摘要:

AbstractA new set of equations is derived for nearly circular flow in gradient balance. For precisely axisymmetric motion, the system reduces to the well‐known balanced vortex equations of Eliassen. The derivation is based on the assumption that the radial component of velocity is small in comparison to the azimuthal component. By applying this approximation to Hamilton's principle for a continuum of fluid parcels, while preserving the time and particle‐labelling symmetries of the primitive equations, it is ensured that the resulting system possesses conservation laws for energy and potential vorticity. In potential radius coordinates, the Lagrangian equations of motion take the form of the geostrophic and hydrostatic balance conditions. The system is also presented in Eulerian form, and a practical integration scheme, based on a linear elliptic equation for geopotential tendency, is described. Finally, the set is rederived by a conventional scale analysis in order to determine constraints on the diabatic forcings which are required for consistency with the approximat

ISSN:0035-9009    

DOI:10.1002/qj.49711749902

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe available enthalpy is an early form of the modern thermodynamic concept of exergy, which is the generic name for the amount of work obtainable when some matter is brought to a state of equilibrium with its surroundings by means of reversible processes.It is shown in this paper that a study of the hydrodynamic properties of available enthalpy leads to a generalization of the global meteorological available energies previously introduced by Lorenz, Dutton and Pearce. A local energy cycle is derived without approximation. Moreover, static instabilities or topography do not prevent this theory from having practical applications. The concept of available enthalpy is also presented in terms of the potential change in total entropy. Using the hydrostatic assumption, limited‐area energetics is then rigorously defined, including new boundary fluxes and new energy components. This innovative approach is especially suitable for the study of energy conversions between isobaric layers of an open limited atmospheric domain.Numerical evaluations of various energy components are presented for a hemispheric field of zonal‐average temperature. It is further shown that this new energetic scheme realizes a hierarchical partition of the components so that the smallest of those available enthalpy reservoirs are almost of the same magnitude as the kinetic energy. This is actually the fundamental property that induced Margules to define the primary concept of available kinetic energy in meteorol

ISSN:0035-9009    

DOI:10.1002/qj.49711749903

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper reports an analysis of the roles of temporal scale interactions (seasonal, intraseasonal and high‐frequency components) in the generation and maintenance of a pronounced block over the North Atlantic that lasted for three weeks in February 1983. This blocking disturbance had a distinct dipole structure initially oriented in an east‐west direction downstream from a strongly diffluent south‐west‐north‐east oriented seasonal jet. Although it has an equivalent barotropic structure, there is a well‐defined vertical velocity field with ascending (descending) motion on its western (eastern) flank. As it develops, matures and decays, it rotates systematically in a clockwise direction.The contributions from the various temporal scale interactions to the episodal average local energetics of this block are evaluated. There are five comparably important processes controlling the intensity, configuration, and evolution of the block. The synoptic eddy‐straining mechanism proposed by Shutts is manifested in three energetics terms, of which one is found to be particularly large. The blocking disturbance also barotropically extracts kinetic energy at a significant rate from the seasonal diffluent jet under the influence of the latter's strong deformation field. The pressure work process, the baroclinic conversion process, and above all, the nonlinear dynamics of the blocking disturbance itself are quantitatively important in redistributing the energy within the blocking region. The effects of the diabatic and subgridscale processes are found, as residues, to be substantially dissipative

ISSN:0035-9009    

DOI:10.1002/qj.49711749904

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA three‐dimensional, non‐hydrostatic, anelastic model using interactive grid nesting is employed to simulate the airflow over and around the Alps during a strong foehn event on 8 November 1982. In the model, a single upstream sounding is used to initialize the mean flow. This single sounding was obtained from the output of a three‐dimensional objective analysis of rawinsonde data. The model results show that in low levels the airflow is forced around the Alps, in particular at its western edges, whereas above 700 hPa the flow is over the Alps. Above northern Italy a convergence line between the easterly flow and the foehn forced by the Apennine Mountains is simulated in accordance with observations. To the west of Milan vertical vortices are simulated in agreement with the complex circulation observed in this region.The simulations show that there is significant horizontal variability in the local vectors of the pressure drag and the momentum flux. This variability complicates the comparison between model and observational data as well as restricting one's ability to extrapolate accurately local cross‐sectional observations of pressure drag and momentum flux to values representative for the entire Alpine complex. Unfortunately, there were no measurements of surface pressure drag for the entire Alps on 8 November 1982. However, measurements during ALPEX during four foehn events obtained meridional and zonal values of −4.3 and 1.8 × 1011N. The current values of −4.7 and 1.7 × 1011N obtained for the simulations of the 8 November 1982 case using 5 km horizontal resolution are very close to the previous observations. There were observations on a cross‐section between Vicenza and Munich on this day. The values obtained were −0.67 × 106N m−1for the surface pressure drag and −0.75 × 105N m−1for the momentum flux averaged between 5 and 10 km above mean sea level. The simulated values for the same cross‐section were −0.62 and −0.50 × 106Nm−1for the pressure drag and momentum flux, respectively. Overall, the averaged simulated meridional momentum flux between 5 and 10 km was −2.2 × 1011N which is about 47% of the surface pressure drag. These results and comparisons with observations suggest that while the model appears to predict reasonable values for the surface pressure drag the amplitude of the momentum flux values is too large. The simulated values are, for example, six times those observed for the Vicenza to Munich cross‐section. Simulations using even finer resolution over a reduced region suggest that poorly simulated dissipative forces by the model may be responsible for some of this discrepancy. Some other factors such as surface

ISSN:0035-9009    

DOI:10.1002/qj.49711749905

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA three‐dimensional numerical model with interactive grid nesting is used to study the pressure drag and associated momentum fluxes due to the Alpine complex (for a specified upstream wind and static stability profile). Four basic questions are addressed which are relevant to the problems of flow description in the vicinity of mountains and the impact of orography in the context of mesoscale numerical weather prediction and general circulation models:(i)What is the dependence of basic quantities such as the pressure drag on the model's horizontal resolution?(ii)Is there a need for non‐hydrostatic dynamics to account properly for the flow characteristics near steep mountains?(iii)Is there an effective role for enhanced orography such as an envelope formulation?(iv)Might a ‘gravity‐wave‐drag’ parametrization scheme be able to represent adequately the highest resolution fluxes and surface drag in a much coarser resolution model?A series of experiments with both hydrostatic and non‐hydrostatic models at resolutions of 80, 40, 20, 10 and 5 km is analysed, and two of these experiments are repeated with an envelope orography.It is concluded that hydrostatic simulations are sufficient to describe the basic dynamics even at 5 km resolution; however, there is a strong dependence of the drag and momentum fluxes on resolution, with the drag at 80 km resolution being almost half that at the highest resolution. It is also shown that the use of an envelope orography at coarser resolutions can compensate significantly for the drag under‐estimation, but is less effective in representing the vertical stress profiles or the direction of the stress vectors, which are systematically in error at the coarsest resolution. The potential role of gravity wave drag is confirmed and possible improvements considered. It is suggested that both envelope orography and gravity wave drag may make a significant contribution until resolutions are as high

ISSN:0035-9009    

DOI:10.1002/qj.49711749906

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe atmospheric forcing of large sea‐level oscillations (up to 1.5 m amplitude with about a 10 min period) in some bays and inlets of the Balearic Islands is described using simultaneous measurements of pressure and sea‐level elevation in the port of Ciutadella (at the end of a large and narrow inlet) during 5–7 July 1989. The influence of atmospheric pressure oscillations on these large sea‐level variations, locally known as ‘rissaga’, is investigated. Coherence and cross‐correlation functions reveal that the large oscillations in the inlet are associated with and probably forced by a 10 min gravity wave in the atmosphere. The effect of longer‐period waves on the inlet is seen in the well‐known inverted barometric effect, forcing small oscillations in the water level of just some centimetres. These latter waves have a period of around 50 min and an unusually large amplitude of some 3 mb. The phase spectrum between sea level and pressure suggests that the inlet may behave as a damped harmonic oscillator which, during rissaga, is externally forced by the atmospheric pres

ISSN:0035-9009    

DOI:10.1002/qj.49711749907

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA study of the cyclic fluctuations in the earth's rotation, the geomagnetic field, the global atmospheric circulation and solar activity reveals the existence of 50‐day and 120‐day oscillations common to all. Our results, as well as the results obtained by radiometric measurements from the satellites Nimbus‐7 and the Solar Maximum Mission (Wilson 1982; Pap 1985), suggest that their origin lies in the physical processes in the sun. The mechanism remains unexplained but from this work it follows that the role of the interplanetary magnetic field could very well be impo

ISSN:0035-9009    

DOI:10.1002/qj.49711749908

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have obtained the vertical and detrained mass fluxes through the life cycles of four thunderstorms using measurements from four Doppler radars and an instrumented aircraft. The storms formed over the Magdalena Mountains of central New Mexico, and remained near the mountains through their entire life.Updraughts appeared to entrain a certain amount of surrounding radar‐invisible air. Thermodynamic considerations suggest that this air came from neighbouring towering cumulus clouds rather than directly from the environment. Entrained air did not immediatly mix with cloud‐base air, but tended to maintain its own identity in ascent. Levels with decreasing parcel buoyancy induced significant detrainment from the updraught. Downdraughts were confined primarily to levels below 7–8 km above mean sea level.The net mass flux entering or leaving the underside of the thunderstorms equalled that supplied by the mountain upslope flow. Since this net flux is a combination of updraughts and downdraughts, unstable air at low levels is gradually replaced by stable downdraught air, thus ensuring the demise of the

ISSN:0035-9009    

DOI:10.1002/qj.49711749909

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo case studies are presented of the direct measurement of cloud droplet fluxes to a forest canopy by the eddy correlation technique. Two instruments have been used for the liquid water measurements, and close agreement for values of liquid water content and liquid water flux have been obtained. The case studies were conducted in different weather conditions: case 1 with high values of liquid water content (typically 0.3 g m−3) and low wind speeds (2–3 m s−1), and case 2 with low liquid water content (0.1 g m−3) and higher wind speeds (typically 6 m s−1). In both cases the deposition velocity for liquid water was markedly less than for momentum. For case study 2 the cause of the small deposition velocity for liquid water was the small droplet size; the typical modal radius was 4.4 μm. The deposition velocity increased as a function of droplet size, exceeding that for momentum for droplets larger than about 6 μm. When normalized, the results agreed reasonably well with those obtained over grassland using the gradient technique. The results are compared with the predictions of the models of both Lovet

ISSN:0035-9009    

DOI:10.1002/qj.49711749910

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0035-9009    

DOI:10.1002/qj.49711749911

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY