共查询到20条相似文献，搜索用时 859 毫秒
1.
Significant improvements are occurring in the representation of physical processes in atmospheric convection models. They should go along with parallel improvements in the parameterization of subgrid scale turbulent processes. This problem appears to be particularly delicate in the presence of clouds, due to the local release of latent heat.Two important points are the choice of adequate turbulent thermodynamic variables and of the method for truncating the statistical moment equations. These topics are discussed here within the framework of the three-dimensional convection model under development at the Laboratoire de Météorologie Dynamique. Assuming the need for at least a simplified second-order closure, two improvements are tested on a numerical simulation of the Porto Rico experiment conducted by the National Center for Atmospheric Research (U.S.A.) in 1972. They concern the use of a rate equation for sub-grid scale turbulent kinetic energy and of specific variables which are approximately conserved in the condensation process. 相似文献
2.
Analysis of turbulent transfer inside a vegetative canopy can be realized by means of several methods. In our case, we have used principally the aerodynamic and the thoron methods. The thoron diffusivity profiles show an important distortion in the middle zone of the canopy, below the maximum of leaf area density. This distortion is associated with a maximum source of sensible heat flux at these levels, which partially invalidates the aerodynamic approach.Centre de Physique Atomique et Nucléaire, Université Paul Sabatier, Toulouse, France.Bioclimatologie, Institut National de la Recherche Agronomique, Route de St. Cyr, Versailles, France. 相似文献
3.
4.
The turbulent heat flux is usually assumed constant with height in the atmospheric surface layer. The validity of this hypothesis is known to be questionable, due to a possible variation along the vertical of the infrared radiative heat flux.This problem is approached theoretically, using semi-empirical expressions for emissivities, and assuming logarithmic temperature and humidity profiles. A first approximation of the radiative heat flux divergence is thus obtained analytically, as a function of the surface layer parameters. Numerical application to the case of an underlying water surface reveals appreciable variations of the radiative and turbulent heat fluxes in the first ten meters of the atmosphere, especially when wind velocity is low and humidity is high.These preliminary results are presented here for discussion. If accepted, they could lead to a reinterpretation of some experimental data, and should permit an extension of turbulent transfer theories to the case of a variable heat flux.Chargé de Recherches au C.N.R.S.Assistant I.N.R.A., Station de Bioclimatologie de Montfavet.Contributed paper to IUGG-IAMAP-AMS Conference on Planetary Boundary Layers, Boulder (Colorado), March 18–21, 1970. 相似文献
5.
《大气与海洋》2013,51(3):187-201
Abstract This paper investigates the formation and maintenance of the North Water Polynya, Baffin Bay in winter using a multi‐category sea‐ice model coupled with the Princeton ocean model. Monthly climatological atmospheric data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis provides the forcing. An objectively‐analysed climatology provides the initial ocean temperature and salinity. Wind stress drives the ice in a cyclonic gyre around northern Baffin Bay. Localized regions of thin ice form where wind drives ice away from coastlines or fast ice. The regions of thin ice are characterized by enhanced ice growth, exceeding 1.2 m mo?1. In the regions of thin ice, surface ocean heat flux is also enhanced and is between 30–60 W m?2. Surface heat flux is, in part, attributable to convective mixing and entrainment driven by ice growth. The surface heat flux reflects advection of the warm West Greenland Current. Heat and salt balances show that horizontal advective exchange counterbalances surface fluxes of heat and salt. 相似文献
6.
The parameterization of the dimensionless entrainment rate (w
e
/w
*) versus the convective Richardson number (Ri
δθ
) is discussed in the framework of a first-order jump model (FOM). A theoretical estimation for the proportionality coefficient
in this parameterization, namely, the total entrainment flux ratio, is derived. This states that the total entrainment flux
ratio in FOM can be estimated as the ratio of the entrainment zone thickness to the mixed-layer depth, a relationship that
is supported by earlier tank experiments, and suggesting that the total entrainment flux ratio should be treated as a variable.
Analyses show that the variability of the total entrainment flux ratio is actually the effect of stratification in the free
atmosphere on the entrainment process, which should be taken into account in the parameterization. Further examination of
data from tank experiments and large-eddy simulations demonstrate that the different power laws for w
e
/w
* versus Ri
δθ
can be interpreted as the variability of the total entrainment flux ratio. These results indicate that the dimensionless
entrainment rate depends not only on the convective Richardson number but also upon the total entrainment flux ratio. 相似文献
7.
A. G. M. Driedonks 《Boundary-Layer Meteorology》1982,22(4):475-480
Jump or slab models are frequently used to calculate the depth of the convectively mixed layer and its potential temperature during the course of a clear day. Much attention has been paid theoretically to the parameterization of the budget for turbulent kinetic energy that is required in these models. However, for practical applications the sensitivity of the solutions of the model equations to variations in the entrainment formulation and in the initial and boundary conditions is also very important. We analyzed this sensitivity on the basis of an analytical solution for the model which uses the well-known constant heat flux ratio. The initial conditions for the mixed-layer height (h) and potential temperature (
m
) quickly lose their influence. Only the initial temperature deficit is important. The mixed-layer temperature at noon on convective days is insensitive to the entrainment coefficient c. It is governed by the integral of the heat input and by the stable lapse rate. A change in c from 0.2 to 0.5 leads to a variation of 20% in h. This is not very much considering the accuracy in the determination of h from actual observations. 相似文献
8.
A model is presented for the height of the mixed layer and the depth of the entrainment zone under near-neutral and unstable atmospheric conditions. It is based on the zero-order mixed-layer height model of Batchvarova and Gryning (1991) and the parameterization of the entrainment zone depth proposed by Gryning and Batchvarova (1994). However, most zero-order slab type models of mixed-layer height may be applied. The use of the model requires only information on those meteorological parameters that are needed in operational applications of ordinary zero-order slab type models of mixed-layer height: friction velocity, kinematic heat flux near the ground and potential temperature gradient in the free atmosphere above the entrainment zone. When information is available on the horizontal divergence of the large-scale flow field, the model also takes into account the effect of subsidence, although this is usually neglected in operational models of mixed-layer height owing to lack of data. Model performance is tested using data from the CIRCE experiment. 相似文献
9.
G. Dubosclard 《Boundary-Layer Meteorology》1980,18(4):473-483
A new method is presented for determining experimentally the entrainment coefficient % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeyqaiabg2% da9iabgkHiTiaacIcadaqdaaqaaiabeI7aXjaacEcacaWG3bGaai4j% aaaacaGGPaGaamyAaiabg+caViaacIcadaqdaaqaaiabeI7aXjaacE% cacaWG3bGaai4jaaaacaGGPaWaaSbaaSqaaiaaicdaaeqaaaaa!4646!\[{\text{A}} = - (\overline {\theta 'w'} )i/(\overline {\theta 'w'} )_0 \] characteristic of a convective, planetary boundary layer. This method, which makes use of sodar records together with simultaneous meteorological observations, can be applied to morning convection situations (i.e. shallow mixed layer capped by a marked temperature inversion). Data from the Voves experiment (France, summer 1977) yield A values between 0 and 1, thus departing from the 0.2 ± 0.1 interval which is the range of commonly accepted values.A comparison between these results and theoretical predictions using models developed by Stull (1976) and Zeman and Tennekes (1977) indicates a fair amount of agreement; the importance of mechanically driven turbulence in the entrainment process, especially for the early morning hours, is therefore confirmed.
Résumé Une méthode de détermination expérimentale du coefficient d'entraînement % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeyqaiabg2% da9iabgkHiTiaacIcadaqdaaqaaiabeI7aXjaacEcacaWG3bGaai4j% aaaacaGGPaGaamyAaiabg+caViaacIcadaqdaaqaaiabeI7aXjaacE% cacaWG3bGaai4jaaaacaGGPaWaaSbaaSqaaiaaicdaaeqaaaaa!4646!\[{\text{A}} = - (\overline {\theta 'w'} )i/(\overline {\theta 'w'} )_0 \] dans une couche limite planétaire convective est proposée. Cette méthode, qui combine les données enregistrées par un sodar à des mesures météorologiques in situ, s'applique aux cas de convection matinale (couche de mélange assez peu développée surmontée par une inversion de température marquée.) Dans le cas des observations recueillies lors de la campagne de Voves (1977) elle fournit des valeurs de A qui s'écartent parfois de 0.2 ± 0.1 (gamme des valeurs souvent adoptées) et couvrent la totalité de l'intervalle 0-1.La comparaison entre les valeurs de A déterminées par cette méthode et celles prédites à partir des modèles de Stull (1976) et Zeman (1977) conduit à un accord satisfaisant, ce qui confirme le rôle joué par la turbulence mécanique dans le processus d'entraînement durant les premières heures de la convection matinale.相似文献
10.
John C. Wyngaard 《Boundary-Layer Meteorology》1990,50(1-4):49-75
I outline the general features of the vertical profile of the vertical flux of a conservative scalar in the planetary boundary layer, giving special emphasis to the convective case and emphasizing the importance of the Webb correction. After the influence of thermal stability on the structure of the turbulent eddies carrying this flux is reviewed, recent developments in parameterizing vertical transport in the convective boundary layer are discussed. I then survey three approaches to the numerical modeling of this transport — second-order closure, large-eddy simulation, and direct numerical simulation. Eddy-correlation, eddy-accumulation, and indirect techniques for measuring scalar fluxes are surveyed and contrasted. Finally, I discuss the physics of probe-induced flow distortion and its impact on scalar flux measurement, showing that it can be quite severe for trace species density fluxes measured from aircraft.Based on lectures given at the workshop Measurement and Parameterization of Land-Surface Evaporation Fluxes, Banyuls, France, October, 1988.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
Twenty-six months of continuous ceilometer data are used to estimate the convective mixed-layer height for 710 days by identifying
backscatter gradients associated with the entrainment zone. To accomplish this, a semi-automatic procedure is developed that
removes all non-applicable data before applying a mixed-layer height algorithm to the backscatter profiles. Two different
algorithms for estimating the mixed-layer height are assessed: the minimum-gradient method and the ideal-profile method. The
latter of these two algorithms is found to be more robust. Comparisons of mixed-layer height values estimated from the ceilometer
agree with previous observations with slightly higher estimates in the mornings and evenings. For clear days with no cumulus
cloud formation, the seasonal cycle in mixed-layer heights peaks in late June to early July. Daily maximum values are suppressed
by the site’s coastal location, remaining below 800 m for all but a few days. The mean daily maximum mixed-layer height increases
by 384 m for days with boundary-layer clouds. The mean summer diurnal trend is found not to differ greatly from that in spring
on clear days, while days with boundary-layer clouds have higher spring values than in summer. Net surface heat flux and synoptic
stability likely have the largest influence on the mixed-layer heights. Additionally, large intra-monthly variability suggests
a strong influence from regional dynamics. 相似文献
12.
R. B. Montgomery 《Meteorology and Atmospheric Physics》1954,7(1):125-132
Summary Several aspects of the formulation and physical meaning of heat flux by convection are discussed. Convective heat flux, is uniquely determined only when the flux of each constituent substance vanishes. For uniform composition, the physically satisfactory formulation of eddy flux of heat is in terms of the velocity fluctuation about the weighted mean introduced byHesselberg but in some important problems this formulation is practically the same asSwinbank's. It is suggested that convective heat flux be interpreted to include the flux of not only enthalpy but also potential energy.
This research was sponsored by the Office of Naval Research, U. S. Department of the Navy, under contract with Brown University.Contribution No. 701 from the Woods Hole, Oceanographic Institution. 相似文献
Zusammenfassung Es werden mehrere Möglichkeiten der Formulierung und der physikalischen Interpretation des Wärmeflusses durch Konvektion diskutiert. Der konvektive Wärmefluß ist nur dann eindeutig bestimmt, wenn der Fluß der einzelnen Komponenten verschwindet. Eine physikalisch befriedigende Formulierung der Wärmescheinleitung im Falle eines homogenen Mediums läßt sich mittels Geschwindigkeitsschwankungen um die ausgeglichene Bewegung gewinnen, wie sie vonHesselberg eingeführt wurden; doch ist diese Formulierung bei einigen wichtigen Problemen praktisch identisch mit der vonSwinbank. Es wird vorgeschlagen, unter konvektivem Wärmefluß nicht nur den Fluß von Enthalpie, sondern auch den von potentieller Energie zu verstehen.
Résumé Cet exposé discute les divers aspects du sens physique du flux calorifique dû à la convection. Le flux convectif de chaleur n'est déterminé absolument que lorsque de flux le chaque constituant est égal à zéro. Pour une composition uniforme, la formule physiquement satisfaisante du flux calorifique dû à la turbulence est en fonction de la fluctuation de la vitesse par rapport à la moyenne pondérée introduite parHesselberg. Dans certains problèmes importants, cette formule est cependant pratiquement la même que celle deSwinbank. L'auteur propose d'interpréter le flux de chaleur convectif de manière à y inclure non seulement le flux d'enthalpie, mais aussi le flux d'énergie potentielle.
This research was sponsored by the Office of Naval Research, U. S. Department of the Navy, under contract with Brown University.Contribution No. 701 from the Woods Hole, Oceanographic Institution. 相似文献
13.
Gary A. Briggs 《Boundary-Layer Meteorology》1988,45(1-2):117-135
It is suggested that convective scaling, with appropriate extensions, provides the most useful framework for estimating the effects of urban-scale surface inhomogeneities on diffusion in convective conditions. Strong contrasts in surface heat flux exist between cropland, forests, urban areas, and water or marshland surfaces. It is argued that a typical fetch for convective turbulence to readjust to changed heat (or buoyancy) input from the surface below is 2(U/w
*)h, where U is the mean wind speed in the mixing layer, w
* is the convective scaling velocity, and h is the mixing depth. In contrast, the fetch required for wind speed to readjust to new underlying surface roughness is of the order (U/u
*)2h/2, where u
* is the friction velocity.The ratio w
*/U is the best index of diffusion rates in moderately to very unstable conditions. General urban effects on heat flux, h, and U are discussed separately, then their combined effects on w
*/U are estimated. While this ratio can double over a large city during light winds, its increase is much less for small cities, or during moderate winds. Finally, some examples of heat flux in- homogeneities causing stationary convective features are presented. Steady downdrafts associated with these features are of the order of 0.4w
*, and could significantly increase surface concentrations from elevated sources.On assignment from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce.This paper is based on a presentation made at the AMS Specialty Conference on Air Quality Modeling of the Urban Boundary Layer, in Baltimore, late 1983. 相似文献
14.
Summary Evaporation and sensible heat flux have been calculated for each month over the Polar Ocean and the Norwegian-Barents Sea.
Sverdrup's evaporation formula was used, and it was first examined how the K-coefficient in that formula depends on the wind speed frequency distribution. Thus the effect of the Arctic wind conditions could be taken into account. Seasonal maps were constructed of mean wind speed. Previously obtained surface temperatures were used, but some additional examinations were carried out, using various assumptions for extreme surface temperatures in summer and winter.Evaporation and sensible heat flux were calculated separately for the following areas: Central Polar Ocean, Kara-Laptev Sea, East Siberian Sea, Beaufort Sea, and belts of 5° latitude of the Norwegian-Barents Sea.The values for the different areas are presented in tables and figures. Evaporation over ice surfaces has a double maximum—in spring and fall—and a main minimum in winter. Over open water surfaces the evaporation shows a summer minimum and a broad maximum in winter. If small parts of the ocean were to remain open longer in the fall, or during the whole winter, the heat loss would increase very rapidly.Sensible heat flux is often calculated from evaporation by theBowen ratio. The small evaporation values over the Polar Ocean give unreliable values for sensible heat flux, and instead the formula byShuleikin was used. This permits the determination of sensible heat flux independent of evaporation. The characteristic sensible heat flux curves are quite similar to the evaporation curves. The open water areas in the Polar Ocean show very high values for sensible heat flux. One percent open water, from October to May would increase the heat flux from the Central Polar Ocean from 3.7 to 5.2 Kcal cm–2, year–1. Open areas must remain small as there is not sufficient energy available to maintain such fluxes.Finally, a table gives the monthly values of the total heat loss for the various areas, by evaporation and sensible heat flux.
With 6 Figures
The research reported in this paper was sponsored in part by the Air Force Cambridge Research Laboratories, Office of Aerospace Research, under Contract AF 19(604)7415. 相似文献
Zusammenfassung Monatswerte für Verdunstung und Wärmefluß wurden für das Polarmeer und für Nordmeer-Barentssee berechnet. Zur Verdungstungsberechnung wurde die Formel vonSverdrup benutzt, deren K-Koeffizient in seiner Windabhängigkeit neu berechnet wurde. Auf Grund neu konstruierter jahreszeitlicher Karten der mittleren Windgeschwindigkeit konnten die arktischen Windverhältnisse berücksichtigt werden. Wegen der Unsicherheit früher bestimmter Oberflächentemperaturen wurden zusätzliche Berechnungen für Extremfälle im Sommer und Winter durchgeführt, um mögliche Fehlerquellen abzuschätzen. Verdunstung sowie Wärmefluß wurden gesondert für die folgenden Gebiete berechnet: Zentrales Polarmeer, Kara-Laptev-See, Beaufort-See sowie für Bänder von 5° Breite im Gebiet Nordmeer-Barentssee.Die Resultate für die einzelnen Gebiete werden an Hand von Diagrammen und Tabellen diskutiert. Über Eis zeigt die Verdunstung ein doppeltes Maximum im Frühling und Herbst und das Hauptminimum im Winter, während sich über offenem Wasser ein Sommerminimum und ein breites Wintermaximum ergeben. Es zeigt sich, daß bereits relativ kleine Wasserflächen, die länger im Herbst oder während des ganzen Winters offen bleiben, im Polarmeer zu sehr hohen Wärmeverlusten führen.Der Wärmefluß wird oft auf Grund der Verdunstung mit Hilfe derBowen-Formel berechnet. Wegen der geringen Verdunstung über dem Polarmeer führt diese Formel jedoch zu unrichtigen Werten, und es wird deshalb hier dieShuleikin-Formel benützt, die eine Bestimmung des Wärmeflusses unabhängig von der Verdunstung ermöglicht; die charakteristischen Kurven des Wärmeflusses sind den Verdunstungskurven sehr ähnlich. Offenes Wasser im Polarmeer führt auch hier zu sehr hohen Werten; eine offene Wasserfläche von 1% in der Zeit von Oktober bis Mai würde den Wärmefluß vom zentralen Polarmeer von 3,7 auf 5,2 Kcal/cm2 pro Jahr erhöhen. Offene Flächen müssen daher klein bleiben, da der Energievorrat nicht genügend groß für die Aufrechterhaltung eines solchen Energieflusses wäre. Zum Schlusse werden in einer Tabelle Monatswerte der gesamten Wärmeverluste durch Verdunstung und Wärmefluß für die verschiedenen Gebiete gegeben.
Résumé On a calculé des valeurs mensuelles de l'évaporation et du flux de chaleur pour l'Océan Glacial Arctique et pour la région située entre la Mer du Groenland et la Mer de Barents. Dans le cas de l'évaporation, on s'est servi de la formule deSverdrup dont on a déterminé à nouveau le coefficient K en tenant compte de sa dépendance du vent. Il a été possible de tenir compte du vent dans les régions arctiques grâce à l'établissement récent de cartes saisonnières de la vitesse moyenne du vent. En raison de l'incertitude des déterminations antérieures de la température de surface, on a procédé à des calculs supplémentaires pour des cas extrêmes en été et en hiver afin d'évaluer les sources d'erreurs possibles. On a calculé séparément l'évaporation et le flux de chaleur pour les régions suivantes: Centre de l'Océan Glacial Arctique, Mer de Kara-Mer de Laptev, Mer de Beaufort ainsi que pour de bandes de 5° de largeur dans la région comprise entre la Mer du Groenland et la Mer de Barents.On discute les résultats obtenus pour ces différentes zones en partant de diagrammes et de tableaux. Au-dessus de la glace, l'évaporation présente deux maximums, l'un au printemps, l'autre en automme et un minimum principal en hiver. Sur la mer libre, on constate au contraire un minimum en été et un maximum très large en hiver. Il en résulte que des surfaces libres de glace relativement peu étendues qui se maintiennent en automne, voire durant tout l'hiver peuvent déjà provoquer des pertes de chaleur considérables dans l'Océan Glacial Arctique.On calcule souvent le flux de chaleur en se basant sur l'évaporation selon la formule deBowen. Cependant, en raison des faibles évaporations constatées sur l'Océan Glacial, cette formule conduirait à des valeurs fausses. On a donc utilisé ici la formule deShuleikin qui permet la détermination du flux de chaleur indépendamment de l'évaporation. Les courbes caractéristiques du flux de chaleur sont très semblables à celles de l'évaporation. Les surfaces libres de glace de l'Océan Glacial conduisent ici aussi à des valeurs très élevées. Une surface d'eau de 1% restant libre de glace d'octobre à mai augmenterait de flux de chaleur de l'océan de 3,7 à 5,2 Kcal/cm2 par année. Les surfaces d'eau doivent donc rester très petites, car les réserves d'énergie sont insuffisantes pour maintenir un tel flux d'énergie calorifique. On donne enfin dans une table les pertes mensuelles totales de chaleur dues à l'évaporation et au flux de chaleur et cela pour chacune des régions considérées.
With 6 Figures
The research reported in this paper was sponsored in part by the Air Force Cambridge Research Laboratories, Office of Aerospace Research, under Contract AF 19(604)7415. 相似文献
15.
G. Malkowski 《Meteorology and Atmospheric Physics》1961,12(3):382-388
Zusammenfassung An Hand der seit Juni 1958 vom Berliner Institut für Meteorologie und Geophysik täglich veröffentlichten Radarbeobachtungen in der 12 Uhr GMT-Bodenwetterkarte wird der Zusammenhang zwischen dem Auftreten von Radarechos und der Isobarenkrümmung untersucht. Als Ergänzung wird noch die 500 mb-Karte vom gleichen Termin in Betracht gezogen.
Mit 1 Textabbildung 相似文献
Summary The daily radar observations published in the 1200 GMT surface weather map of the Berlin Institute of Meteorology and Geophysics since June, 1958, are used to investigate the relationship between radar echoes and the curvature of isobars. The corresponding 500 mb charts are used as supplementary information.
Résumé Utilisant les observations de radar publiées quotidiennement sur la carte du temps de 12 h. T. U. depuis le mois de mai 1958 par l'Institut de Météorologie et de Géophysique de Berlin, l'auteur étudie la relation entre l'apparition d'échos de radar et la courbure des isobares. La carte du niveau de 500 mb de la même heure est aussi mise à contribution.
Mit 1 Textabbildung 相似文献
16.
étude expérimentale de la couche limite au-dessus d'un relief modéré proche d'une chaîne de montagne
A. Druilhet J. Noilhan B. Benech G. Dubosclard D. Guedalia J. Frangi 《Boundary-Layer Meteorology》1983,25(1):3-16
For the heterogeneous site described in the first part, some aspects of the turbulent structure of the planetary boundary layer are studied. Using mixed-layer scaling, the normalized profiles are compared with those obtained over flat terrain during convective conditions. The measurements were made with the same instrumented aircraft at both sites. The dissipative and spectral length scales are smaller over complex terrain within the whole boundary layer. This is due to the shifting of the wavelength peak toward the high frequencies by dynamic turbulence.This last effect can also explain the increase of the dissipation rate over the heterogeneous site during strong wind conditions. The vertical profiles of sensible heat flux and temperature-water vapor correlation show a lack of entrainment process at the top of the boundary layer. This fact suggests that the investigated boundary layer is advected from the neighbouring plain over the complex site (plateau de Lannemezan). 相似文献
17.
D. G. Steyn 《Boundary-Layer Meteorology》1990,53(1-2):21-31
A slab mixed-layer model with zero-order entrainment for both temperature and humidity is developed in order to examine the relative magnitude of advective and turbulence flux convergence effects. The model formulation provides an analytic function for the ratio of surface-layer to entrainment-layer humidity flux. Model results are compared with measured mixed-layer properties over one day at a coastal location. It is concluded that the model is highly successful at simulating the mixed-layer depth, and mean mixed-layer humidity. It is suggested that a first-order model may be more appropriate for the latter half of the day when the mixed-layer depth is decreasing due to the dominance of advection over vertical turbulence flux convergence. 相似文献
18.
19.
S. Casadio A. Di Sarra G. Fiocco D. Fuà F. Lena M. P. Rao 《Boundary-Layer Meteorology》1996,79(4):375-391
Convective plume patterns, characteristic of clear sky and light wind daytime boundary layers over land, were observed for two nights with a tri-axial Doppler sodar operated in the central area of Rome during the summer of 1994. An urban heat island effect, combined with a continuation of a breeze from the sea late into night during both days, is believed to be responsible for the observed nocturnal convection. Estimates of the surface heat flux and the vertical velocity scaling parameter are obtained from profiles of vertical velocity variance, and the Raman lidar water vapor measurements are used to obtain the humidity scaling parameter. Convective scaling results for vertical wind and humidity fairly agree with the results of other experiments and models. On the basis of available measurements, it appears that mixed-layer similarity formulations used to characterize the daytime convective boundary layer over horizontally homogeneous surfaces can also be applied to the nocturnal urban boundary layer during periods of reasonable convective activity. 相似文献
20.
Gustav Hofmann 《Meteorology and Atmospheric Physics》1960,11(4):474-502
Zusammenfassung Der Feststellung, daß in der Energiebilanz einer horizontalen Oberfläche keine advektiven Glieder auftreten können, scheint auf den ersten Blick die Angabe von Advektionsgliedern in einigen Arbeiten zu widersprechen. Es zeigt sich aber, daß es sich dabei entweder um die Energiebilanz eines Volumens handelt, wobei die Glieder der Vergleichbarkeit wegen auf die Bodenoberfläche bezogen sind, oder daß Meß- bzw. Überlegungsfehler vorliegen.Advektive Wärmeströme können nur bei einem Volumen eine Rolle spielen. Die Betrachtung der Energiebilanz eines festen Volumens ergibt dann, daß auch bei stationären Verhältnissen der Wärmestrom von der Luft zum Boden im allgemeinen nicht gleich dem vertikalen Austauschwärmestrom oberhalb der Bodenoberfläche ist. Vielmehr treten vier weitere Wärmeströme hinzu, die als Durchflußwärmestrom, vertikaler Mitführungswärmestrom, advektiver Mitführungswärmestrom und advektiver Austauschwärmestrom bezeichnet werden. Ihr Anteil am Wärmestrom von der Luft zum Boden hängt nicht nur von den meteorologischen Verhältnissen, sondern auch von der Höhenlage der Zählfläche ab, für die der Austauschwärmestrom bestimmt wird. Ihre Abschätzung an Hand einfacher, plausibler Annahmen zeigt, daß sie im allgemeinen nicht vernachlässigt werden dürfen. Eine hinreichende Bedingung für ihr Verschwinden ist die Annahme, daß im zeitlichen Mittel alle Parameter in gleicher Höhe den gleichen Wert haben. Auch für instationäre Verhältnisse und den Wärmetransport in einem inhomogenen Medium läßt sich die Energiebilanz aufstellen, was aber bei Änderungen der im Volumen enthaltenen Masse an Beimengung nicht mehr willkürfrei möglich ist.
Summary The statement that no advective terms occur in the energy balance of a horizontal surface seems at first sight to be in contradiction to the quotation of advective terms in some publications. It proves, however, that in that case it is a question of energy balance of a volume, where for comparability the terms are related to the ground surface, or that it is due to errors of measurement or consideration. Advective heat fluxes are merely of importance with three-dimensional problems. The study of the energy balance of a solid volume shows that the heat flux from the air to the ground is generally not equal to the vertical exchange heat flux above the ground surface, even with stationary conditions. Four further heat fluxes supervene which may be designated as passing heat flux, vertical convection heat flux, advective convection heat flux and advective exchange heat flux. Their share of heat flux from the air to the ground depends not only on the meteorological conditions but also on the altitude of the reference surface for which the exchange heat flux is determined. Its estimation by simple, plausible assumptions shows that in general they should not be neglected. A sufficient condition for their disappearance is the assumption that all parameters at the same level have the same temporal mean value. The energy balance can be set up also for unstationary conditions and for the heat transport in an inhomogeneous medium. In the case where the mass of admixtures contained in the volume undergoes changes the energy balance cannot be established without arbitrary assumptions.
Résumé Le fait que dans le bilan énergétique d'une surface horizontale il ne peut y avoir de terme advectif semble à première vue contredire certains travaux qui en ont fait état. Mais il s'avère qu'il s'agit soit du bilan énergétique d'une volume, soit d'une erreur de mesure ou de raisonnement.Des courants advectifs de chaleur ne peuvent jouer de rôle que dans le cas d'un volume. Considérant le bilan énergétique d'un volume fixe, on voit que même dans l'état stationnaire le flux de chaleur dirigé de l'air vers le sol n'est pas égal en général au courant vertical d'échange turbulent au-dessus du sol; bien plus, il existe en réalité quatre autres flux (à savoir le flux de chaleur traversant, le flux vertical de chaleur convective, le flux de chaleur advective et le flux d'échange de chaleur advective) dont l'apport au flux de chaleur air/sol ne dépend pas seulement des conditions météorologiques, mais aussi de l'altitude de la surface choisie pour le calcul. L'estimation de ces flux, faite sur la base d'hypothèses simples et plausibles, montre qu'on ne peut pas en général les négliger. Ils ne peuvent disparaître que si en moyenne, dans un temps donné, tous les paramètres sont égaux, à la même altitude. Dans le cas d'états non stationnaires et de milieu non homogène, on peut dresser le bilan énergétique, ce qui n'est plus possible sans arbitraire lorsque la masse d'éléments adjonctifs du volume se modifie.相似文献