind speeds/ui * were plotted as a function only of a local stability parameter. The values under near-neutral conditions were 2.15, 1.61, and 1.19 at 47 m, 2.39, 1.75,and 1.21 at 140 m, and 2.51, 1.77, and 1.30 at 280 m, showing a clear increase with height. The normalized standard deviation of wind components fitted the 1/3 law under unstable stratification conditions and decreased with height under both stable and unstable conditions.(2) The normalized standard deviation of temperature fitted the.1/3 law in the free convection limit, but was quite scattered with different characteristics under near-neutral conditions. The normalized standard deviations of humidity and the CO2 concentration fitted the.1/3 law under unstable conditions, and remained constant under near-neutral and stable stratification. The normalized standard deviation of scalars, i.e., temperature, humidity, and CO2 concentration, all increased with height.(3) Compared with momentum, and the water vapor and CO2 concentrations, the turbulence correlation coefficient for heat was smaller under near-neutral conditions, but larger under both stable and unstable conditions. A dissimilarity between heat, and the water vapor and CO2 concentrations was observed in urban areas. The relative correlation coefficients between heat and each of momentum, humidity, and CO2 concentration(|rwT/ruw|, |rwT/rwc| and |rwT/ruq|) in the lower layers were always larger than in higher layers, except for the relative correlation coefficient between heat and humidity in an unstable stratification. Therefore, the ratio between heat and each of momentum, humidity, and CO2 concentration decreased with height.     

耗能减震技术研究及应用的新进展

本文总结了耗能减震技术近年来的研究与应用情况,主要包括各种新型耗能减震装置的原理、性能及应用。文中介绍了有关国家耗能减振技术标准发展的情况,提出了该项技术今后应加强研究的若干问题,并预测了其发展前景。     

Recent advances in the chemistry and properties of atmospheric nucleants: a review

Summary A survey is carried out of recent progress in the investigation of weather-active atmospheric nucleants. Emphasis is placed on the work date during the last decade, and some resulting implications are discussed.     

Effect of the annular solar eclipse of 15 January 2010 on the lower atmospheric boundary layer over a tropical rural station

This paper documents the effect of the annular solar eclipse of 15 January 2010 on the lower atmospheric boundary layer dynamics over a complex terrain environment at Gadanki (13.5°N, 79.2°E,) using a suite of instruments namely automatic weather station, mini boundary layer mast (15 m), Doppler SODAR, GPS radiosonde and ozonesonde observations. The net heating rates are estimated using radiative transfer algorithm before, during and after the eclipse. Effect on soil temperature is seen clearly up to 20 cm depth and at all the levels up to 15 m. Decrease in the thermal plume level, a dip in the surface layer and a strong vertical downdrafts (subsidence) are noticed during the peak eclipse. Upper layer winds did not show any variation during the eclipse. It is also found to have pronounced effect on all the surface meteorological parameters for a two-day period.