摘要:

AbstractA consideration of the parameters best suited to characterising a circular vortex leads to the conclusion that an intensity factor, the central pressure defect (or excess) and a scale, or size factor are fundamental.General expressions are given for the mass defect of a cyclone, its total potential energy, and the total kinetic energy of geostrophic winds. These parameters are estimated for 17 cyclones on the basis of an assumed pressure‐profile shape. It is shown that the ratio of the mean geostrophic kinetic energy to the mean potential energy is of the order 0.08.A dimensionless measure of the‘flexure’ or bending of a pressure profile is shown to vary relatively slightly from cyclone to cyclone, suggesting that the profile shape is roughly the same for all symmetrical lows.The kinetic energy arising from ageostrophic components of wind are also discussed and it is shown that a quasi‐geostrophic vortex in bodily movement has the same (ageostrophic) kinetic energy as a rigid body moving with the same speed and having a specified mass, the virtual mass of the vortex. It is shown that the virtual mass of a cyclone is of the same order as the total mass defect.It is shown how elleptical vortices, troughs and wedges may be treated, and a‘front’ is shown formally to be representable as a line distribution of circular vortices.On the basis of the models introduced, a dynamic theory of quasi‐geostrophic vortex interaction is put forward, based on the hypothesis that in mutual interaction the pressure profiles of individual vortices are conserved.This theory leads to the conception of a potential barrier inhibiting the over‐close approach of two vortices, and permits vortex interaction to be conceived as the motion of attracting and repelling'ce

ISSN:0035-9009    

DOI:10.1002/qj.49707632902

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

摘要:

AbstractThe paper gives an account of variations in thunderstorm severity in Great Britain based on statistics of breakdowns caused by lightning on the Grid system during the 14‐year period 1934 ‐ 1947. Data are given for the seasonal and diurnal variations and for the fluctuations from year to year. The breakdown data are compared with the corresponding statistics of thunderstorm‐days, and it is shown that the thunderstorm‐day observations, if used directly, do not give an adequate indication of storm severity. It is proposed to introduce a “severity index” (s) such that the severity is proportional toTs, whereTis the number of thunderstorm‐days. For the data examined,shas values o

ISSN:0035-9009    

DOI:10.1002/qj.49707632903

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

摘要:

AbstractA previous observational study (Pasquill 1949 a) has been supplemented by further measurements of evaporation and the associated vertical profiles of wind velocity and vapour pressure in the first two metres above a clayland pasture with grass of moderate length, mainly in effectively adiabatic conditions of flow. The evaporation measurements, using a simple form of soil evaporimeter, included two series of statistically designed measurements, in order further to examine the “reliability” of the technique. The data so obtained, though not comprehensive, indicate no substantial error due to the necessary isolation of test soil from underlying layers, but there is a suggestion that the rates of evaporation ultimately adopted might be underestimates, owing to unavoidable disturbance of root and soil continuity in the vertical at the perimeters of the soil cores contained in the evaporimeters.The observed rates of evaporation(Eo)are compared with those computed(Ec)from the following formula, which is based on the Prandtl form of the law relating drag and wind profile over a rough surface in adiabatic conditions,Ec= ρk2(u2–u1) (q1–q2)/[log (z2–d/z1–d)]2whereu1,u2,q1,q2are the wind velocities and specific humidities at heightsz1,z1above the soil surface,dis a‘zero point displacement’ associated with the vegetation cover, ρ is air density andkis von Kàrmàn's constant, of magnitude 0.4. For the present measurements the usual “roughness parameter,” deduced from the wind profiles, was 0.51 cm as compared with 0.25 cm for the previous series. The two series include 19 separate determinations of rate of evaporation over periods of about one hour, and in terms of different sections of the observed profiles, provide 41 values ofEc/Eoin effectively adiabatic conditions, with wind velocities at a height of 2 m ranging from 3 to 9 m/sec. The mean values ofEc/Eois 0.99 and the individual deviations from 10 are within 10, 20 and 30 per cent in 24, 66 and 90 per cent of cases. It is demonstrated that deviations of this order are to be expected from local variations in the various factors involved.Although somea prioriuncertainty remains concerning the precise validity of the evaporation measurements, the consistency so demonstrated in terms of a semi‐theoretical treatment which has been established in other connections (Calder 1949) suggests that the ultimate result may be accepted with confidence. Brief consideration is then given to the validity and practicability of applying the above formula to evaporation fr

ISSN:0035-9009    

DOI:10.1002/qj.49707632904

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

摘要:

AbstractFrom a consideration of experimental measurements of the terminal velocity of water drops and of the drag coefficient of rigid spheres it is suggested that a formula of the typeV = Aexpbz{ 1 – exp [– (d/a)n]} may be used to represent the terminal velocity of water drops which are larger than those to which Stokes's law is applicable and which are falling through a standard atmosphere. IfV(the terminal velocity) is measured in cm/sec,z(the height) in km andd(the drop diameter) in mm the values of the constants are as follows:— I.C.A.N. atmosphere Summer tropical atmosphere Range ofdmmA b a n A b a n0.3 to 6.0 932 0.0405 1.77 1.147 958 0.0354 1.77 1.147 0.05 to 0.3 191 0.0290 0.316 1.754 188 0.0256 0.304 1.819 If the drops have diameter less than 0.05 mm, Stokes's law is applicable andV = A d2expbzwhereAis 3040 and 2840 in the I.C.A.N. and S.T. atmospheres respectively andbhas the values 0.0191 and 0.0172 in these two atmosp

ISSN:0035-9009    

DOI:10.1002/qj.49707632905

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

摘要:

AbstractEvidence is produced to support the belief that temperatures at the tops of weather echoes are an indication of the relative strengths of the vertical currents within the echoes. Two types of weather echo are indicated according as the vertical currents are strong or weak, giving support to a theory for two different methods for the production of water drops of raindrop size in the atmosphere.

ISSN:0035-9009    

DOI:10.1002/qj.49707632906

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49707632907

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49707632908

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49707632909

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49707632910

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY

摘要:

AbstractThe ratio of the wind at 50 ft to the wind at 2000 ft has been calculated for a number of cases from ocean weather ship observations over the North Atlantic and mean values classified according to the lapse rate and the velocity of the wind at 2000 ft. Curves have been drawn showing the variation of the ratiov50/v2000with lapse rate andv2000respectively.

ISSN:0035-9009    

DOI:10.1002/qj.49707632911

出版商:John Wiley&Sons, Ltd    

年代:1950

数据来源: WILEY