摘要:

AbstractResults are presented for the baroclinic instability of zonal flows on a β‐plane according to the modified quasi‐geostrophic equations (which retain a non‐Doppler term in the rigid horizontal boundary condition).Numerical techniques, with up to 180 interior levels, are used. In the absence of a β‐effect the instability of the longer waves is fairly sensitive to the non‐Doppler term, the more so if static compressibility is neglected. A realistic β‐effect markedly reduces this sensitivity: the weakly unstable long waves are essentially internal mode phenomena and are consequently little affected by the non‐Doppler term. It is confirmed that the stable external mode Rossby waves, where they exist, are radically altered when the t

ISSN:0035-9009    

DOI:10.1002/qj.49710544602

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractFluxes of sulphur dioxide to wheat were measured over two growing seasons. The deposition velocity,vg, depended primarily on affinities of surfaces for SO2and varied from less than 0.1 to about 1.5cms−1. Stomata were an important sink, and diurnal changes in stomatal resistance accounted for most of the variation invgwhen leaves were green and dry. When leaves were wet with dew,vgwas generally large, irrespective of the physiological state of vegetation. A resistance analogue of transfer to the canopy agrees well with published work and is used to estimate seasonal uptake of SO2by the crop, showing that 30% of the sulphur content of the crop at harvest was probably supplied by absorption of SO2through stomat

ISSN:0035-9009    

DOI:10.1002/qj.49710544603

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractResults from an investigation of the turbulence structure of the lower half of the convective boundary layer over the sea around the UK in a wide variety of meteorological conditions are presented. The data were obtained on eight flights made by the Hercules aircraft of the Meteorological Research Flight.Differences in structure between boundary layers over sea and over land are emphasized, the most notable being the relatively increased importance of mechanically driven mixing over the sea. This means that a more general scaling scheme is required which retains bothu*andzias scaling parameters. Such a scheme orders the results quite effectively. Dimensionless profiles of momentum, sensible heat and latent heat fluxes are presented, together with dimensionless variance profiles. Excellent agreement is found between these and theoretical predictions from numerical models. Surface fluxes are estimated and compared with bulk aerodynamic formulae.The turbulence statistics are shown to be in good agreement with those published by other workers.

ISSN:0035-9009    

DOI:10.1002/qj.49710544604

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractA method is proposed for explicitly incorporating climatological information into a Backus‐Gilbert variational scheme for atmospheric temperature retrieval by a remote sounding radiometer. The method is applied to a study of the retrieval ability of a ground‐based microwave radiome

ISSN:0035-9009    

DOI:10.1002/qj.49710544605

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractResults from a series of boundary layer measurements carried out at Ashchurch, Worcestershire during July 1976 are combined with those from the 1973 Minnesota experiment. This data set provides a more complete description of the behaviour of some turbulence statistics through the depth of the convective boundary layer and into the stable air of the free atmosphere. Although the two experimental regions differ quite markedly topographically, the two sets of data are found to merge together quite well in the middle of the boundary layer and do not reveal any systematic differences that might be attributable to surface effects. The vertical profiles of turbulence statistics are compared, where possible, with other results from numerical models and laboratory experiments.

ISSN:0035-9009    

DOI:10.1002/qj.49710544606

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractNumerical calculations of the forces involved in Ekman layer flow past three‐dimensional topography are presented. The forces are obtained from finite‐difference solutions of the Navier‐Stokes equations. The results confirm expectations from earlier two‐dimensional work that many flows produce no significant change in total momentum transfer between the fluid and the surface. Only flows generating some form of trailing vortex system appear capable of changing the total force on the lower boundary. The effects of Ekman boundary layer instabilities, and their interaction with topography, are also di

ISSN:0035-9009    

DOI:10.1002/qj.49710544607

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractEulerian observations of wind direction fluctuations in slightly unstable conditions are analysed in terms of Taylor's statistical theory of dispersion which, with the Hay‐Pasquill assumption of similar shapes for Lagrangian and Eulerian spectra, relates the standard deviation of the crosswind material distribution, σy, to the standard deviation of fluctuations in wind direction, σθ. The dependence of the predicted cross‐wind dispersion parameter,S=σy/(σθx), where × is the distance downwind from the source, on travel time,T, is examined, and it is concluded that the data are well represented by an empirical form originally proposed by Draxler to fit observed crosswind dispersion.In contrast to direct dispersion observations, the present data show little scatter and unambiguously demonstrate that the common assumption of an exponentially decaying correlogram results in a less accurate representation. In particular, the exponential form approaches the large‐time limit,S2α 1/T, too rapidly, and thus may be expected to perform poorly in extrapolating from a limited range of data.The consistency of the Draxler form in representing both the Eulerian measurements presented here, and direct Lagrangian dispersion observations, serves to support not only the form itself, but also, indirectly, the Hay‐Pasquill hypothesis.Evidence of a correlation between the intensity and scale of turbulence is also presented, which, if confirmed over a larger range of atmospheric stability conditions than considered here, will be very useful for estimating dispersion from

ISSN:0035-9009    

DOI:10.1002/qj.49710544608

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractCalculations of the various terms in the kinetic energy budget of the atmosphere were carried out for the area of the British Isles using aerological data for the period 1974–76. The residual term (‘dissipation’) necessary to balance the equation is interpreted as representing the forcing effect of sub‐grid scale processes. The results are compared with earlier calculations for the same area, and with corresponding results for the area of North America.The results show that the annual mean dissipation of kinetic energy in the boundary layer (below 850 mb) is 3.4 Wm−2, which is considerably larger than that found for the area of North America. The corresponding values for winter, spring, summer and autumn are 6.2, 2.3, 2.0 and 3.2 Wm−2, respectively.Results for the British Isles in the free atmosphere are very different from those for North America. Whereas there is, on average, generation of kinetic energy by pressure forces (−V.▽Φ>0) and net export of kinetic energy over North America, the contrary is true over the British Isles.The mean residual term in the kinetic energy equation over the British Isles is relatively small between about 850 and 400 mb. However, higher up, the term is definitely positive, indicating (if interpreted physically) an energy input from sub‐grid scales to the synoptic scale: a situation opposite to that prevailing, in the annual mean, over North America. It is suggested that this ‘negative viscosity’ phenomenon may in general be typical for diffluent flows (such as are found in the exit areas of jet streams) and could be due to horizontal and vertical convergence of momentum flux associated with jet streaks and other su

ISSN:0035-9009    

DOI:10.1002/qj.49710544609

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractDifferent terms in the equations of zonal and meridional motion for large scale flow in the atmosphere have been evaluated using British aerological data for the period 1974‐76; the effect of motion on scales smaller than a few hundred kilometres on large scale flow is evaluated as the residual term in these equations.In the long‐term mean there is horizontal advection of zonal momentum into the area of the British Isles. This advection, which is characteristic of both the time‐mean flow and transient disturbances and takes place mainly in the zonal plane, is to a large extent compensated for by Ferrel‐type ageostrophic meridional circulation. The momentum budget in the meridional direction reflects the high degree of geostrophic balance in the time‐mean zonal flow in the free atmosphere.The mean residual forces in the atmosphere below 700mb are used to infer the vertical sub‐grid scale flux of momentum by assuming that the residual forces at these levels are due to vertical eddy stresses (i.e. stresses involving the vertical velocity component) only, and by evaluating the stress at the earth's surface with the aid of the geostrophic drag law. The results indicate that the annual mean vertical flux of zonal momentum above about 900mb is downwards but relatively small; the corresponding flux of meridional momentum is relatively large and upwards. Mesoscale circulations in connection with fronts are suggested as a possible explanation of the latter phenomenon which, however, may also partly arise in calculations as the result of the poor vertical resolution of the routine upper wind observations in the atmospheric boundary layer.The residual force in the upper troposphere is very variable. However, consistent with an earlier analysis of the kinetic energy budget using the same data, it exhibits the ‘negative viscosity’ phenomenon, implying acceleration of the large scale flow by motion on scales smaller than the average distance between aerol

ISSN:0035-9009    

DOI:10.1002/qj.49710544610

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractHorizontal empirical orthogonal functions (EOFs) were determined from a sample of 11 876 500 mb analyses given at 1404 gridpoints covering the northern hemisphere north of 20°N. Due to computer restrictions a joining method had to be applied. The set of 175 EOFs determined explains 99.5% of the total variance in the dependent sample and 99.6 to 99.7% in the independent samples

ISSN:0035-9009    

DOI:10.1002/qj.49710544611

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY