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doi: 10.1002/qj.49708134902pmid: N/A
Wind speeds were measured over the sea at five heights up to 8 m. Though the fetch was limited, the wind profiles obtained are considered representative of flow over the sea.
doi: 10.1002/qj.49708134903pmid: N/A
The form drag of wind on an irregular surface is found to equal the product of U2 (U is anemometer wind‐speed) and a function of the two‐dimensional spectrum of this surface. For a solid surface this function is, of course, independent of U and the form drag is proportional to U2, as observed over land. Over water, Neumann's frequency spectrum and the glitter measurements by Cox and Munk make this function proportional to U, and hence the form drag proportional to U3. The computed form drag is not far out of line with measurements by Van Dorn and others.
Darbyshire, J.; Darbyshire, Mollie
doi: 10.1002/qj.49708134904pmid: N/A
Continuous records of water level were taken at four points on the perimeter of Lough Neagh in N. Ireland during April 1949. The values of level at each point were measured over three‐hourly intervals to eliminate the effect of seiches and the differences in the values of level so obtained were found for all pairs of stations and are correlated with the wind speed and direction. The temperature difference between water and air is taken as a measure of the atmospheric stability.
doi: 10.1002/qj.49708134905pmid: N/A
Separation of flow may be two‐dimensional when the wake or eddy is closed, or three‐dimensional when the air is continuously replaced. It often occurs at a salient edge. When it occurs the effect of the mountain on the high‐level flow is reduced. If the airflow is temporarily induced to follow the ground in an airstream favourable to separation, very large vertical velocities may result. Eddies may be shed periodically from the lee slope of a ridge. Lee waves inhibit separation and so do katabatic winds and downdraughts in heavy rain. Convection makes it more likely over lee slopes but inhibits it at the top of windward slopes.
doi: 10.1002/qj.49708134906pmid: N/A
A method is derived for calculating the velocity, temperature and pressure distributions of the sea‐breeze produced when an initially isothermal and static atmosphere is heated differentially across a long straight coastline. Heat is assumed to be distributed vertically from the land surface by convection currents; internal friction is included but surface drag is taken as zero. The motion is separated into two parts, a rotational non‐divergent component near the coast and a mainly irrotational large‐scale tidal motion transferring mass from land to sea. The former is considered first and a numerical method devised to enable the non‐linear equations to be solved. The solutions are given as a set of diagrams each showing values of velocity, temperature and pressure calculated over a network of points, and each referring to a particular time in the development of the motion. In Section 5 the tidal motion is considered and an analytical solution obtained since the equations can be linearized. The rotational solution represents the spread inland of a tongue of cold air; well inland the wind rises some hours after heating has started, and is accompanied by a fall in temperature. An upper return current occurs in all the diagrams as well as subsidence over the sea and upper cooling inland. The vertical temperature profiles show a sharpening of the discontinuity in lapse rate at the top of the convection layer produced by the vertical velocity component. Conditions for convective instability are found to be produced dynamically in a shallow layer of the upper return current. Comments are made on the formation of ‘heat lows’ and ‘cold highs’ over continents.
doi: 10.1002/qj.49708134907pmid: N/A
The velocity field of a stable atmosphere over and around a heated land mass is found, as a function of both time and distance, by consideration of the equations of motion, continuity and added heat. A heat function is introduced, in the last of these, which is not only fairly simple mathematically but also bears a good resemblance to the atmospheric picture. Certain terms are neglected initially to simplify the mathematics of the problem but they are used later to check the validity of the results and it is found that, in general, the solution would have been negligibly affected by the inclusion of these terms. There is difficulty in using the boundary condition at infinite height but this is overcome by evaluating the problem by two methods.
Bushby, F. H.; Hinds, Mavis K.
doi: 10.1002/qj.49708134908pmid: N/A
The results of 13 computed 24‐hr forecasts, using the Sawyer‐Bushby (1953) two‐parameter model atmosphere, are discussed, and further computations to investigate the apparent limitations of the model are described. The effects of the neglect of heating of the atmosphere over the sea, of the use of incorrect boundary conditions and of the use of 500‐mb rather than 600‐mb data are investigated. It is concluded that the imposition of artificial boundary conditions can cause considerable errors, although these will not be serious in the region of the British Isles, and that the effects of non‐adiabatic heating of the air over the sea should be included in the computations.
doi: 10.1002/qj.49708134909pmid: N/A
Aerological data for the British Isles, 1953, at nine pressure levels, are analysed, to give the geostrophic and ageostrophic components of the wind and the radius of curvature of the isobars. The mean total energy over unit surface area is found to be 1·71 × 109 erg cm−2.
doi: 10.1002/qj.49708134910pmid: N/A
The radiant‐heat flux in a homogeneous atmosphere constitutes an irrotational vector field. As a consequence, the flux can be represented as the gradient of a suitably‐defined radiant‐heat potential. This potential is shown to be a functional of the product of the radiant‐source function at all points in the atmosphere and an attenuation factor to allow for the absorption of the intervening medium.
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