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  • 1
    Electronic Resource
    Electronic Resource
    Wind tunnel and field testing of a simple sand catcher for sampling inhomogeneously saltating sand in desertified environments (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 43 (1996), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Problems of vertical alignment and vibrations of disposable coffee cups used in a modified version of the De Ploey saltating sand catcher were solved. The new version was tested in a sediment wind tunnel. Its catches appeared linearly related to amounts of eroded sand, largely independent of wind speed and wind direction, and depended logarithmically on height. The catch efficiency may therefore be taken to be approximately independent of wind speed and direction. The instrument performed well under conditions of inhomogeneously saltating sand in a strongly desertified environment in Central Sudan. Use and results show the improved simple catcher to be easy to assemble, reproducible and cheap, suitable for multipoint use to cover all inhomogeneities in outdoor saltating sand fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.1996.d01-24.x
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  • 2
    Electronic Resource
    Electronic Resource
    Campbell-stokes data for radiation calibration purposes in East Africa (1981)
    Springer
    Meteorology and atmospheric physics 29 (1981), S. 99-109 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Es wird gezeigt, daß auf Grund von Angaben in der Literatur die Konstanten für die statistische Beziehung zwischen der Globalstrahlung und der Sonnenscheindauer für Ostafrika nun hinreichend gesichert angegeben werden können. Werden die Unterschiede der Fehler bei der Datenerfassung mit anderen einfachen Meßmethoden der solaren Einstrahlung berücksichtigt, kann gezeigt werden, daß Campbell-Stokes Meßwerte gut geeignet sind zur Überprüfung, Kalibrierung oder zum zeitweisen Ersatz sonstiger Meßmethoden, wo in den Tropen keine geeichten Pyranometer verfügbar sind. Ein Beispiel wird gegeben für Gunn-Bellanis.
    Notes: Summary It is shown from literature research that constants in the statistical relationship between total global solar radiation and sunshine duration are now well established for East Africa. Taking into account the differences in data collection errors with other simple methods of solar radiation determination, we show Campbell-Stokes data to be suitable for checking, calibrating or temporarily replacing these other methods where no calibrated pyranometers are available in the tropics. An example is given for Gunn-Bellanis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02278194
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  • 3
    Electronic Resource
    Electronic Resource
    Understanding the Piche evaporimeter as a simple integrating mass transfer meter (1981)
    Springer
    Flow, turbulence and combustion 37 (1981), S. 213-223 
    Details
    ISSN: 1573-1987
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Results are presented of a comparison of measured and calculated evaporation rates of the Piche evaporimeter under indoor and outdoor (within a meteorological screen) conditions. In both cases, application of mass transfer formulae in use for horizontal (turbulent) flow to the evaporating blotting paper of the instrument yield very good results under pure forced convection conditions. For mixed convection regimes, comparisons using either pure free (combined heat and mass transfer) or pure forced convection equations give as expected too low calculated values. Reasons for such differences with measured values are reviewed. Our forced convection results confirm that main stream turbulence is only of influence on mass transfer to a zero incidence flow in combination with pressure gradient (bluff body) effects, which under our conditions appear to be absent around the Piche surfaces. The same results prove absence of any influence of the particular temperature distribution over the blotting paper on the mass transfer. The understanding and importance of these conclusions in relation to the use of the Piche evaporimeter as a simple integrating mass transfer meter under actual farming conditions are discussed. The importance to obtain such mass transfer data is explained in the introduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00951248
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  • 4
    Electronic Resource
    Electronic Resource
    Wind Regimes Windward of a Shelterbelt Protecting Gravity Irrigated Crop Land from Moving Sand in the Gezira Scheme (Sudan) (1999)
    Springer
    Theoretical and applied climatology 62 (1999), S. 221-231 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary  The work reported on was part of a more comprehensive study dealing with threatening sand movement towards the northwestern part of the Gezira irrigation scheme, Sudan. An irrigated sand blocking shelterbelt Eucalyptus microtheca is used to prevent canals and gravity irrigated crop land to be further affected. The objective of this paper is to report on the wind data that were obtained, mainly windward of this belt, and to deal with their implications and those of the belt characteristics and deposited sand in interaction with the wind for combating local sand movements and further desertification. Outside the influence of the belt, wind speed over eroded land was increasingly higher than that over irrigated land with the growth of cotton. Both these values were considerably higher than those reported from the nearest meteorological stations. The two prevailing winds, of which the summer SW wind was perpendicular to the belt, had consistent annual patterns during three years of observation. Also the diurnal patterns were very reproducible. Wind speed within the belt, at 1 m height, showed fast reduction inwards above the deposited sand. Efforts to control moving sand in the source area should be joined with those made at the borders of agricultural land.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007040050086
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  • 5
    Electronic Resource
    Electronic Resource
    Evaporation from the reservoir of the High Aswan Dam, Egypt: A new comparison of relevant methods with limited data (1997)
    Springer
    Theoretical and applied climatology 56 (1997), S. 57-66 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Previous estimates of average annual evaporation from the lake formed by the High Dam at Aswan, Egypt, fall in the range from 4.65 mm d−1 to 7.95 mm d−1. The difference between these limits, more than 7 billion m3 yr−1 at the highest storage level, is nearly one-eighth the share by treaty of Egypt, and more than one-third of the share of the Sudan. It is also more than the estimated increase of the annual water need for Egypt between 1990 and 2000. This state of affairs renders proper management of the river flow for the sake of Egypt and the Sudan quite difficult. This paper compares the relevant methods of estimating evaporation from the limited data available. These methods are:water-balance, energy budget, bulk aerodynamic (Dalton),combination (Penman) andComplementary Relations Lake Evaporation (CRLE) model (Morton). The new estimates have a much narrower range, from 5.70 mm d−1 to 7.05 mm d−1, or only a bit more than 4% of the annual Nile flow below the High Aswan Dam. The average of these annual estimates of evaporation, after excluding the bulk aerodynamic method because of its severe limitations, is 6.0 ± 0.3 mm d−1 or 20% less than the 7.5 mm d−1 adopted by the irrigation authorities in Egypt and the Sudan. This difference corresponds to 3 billion m3 yr−1 at the highest storage level or more than 5% of the annual outflow from the reservoir. Even when the higher estimates from the bulk aerodynamic method and from the Penman method with its usual wind function are included, the new average is still 15% less than the figure of 7.5 mm d−1. The monthly distribution of the annual evaporation varies more widely with the method applied. Similar comparative studies in future, aiming at obtaining improved estimates of evaporation, require all the data relevant to all the methods to be collected properly for a common period of several years at relatively stable lake level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00863783
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  • 6
    Electronic Resource
    Electronic Resource
    An improved radiation protected differential thermocouple psychrometer for crop environment (1976)
    Springer
    Theoretical and applied climatology 24 (1976), S. 177-187 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Es werden Verbesserung und Verwendung eines thermoelektrischen Psychrometers beschrieben. Besondere Beachtung wird der Verbesserung der Form des Instrumentes und den die Eichung betreffenden Überlegungen gewidmet. Das Instrument ist speziell für Messungen in Vegetationsbeständen geeignet.
    Notes: Summary Choice, improvement and field use of a differential thermocouple psychrometer are described. Special attention is paid to improved design features and considerations regarding calibration. The instrument is specially suitable for within crop measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02243338
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  • 7
    Electronic Resource
    Electronic Resource
    Precipitation measurements above a maize crop (1976)
    Springer
    Theoretical and applied climatology 24 (1976), S. 95-108 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Wegen der Bedeutung von Messungen des flüssigen Niederschlages über Vegetationsbeständen bei manchen Feldstudien wird in dieser Arbeit eine Interpretation und Fehlerschätzung für Niederschlagsmessungen über Maisfeldern gegeben. Bei Messungen mit Regenmessern nach Snowdon von 20 bis 40 cm Höhe über Maisfeldern scheinen die Fehler nicht größer zu sein als bei Messungen mit einem 40 cm-Snowdon-Regenmesser über Gras, sobald das Windfeld sich wieder an die neuen Rauhigkeitsverhältnisse angeglichen hat und die Turbulenz nicht auf andere Art vergrößert worden ist. Die Unterschiede, die zwischen den Angaben von richtig und nichtrichtig exponierten Regenmessern gefunden wurden, sind zufolge der Tatsache, daß in den Niederlanden die Wachstumsperiode von Mais gerade in die Zeit fällt, in der der Wind den kleinsten Einfluß auf Regenmesser hat, relativ klein. Vergleichsmessungen mit einem 40 cm-Snowdon-Regenmesser über Gras und einem Bodenregenmesser nach Snowdon, der nach den letzten WMO-Empfehlungen aufgestellt ist, scheinen für eine endgültige Fehlerschätzung unerläßlich zu sein.
    Notes: Summary Because of the importance in some field studies of above crop liquid precipitation measurements, in this article an interpretation and an error assessment of above maize precipitation measurements are given. With Snowdon rain gauges from 20 to 40 cm above the maize, errors seem not to be higher than with a 40 cm Snowdon gauge above grass, as long as the wind field is again adjusted to new roughness conditions and turbulence is not enhanced otherwise. Differences found between gauges correctly and incorrectly exposed were relatively small due to the fact that the maize growing season falls clearly within the period of lowest influence of wind on rain gauge catch in the Netherlands. The use of comparative measurements between a 40 cm Snowdon gauge above grass and Snowdon ground level gauges installed following latest W. M. O.-recommendations appeared to be indispensable for ultimate error assessment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02243389
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  • 8
    Electronic Resource
    Electronic Resource
    Water vapour pressure within a maize crop (1976)
    Springer
    Theoretical and applied climatology 24 (1976), S. 349-359 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Description / Table of Contents: Zusammenfassung Nach einer Übersicht über im Laufe der Zeit durchgeführte Untersuchungen der Verteilung des Wasserdampfes innerhalb und knapp über Pflanzenbeständen wird über in einem Maisfeld gemessene Dampfdruckprofile berichtet. Besondere Beachtung wird der gemessenen horizontalen Homogenität der Dampfdruckverteilung in bezug auf die für Berechnungen des mittleren vertikalen Flusses erforderliche Genauigkeit und den zeitlich gemittelten Einzelmessungen gewidmet.
    Notes: Summary After review of the purposes that have in the course of time been served by investigations on aerial water vapour pressure inside and just above plant stands, measured vapour pressure profiles within a maize crop are reported and discussed. Special attention is paid to measured horizontal homogeneity of water vapour pressure, of importance in relation to accuracy needed for mean vertical flux calculations and time averaged single measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263465
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  • 9
    Electronic Resource
    Electronic Resource
    On the pressure dependence of the wind function in Dalton's and Penman's evaporation equations (1978)
    Springer
    Meteorology and atmospheric physics 27 (1978), S. 147-153 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Es wird eine systematische Analyse über die Einflüsse der Druckabhängigkeit der Psychrometerkonstante und der damit zusammenhängenden Druckabhängigkeit der Windfunktion in den allgemein für Berechnungen der Verdunstung von freien Wasser- und Vegetations-flächen verwendeten Gleichungen vorgelegt. Es wird gezeigt, daß die Druckabhängigkeit der Windfunktion in den Penman-Gleichungen nur in außergewöhnlichen Fällen zu berücksichtigen ist. Die Ergebnisse zeigen jedoch, daß die Druckabhängigkeiten der Windfunktion in Verdunstungsgleichungen, die der von Dalton ähnlich sind, von den in Verwendung stehenden verschieden sind.
    Notes: Summary A systematic analysis is presented on the influences of the pressure dependence of the psychrometric “constant” and the inherent pressure dependence of the wind function in expressions commonly used for calculations of evaporation from open water and crops. It is shown that the pressure dependence of the wind function has to be incorporated in the Penman equations in exceptional cases only. However, the results show that the pressure dependences of the wind function in Dalton-like evaporation expressions have to be different from those in use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02246691
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  • 10
    Electronic Resource
    Electronic Resource
    Traditional use of shade: A method of microclimate manipulation (1984)
    Springer
    Meteorology and atmospheric physics 34 (1984), S. 203-210 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Diese Arbeit berichtet über Methoden, die Bauern zur Beschattung von Boden, Säumlingen, Pflanzen und Pflanzenbeständen anwenden, um sie gegen Umweltbelastungen zu schützen und ihre Ertragskapazität zu verbessern. Es werden natürliche und künstliche Beschattungen besprochen, beide in der Form von offenen Beschattungen und von Mulch, wie auch andere Bedeckungsmittel. Vom Gesichtspunkt der Modifizierung der Faktoren der Energiebilanz der Oberflächen wird ein Überblick über die Wirkungen der Beschattungen und einer Schattenreduktion gegeben. Andere Wirkungen von Beschattungstechniken und andere eine Beschattung als Nebeneffekt liefernde Manipulationen werden auch in Betracht gezogen. Einige spezifische aus der Praxis in Tanzania gesammelte Beispiele werden als Nachweis für den heutigen Gebrauch von Beschattungsmethoden in der Landwirtschaft beschrieben. Es wird geschlossen, daß wir in dieser Hinsicht einiges von den Kleinbauern lernen können, daß aber die Wissenschaft der Mikrometeorologie bei der Verbesserung der Leistungsfähigkeit und der Arbeitserfordernisse der herkömmlich angewendeten Techniken wie auch ihrer weiteren Verbreitung in der Bauernschaft helfen könnte.
    Notes: Summary This paper reports on the methods smallholders employ to shade soil, seedlings, plants and crops to protect them from environmental stresses and to improve their yield capacity. Natural and artificial shading are discussed, both in the form of open shades and mulches, as well as other means of covering. Consequences of shading and shade reduction are reviewed from the point of view of modifying terms of the energy balance of surfaces. Other consequences of shading techniques and other manipulations providing shade as a side effect are considered. Some specific examples collected from Tanzanian practice are described as evidence of today’s use of shading methods in traditional farming. It is concluded that we can learn a lot from small farmers in this respect but that the science of micrometeorology could assist in improving efficiency and labour requirements of traditionally employed techniques, as well as in their wider dissemination in the farmer community.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275684
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