ISSN:0035-9009    

DOI:10.1002/qj.49709540502

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractStudies have been made using instrumented aircraft of the electrical and microphysical properties of cumulus and cumulonimbus clouds over Flagstaff, Arizona. Measurements were made throughout the life‐cycle of these clouds either by making horizontal penetrations through the cloud at intervals of 2 Centigrade degrees or by entering the cloud at the highest level attainable and spiralling down to cloud base. The aircraft could attain an altitude of around 32,000 ft (9·7 km), corresponding to a temperature ceiling of approximately −30°C. Continuous measurements were made of vertical electric field strength,F, the charge carried on larger hydrometeors,Q, the concentrations, types and dimensions of cloud particles, liquid‐water content, temperature and other meteorological parameters.Fwas measured using a rotating cylindrical field‐mill of the type devised by Kasemir (1964), which enabled fields ranging from about 100 Volt m−1to corona values to be measured with an accuracy of about 10 per cent.Qwas measured using a double‐sheath induction technique which permitted charges ranging in magnitude from about 10−2to 1·0 e.s.u. to be measured to within 10 per cent. A series of careful subsidiary experiments established the range of conditions over which these electrical instruments provided reliable results. The concentrations, types and dimensions of cloud particles were measured using the continuous particle sampler described by MacCready (1962).The measured electrical characteristics of the clouds studied varied markedly from cloud to cloud but it was possible to isolate certain recurrent patterns and correlations. The measured values ofQwere found generally to be carried on rimed aggregates of ice crystals. The degree of electrification, represented by the values ofFandQ, was highest in clouds where these aggregates coexisted with appreciable quantities of supercooled water droplets and ice crystals. At all levels within the clouds positive and negative values ofQwere obtained, but the proportion of positively charged larger hydrometeors increased with increasing temperature within the cloud. Small clouds or clouds in their early stages of development usually possessed a simple electrical structure, with positive fields existing throughout most of their volume. Larger, more mature clouds possessed extremely complex electrical structures and a much higher degree of electrification. Sharp reversals of the dominant sign ofQwere often observed to occur once or twice during the horizontal penetration of a precipitation shaft below cloud base at temperatures above 0°C.Lack of vital information, particularly concerning the cloud dynamics, rendered it impossible to assess the measurements in terms of all current theories of thunderstorm electrification. However, it can be shown that both the Reynolds‐Brook process and the Müller‐Hillebrand mechanism probably contributed significantly to the electrification of the clouds studied. It is difficult to distinguish the respective roles of these processes. The evidence suggests, however, that clouds possessing a simple structure, or clouds in the early stages of their maturity, have an electrical structure that is largely compatible with the predictions of the inductive process, whereas the gross electrical characteristics of more complex clouds are often explicable in terms of the

ISSN:0035-9009    

DOI:10.1002/qj.49709540503

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractIn an attempt to broaden the observational basis of the seasonal variation of the large‐scale atmospheric circulation, Fourier analysis was applied to time series of important kinetic energy variables which were computed for a 5‐year period over the North American Continent. The variance spectra of the direct Fourier analysis are also presented.The year‐to‐year fluctuation of the seasonal variation of the energy variables is apparent. After filtering out the year‐to‐year irregularity, clear basic features of the seasonal evolution were obtained. The kinetic energy level can be described essentially by the one‐year cycle. However, the energy generation, outflow, and dissipation show an important half‐year cycle in addition to the prominent

ISSN:0035-9009    

DOI:10.1002/qj.49709540504

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe negative charge involved in lightning flashes to ground is found to be distributed in a manner strongly dependent upon the direction of movement of the storm, and does not, in general, constitute a nearly vertical column as proposed by Malan and Schonland. Based on a study of electric field‐changes measured at two stations 10 km apart involving 539 return strokes from 84 flashes in 10 storms, we conclude that the horizontal component of the in‐cloud channel on the average exceeds the vertical component, and points in the direction of storm motion.An analysis is given of the five methods of Malan and Schonland, on the basis of which we suggest that significant horizontal components are also compatible with their observations of a vertical column, and that the ‘nearly vertical’ aspect of the charge distribution has been over‐e

ISSN:0035-9009    

DOI:10.1002/qj.49709540505

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe number of condensation nuclei produced by the bursting of a single bubble in sea‐water, and detectable at a few per cent supersaturation, is shown to be markedly dependent on the film pressure of naturally occurring surface‐active material adsorbed on the surface.At low film pressures around 1 dyne cm−1the presence of the film increases the variability of the number produced, but the number is always less than that expected for a clean water surface. With increase of film pressure the number of nuclei produced decreases markedly.The dependence of nucleus number on the state of any surface‐adsorbed film has important consequences for the sea‐to‐air transport of organic material. This i

ISSN:0035-9009    

DOI:10.1002/qj.49709540506

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractA radiometer sonde has been constructed to observe radiation from the atmosphere above the radiometer in the spectral region 5–7 μ with a spectral resolution of about 0·3 μ. The results from a flight of the instrument at night up to a height of 25 km are presented. Emission from water‐vapour indicates a dry stratosphere with a mass mixing ratio of about 3 × 10−6. An energy flux originating above 25 km amounting to about 2 μW cm−2has been observed near 5·7 μ. Various possible sources for this additional radiation

ISSN:0035-9009    

DOI:10.1002/qj.49709540507

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractDoppler radar observations during widespread frontal precipitation in England on 20 February 1967 show significant perturbations of the wind in and near the melting layer. The analysis suggests the following hypotheses: (i) Mesoscale oscillations of the wind near the melting layer are produced by pressure perturbations due to horizontal variations in cooling by melting snow associated with the precipitation pattern. A simple theoretical analysis of the effect is presented. In simple patterns, the perturbed wind has a maximum on the low pressure side of the rainfall. The perturbations propagate with the velocity of the precipitation generators and their magnitude increases with the precipitation rate. This hypothesis is in accord with the finding that the oscillation in the tangential wind across hurricane rain bands is generally a maximum on the low pressure side of the bands. (ii) Smaller scale wind perturbations were also observed in the melting layer with scale of a few kilometers comparable to those reported by Harrold and Browning (1967). However, unlike their observations, these perturbations did not appear to move with the melting layer winds. A tentative suggestion is made that these may represent wave motions.

ISSN:0035-9009    

DOI:10.1002/qj.49709540508

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractA theory is developed which describes the adjustment of the flow of a hydrostatically neutral fluid in the lower portion of a fully‐turbulent boundary layer, after an abrupt change in surface roughness.The model is based on the hypothesis that the horizontal shear stress is proportional to the turbulent energy. The theory postulates that the flow is primarily governed by the dominant terms of the horizontal‐momentum, continuity, and turbulent‐energy equations. The model was solved by numerical techniques on a digital computer.Unlike previous models there are noa prioriassumptions about the distribution of velocity or stress, the behaviour of the nondimensional wind shear, mixing length, or momentum‐exchange coefficient in the transition region.The theory, in contrast to earlier theories, suggests the distribution of turbulent energy, as well as velocity. An inflection point is predicted in the transition velocity‐profile. The nondimensional wind shear is found to differ significantly from unity in the transition region. These predictions agree with ob

ISSN:0035-9009    

DOI:10.1002/qj.49709540509

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractA set of empirical orthogonal functions is produced which enable the large‐scale features of the 500 mb topography over the Northern Hemisphere to be represented with near optimal efficiency. The more important functions are described. Some of the properties of the coefficients of these functions which best represent the 500 mb charts for each day of the years 1965 to 1967 are summarized. The question of the number of functions required to obtain the most satisfactory representation of the 500 mb fields is discusse

ISSN:0035-9009    

DOI:10.1002/qj.49709540510

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractA short‐range prediction experiment is performed to study the dynamical structure of the tropical atmosphere in equatorial latitudes. The initial field includes the intertropical convergence zone and associated disturbances over the western Pacific Ocean during March 1965. A complete initial state is constructed using a consistent balanced system of equations. The procedure involves construction of pressure, temperature and vertical motion distributions starting from the rotational part of the observed wind field. It is shown that this procedure, the validity of which assumes a small Rossby number, does not yield a realistic field of vertical motion.A short‐range prediction with a multi‐level prediction model yields some interesting solutions in the vicinity of the intertropical convergence zone. During the first 18 hours of prediction there occurs an adjustment of the motion and the mass field, with gravity‐inertia oscillations.An important feature of the model is a parameterization of cumulus convection as a function of the largescale moisture convergence. The role of cumulus scale heating in the vicinity of the intertropical convergence zone is investigated and it is shown that during the adjustment process a convergence zone forms which exhibits a strong coupling with the zone of frictional vertical rising motion and the field of computed cloud cover. The formation of this feature appears to represent the numerical simulation of a tropica

ISSN:0035-9009    

DOI:10.1002/qj.49709540511

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY