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  • 1
    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.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 34 (1984), S. 203-210 
    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.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 27 (1978), S. 147-153 
    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.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 35 (1984), S. 147-154 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Description / Table of Contents: Zusammenfassung Einleitend wird eine kurze Übersicht über die Verwendung und die Wirkung von Mulchdecken gegeben. Es werden dann in Landwirtschaftsbetrieben in Tanzania angewendete Formen von Mulchdecken mit Verwendung von allgemeinen und speziellen Beispielen dieser Art von Umweltbeeinflussung, die durch eine öffentliche Erhebung in Erfahrung gebracht worden sind, besprochen. Auf Grund dieser Informationen wird gezeigt, daß heute die Verwendung von Mulchdecken bedeutende einheimische Komponenten enthält. Spezielle Beispiele zeigen die Findigkeit lokaler Praktiken und den großen Umfang empirischer Erkenntnisse. Es scheint jedoch, daß die quantitative Information über vorhandene Praktiken in der Überlieferung aus der Landwirtschaft noch mangelhaft ist. Es wird gefolgert, daß eine mikrometeorologische Erforschung dieser überlieferten Methoden der Beeinflussung von Boden- und Luftklima von großem Wert sein würde.
    Notes: Summary This paper starts with a short review on the use and the effects of mulching. Then mulching as employed in smallholder fanning in Tanzania is considered, using general and specific examples of environmental management which were obtained from a public contest. It is shown from the same information that today's mulch use contains important indigenous components. Specific examples show the ingenuity of the local practices and the vast extent of empirical knowledge. However, it appears that quantitative information on existing practices in traditional fanning is almost lacking. It is concluded that micrometeorological research on these traditional methods of soil and aerial climate management would be of much value.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 29 (1981), S. 99-109 
    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.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied climatology 24 (1976), S. 95-108 
    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.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied climatology 24 (1976), S. 177-187 
    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.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Flow, turbulence and combustion 37 (1981), S. 213-223 
    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.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied climatology 62 (1999), S. 221-231 
    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.
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  • 10
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary  Global radiation, soil temperature and soil moisture data were obtained from a 4–6 year old Cassia siamea/maize (CM) alley cropping (or hedgerow intercropping) system, at a semi-arid site at Machakos, Kenya, in the late eighties. With the growing need to explore and manage variations in agro-ecosystems these results deserve new attention. They quantify, in a simple but detailed manner, the influence of hedgerows on the microclimate of their intercrop and for comparison provide a sole maize (SM) control. Due to inhomogeneity of Cassia and maize, as well as limited budgets, the sampling methodology and the choice of appropriate equipment, including the sensors, demanded special attention. The diurnal patterns of soil temperatures at 7.5 cm depth represented well the shading patterns of the hedgerows. This can be developed into an operational auxiliary methodology of integrated shade quantification. With proper precautions, the developed sampling methodologies showed appropriately the time integrated values of the three microclimatic parameters with enough detail to understand yield differences between treatments and between rows. This approach may therefore be recommended for on-farm quantification of even greater spatial variability of parameters. The limitations of the selected methods are highlighted. Experiences with some alternative methods are also discussed.
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