摘要:

AbstractThis is a review of turbulence in the upper ocean close to the sea surface, particularly of the information that has been obtained from sonar observations of bubble clouds produced by breaking wind waves. These clouds provide tracers of the turbulent motions and are important, especially at high wind speeds, in the process of air‐sea gas transfer. the observations of bubble clouds are here related to other measurements of turbulence, particularly to direct measurements of currents and temperatures in lakes or at sea, and to laboratory studies. Some novel observations of bubble clouds and breaking waves, their frequency and relation to Langmuir circulation, are presented.There is now emerging a pattern of clues that point to the dominance of breaking surface gravity waves as a source of turbulence to a depth below the surface of 0.04 to 0.2 times the wavelength of the dominant breaking waves, although the effect of swell has yet to be clarified. the relative depth appears to increase with increasing values of W,1/c, where W10 is the wind speed andcthe phase speed of the dominant waves. Below this region the generation of turbulence may be dominated by shear‐stress or convection. Here, turbulence is generally similar to that in the atmospheric boundary layer. There are, however, coherent motions on the scale of the mixing layer that persist for periods of a few minutes to an hour or so, to which the transport of a large part of the momentum and heat fluxes can be attributed, and which strongly affect the dispersion of buoyant particles or bubbles. These motions deserve special study to establish their contribution to heat and momentum transport, and hence to determine if, or when, they should be specifically represented in models of the upper ocean devised, for example, to describe the dispersion of passive and non‐passive tracers or the air‐sea transfer o

ISSN:0035-9009    

DOI:10.1002/qj.49711850302

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA time‐dependent primitive‐equation model of the southern hemisphere winter troposphere with an idealized dome‐shaped continent centred at 80°S has been used to assess the potential of Antarctica to force stationary waves and to determine the location of the mid‐latitude baroclinic storm track. Several integrations of the model for two hundred days were made with the zonal‐mean fields fixed at the climatological values. In the time mean of each run an anticyclonic wave response formed over the mountain and a planetary wave propagated into the mid latitudes with substantial amplitude. This suggests that much of the observed stationary asymmetry in the southern, mid and high latitudes may be due to Antarctica.The response to the Antarctic forcing was different in a steady, linear version of the model. However, interaction between the steady waves appears to be of minor importance to the time‐mean pattern. Rather, E‐vector fields point to a substantial effect of the transients on the pattern. In particular, the low‐frequency transients appear to be important in the balance of the time‐mean equations

ISSN:0035-9009    

DOI:10.1002/qj.49711850303

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA recent version of the GLA fourth‐order GCM is used to investigate the short‐term relationship between tropical heating and upper tropospheric subtropical westerly maxima in the summer hemisphere. Emphasis is focused on a 15‐day forecast of the circulation corresponding to 6‐20 January 1979. During this time, observational data from the FGGE suggested that strong convection over the South Pacific was helping to maintain a nearby subtropical jet. the dominant term in the zonal momentum budget was the Coriolis force applied to the diabatically driven meridional circulation, although the mean advection of zonal momentum and transient eddy momentum and sensible‐heat transports made important contributions. A ‘full‐physics’ forecast made with the GCM is able to simulate these processes to a reasonable degree of accuracy.To examine the impact of direct meridional overturning on the rotational flow in the South Pacific, the latent energy supplied to the model atmosphere is reduced in two ways. First, negative sea‐surface‐temperature anomalies are imposed in the area of maximum convection. Second, temperature changes resulting from precipitation processes are ignored in the model thermodynamic equation. Results from both types of experiments are consistent, and they substantiate our earlier observational findings that, at least for this case study, summertime subtropical westerly maxima are largely forced by divergent outfl

ISSN:0035-9009    

DOI:10.1002/qj.49711850304

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe role of the Conditional Symmetric Instability (CSI) in the formation of convective systems in the cold airmass located at the rear of a secondary cold‐frontal system is evaluated. This study is based on observations made on 4 June 1984 during the French experiment LANDES‐FRONTS 84. In particular, the mesoscale three‐dimensional circulation deduced from Doppler‐radar data within one of these convective systems is studied in detail and compared with that predicted by the CSI theory. In spite of the fact that, on the one hand, notable convective‐scale motion masks the mesoscale circulation, and that, on the other hand, the synoptic‐scale circulation is poorly described, this comparison shows that, among the various theories involved at the mesoscale, only CSI gives a proper account of the observed mesoscale

ISSN:0035-9009    

DOI:10.1002/qj.49711850305

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSquall lines stand out from ordinary cumulonimbus convection because of a special structure that dramatically extends their duration, precipitation output and area of influence. Time‐dependent models have identified surface outflow boundaries and low‐level environmental wind shear as the crucial elements in squall‐line formation and/or maintenance. Steady‐state models have shown how properties of the downdraught reservoir, or ‘cold pool’, must be matched to the far‐field wind and thermodynamic profiles to sustain the convection. However, the dynamical role of the environmental shear and the nature of the interaction between the positively and negatively buoyant air have remained uncertain. For help with these issues, a time‐dependent numerical model is developed with all moist processes either parametrized or based onad hocassumptions. the simplifications make it possible to distinguish more clearly than in the past between the formation and maintenance of squall lines and between the initial and disturbed far‐field environments.The convective updraught forms within an expanding region of disturbed flow separated from the undisturbed environment by ‘storm fronts’. Forced (or neutral) ascent occurs at a surface ‘gust front’ on the upwind side of the cold pool. We distinguish squall lines from ordinary convection by looking at the coherence between the forced and convective updraughts. It is found that subsidence over the cold pool disorganizes the updraughts, whereas a deep overturning circulation downshear from the gust front has an organizing effect. Hence, factors which allow the initial subsidence to occur ahead of the gust front, namely contrasting lower‐and upper‐level winds and large potential buoyancy, favour squall‐line development. It is argued that, in cases with large convective potential energy, the deep mesoscale circulation is more important in the formation and maintenance of the line than either the vertical shear of the air reaching the cold pool or the s

ISSN:0035-9009    

DOI:10.1002/qj.49711850306

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe late 1930s and early 1940s saw strong climatic anomalies in the tropical Pacific basin. In this paper we combine an ocean‐modelling aproach to the investigation of the Pacific climate of this period with a multi‐parameter data analysis. It is shown that a large and deep pool of warm water in the western Pacific in the late 1930s acted as an energy source for the strong and prolonged El Niño event of the early 1940s and its rapidly following successor. Remote off‐equatorial Rossby‐wave forcing plays a prominent role in the generation of thes

ISSN:0035-9009    

DOI:10.1002/qj.49711850307

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAn idealized simulation of the Indian monsoon is performed using a prescribed heat source representative of the time‐averaged latent heating due to convection over India, and a simple representation of the east African orography. A quasi‐equilibrium model is used to solve this problem in three dimensions on a sphere. the model is shown to be able to simulate the cross‐equatorial flow and monsoon circulations driven by this problem and to be in good agreement with parallel integrations carried out with a hydrostatic primitive‐equation model except in areas affected by orographically forced gravity waves. the solutions given by these time‐dependent models are in good agreement with those found by using linearized steady‐stat

ISSN:0035-9009    

DOI:10.1002/qj.49711850308

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49711850309

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractLaboratory studies show that when soot particles from acetylene combustion are captured by drops of size 0.1 to 1 mm they remain partially submerged in the surface for several hours. the intensity of solar radiation passing through a drop is calculated to be much greater near the surface, and therefore with such particles on the surface will give enhanced absorption compared with the situation in which the particles are uniformly distributed throughout the drop volume. This gives a possible explanation for enhanced cloud absorption when soot particles are present in amounts consistent with field measurements.

ISSN:0035-9009    

DOI:10.1002/qj.49711850310

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49711850311

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY