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doi: 10.1002/qj.49707934003pmid: N/A
The theory of pressure change by barotropic redistribution of absolute vorticity is extended to include the effect of an eddy motion represented by the departure of the daily value from a running five‐day mean. Application is made to a case in which the mean motion at the 500 mb level is featured by quasi‐stationary approximately zonal flow over North America and by slowly moving large vortices farther downstream (blocking situation of June‐July 1949). One result indicates the potentiality of a technique of forecasting the evolution of mean flow based on a persistence tendency of the ‘errors’ in barotropic tendency computations on mean charts. A further result concerns the interpretation of the ‘error’ field in the light of the neglected processes. There is, contrary to earlier results, no evidence of standing perturbations due to mountain ranges, but the horizontal eddy transfer of vorticity is shown to be an important factor. It is demonstrated that the latter transfer, viz., by the smaller eddies on approximately the cyclone‐wave scale, is mainly directed against the gradient of vorticity in the mean flow, thereby playing an essential role in the maintenance of the larger eddies. The transfer coefficient (diffusivity of relative geostrophic vorticity) is therefore predominantly negative, and its magnitude is from 109 cm2 sec−1 to 1010 cm2 sec−1. The action of the individual smaller eddies in transferring mean vorticity is evidenced by their paths in the relevant mean flow patterns.
doi: 10.1002/qj.49707934004pmid: N/A
The object of this paper is to show, in an elementary way, the general significance of the Richardson number for motions of a frictionless perfect gas of variable density subject to gravity. Dimensionless parameters like the Richardson number are important in relation to the concept of dynamical similarity of flow fields, and as a consequence the paper consists largely of discussions of the conditions for dynamical similarity of flow fields of specified kind. It is established that if the flow fields are such that the pressure and density everywhere depart by small fractional amounts only from the values for an equivalent atmosphere in adiabatic equilibrium and if the vertical length scale of the velocity distribution is small compared with the scale height of the atmosphere, the Richardson number is the sole parameter governing dynamical similarity. Various possible forms of the Richardson number are examined.
Murray, R.; Daniels, Sylvia M.
doi: 10.1002/qj.49707934005pmid: N/A
From a statistical examination of wind observations near jet streams, two conclusions are reached:
doi: 10.1002/qj.49707934006pmid: N/A
A table of monthly mean temperatures representative of the English Midlands has been constructed for the period 1698–1952. From 1815 it is derived from the average of the ‘Radcliffe’ (Oxford) and ‘Lancashire’ monthly means. From 1771–1815 it has been built up by averaging the departures, or anomalies, for each month at a number of inland stations whose records are long enough to be bridged into the years 1815–1840; from 1771–1798 the values thus obtained are reinforced by direct values based on the long Midland record at Lyndon. Before 1771 the existing Edinburgh, Greenwich and Lancashire means are supplemented by further direct values based on Lyndon and Exeter. For all years previous to 1752 the Old Style calendar months have been rectified to the New Style, and the direct values derived from early MS. journals in London, Plymouth, and the Midlands have been carefully collated back to 1728, and extended by means of other short records from Halifax, London and elsewhere back to November 1722. Finally, a direct reduction of Derham's Upminster record, 1699–1706, has been used as a basis for the earliest years. For the intervening years estimates are provided from a consideration of the Utrecht reductions, supplemented for 1713–1722 by non‐instrumental observations of wind and weather in England. Some corroboration of the values so obtained during the eighteenth century is provided; it is hoped that the table can serve as a general standard for studies of English temperature variations until such time as something better can be provided.
doi: 10.1002/qj.49707934007pmid: N/A
Mean daily temperatures at Edinburgh for a period of 150 years are examined for evidence of persistent annual recurrences of unseasonal character. The recurrences are found to be very largely casual in their incidence but, as a result of tests applied, it is concluded that there is only a very small probability that their nature is completely random. Recurrences on the days of ‘Buchan spells’ are found not to depart to a significant degree from chance expectations.
doi: 10.1002/qj.49707934008pmid: N/A
Decadal means of air and sea temperature for the year, the month of July and for the season December to March were computed from ships' observations for the sea areas between 60°N. and 70°N. between Greenland and Norway. The climatic fluctuations in different parts of the area are compared.
doi: 10.1002/qj.49707934010pmid: N/A
Measurements of particle size and concentration of atmospheric dust have been made at Alexandria in various degrees of turbidity. Except for ‘dust haze,’ reasonable agreement is obtained between the measurements and Koschmieder's equation for visibility in terms of optical attenuation. In ‘duststorms’ the required attenuation implies a scatter coefficient per particle 8/3 times the cross‐sectional area of the particles, while in occasions of ‘dust’ the scatter coefficient implied per particle is 4 times the cross‐sectional area of the particles. The results are as follows:
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