The Quarterly Journal of the Royal Meteorological Society

doi: 10.1002/qj.49709138701pmid: N/A

Townsend, A. A.

doi: 10.1002/qj.49709138702pmid: N/A

Recently published measurements of shadow‐band patterns produced by star‐light at ground level are analysed using the theory of wave‐propagation in a turbulent medium. The measured spatial and time spectra of the patterns can be described quantitatively by assuming that the optical inhomogeneities are produced by turbulent mixing in the earth's boundary‐layer and in shallow layers at heights around 8 km. Characteristics of the assumed turbulence in the upper air are estimated to be: mean height 8 km, layer depth 90–200 m, r.m.s. velocity fluctuation in wind direction 1·5‐2·0 m sec−1, r.m.s. temperature fluctuation 0·2°C.

Kao, S.‐K.

doi: 10.1002/qj.49709138703pmid: N/A

The Eulerian and Lagrangian autocorrelations and energy spectra of the large‐scale turbulent motion in the atmosphere are computed and analysed. It is found that the distributions of the Eulerian and Lagrangian autocorrelations of the zonal velocities show the characteristic of an exponentially decreasing function, whereas those of the meridional velocities exhibit the behaviour of a sinusoidal function with a damping amplitude. The energy spectra appear to be proportional to the minus second power of the frequency in the high frequencies.

Crawford, T. V.

doi: 10.1002/qj.49709138704pmid: N/A

The vertical transfer of moisture is examined under conditions where the Richardson number varies from − 2.5 to + 2.9. The use of a non‐dimensional evaporative flux, similar to Priestley's (1959) non‐dimensional sensible heat flux, and extensive data from the Davis lysimeter field show a smooth transition from forced to free convection. An equation for this transitional regime of mixed convection is derived by dimensional analysis and fitted to the data for different Richardson number ranges. A free convection interpretation of the data for −2.5 < Ri < −0.025 gives a proportionality constant of 1.40.

Frenzen, P.

doi: 10.1002/qj.49709138705pmid: N/A

Using a ‘variance function’ to specify the variance retained by a time series smoothed via running means, it is shown that the rate of turbulence dissipation can be computed from an Eulerian wind record supplied by a single, 3‐cup anemometer through the relation ϵ = (A) [( ‐)/(Tk2/3 ‐ Tj2/3)]3/2 Here A ≈︁ 3.3 derives from the Kolmogoroff law, Ū is the mean flow, and the numerator of the bracketed term represents the additional reduction in variance effected by increasing the averaging interval from Tj to Tk. Preliminary verifications of the relation are presented, and an experimental programme designed to use the method is outlined.

Woods, J. D.; Mason, B. J.

doi: 10.1002/qj.49709138706pmid: N/A

A technique is described for evaluating directly from a single streak photograph the impact parameter for a collision between two falling water drops of similar size. Collision results from one member of a pair of drops being accelerated in the wake of the other. An analysis of many such photographs allows the collection efficiency to be determined. No coalescences were observed between droplets of radius R < 35 μ. Droplets of 40 μ < R < 100 μ had well‐developed wakes, and coalescences occurred relatively frequently, the collection efficiencies being close to unity. No evidence is found for the much larger values of collection efficiency reported by other workers. Collisions between droplets of this size appear always to be followed by coalescence.

Maccready, P. B.; Proudfit, A.

doi: 10.1002/qj.49709138707pmid: N/A

Systematic observations were made of hydrometeor charges associated with thunderstorms at Flagstaff, Arizona. The measurements were made from a light aircraft by the standard induced‐charge method, in and below clouds which were entirely supercooled. The aircraft would spiral within the central upcurrent up into the cloud and later spiral down through the precipitation shafts. From these limited cases, a rather consistent picture emerged: (a) generally, charges on graupel and hail within the supercooled clouds were positive (measurements made as high as the −17.5°C level), (b) below the cloud at the + 2° to + 8°C level, just where the melting of the hydrometeors was apparently complete, the hydrometeors became abruptly negative, (c) at still lower, warmer levels the charge magnitudes were consistently smaller, with both signs represented but predominantly negative. The data suggest that a strong hydrometeor charging mechanism is associated with the melting of ice hydrometeors outside the cloud. The maximum charge magnitudes appeared comparable to the amounts which would be limited by breakdown gradients at the hydrometeor surface.

Maccready, P. B.; Proudfit, A.

doi: 10.1002/qj.49709138708pmid: N/A

A brief laboratory investigation was initiated to try to duplicate a phenomenon which had been repeatedly observed in certain flight measurements during the Flagstaff cumulus studies: the apparent strong negative charging of ice hydrometeors in the final stage of melting during their fall outside of the cloud. Sample ice structures of 1 cm3 from distilled water were melted in an 8 m sec−1 air stream at ambient temperatures. Regardless of the technique of measurement used (current into the sample, charge into the sample, or charge into an open Faraday cage around the sample), certain features were observed consistently: (a) a positive charge was acquired by the sample, (b) the magnitude of the charge was of the order of 30 picocoulombs (0.1 esu), and (c) the acquisition of charge occurred primarily during the later portion of the melting process. Generally similar but more erratic results were obtained with actual hail samples.

Reiter, R.

doi: 10.1002/qj.49709138709pmid: N/A

Based on the evaluation of atmospheric electricity data recorded synoptically over a period of several years in a high‐mountain area between 600 and 3,000 metres above sea‐level, observations of the behaviour of several atmospheric electricity parameters are briefly presented. Besides providing information on charge separation occurring during drifting snow and on cloud charges, the results show the fundamental importance, with respect to atmospheric electricity phenomena, of the melting zone of falling precipitation and of the intensity of atmospheric turbulence and its dependence on altitude. A generally applicable mathematical formulation is given for the relation between the potential gradient and the precipitation current density. This is valid for both low and high altitudes above sea‐level and takes the differences between different types of precipitation into account.

Booker, D. V.

doi: 10.1002/qj.49709138710pmid: N/A

Measurements have been made of the activity collected by a stream of distilled‐water droplets falling through an atmosphere saturated with tritiated water vapour. The results, combined with those of Friedman et al. (1962), confirm theoretical predictions of the rate of exchange between droplets of radius 40‐1500 microns and the surrounding vapour.