摘要:

AbstractThe dominant features of large‐scale atmospheric motion emerge from a relatively simple treatment of the hydrodynamic equations, thus providing clear, intuitive understanding of the relation between cause and effect in the general circulation. The analysis is made possible by applying the perturbation equations to a sloping stream surface located in the middle troposphere. For reasonable values of the arbitrary parameters, the results show that baroclinic disturbances are unstable poleward of a critical latitude, roughly 35°, and that the preferred number of such unstable disturbances at any one time decreases from about 10 at 45°, to 2 at 80°. Greatest intensity occurs at about 60°. Jet streams must form close to the critical latitude and, in the case of long disturbances, at higher latitudes. Anticyclonic shear has a stabilizing influence, so that the normal velocity distribution in middle latitudes offers considerable resistance to penetration of disturbances to low latitudes. Below the critical latitude unstable disturbances are possible only in relatively small areas where the hydrostatic stability is nearly zero. Growth of these disturbances is favoured by anticyclonic shear, as well as by baroclinicity and by high latitude. Disturbances of maximum rate of growth are practically non‐dispersive so that their growth depends mostly on available potential energy. If sufficient energy is available, the identity of individual disturbances can be maintained over extended time periods. Wave speed relative to the zonal current exhibits a maximum positive value at a high l

ISSN:0035-9009    

DOI:10.1002/qj.49708335502

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractThe heat balance is calculated for the Pacific north‐east trade during summer and it is shown that the trade exports sensible as well as latent heat. The sensible‐heat gain is related to the surface pressure distribution; it is found that the low‐level circulation in the region considered is self‐

ISSN:0035-9009    

DOI:10.1002/qj.49708335503

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractAverage zonal (eastward) and meridional (northward) transfers of water vapour for the period June‐August 1954 are computed at four aerological stations in southern England ‐ Liverpool, Hemsby, Crawley and Camborne‐at levels corresponding to the earth's surface, 950, 900, 850, 800, 750, 650, 550, 450, and 350 mb.In the zonal direction average transfers are eastwards and reach a maximum of 400–500 g (cm 100 mb sec)−1below 900 mb. In the meridional direction both northward and southward transfers occur and their vertical distribution varies from station to station. Largest meridional transfers are of the order of 100 g (cm 100 mb sec)−1and normally occur below 800 mb. Both zonal and meridional transfers become small near 350 mb. Vertically integrated eastward and northward transfers are respectively: Liverpool 1461, ‐13; Hemsby 1541, 226; Crawley 1701, 132; Camborne 1781, ‐42 g (cm sec)−1..Average zonal eddy‐transfers are normally eastward and amount to only a small percentage of the total zonal transfer. Average meridional eddy‐transfers are northward, amount to a large percentage of the total meridional transfer and in some cases are oppositely directed. Vertically integrated eastward and northward eddy‐transfers are respectively: Liverpool 63, 73; Hemsby 81, 58; Crawley 97, 27; Camborne 113, 125 g (cm sec)−1.Although directed roughly from high to low values of average specific humidity, average eddy‐transfer vectors at a given (geometric or pressure) level bear little quantitative relation to average (horizontal or isobaric) specific humidity gradients at the same level.Assuming the above transfers to vary linearly between stations, computation of the net horizontal outflow of water vapour from the region shows marked convergence of water vapour from the surface to 850 mb with divergence above this. For the three months' period this amounts to a net inflow of 31 g cm−2at low levels and a net outflow of 23 g cm−2at higher levels. Increase in storage amounts to approximately 1 g cm−2, thus leaving a surplus of precipitation over evaporation of approximately 7 g cm−2.Estimation of precipitation from isohyetal charts and evapotranspiration by empirical methods yields a corresponding surplus of 6 g cm−2..Computation of the large‐scale vertical transfer of water vapour (using instantaneous kinematically‐computed vertical velocities) at 900, 800, 700 and 600 mb showed that at these levels large‐scale vertical eddy‐transfer of water vapour is negligibly small. Using mean vertical velocities and specific humidity averaged over the area at 950, 850, 750, 650, 550 and 450 mb, computations yield large‐scale upward transfers of water vapour for the three months' period amounting to 17, 23, 13, 6, 2, 0 g cm−2respectively at the above levels. This flux is shown to be inadequate for water‐balance requirements and it is concluded that a considerable part of the upward transfer is carried by turbulent a

ISSN:0035-9009    

DOI:10.1002/qj.49708335504

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractEvidence of atmospheric gravity waves, almost certainly due to orography, is obtained from a study of British radiosonde data. It is shown that such data can usefully be exploited to study some aspects of the flow of air in the neighbourhood of mountains.

ISSN:0035-9009    

DOI:10.1002/qj.49708335505

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractIn a fair‐weather cumulus, the largest droplets, which are of 18 microns radius, grow too slowly by differential settling to become precipitation (although the time to reach raindrop size from 50 μ, for instance, would be comparatively short). Even at 18 μ their terminal speed is sufficient for growth, were it not that most of the droplets they encounter are small enough to avoid capture. Using Langmuir's collision efficiencies, the calculated time to grow from 18 to 50 μ radius is 2 hr. This time would be reduced to 12 min if the cloud sample had first ascended until there were 4 g of condensed water per kg of air, as must take place in the updraught of a cumulus congestus.Condensation and coalescence actually occur simultaneously and the first 50 μ droplets appear at about the 6 g/kg level; this is about the level at which the first radar echo should, and does, appear. The apparent descent of the echo can be accounted for by droplet growth at lower levels. The rapid development of precipitation in cumulus can be explained thus without invoking giant nuclei or ice.The intensity required for turbulence to be a potent coalescing agency was found to be greater by a factor ten than the intensity of turbulence deduced from aircraft measure

ISSN:0035-9009    

DOI:10.1002/qj.49708335506

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractThe effective collision cross‐sections between pairs of small water droplets, falling freely through air under the influence of gravity, have been computed on the assumption of hydrodynamical effects alone being important. It has been assumed that each droplet tends to fall freely at its terminal velocity with respect to the surrounding medium, which also moves under the influence of the motion of a neighbouring droplet. By the use of previously computed fields of flow of a viscous medium around a uniformly translated sphere, the trajectories of motion of one droplet with respect to another were computed for a range of droplets having radii between 4 μ and 200 μ.It is found that the collision cross‐sections increase to values considerably greater than the corresponding geometrical cross‐section as the droplets approach equality of size. As the difference in size increases, the collision cross‐section decreases to values close to the geometrical cross‐section, and finally decreases to zero. For any one particular size of the collecting droplet there is a minimum size of collected droplet below which no collection is possible. This size decreases with increasing size of the larger droplet greater than 10 μ in radius. For droplets smaller than 10 μ in radius, collision can occur only between droplets of nearly equal size. The results could account for coalescence becoming an important factor in the rapid formation of raindrops for droplets of radii grea

ISSN:0035-9009    

DOI:10.1002/qj.49708335507

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractRecords of seiches in Lough Neagh during April 1949 were investigated. Fourier analysis of the records indicated three period bands centred round 1.6 hr, 1.15 hr, and 0.75 hr. The two longer periods appeared to have a nodal line across the centre of the lake, parallel to the shorter sides. Methods of deriving these periods in terms of the shape of the lake basin are discussed.The amplitudes of the seiches were compared with the wind records and a high degree of correlation was obtained between the amplitude andWdθ/dt, whereWis the wind speed and dθ/dt is the rate of change of wind direction.An estimate was made of the coefficient of damping of the seiche amplitude and it was found to correspond to a decay to half value in 10 h

ISSN:0035-9009    

DOI:10.1002/qj.49708335508

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractSlow electric‐field changes produced by lightning discharges within clouds have been recorded simultaneously at two stations 13.2 km apart. It is found that the same cloud discharge may give field changes of different types (simple and complex), or of opposite sign (reversal effect), or both, at the two stations. Two main types of complex slow field change are described. The interpretation of slow field changes is discussed in terms of movement of charge. It is shown that, in the most frequent case, the cloud discharge involves the raising of negative charg

ISSN:0035-9009    

DOI:10.1002/qj.49708335509

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractBarometric tendencies at Changi are ‘corrected’ for the diurnal effect and then examined in relation to the occurrence of rain in the following period. It is shown that the three‐hourly corrected tendencies are of no value in forecasting

ISSN:0035-9009    

DOI:10.1002/qj.49708335510

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY

摘要:

AbstractA study is made of several cases of high‐level turbulence in which the intensity varied with the direction of flight of the aircraft. The direction of maximum turbulence is found to coincide fairly well with the direction of the contour lines. A theory is developed which attributes this type of turbulence to quasi‐horizontal gusts associated with strong horizontal wind shear. Gravity waves are examined as a possible alternative explanation and tentatively rejec

ISSN:0035-9009    

DOI:10.1002/qj.49708335511

出版商:John Wiley&Sons, Ltd    

年代:1957

数据来源: WILEY