摘要:

AbstractIt is well‐known that lee waves are usually associated with the presence of an inversion layer. A mathematical model in which the atmosphere is divided into three layers, the middle one being of high stability and the other two of much lower stability, enables criteria for the occurrence of lee waves to be calculated, the only parameters entering being Scorer's ‘l2’ for the middle and adjacent layers and the thickness of the middle layer expressed as a multiple of its height above the ground. Data from four cases in which lee waves were observed are compared with the characteristics of the model and reasonable quantitative agreement of wavelengths obtained.The increase in wavelength and frequent disappearance of lee waves associated with convective heating of the lower layers can be deduced from the theoretical behaviour of the model as the parameters are changed to simulate the heating pr

ISSN:0035-9009    

DOI:10.1002/qj.49709339602

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractMeasurements of horizontally averaged temperature within a convection chamber suggest that as the Rayleigh number is increased, there is a tendency for Priestley's constantH∗︁ of the free‐convection temperature profile to approach the atmospheric value. An extrapolation of this trend implies that an atmospheric layer in which the temperature gradient varies asz−4/3is truly representative of free convection and is not influenced by very small values of mean wind shear.In Townsend's open‐box convection experiment, the downdraught which persisted at the location of temperature measurements is considered here to have suppressed the appearance of a — 4/3 power region and perhaps to have caused an extended — 2 power region in the temperature gradient.A small‐scale field experiment is proposed to settle the controversy of the power dependence of the free‐convection temperature gradient in wi

ISSN:0035-9009    

DOI:10.1002/qj.49709339603

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractDetailed time‐height sections and meridional cross‐sections of zonal wind are presented for the zonally averaged conditions between 32°N and 20°S. The patterns which appear in the sections vary slowly and systematically with latitude and time. The biennial wind oscillation is evident in the sections, but since 1963, the two year periodicity, as such, has vanished and the wind fluctuations, though still similar in form to the previous ones, have become much less predictable. The sections suggest that the lower edges of westerly regimes propagate downwards more rapidly than those of easterly regimes.The momentum budget of the region is then examined, term by term, and it is concluded that a mean downward motion is necessary over the Equator to account for the downward propagation of the wind regimes there. It is suggested that the enhanced vertical motion during the descent of westerly regimes at the Equator might account for the observed downward propagation at sub‐tropical latitudes. The heat budget is then examined with respect to the vertical motions suggested from momentum considerations. It is found that a heat sink in the equatorial stratosphere would be required to support the vertical motion field. It is shown that enhanced downward motion during the descent of westerly regimes (which the zonal wind data suggest) is necessary to keep the temperature field in geostrophic equilibrium with the win

ISSN:0035-9009    

DOI:10.1002/qj.49709339604

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractMeasurements of global and diffuse radiation were made at Lerwick on a number of cloudless summer days, most of them in a very clear atmosphere. Even on the clear days about 10 per cent of the global radiation appears to be absorbed, in addition to that predicted for a model atmosphere and the amount of scattered radiation is about twice the computed Rayleigh scattering. Whereas extra scattering increases with air mass as expected, the apparent absorption decreases with increasing air mass. No physical explanation of this absorption anomaly is apparent, and no reasonable adjustment to the assumed coefficients of scattering and absorption removes it. It would be removed if the sensitivity of the Kipp solarimeter were assumed to vary with the angle or intensity of the incident radiation by as much as 10 per cent over the range concerned but special tests, carried out on Kipp solarimeters at Kew, do not provide evidence to support this assumption.

ISSN:0035-9009    

DOI:10.1002/qj.49709339605

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractA theoretical study has been made of the assumptions underlying the simple heat balance relations which have been used so far to predict the surface temperatures of ice deposits being formed by the accretion of supercooled water droplets. Calculations have been made of the freezing and subsequent cooling times of a thin water film on the surface of a ventilated sphere initially at a uniform temperature. It is demonstrated that this effectively simulates hailstone growth. The calculations show that both the freezing and cooling processes are dominated by the sphere temperature although, during freezing, the temperature of the water film may rise to a value close to 0°C. They also show that, except at sphere temperatures within a few degrees of 0°C, the freezing time of the water film is short compared with the total time taken to remove the latent heat of fusion by the forced convection process. The reason for this is that the heat of fusion is first conducted rapidly into the sphere, and then more slowly dissipated through the air boundary layer on the surface of the sphere to the environment.Values of the freezing and subsequent cooling times of the water film are presented for various values of the ambient temperature, sphere radius and film thickness. Film thicknesses have been related to the radii of the cloud droplets by a semi‐empirical relation. The liquid water concentrations required to maintain a sphere at a steady temperature have been computed and found to compare well with those given by the simple heat balance relation for a spherical hailstone. Thus, although the simple heat balance relations completely ignore the physical processes involved in the accretion of individual droplets, they are useful for predicting values for the mean temperatures of an accreting surface in a steady state situat

ISSN:0035-9009    

DOI:10.1002/qj.49709339606

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractAn objective method of translating a map of 700‐mb height into its accompanying chart of sea‐level pressure is derived by applying the screening regression technique to 17 years of synoptic data at 469 grid points covering the Northern Hemisphere for every other month of the year. On the average the regression equations explain almost 70 per cent of the pressure variance by means of approximately 3 heights and have a standard error of estimate of about 4 mb. The variation of these properties with geography, latitude, and month is illustrated and discussed. Valuable climatological material is also presented on the standard deviation of daily 700‐mb height and sea‐level pressure and the correlation between these variables.The equations have been programmed for the electronic computer so that automatic, curve‐followed, and hemispheric sea‐level pressure maps can be produced in a few minutes. The programme has been applied to numerical prognostic heights prepared in the National Meteorological Center. The resulting objective forecasts of the sea‐level pressure field are illustrated and compared with predictions produced by

ISSN:0035-9009    

DOI:10.1002/qj.49709339607

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractThe method used to measure vertical gust components from aircraft and the instrumentation for this work installed in the Canberra aircraft of the Meteorological Research Flight are described. Sections showing the vertical gust components obtained during penetrations of altocumulus cloud are presented. Root mean square values were found to be about 0·5 m sec−1in the middle of the cloud. There appeared to be some damping of the turbulence in the top of the cloud when it was under an inversi

ISSN:0035-9009    

DOI:10.1002/qj.49709339608

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractDiffusion of matter from an instantaneous point source in a directional wind shear is treated theoretically using the eddy diffusion equation, and the results are compared with medium‐scale diffusion experiments by Pasquill (1962) and with deductions based on a statistical theory by Högstrom (1964). The effect of ‘shearing advection’ on the theoretical solution is also considered and (contrary to previous results by Gee and Davies (1963, 1964) concerning diffusion near the surface) this is shown to be small, if the theory is based on the assumptions that the vertical eddy diffusivity and the vertical mixing length are con

ISSN:0035-9009    

DOI:10.1002/qj.49709339609

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractViscosity and thermal conduction are included in the current tidal oscillation theory. The solution in which the energy density remains finite as height increases is treated. For all equivalent depths for which the tide is oscillatory in the vertical direction, this solution is a wave whose energy propagates upwards, thus suggesting that the choice of ‘energy propagation upwards’ as the upper‐level boundary condition is consistent with the effect of damping at these levels. Similar work by Pekeris is disc

ISSN:0035-9009    

DOI:10.1002/qj.49709339610

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractIn a laboratory wind tunnel, air was circulated above water which itself was moved by a pump. The resultant waves were measured photographically at fetches less than 7·3 m, and crudely averaged. With opposing water currents, both wave heights and wave lengths were larger than those produced with the same relative wind speed but with no water current: with an assisting water current, wave heights and lengths were both smaller. The waves were of the same steepness ratio for all wind speeds, and were breaking

ISSN:0035-9009    

DOI:10.1002/qj.49709339611

出版商:John Wiley&Sons, Ltd    

年代:1967

数据来源: WILEY