摘要:

AbstractA feature of integrations with a general circulation model of the troposphere and stratosphere was that events were spontaneously produced closely resembling stratospheric sudden warmings. One example is examined in detail by means of momentum, heat and energy budget calculations, after a description of its main synoptic developments. Brief reference is made to two other model‐simulated warmings. It is argued that Matsuno's simplest idealization of stratospheric sudden warmings does not provide an adequate description of these events. The appearance of equatorward eddy momentum fluxes was found to have played a central role in their evolution. A mechanism is proposed by means of which such a flux reversal might occur in the stratosphere. The model warmings were apparently instigated by planetary‐scale changes in the troposphere, rather than by internal hydrodynamic instabil

ISSN:0035-9009    

DOI:10.1002/qj.49710645002

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe entropy balance associated with a Budyko‐Sellers climatic model is developed. It is shown that different regimes, associated with decreasing, as well as increasing values of entropy production (which measures the rate of dissipation in the system) in the course of time are possible. This immediately poses the problem of stability of steady states of the climatic system. An explicit criterion of climatic stability is thus derived, which is expressed in terms of thermodynamic quantities related to excess entropy production. The results are illustrated on simple cases involving diffusive energy transport. A comparison with Paltridge's minimum entropy exchange principle is also attempte

ISSN:0035-9009    

DOI:10.1002/qj.49710645003

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe use of diagnostics based on different forms for the forcing term in the omega equation is explored. These forms are the two‐level and continuous versions of the approximation used by Sutcliffe (1947) in his development theory, the usual dynamical meteorology version involving vorticity and thermal advection, and that involving the so‐called Q‐vectors which was introduced by Hoskinset al.(1978). The diagnostics are applied to a model baroclinic wave and to a subjectively analysed real data case. The Sutcliffe form is simplest and gives a global view of the system movement and development, but details such as active frontal regions are missed. The vorticity and thermal advection form has few advantages. It is demonstrated that the Q‐vector analysis can provide more information than the Sutcliffe form in describing details of system development, particularly with respect to (a) a vectorial view of the horizontal ageostrophic motion field, and (b) some indication of the intensity of frontal circulations. A case is presented for including Q‐vector fields in low‐ and mid‐tropospheric fo

ISSN:0035-9009    

DOI:10.1002/qj.49710645004

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractWe examine the kinetic energy that may be generated from surface heating. Cumulonimbus, cumulus, mesoscale and large‐scale conversion of potential into kinetic energy can be identified in an idealized way, as distinct processes. Each has a characteristic thermodynamic efficienc

ISSN:0035-9009    

DOI:10.1002/qj.49710645005

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractMesoscale circulations, induced by mesoscale available potential energy diabatically generated in the boundary layer are studied through the numerical integration of primitive equations. The energetics of a sea‐breeze simulation is studied in some detail. After 12 hours of simulation the kinetic energy is about a quarter of the mesoscale available potential energy diabatically produced. We comment on the energy lost by the upstream difference scheme, and on some aspects of the unavailability of available potential energy in such a system that together describe this level of inefficienc

ISSN:0035-9009    

DOI:10.1002/qj.49710645006

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA two‐dimensional primitive‐equation model is used to investigate various aspects of the sea‐breeze phenomenon. The influence of soil moisture content is examined by varying the Bowen ratio of the underlying land surface. This is equivalent to controlling the magnitude of the sensible heat flux at the ground since the diurnal variation of net radiation minus ground heat flux is approximately the same in all cases. It is found that the inland penetration rate of the sea breeze varies significantly with the degree of soil moisture. The model predicts a significant slowing of the frontal advance around midday for the case of ‘relatively weak’ sensible heating over the land, as well as reproducing the frontal acceleration observed in late afternoon for all cases. The sea‐breeze circulation detaches itself from the coastline around sunset and moves rapidly inland with diminishing magnitude and this aspect is discussed in relation to observations in the south of England.An attempt is made to model the southern England sea breeze of 14 June 1973. Various experiments are discussed, including one in which different values of Bowen ratio are specified ahead of and behind the front. Fairly good agreement is found, although it is not possible to reproduce all features of the inland penetration curve for that day.Some implications of these experiments for the production of daily forecasts by mesoscale models are briefl

ISSN:0035-9009    

DOI:10.1002/qj.49710645007

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA cloud parametrization scheme which allows for low, medium, high and convective clouds has been developed from GATE data for use in the Meteorological Office 11‐layer tropical model. The problems involved in using synoptic observations to derive methods of predicting clouds are discussed. Only limited success was obtained in relating observed cloud amounts to relative humidity and atmospheric temperature structure. The restrictions imposed on the cloud scheme by the model's resolution and by its inability to produce a perfect simulation are considered. In the light of these difficulties a simple approach was adopted based on the assumption that condensation on the smallest scales is part of a larger‐scale condensation regime related to the synoptic scale situation. The scheme has been designed to reproduce the main features of a cloud field by relating the large‐scale meteorological features associated with a cloud distribution to model variables. Low, medium and high cloud amounts are determined from a quadratic relationship with relative humidity. Low cloud has also been related to the temperature lapse rate in an attempt to model the persistent areas of sub‐tropical stratocumulus occurring under inversions. A relative humidity relationship is inappropriate for convective cloud which has, therefore, been related to the convective mass flux calculated in the convection scheme of the model. The scheme has been reasonably successful in predicting the cloudiness associated with the ITCZ and the NE. and SE. trades. The cloud fields showed a good degree of coherence from day to day and there were no signs of unrealistic feedbacks between radiation, cloud and d

ISSN:0035-9009    

DOI:10.1002/qj.49710645008

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractInfrared radiative properties of Arctic stratus clouds in the 10.1 to 12.7μm wavelength region are determined from a series of aircraft measurements. The average emissivity of the clouds when scattering is neglected is unity for cloud depths greater than 350m. Under the assumption that the cloud layers are homogeneous the cloud droplet volume absorption coefficient is estimated as 17±5km−1. Several mass absorption coefficients are estimated for several assumed liquid water distributions. It is also concluded that the cloud reflectance is not larger than 2(

ISSN:0035-9009    

DOI:10.1002/qj.49710645009

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA model of radiation fog is described containing an explicit formulation of the microphysics of the condensation process. The coupling between the radiative and microphysical processes within the model means that apart from the specification of the turbulence and CCN spectrum it is deterministic.Results are presented which indicated that:(i) The drop‐size distribution is sensitive to the CCN concentration but not to the presence of large CCN.(ii) Radiative loss from the drops can have a significant effect upon their growth.(iii) The drop‐size distribution is very sensitive to reductions in the condensation coefficient to a value below 0.033.Differences between observed and model drop‐size distributions are attributed to an underestimate in the model of the level of mixing within a

ISSN:0035-9009    

DOI:10.1002/qj.49710645010

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractObservations from two towers situated in flat, tree‐covered terrain (z0lying between 0.4 and 0.9 m) have been used to investigate the flux‐profile relations in the height rangez/z0from 5 to 85, wherezis the height above the zero‐plane displacement. The analysis confirms a lower height limit (atz = z*) to the validity of the Monin and Obukhov functions ϕM,H(z/L) in unstable conditions and, by implication, of the logarithmic wind law in neutral conditions. We findz*/z0≃ 35 and 150 for wind at the denser and less dense (lowerz0) surfaces, whilst for temperaturez*/z0≃ 100.The levelz*corresponds with the top of the transition layer, within which it is assumed the profiles depend additionally upon a length scalezs, related to surface wake generation. On the assumption thatz*αzs, modification of the profiles in the transition layer is then described through a function ø(z/z*) whose explicit form is derived from length‐scale considerations in a region of wake‐shear interaction. The observed non‐dimensional profiles ϕ° are well represented byϕ° ≃ 0.5ϕ(z/L)exp(0.7z/z*)Both for wind and temperature. For wind at both surfaces, the depthz*is approximately constant in unstable conditions and equal to 3δ, δbeing the tree spacing. We tentatively conclude that δ is the relevant surface length scalezscharacterizing the wake fiel

ISSN:0035-9009    

DOI:10.1002/qj.49710645011

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY