摘要:

AbstractRocket sampling in latitude 66°N has shown that at heights around that of the mesopause, dust nuclei are far more abundant there when noctilucent clouds (hereinafter abbreviated to NLC) are present than when they are absent. The dust particles appear to be nickel‐based micrometeorites, and many of them, when NLC are present, appear to be ice‐coated. Hence the occurrence of NLC seems to require an adequate density of both water vapour and dust. The water vapour is supposed to rise to the mesopause by convection (in summer in latitudes above 45°); thence it diffuses into the thermosphere, where its upward penetration is limited by dissociation by ultra‐violet light, so that its effective scale height is estimated to be less than 2 km. Assuming that the air just above the mesopause is non‐turbulent, the scale height of the uncoated dust passing steadily downwards there is the same as that of the air, about 4.5 km. The estimated scale height of the NLC particles is about 1.5 km. Eddy diffusion below the mesopause causes the number density of both NLC and uncoated dust particles to decrease sharply just below the mesopause. Thus both the thinness and the location of NLC are explained.The diffusion problems considered refer to both the dust and the water vapour; the recent study of dust diffusion by Yu and Klein (1964) is extended. Also the influence of upward dust convection is considered. Conclusions are drawn as to the form of the NLC particles from their estimated rate of descent.The appearance of NLC is ascribed to the simultaneous occurrence (mainly, if not exclusively in the higher latitudes in summer) of a descent of the turbopause to the mesopause, a low mesopause temperature, and humid air below the

ISSN:0035-9009    

DOI:10.1002/qj.49709138802

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe stability of an airstream in geostrophic balance, with a transverse velocity gradient, to horizontal displacements of a single particle has previously been investigated. Here, the effect on such an airstream of a general three‐dimensional disturbance, taking account of the stable density gradient of the air, is considered. A necessary and sufficient condition for instability is obtained for an inviscid airstream and a two‐dimensional disturbance (independent of the downstream coordinate). Finally we discuss how this criterion is modified if viscosity is introduced, and also if the disturbance is allowed to be three‐dimens

ISSN:0035-9009    

DOI:10.1002/qj.49709138803

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractWind observations in the troposphere above seven stations in the vicinity of the Equator have been analysed for the years 1961 and 1962. Strong mean meridional circulations emerge as features of the tropospheric wind regime. Easterly winds occur throughout most of the troposphere, but at times during the northern hemisphere winter a net westerly wind appears to exist in the upper troposphere. There is a strong momentum flux towards the summer hemisphere; the greatest contribution to this comes from the standing eddy flux which is due largely to strong monsoon influences on the flow patterns at 200 mb and above in the Indian Ocean‐West Pacific secto

ISSN:0035-9009    

DOI:10.1002/qj.49709138804

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractData obtained during February and December 1962 at a carefully‐chosen micrometeorological site at Kerang in Northern Victoria are used to examine the flux‐gradient relation for sensible heat transfer. The analysis is carried out for 70 half‐hour runs specially selected for steady state lapse conditions to determine the variation with the stability parameter,z/L, of the Monin‐Obukhov ‘universal function,’øH.In the range 0.02<|z/L|0.2 yields a value of ϵ of −0.50 ± 0.02. The suggestion is offered that the motions observed by Townsend may occur in the atmosphere but as transient phenomena in which the applicability of the conventional similarity principles is to be questioned.The formulaH= 24Δθ3/2based on Priestley's regime with sensible heatHin mw cm−‐2, and potential temperature difference Δθ between 1 and 4 metres in ° provides a practical basis for the evaluati

ISSN:0035-9009    

DOI:10.1002/qj.49709138805

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractFeatures of analytical solutions of atmospheric diffusion equations show that the effect of wind shear and vertical diffusion on horizontal dispersion is important at great distances. Methods of using an analogue or a digital computer to solve the equations for all but very short distances are described. Computations indicate that the wind shear effect is probably dominant over a wide range, and these indications are confirmed by reference to broad and specific deductions from experimental data.

ISSN:0035-9009    

DOI:10.1002/qj.49709138806

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractExperiments have been carried out to determine vertical diffusion in stable conditions at distances of 100 or 200 m from a continuous cross‐wind line source. Simultaneous measurements of vertical turbulence provide the opportunity to test an empirical method of estimating diffusion from wind fluctuation measurements, based essentially on the ideas of Hay and Pasquill (1959), but also attempting to take into account the variation of turbulence with height. The results suggest a fairly systematic variation with stability of the ratio of the Lagrangian and Eulerian scales of turbulence, from values of about two in near neutral stability, to at least ten in rather stable condition

ISSN:0035-9009    

DOI:10.1002/qj.49709138807

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe statistical method of principal components, when applied to mean sea level pressure data from the Australian region, shows that, in addition to the well‐known eastward succession of cyclones and anticyclones and the zonal pressure index type of oscillation, an important source of pressure variability is a quasi‐periodic oscillation of pressure over the eastern Australian region, which has ‘periods’ considerably longer than those due to the normal succession of cyclones and anticyclones. These several effects are revealed in the first three principal components which together account for 75 per cent of the total pressure va

ISSN:0035-9009    

DOI:10.1002/qj.49709138808

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractDaily rainfalls of an inch or more for 100 years at one station have been classified according to the phase of the moon with which they occurred. An apparent significant correlation between two 50‐year smoothed sub‐series is found to have been induced by the filtering process of taking running sums. When the effects of the ensuing serial dependence are eliminated, the results are not indicative of a significant overall relationship between the series of rainfalls and moon phase.In both sub‐series, a persistent trough in frequency count of heavy rainfalls about full moon has been investigated further by examining data from three additional stations in different rainfall regimes. The trough was evident in the data from each of the frequency counts of rainfalls near full moon. However, when each series was viewed in isolation, statistical tests revealed that the observed numbers of rainfall occurrences were not significantly different from the expectations based on the assumption that the series were random. The consistency of the trough rather than its amplitude suggested a weak non‐random influence might be present.An additional product of the statistical analysis of the single station data is an indication of the differing filtering effects of the smoothing process as the number of elements in the running sums is increased progressively from one

ISSN:0035-9009    

DOI:10.1002/qj.49709138809

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractAnalysis of a simple two‐level linearized baroclinic model shows that the effects of surface friction are quite significant with respect to the growth characteristics of harmonic waves. As expected, friction generally tends to reduce the amplification; however, some waves on the fringes of the unstable band which would otherwise be stable may amplify with friction. Increasing the drag coefficient has a similar effect on amplification as decreasing the thermal wind. A wave solution, comprised of two stable components travelling at different speeds, may amplify temporarily due to the resulting interference pattern which exhibits a periodic amplitude and propagation speed.The phase difference between the thermal and pressure waves is also markedly affected by the friction; for example, for the drag coefficients used, the limiting phase difference may differ by as much as 40° from the frictionless ca

ISSN:0035-9009    

DOI:10.1002/qj.49709138810

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractMean values of dimensionless characteristic quantities of turbulence near the ground in relation to stability are given, as derived from data published by Lettau and Davidson (1957).

ISSN:0035-9009    

DOI:10.1002/qj.49709138811

出版商:John Wiley&Sons, Ltd    

年代:1965

数据来源: WILEY