摘要:

AbstractA linear model is fitted to the precipitation series of each group of stations formed by principal component analysis on 157 precipitation records (Dyer 1975). Precipitation can thus be decomposed into independent components one each for regional temporal effect, regional spatial effect, and a residual or micro‐effect. Each region has a temporal effect which is analysed for trend, enabling the conclusion to be made that Southern Africa's precipitation budget is stationary. On the other hand, trend on a microscale is present over randomly distributed parts of the country. Spectral analysis shows the oscillatory behaviour of the regional temporal effects, and provides information useful to the fitting of stochastic forecasting models to the data. The technique solves the problem of dependence between meteorological time series, and can be applied to any variabl

ISSN:0035-9009    

DOI:10.1002/qj.49710243112

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractGiven is a horizontal plot of land P, a fraction of the area of which is assigned to an activity that produces air pollution. The latter area will be denoted S (source). Although the fraction of P allocated to S is fixed, we are otherwise free to determine the location and shape of S within the confines of P. Also given is either a second piece of land or a finite set of points in the same horizontal plane as P. That second piece of land, or set of points, will be denoted R (receptor). We assume that: the source strength density is steady and uniform across S; the wind and the turbulence are likewise steady and uniform along horizontal planes. We now wish to determine the shape of S and its location within P so as to minimize, or to maximize, the average pollution concentration in air at R due to S. By providing a duality principle and applying it to the present case, we show that the bounding curve of S is fixed by a concentration isopleth ‘associated’ with a hypothetical area source represented by R and the given boundary of P. The isopleth of concern is the one that encloses the prescribed area of S within the limits of P. Further, it is pointed out that the case of maximization is ordinarily simpler than that of minimization. In some cases S is not ‘connected’.Examples are given for the application of the theoretical

ISSN:0035-9009    

DOI:10.1002/qj.49710243113

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractA theoretical model for vertical distribution of air temperature in lower layers during night‐time calm periods has been developed by modifying some boundary conditions of the classical Brunt's model, on the ground of a more realistic behaviour of low atmosphere.The model allows the vertical temperature profile to be deduced from screen data records and it fits with experimental data collected from a meteorological tower better than the classical model.Radiative heat exchange is assumed to play the principal role, with diffusion thermal coefficient constant with height and time; previous work has shown that such an assumption holds true in the Po Valley air flow, when sky is cloudless and winds are ligh

ISSN:0035-9009    

DOI:10.1002/qj.49710243114

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe process of modification of the Bowen ratio, with distance downwind of a change in surface wetness, is considered to establish the ratio of the fluxes of sensible and latent heat when unaffected by surface inhomogeneity. The case of steady‐state two‐dimensional advection is considered. It is shown that the coupled, simultaneous, diffusion equations for heat and moisture transfer from natural vegetated or wet surfaces can be used to generate two independent diffusion equations in composite variables. The vegetated surface is represented as an extensive single leaf. The height integral of the reciprocal effective eddy diffusivity is assumed to become indefinitely large with height so that heat and moisture continuously accumulate within the overpassing air. As a result equilibrium does not obtain. However, the surface latent heat flux approaches a quasi‐equilibrium value given, in conventional symbols, byLE = (s/(s+γ)) (Rn −G).For terrestrial surfaces, where the available energy depends only slightly on surface temperature, the Bowen ratio approachesγ/s.For deep water bodies and melting snow the heat flux into the surface also evolves with distance and the above relationship is approached only in the trivial sense thatRn = GandLE = 0. This model for terrestrial surfaces is consistent with some recent experimental obs

ISSN:0035-9009    

DOI:10.1002/qj.49710243115

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractUsing the model and methods developed in Part I of this study, it is shown that steady‐state evaporation, downwind of a sharp boundary separating uniform regions with constant but different surface resistances and available energies, can be written as\documentclass{article}\pagestyle{empty}\begin{document}$$ E\; = \;(S/(S + Y))\;(Rn\; - \;G)\; + \;(S/(S\; + \;Y))\;(1/r_s [r_s (Rn\; - \;G)\; - \;r_s (Rn\; - \;G)]\Phi _x $$\end{document}where ϕxis a dimensionless ‘exchange function’ that decreases from unity to zero as distance increases downwind of the boundary. The symbols have their conventional meanings and the primes signify upwind values. The form of ϕxdepends on the profiles of wind speed and effective diffusivity, and on the downwind surface resistance and temperature via the parameterγrs/(s+γ).Empirical expressions for ϕxare obtained from a known solution of the atmospheric diffusion equations assuming power law forms of the wind speed and effective diffusivity profiles and from a simple model assuming perfect vertical mixing and constant wind speed beneath an impermeable inversion base. These may give some indication of the form and magnitude of ϕxat small and at large distances r

ISSN:0035-9009    

DOI:10.1002/qj.49710243116

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractAs part of an attempt to implement more efficient integration procedures, a semi‐implicit time differencing procedure has been evaluated within the context of a southern hemisphere, six‐level primitive equations model. The model employs the flux form of the primitive equations and includes processes such as convection, vertical and horizontal diffusion, and orography.Comparative explicit/semi‐implicit integrations show only marginal meteorological differences. However, the semi‐implicit scheme allows a timestep about five times as large. This represents a net saving factor of approximately 2.5 for integrations involving no orography. In instances where high orography is included net efficiency advantages may be degraded significantly when using the flux form of the primitive equations unless special numerical procedures are adopted during the solution of key model equations.On the basis of these successful results, the semi‐implicit scheme is now being used in the separate development of a limited‐area prediction model to provide routine forecasts for the Australa

ISSN:0035-9009    

DOI:10.1002/qj.49710243117

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49710243118

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe representativity of station wind measurements can be increased by elimination of sheltering effects caused by small‐scale obstacles. It is shown how correction factors for this purpose can be obtained for each wind azimuth sector from analog wind records of the station itself, by extracting maximum gust speeds during periods with strong wind. The transformation is achieved using a gust factor model (Wieringa 1973) which relates the ratio of maximum and average wind speed to measuring height, surrounding roughness and gust wavelength. The concept of ‘effective height’ is criticized. It is indicated how the actual duration of the recorded maximum gusts can be obtained from station instrumentation response specifications, and it is shown that this duration exceeds 10 seconds for the usual combination of cup anemometer and galvanometric recorder. A trial climatological application shows how omission of exposure correction may lead to exaggeration of mesoscale horizontal wind grad

ISSN:0035-9009    

DOI:10.1002/qj.49710243119

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractObservations from many sources have been brought together to study the relationship between the ratio of standard deviation of vertical velocity to friction velocity, andz/Lwherezis the height andLthe Monin‐Obukhov length. A good compromise for this relationship is:\documentclass{article}\pagestyle{empty}\begin{document}$$ \sigma _w /\upsilon _* \; = \;1.3[\phi _M \; - \;2.5z/L]^ + $$\end{document}where ϕMis the normalized wind shear.This equation has been combined with theoretical expressions for the wind profile to derive a nomogram for the standard deviation of vertical angle as function ofz/Landz/z0, wherez0is the roughness leng

ISSN:0035-9009    

DOI:10.1002/qj.49710243120

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractMany recent measurements of vertical‐velocity spectra in the atmospheric boundary layer are combined in order to derive the dependence of the maximum of the logarithmic spectrum, normalized by surface stress, on stability. An empirical equation is suggested which fits the observations and has the proper limiting form for free convection. It is suggested that this equation can be used to derive surface stresses from relatively simple measurements of the most energetic part of the spectrum, and from a stability paramete

ISSN:0035-9009    

DOI:10.1002/qj.49710243121

出版商:John Wiley&Sons, Ltd    

年代:1976

数据来源: WILEY