ISSN:0035-9009    

DOI:10.1002/qj.49710745102

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA dynamical classification of organized convection is presented, and previously published and additional models are collated in a more general theory. the transport properties of each type are represented by flux laws, the motivation being to understand convective transports in the context of parametrization schemes for organized convection.Five distinct models, derived as analytic solutions to a general displacement equation obtained from conservation properties of the Boussinesq equations, are necessary to describe the dynamics. These models, designated propagating, steering‐level, jump, cellular and classical, have very distinctive dynamical structures, and can be combined to represent more complex types of organized convection.The propagating and steering‐level types export a significant amount of kinetic energy, momentum and entropy, while the jump and cellular types store a considerable amount of energy as work done on the environment by the pressure field. the classical type does not transport momentum, and is a representation of the classical thunderstorm in weakly sheared flow.Apart from the cellular model, although the entropy transports are broadly similar, the momentum and kinetic energy transports are very distinctive, with counter‐gradient momentum transport the rule rather than the exception. Thus by effecting organized updraught/downdraught circulations, a completely different transport problem from small‐scale cumulus and mixed‐layer convection is posed, with fundamental inferences regarding parametrization. the dynamical necessity of a mesoscale response in the cellular and propagating types suggests that this scale may, in certain cases, need to be represented explicitly in convective parametrization schemes for large‐scale models.These prototypes have been deliberately simplified for the sake of elucidating fundamental principles, and to give a dynamical basis for experimentation and generalization, through exploiting both cloud‐scale and larger‐scale numerical simulation models, as well as providing guidance in observational analyses, budget studie

ISSN:0035-9009    

DOI:10.1002/qj.49710745103

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA description is given of a numerical model which has been used to simulate the steady baroclinic waves which may be observed in a fluid rotating about a vertical axis and subjected to a radial temperature gradient. the model is designed to provide accurate simulations of the observed flow without recourse to parametrization of small eddies. the model is verified by comparing the results of integrations with observed flows; many of the differences between the simulated and observed flows may be ascribed to the limited resolution of the model. the numerical model is used to provide data on the non‐linear interactions between different scales of motion present in the steady flows. It is demonstrated that the predominant non‐linear interaction, in the numerical model, involving the sidebands of the dominant wave is an interaction with the first harmonic of the dominant wave; this contrasts with an interaction with the long wave which was suggested by earlier workers. Experimental evidence is advanced to show that the sidebands may be enhanced by weak asymmetrical forcing and this sensitivity has been verified through the results the further numerical integrati

ISSN:0035-9009    

DOI:10.1002/qj.49710745104

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractPrevious studies have shown how simple baroclinic waves may exhibit either a primary cold front or a primary warm front. In this paper it is shown that many of the quite realistic differences between the cold and warm fronts are a consequence of the forward tilt of the temperature wave with height. This forward tilt is proved to be a necessary feature of a growing baroclinic wave. Thus a dynamical distinction between cold and warm fronts is postulated.

ISSN:0035-9009    

DOI:10.1002/qj.49710745105

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractWind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough, bell‐shaped, two‐dimensional hill, with heighthand maximum slope 0.26, placed in a neutrally stable boundary layer of thickness 10hand roughness length zo= 0.02 h. Close agreement is found between the mean velocity and predictions obtained from Taylor's (1977) computational model and Jackson and Hunt's (1975) analytical linearized model, for locations at or upwind of the hill top but not in the wake. Examination of the models shows that the shear stresses are only important in an inner region close to the hill surface, so that, as suggested by Jackson and Hunt (1975), the perturbation to the mean flow outside this region is essentially inviscid. the theory shows that over very rough surfaces, such as wooded or urban terrain, the height of this inner region can be of the same order as the height of the roughness elements (so that in our experiments no measurements could be made in this region).In a second experiment flow over asmoothhill on a rough surface was studied. the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness (in this case rough to smooth). In the lee of a hill, however, the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate.Finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface. Calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the fi

ISSN:0035-9009    

DOI:10.1002/qj.49710745106

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA numerical model of the local flow above an infinite series of two dimensional ridges is used to investigate the extent to which form drag on the ridges is balanced by reductions in surface shear stress compared to that for a plane surface. With a constant eddy viscosity Mason and Sykes (1979) results an confirmed and there is only a relatively small net increase in the horizontal force on the terrain due to the presence of topography. A larger increase is found when height dependent eddy viscosities are used. the nature of velocity defects produced by individual ridges are examined for the two cases.

ISSN:0035-9009    

DOI:10.1002/qj.49710745107

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractTwo well‐posed initial‐boundary value problems for the quasi‐geostrophic equations have been identified. the first is defined in a vertical annular cylinder with specified temperatures on the horizontal bottom and top surfaces. the second is defined in a box with periodic boundary conditions on the sides and with rigid bottom and top surfaces; bottom topography is included. Well‐posedness is established by theorems which determine conditions under which there exist unique solutions depending continuously on the initial and other data. the theorems are stated here, but proved elsewhere.Completely rigidly contained quasi‐geostrophic motion is in general an ill‐posed problem, due to over‐specification of circulation integrals around edges where vertical and horizontal boundaries meet.The theorems are used to infer (1) sufficient conditions for the convergence of finite‐element Galerkin approximations of Fix (1975) to exact solutions, (2) the predictability type of the solutions as defined by Lorenz (1969), and (3) that the long‐time high wave‐number spectra of the equations are steeper than the inertial ranges and the statistical equilibrium spectra of Kraichnan (1967). Implications for numerical circulati

ISSN:0035-9009    

DOI:10.1002/qj.49710745108

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA very simple energy‐balance equation for the mean surface temperature of the planet (Budyko‐type model) is perturbed by a stochastic term, simulating the numerous ‘weather’ processes not considered in the deterministic feed‐back term. In the first instance, a symmetrical deterministic process with three equilibrium states is considered. Using standard methods for determination of the probability density distribution, the characteristic time which the climate system spends in the neighbourhood of one stable equilibrium before shifting to the other is expressed in terms of the characteristic time of the feed‐back process and the time constant of the perturbing process. Realistic corresponding values are found. an Appendix discusses the possibility of using the analogy between stochastically perturbed Newtonian and quantum‐dynamical systems in research on c

ISSN:0035-9009    

DOI:10.1002/qj.49710745109

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractIn a zonally‐average energy balance climate model (principal features as with Paltridge 1975) with the four unknowns ‐ surface temperatureT, cloud amountN, total meridional heat fluxes within the ocean and the atmosphere Om+Am, and total vertical heat fluxLE+CH, the maximum entropy production by meridional heat fluxes is used as a constraint to solve the system for the four unknowns in all 10 boxes of the model. Since the solution at maximum entropy production by meridional heat fluxes agrees quite well with present mean conditions, this maximum principle is used as a working hypothesis for climate sensitivity studies avoiding the use of fixed cloud amount and meridional heat fluxes. the resulting sensitivities partly agree and disagree with those of similar energy balance climate models. Disagreement is particularly high if an ice‐albedo feed‐back is included. the feed‐back is strongly reduced because of opposing effects of cloud amount in high

ISSN:0035-9009    

DOI:10.1002/qj.49710745110

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA three‐dimensional semi‐implicit mesoscale numerical model based on the Navier‐Stokes equations is described and tested. Numerical techniques for achieving numerical stability with long time steps are discussed. In simulating flow over mountains the model accurately reproduces the results of an explicit model. Low vertical resolution causes moderate damping of the orographically forced responses, but adjustment rates are not seriously affected. the model is stable with time steps six times those of a similar explicit model and its computational efficiency is about three times greater.A cross‐section version is used to examine the response characteristics. With four layers in the vertical, the phase speeds of external gravity waves with wavelengths 8 Δx to 30 Δx are slowed to 50% to 85% of the analytic phase speeds, respectively. Even so, simulations with eight and sixteen layers show that the semi‐implicit model reproduces the features of simulations with the explicit model and has comparable mass and energy conservation characteristics.Adjustment rates of the mass and momentum fields towards a steady state are studied for mountain wave and jet stream circulations. Despite the reduced gravity wave phase speeds, root‐mean‐square error calculations show very little difference between the semi‐implicit and explicit models. This is attributed to the fact that most of the adjustment is effected by relatively slow internal modes which are not greatly slowed in the semi‐implicit model. the verification that the semi‐implicit model produces adjustments between mass and momentum fields about as well as an explicit model is an important step in ensuring that the semi‐implicit technique can be successfully applied t

ISSN:0035-9009    

DOI:10.1002/qj.49710745111

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY