Boundary Layer Climate Research Articles

Accessibility of high temperature and high humidity for the mesofauna of a harsh habitat—the case of exposed tree trunks

I studied the boundary-layer climate of exposed tree trunks and demonstrated that bark dwelling arthropods can potentially profit from three benefits: (1) temperature and humidity strongly depend on microclimatic, as opposed to mesoclimatic, impacts. Hence, the arthropods can track high temperatures and high humidities by small-scale redistribution. (2) High absolute temperatures and high temperatures relative to the ambient mesoclimate are favored by opposite impacts. Hence, high temperatures are available—in one way or the other—most of the time. The same applies to high humidity due to low saturation deficit and due to influx of water vapor. (3) High temperature and high humidity are often mutually non-exclusive.

SE—Structures and Environment: Convective and Ventilation Transfers in Greenhouses, Part 2: Determination of the Distributed Greenhouse Climate

In this paper, the characterisation and modelling of the most relevant convective transfers contributing to the description of the distributed greenhouse climate are studied in detail. After a brief review of the equations governing flows within the greenhouse, the major theoretical approaches are recalled. The focus is on the study of the distributed climate which requires the equations governing the fluid flow and includes the turbulent transfer. The digitisation of these equations and their solution using computer fluid dynamics (CFD) software are presented. The measurement techniques associated with this approach are also presented, with special attention paid to the determination of air flows and climate patterns using advanced flow measurement techniques such as particle imagery visualisation (PIV) and sonic anemometry. A complete panorama of the studies pertaining to air movement inside the various greenhouse types is presented and it is particularly focused on recent studies dealing with plant–air interactions, particularly the leaf boundary layer climate and the air flows within the crop canopy. Despite the difficulties of modelling turbulent transfers, it is shown that simulations involving CFD software are becoming more realistic and able to describe with good accuracy the main features of the distributed climate inside the greenhouse. The major consequences of this progress are discussed with respect to improvement of the greenhouse climate through better plant protection and enhancements of greenhouse design and control.

Tomato leaf boundary layer climate: implications for microbiological whitefly control in greenhouses

The efficiency of mycoinsecticides as a means of whitefly control was examined under greenhouse conditions, focusing in particular on the high humidity levels favouring infection of the whitefly larvae infesting the under leaf surface. The theory of the moisture transfers occurring within the leaf boundary layer under laminar conditions is outlined and a model for the air temperature and humidity distribution is developed. Measurements were made of the humidity of the air in the boundary layer on the underside of leaves of a tomato crop grown in a full scale greenhouse. A considerable increase in relative humidity was detected 5 mm from the underside of the leaves, particularly during day-time when crop transpiration reached its maximum. These measurements were compared with the results of the model based on boundary layer theory and it was established that the data recorded were accurately predicted by the model during day-time from both the qualitative and quantitative points of view, but they were underestimated at night. The implications of these findings were examined and discussed in the context of the microbiological control of whiteflies under the conditions of confinement pertaining in various greenhouses and similar cultural systems. It is suggested that the concept of the microclimate pertaining in the leaf boundary layer developed here could be applied to the biological control of insects and microbial pathogens, in both protected and open crop growth systems.

Temperature cross-section features in an urban area

This study examines the connection between the built-up urban surface and near-surface air temperature. The studied city (Szeged, Hungary) is located on a low and flat flood plain with a population of 160,000. Data were collected by mobile measurements under different weather conditions between March 1999 and February 2000. The efforts have been focussed on investigating the maximum development of the urban heat island (UHI) along an urban cross-section. According to the results, the UHI intensity changed according to season and month, as a consequence of the prevailing weather conditions. The role of cloudiness and wind speed on the temporal variation of the largest UHI, which represents the increasing effect of Szeged on temperature, is clearly recognized during most of the time in the studied period. The seasonal profiles follow remarkably well the general cross-section of the typical UHI described by Oke (Oke, T.R., 1987. Boundary Layer Climates. Routledge, London) who defines its characteristic parts as ‘cliff’, ‘plateau’ and ‘peak’. The usefulness of the normalized values in the investigation is proved, the form of the seasonal mean UHI profile is independent of the seasonal climatological conditions, and is determined to a high degree by urban surface factors. As a conclusion, we suggest a modified model describing the metropolitan temperature variable for cities situated in simple geographical conditions: it is equal to the sum of components of the basic climate of the region and of the production of urbanization at the surface, where this last term is a multiplication of weather and urban surface factors.

Strategic guidelines for street canyon geometry to achieve sustainable street air quality

This paper is concerned with the motion of air within the urban street canyon and is directed towards a deeper understanding of pollutant dispersion with respect to various simple canyon geometries and source positions. Taking into account the present days typical urban configurations, three principal flow regimes “isolated roughness flow”, “skimming flow” and “wake interference flow” (Boundary Layer Climates, 2nd edition, Methuen, London) and their corresponding pollutant dispersion characteristics are studied for various canopies aspect ratios, namely relative height ( h 2/ h 1), canyon height to width ratio ( h/ w) and canyon length to height ratio ( l/ h). A field-size canyon has been analyzed through numerical simulations using the standard k- ε turbulence closure model. It is found that the pollutant transport and diffusion is strongly dependent upon the type of flow regime inside the canyon and exchange between canyon and the above roof air. Some rules of thumbs have been established to get urban canyon geometries for efficient dispersion of pollutants.

Integration of a numerical model and remotely sensed data to study urban/rural land surface climate processes

Simulation of urban/rural land surface climate processes using boundary layer climate models requires accurate input data with regard to surface thermal and radiative properties. The research reported here resulted in development of a procedure to integrate the satellite-derived surface biophysical parameters with a boundary layer climate model for simulating spatial surface energy exchange. The procedure was tested through spatial surface energy balance simulation of an urban/rural landscape in eastern Nebraska. The modeled surface temperature and net radiation were compared to those derived from the concurrent satellite data. The errors of the modeled surface temperature were small, and were mainly attributed to uncertainties in the estimation of surface moisture availability and satellite-derived surface radiant temperature. Modeled net radiation was also in agreement with the values calculated from satellite data. Modeled turbulent heat fluxes were in general agreement as compared to those reported in the literature, but the model tended to overestimate the latent heat flux for most rural land cover types. It was concluded that by incorporation of satellite-derived surface physical parameters into a boundary layer model, simulation of spatial land surface climate processes was much improved. The method and procedures developed from this study can be utilized in other boundary layer climate models.

The influence of cloud cover on the radiation budget, physical properties, and microwave scattering coefficient (σ°) of first-year and multiyear sea ice

Over sea ice, the shift from predominantly clear conditions in winter to persistent stratus cloud cover in late spring and early summer coincides with a dramatic increase in the net radiation balance at the sea ice surface. Transformation of the boundary layer climate and the geophysical properties of the snow covered sea ice result from this cloud-induced rise in surface energy balance. In this paper, in situ data from the Seasonal Sea Ice Monitoring the Modeling Site (SIMMS'93) experiment are used to examine the extent to which changes in surface radiation, sea ice physical and electrical properties, and microwave scattering are a function of clear versus cloudy conditions over first-year and multiyear sea ice types. The authors use the surface observations to drive a simple forward scattering model used to diagnose the potential mechanisms responsible for the observed changes in microwave scattering by the Earth Resources Satellite-1 (ERS-1). Their results indicate that under cloudy conditions the surface temperature increases because of the surplus in the longwave net radiative energy. This causes an increase in the surface temperature and formation of a temperature wave down through the snow volume into the ice surface. This increases the dielectric constant of the snow basal layer and ice surface over first-year sea ice because of the thin snow cover (relative to the thicker multiyear ice snow cover) and because of the temperature effect on brine volume. The observed increase in scattering is limited to very smooth first-year sea ice types. Models used to diagnose the principal scattering mechanisms suggest that the cloud cover effects the scattering either by creating a dielectrically rough basal layer in the snow volume near the ice surface or by increasing the scattering contribution from snow grains within the basal layer volume. Under either scenario the increase in scattering is small (/spl sim/5 dB) and is only detectable if the target presents a scattering magnitude less than about -20 dB.

Characteristics of snow cover duration across the northeast United States of America

The presence or absence of a snow cover affects a myriad of environmental and societal systems through its modification of the surface radiation balance and its ultimate impact on near-surface air temperatures. Daily snow cover data were collected for a network of 91 stations covering the northeast USA from Maine, south through to West Virginia. The snow cover data along with ancillary temperature, snowfall and precipitation data were used to investigate the characteristics of snow cover duration in this region and the effects of the snow cover on boundary layer climate variables for the snow cover seasons 1948–1949 through to 1987–1988. Results indicate that snow cover duration is variable in both space and time. The duration of a snow cover of 2·5 cm or greater varies from greater than 100 days in northern New England to less than 20 days across areas of Delaware, Maryland and West Virginia. Temporally, snow cover duration for the region as a whole was very short from the late 1940s through to the mid-1950s. From the late 1950s to the end of the period snow cover duration has varied around a consistent mean value. No long-term trends in snow cover duration are apparent in the record for the northeast USA. Principal components analysis and clustering techniques were utilized to isolate spatially coherent regions in which snow cover duration has varied similarly over the period of record. This analysis resulted in the identification of four snow-cover-duration regions across the northeast USA: including (i) the West Virginia area, (ii) the mid-Atlantic from southern New England through to western Pennsylvania, (iii) western and central New York and (iv) northern New England. Snow cover duration is shown to be highly associated with snowfall and temperature but not strongly related to total liquid precipitation. The intra-annual variability of snow cover duration is also investigated for each region. © 1997 Royal Meteorological Society.

HISTORICAL SNOW COVER VARIABILITY IN THE GREAT PLAINS REGION OF THE USA: 1910 THROUGH TO 1993

The duration of seasonal (September–May) snow cover over the central and northern Great Plains region of the USA has varied considerably during this past century. Annual and decadal fluctuations are embedded in a statistically significant trend toward greater seasonal snow cover, from 29 days in the early part of the century to 38 days in recent decades. The variability of snow cover duration also increased throughout the century, exhibiting the largest changes in a north-west-trending zone bisecting the region. Seasonal snowfall, temperature, and precipitation show fluctuations similar to those of snow cover; however, only snowfall has increased significantly since 1910. A post-1970 shift toward longer autumn (September–November) snow cover duration and shorter spring (March–May) duration has been accompanied by decreases in autumn maximum and minimum temperatures and increases in spring minimum temperatures. The reliance on snow cover for hydrological and agricultural purposes in this part of the country, the sensitivity of the boundary layer climate to snow cover conditions in the Plains, and the projections by global climate models for this region to become warmer and dryer as a result of increasing atmospheric concentrations of greenhouse gases, necessitate increased study and hence a better understanding of the variability of snow cover over the Plains.

HISTORICAL SNOW COVER VARIABILITY IN THE GREAT PLAINS REGION OF THE USA: 1910 THROUGH TO 1993

The duration of seasonal (September–May) snow cover over the central and northern Great Plains region of the USA has varied considerably during this past century. Annual and decadal fluctuations are embedded in a statistically significant trend toward greater seasonal snow cover, from 29 days in the early part of the century to 38 days in recent decades. The variability of snow cover duration also increased throughout the century, exhibiting the largest changes in a north-west-trending zone bisecting the region. Seasonal snowfall, temperature, and precipitation show fluctuations similar to those of snow cover; however, only snowfall has increased significantly since 1910. A post-1970 shift toward longer autumn (September–November) snow cover duration and shorter spring (March–May) duration has been accompanied by decreases in autumn maximum and minimum temperatures and increases in spring minimum temperatures. The reliance on snow cover for hydrological and agricultural purposes in this part of the country, the sensitivity of the boundary layer climate to snow cover conditions in the Plains, and the projections by global climate models for this region to become warmer and dryer as a result of increasing atmospheric concentrations of greenhouse gases, necessitate increased study and hence a better understanding of the variability of snow cover over the Plains.

Recent Progress in Mesoscale Climatology

Mesoscale climatological studies by Japanese scientists in the recent decade are reviewed. The spatially dense network of the Automated Meteorological Data Acquisition System (AMeDAS) has provided hourly meteorological information since 1976. This review paper focuses on studies, that utilized AMeDAS data on land/sea breeze, extended sea breeze, regional wind distribution, boundary layer climate, local front, and precipitation. In addition to this theme, studies on the winter monsoon are introduced.

Mesoscale vegetation-breeze circulations and their impact on boundary layer structures at night

The impact of well watered mesoscale wheat over mid—latitude arid areas on mesoscale boundary layer structures (MBLS) and climate has been investigated in the study,using a mesoscale biophysical, meteorological model (BM) developed in the current study. The BM is composed of six modules:mesoscale atmospheric module, soil module, vegetation module, snow-atmosphere interaction module, underlying surface meteorology module and subgrid scale flux parameterization module. The six modules constitute an interacting system by supplying boundary conditions to each other.

Growing season boundary layer climate and surface exchanges in a subarctic lichen woodland

Between June and August 1990, observations were made at two surface micrometeorological towers near Schefferville Quebec (54° 52′N, 66° 40.5′W), one in a fen and one in the subarctic lichen woodland, and at four surface climatological stations. Data from these surface stations were supplemented by regular radiosonde launches. Supporting measurements of radiative components and soil temperatures allowed heat and moisture balances to be obtained at two sites. The overall surface meteorological experiment design and results of micrometeorological observations made on a 30‐m tower in the lichen woodland are presented here. Seasonal variation in the heat and water vapor transport characteristics illustrate the marked effect of the late summer climatological shift in air mass type. During the first half of the summer, average valley sidewalls only 100 m high are sufficient to channel winds along the valley in the entire convective boundary layer. Channeling effects at the surface, known for some time at the long‐term climate station in Schefferville, are observed both at ridge top and in the valley, possibly the response of the flow to the NW‐SE orientation of valleys in the region. Diurnal surface temperature amplitude at ridge top (≈ 10° C) was found to be half that observed in the valley. Relatively large differences in precipitation among these stations and the climatological station at Schefferville airport were observed and attributed to the local topography. Eddy correlation observations of the heat, moisture and momentum transports were obtained from a 30‐m tower above a sparse (≈ 616 stems/ha) black spruce lichen woodland. Properties of the turbulent surface boundary layer agree well with previous wind tunnel studies over idealized rough surfaces. Daytime Bowen ratios of 2.5–3 are larger than those reported in previous studies. Surface layer flux data quality was assessed by looking at the surface layer heat balance. Diurnal and seasonal scale heat budget imbalances were found. We suggest that unmeasured surface heat storage may be responsible for some of the observed imbalance. The presence of the unexplained residual in this and other studies of energy balance over forests casts a note of caution on the interpretation of energy balance components obtained using heat residual methods.

An investigation of three-dimensional characteristics of flow regimes within the urban canyon

Canyon geometry is an important determinant characteristic airflow regimes observed within urban canyons. Three principal flow regimes are: “skimming” flow, “wake interference” flow and “isolated roughness” flow, following the nomenclature of Oke (1987, Boundary Layer Climates, 2nd edn, Methuen, London). The transition between flows is determined by canyon geometry and can be described in terms of threshold height/width ( H/ W) ratios for an arbitrary length/height ( L/ H) ratio. The determination of threshold H/ W ratios has previously relied on repeated wind tunnel experiments or repeated runs of a numerical model, with canyon geometry altered until the observed flow regime changes. The present numerical investigation of typical three-dimensional flows within urban canyons identifies the key parameters which mark transition between flow regimes. On this basis it is possible to establish the geometric thresholds between regimes with analysis of a horizontal cross-section of a few simulated flows.

BOOK REVIEWS

Book reviewed in this article:Boundary Layer Climates by T. R. Oke.Wind Atlas for the North Sea and Norwegian Sea by Ian Ashe Borresen.Weather at Sea. By David Houghton and Fred Saunders.

Human-induced changes in winter surface Albedo

The surface albedo of snow-covered deforested portions of the United States is approximately twice as high as when naturally vegetated. Moderate increases of up to about 0.20 are found for snow-covered farmland developed from former medium and tall grasslands. These changes may be considered representative of other populated regions in the middle latitudes. As a result, the winter surface albedo and, in turn, boundary-layer climates in these zones have become considerably more sensitive to the presence and duration of snow cover. Results are obtained from two models using satellite derived surface brightness fields, aerial albedo measurements of relatively undisturbed sites representative of past vegetation and global land-cover data sets. They refer to a block between 38° and 43°N latitude and 71° and 105°W longitude.

Book Reviews

Book reviewed in this article: The Interpretation of Ordinary Landscapes. Geographical Essays. D. W. Meinig (Ed.). Cities of Peasants. The Political Economy of Third World Urbanization. Bryan Roberts. European Settlement and Development in North America: Essays on Geographical Change in Honour and Memory of Andrew Hill Clark. James R. Gibson (Ed.). Boundary Layer Climates. T. R. Oke. A Political Geography of Africa. E. A. Boateng. Images of the Ohio Valley; A Historical Geography of Travel, 1740–1860. John A. Jukle. Patterns of Disease and Hunger: A Study in Medical Geography. Andrew Learmonth. …And the Desert Shall Rejoice: Conflict, Growth, and Justice in Arid Environments. Arthur Maass and Raymond L. Anderson. Water Management in the Yellow River Basin of China. Charles Greer. Sea-Level Changes: North-West England During the Flandrian Stage. M. J. Tooley.

BOUNDARY LAYER CLIMATES. By T. R. Oke. Methuen & Co. Ltd.

WeatherVolume 34, Issue 9 p. 370-370 BOUNDARY LAYER CLIMATES. By T. R. Oke. Methuen & Co. Ltd. First published: September 1979 https://doi.org/10.1002/j.1477-8696.1979.tb03470.xCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume34, Issue9September 1979Pages 370-370 RelatedInformation

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