ISSN:0035-9009    

DOI:10.1002/qj.49711046302

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractObservations from tethered balloon‐borne instrumentation of small‐scale air motion, temperature fluctuations and microphysical structure occurring within nocturnal stratocumulus are presented and discussed. The cloud top was marked by a very sharp and thin inversion layer whose vertical displacement was monitored with an acoustic sounder. The velocity field indicates the presence of strong downwards convection within the cloud, in which radiatively cooled air is transported away from the region near cloud top in discrete plumes. Droplet data show the preferential location of larger cloud droplets (>7 μm radius) within the convection cells. Some aspects of the droplet observations are explained in terms of a simple Lagrangian model. Although entrainment is excluded from the model the predictions are consistent with the observations. Entrainment effects at cloud top result primarily in droplet concentration fluctuations with little change in the shape of the droplet spectrum, which the model suggests is mainly determined by the effects of radiation on droplet growth by condensation and the effects of vertical motion. Finally, some characteristics of turbulence through the cloud layer, and boundary layer generally, are examined and related to observations from the cloud‐free convective boundary layer and data from laboratory exper

ISSN:0035-9009    

DOI:10.1002/qj.49711046303

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractA model is presented of the vertical structure of turbulence in the convective boundary layer. The model is based on representation of the fluctuating velocity components by trigonometric orthogonal functions. The vertical velocity component is represented by a sine and the horizontal by a cosine expansion. The sine representation of thewcomponent ensures thatw= 0 atz= 0. The expansion coefficients are uncorrelated if the sine functions are eigenfunctions of the vertical correlation function.A simple form, based on the inertial sub‐range, is adapted for the energy spectrum.Constant parameters of the model are evaluated from the surface layer measurements of the wind velocity variances, and it is shown that the model agrees with the measured vertical structure of variances through the whole boundary laye

ISSN:0035-9009    

DOI:10.1002/qj.49711046304

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractA passive optical device has been developed for the ground‐basedin situmeasurement of liquid water content,L, in clouds. Light scattered at five, computationally selected, small forward angles is collected and ‐ with the application of appropriate weighting factors ‐ combined to give a response which is linearly proportional toLover the droplet diameter range 1 to 80 μm.Lcan be measured to within ±0.05 gm−3at a frequency of up to 100 Hz, thus permitting fluctuations in the liquid water content of clouds to be examined on spatial scales of less than one metre. A miniaturized version of the device ‐ for airborne usage ‐ is unde

ISSN:0035-9009    

DOI:10.1002/qj.49711046305

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractHolograms of natural fogs have been made. A fog volume of 22·5 cm3has been analysed from one hologram. Tests have been carried out to see whether the obtained spatial distribution of droplets could be approximated by Poisson statistics, mainly with negative results.A continuation of this type of research and a deeper theoretical study of the effects on coalescence processes of a non‐random spatial distribution of droplets is suggest

ISSN:0035-9009    

DOI:10.1002/qj.49711046306

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractA continuous flow vapour diffusion chamber has been designed and constructed so that ice nuclei can be activated over ranges of temperature and supersaturation similar to those found in natural clouds. A conventional filter‐processing chamber was also built for carrying out comparative measurements. Simultaneous use of the two chambers under similar conditions of temperature and supersaturation has shown that the filter method leads to an underestimate of the concentration of ice nuclei in an air sample. The ratio of the two simultaneous measurements is strongly dependent on the concentration of Aitken nuclei in the air sample and is also dependent on the chamber supersaturation. Some tentative evidence of the presence of condensation‐freezing nuclei active above water saturation is presen

ISSN:0035-9009    

DOI:10.1002/qj.49711046307

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThis paper reports on microphysical and dynamical measurements made from an aircraft in the anvil of a winter cumulonimbus cloud which grew in maritime air near the United Kingdom. The anvil had a well‐organized structure, with ice content in the central region exceeding 1 gm−3. The ice appeared to be distributed uniformly over the size range of crystals, with half the total mass contained in particles larger than 1 mm. The total particle concentration may have exceeded 1501−1in places. A widespread supersaturation of typically 10% with respect to ice ensured that the ice crystals continued to grow by deposition. The microphysical and dynamical structures of the anvil are shown to be closely linked, and semi‐quantitative explanations are given for the evolution of particle size distributions in terms of deposition and gravitational s

ISSN:0035-9009    

DOI:10.1002/qj.49711046308

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractA comparative study of two cloud clusters in the north‐west of Australia highlights synoptic influences on tropical cyclogenesis. Although both clusters developed over land in the same region, the large‐scale flow was conducive to the subsequent development of one cluster into tropical cycloneEnidand suppressed the development of the other cluster. The non‐developing low was under strong upper easterlies from an upper tropospheric ridge. An upper trough in the subtropical westerlies later split the ridge, bringing light and divergent upper winds over the low‐level monsoonal trough. This facilitated the development and intensification of a low‐level cyclonic circulation, tropical cy

ISSN:0035-9009    

DOI:10.1002/qj.49711046309

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThis paper reports observations made over the North Atlantic of a system of convective cloud bands found within the cold air behind an occluded front. The observations were made from an instrumented aircraft which additionally released a pattern of dropsondes, measuring temperature, relative humidity and wind, as functions of pressure. These data are analysed to establish some of the mesoscale, cloud‐scale and microphysical properties of the system.Here, in part I, the mesoscale structure is described and compared with the predictions of various theoretical models. The convective cloud structure emerges as a consequence of the mesoscale organization but appears to play only a minor role in its creation and maintenance. One of the theoretical models considered, conditional symmetric instability, provides a piausible explanation of the mesoscale observation

ISSN:0035-9009    

DOI:10.1002/qj.49711046310

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractNumerical solutions of the shallow water equations in one dimension are presented. The formation and evolution of hydraulic jumps are predicted with a simple centred finite difference model and with a model utilizing Glimm's method. Glimm's method is a special one‐dimensional method, which has been proved to converge to the physically relevant solution of a number of equations in the presence of discontinuities. The solution from it is used to check the finite difference method.Cases presented include examples of jumps produced in the presence of rotation, and a variety of jumps forced by flow over orography. It is shown that a conservative finite difference method, with the addition of artificial diffusion, converges to the correct solution for almost all cases. However, the use of multipoint filters gives poor results. At low resolution, the errors in modelling the flow induced by the orography are larger than errors caused by not resolving the shape of the orograph

ISSN:0035-9009    

DOI:10.1002/qj.49711046311

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY