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1.
The technique of probability imaging is applied to the bright, well resolved, infrared binary star Aqr. It is shown how the second probability density function (pdf) contains all pertinent information to reconstruct the binary system with no ambiguity. Relations between the second pdf and other techniques (speckle masking technique and fork algorithm) are briefly indicated. An analysis of the behaviour of the second pdf under additive signal-independent nose is undertaken. As expected from the general theory of signal processing, the second pdf of the noise is found to blur the second pdf of the signal by means of a convolution relation.Based on observations obtained at ESO, La Silla, Chile. 相似文献
2.
A. Weill C. Mazaudier F. Baudin C. Klapisz F. Leca M. Masmoudi D. Vidal Madjar R. Bernard O. Taconet B. S. Gera A. Sauvaget A. Druilhet P. Durand J. Y. Caneil P. Mery G. Dubosclard A. C. M. Beljaars W. A. A. Monna J. G. Van Der Vliet M. Crochet D. Thomson T. Carlson 《Boundary-Layer Meteorology》1988,42(3):251-264
3.
Jean-Pierre Pagès Jean-Pierre Frangi Pierre Durand Claude Estournel Aimé Druilhet 《Boundary-Layer Meteorology》1988,43(1-2):183-203
This paper presents data concerning the energy budget in the surface layer in the Sahel region (a semi-desert area). The results
are drawn from a measurement campaign made in the Niamey region in the Niger, in April–May 1984 (the Yantala Campaign). The
sensible heat flux is computed with the profile method, the ground heat flux is deduced from measurement of the temperature
field, and the radiative net flux is measured directly with a balancemeter. The latent heat flux, which is deduced from the
energy budget balance is very weak and within the accuracy limit of the method. The diurnal variation of the net flux is symmetrical,
with a maximum at noon. On the other hand, the sensible heat flux variation is asymmetrical, with an afternoon decrease much
slower than the morning increase. After 3.30 pm, it becomes higher than the net flux. This is compensated for by the sign
change of the ground heat flux, whose maximum is found in the morning at 11 am.
The second part of this paper shows the importance of one term in the surface-layer energy budget: the long-wave radiative
divergence between the ground and the top of the surface layer in high superadiabatic conditions. We show, with a radiative
model on the one hand and direct measurement of the radiative divergence on the other hand, that this term reaches several
tens of W m-2 in the superadiabatic conditions found in the Sahel region.
相似文献
4.
The measurements obtained during the ECLATS experiment were used in order to determine the surface energy budget of the Sahel region (Niamey, Niger). This expedition was carried out from November 15 to December 10, 1980, during the dry period. Some data were collected by an instrumented aircraft, from which the turbulent fluxes were obtained in the boundary layer around midday; data were also collected at a surface station in order to estimate the surface energy budget continuously by the profile method. The aircraft measurements show the homogeneity of the vertical fluxes over large areas, allowing generalization to the bushy steppe of the Sahel region. The mean diurnal cycle of the energy budget is characterized by high values of ground heat flux and weak values of latent heat flux (deduced from the balance of the energy budget). This cycle is compared with that of the Koorin expedition, performed in similar conditions (tropical savanna in the dry period). We compare the three midday budgets: during Koorin; during ECLATS, at the ground station, and with the aircraft. The important differences that appear in the net radiative flux are explained by the difference in surface albedo.Ecole des Sciences, Université de Niamey, B.P. 10662 Niamey, Niger. 相似文献
5.
L. Eymard S. Planton P. Durand C. Le Visage P. Y. Le Traon L. Prieur A. Weill D. Hauser J. Rolland J. Pelon F. Baudin B. Bénech J. L. Brenguier G. Caniaux P. De Mey E. Dombrowski A. Druilhet H. Dupuis B. Ferret C. Flamant P. Flamant F. Hernandez D. Jourdan K. Katsaros D. Lambert J. M. Lefèvre P. Le Borgne B. Le Squere A. Marsoin H. Roquet J. Tournadre V. Trouillet A. Tychensky B. Zakardjian 《Annales Geophysicae》1996,14(9):986-1015
The SEMAPHORE (Structure des Echanges Mer-Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale) experiment has been conducted from June to November 1993 in the Northeast Atlantic between the Azores and Madeira. It was centered on the study of the mesoscale ocean circulation and air-sea interactions. The experimental investigation was achieved at the mesoscale using moorings, floats, and ship hydrological survey, and at a smaller scale by one dedicated ship, two instrumented aircraft, and surface drifting buoys, for one and a half month in October-November (IOP: intense observing period). Observations from meteorological operational satellites as well as spaceborne microwave sensors were used in complement. The main studies undertaken concern the mesoscale ocean, the upper ocean, the atmospheric boundary layer, and the sea surface, and first results are presented for the various topics. From data analysis and model simulations, the main characteristics of the ocean circulation were deduced, showing the close relationship between the Azores front meander and the occurrence of Mediterranean water lenses (meddies), and the shift between the Azores current frontal signature at the surface and within the thermocline. Using drifting buoys and ship data in the upper ocean, the gap between the scales of the atmospheric forcing and the oceanic variability was made evident. A 2 °C decrease and a 40-m deepening of the mixed layer were measured within the IOP, associated with a heating loss of about 100 W m−2. This evolution was shown to be strongly connected to the occurrence of storms at the beginning and the end of October. Above the surface, turbulent measurements from ship and aircraft were analyzed across the surface thermal front, showing a 30% difference in heat fluxes between both sides during a 4-day period, and the respective contributions of the wind and the surface temperature were evaluated. The classical momentum flux bulk parameterization was found to fail in low wind and unstable conditions. Finally, the sea surface was investigated using airborne and satellite radars and wave buoys. A wave model, operationally used, was found to get better results compared with radar and wave-buoy measurements, when initialized using an improved wind field, obtained by assimilating satellite and buoy wind data in a meteorological model. A detailed analysis of a 2-day period showed that the swell component, propagating from a far source area, is underestimated in the wave model. A data base has been created, containing all experimental measurements. It will allow us to pursue the interpretation of observations and to test model simulations in the ocean, at the surface and in the atmospheric boundary layer, and to investigate the ocean-atmosphere coupling at the local and mesoscales. 相似文献
6.
Résumé Le radon (Rn86
222) et les descendants du thoron (ThB ou Pb82
212) sont utilisés comme traceurs pour l'étude des échanges verticaux de matière. Diverses méthodes permettant le calcul des coefficients de diffusion sont présentées soit dans l'hypothèse simplificatrice du régime stationnaire, soit dans le cas plus général du régime dépendant du temps. L'application de ces méthodes au calcul des coefficients de diffusion sur des données fournies à partir d'un modèle de simulation numérique permet de préciser le degré d'approximation représenté par les diverses hypothèses simplificatrices. Les méthodes de calcul présentées sont appliquées aux mesures expérimentales du radon et du ThB. Ces mesures ont été réalisées de manière continue durant deux ans en trois points de mesures, entre 0 et 100 m de hauteur. Une statistique est présentée sur la variation diurne des échanges et la variation saisonnière de cette variation diurne, ainsi qu'un exemple particulier du traitement des données en régime dépendant du temps.
Continuous measurements of the concentrations of radon and thorium B have been carried out at 3 levels (1.5, 30 and 100 m) during a period of 2 yr (from October 1966 to October 1968) at the site of the future airport of Paris, at Roissy-en-France; at the same time, standard meteorological elements have been measured at the station by the Météorologie Nationale and the vertical gradients (wind and temperature profiles in the first 100 m) by J. Saissac. The work has been undertaken in order to determine the vertical exchange of matter near the ground.The computation of the exchange coefficients has been carried out by using the standard diffusion equation (K theory). The results in the literature as well as statistical analysis of our data lead us to believe that the flux of Rn and ThB at the ground can be considered as horizontally homogeneous in the neighbourhood of the measurement site (the soil is geologically homogeneous over a large area). The differential equation is thus simplified, containing only one space parameter (z), and timet.In this paper we describe the principal computation methods used for determining the exchange coefficients from the measurement of the vertical gradients of tracers. In order to illustrate the approximation errors and fields of applicability of different methods, we have applied them to the data provided from a numerical integration of the diffusion equation, in which one can introduce any profile of diffusivity.We show that during stable periods, the value of the flux of Rn or ThB can be determined forz = 0.Generally, during daylight hours when the motion near the ground is strongly turbulent, the vertical gradient of concentration is not measurable with sufficient accuracy.The daytime diffusion coefficient is therefore not computed by the general methods presented above. This deficiency can be overcome by assuming that the ratio between the mean concentration observed during these periods and the value of the flux at ground level are characteristic of the whole mixing layer. The values of the exchange coefficients obtained by this method are included and range from 5 to 30 m2s-1.The application of the proposed methods to the experimental results has been made for two atmospheric states. Firstly, we have used a simplified method (stationary state) which is applied to the whole experimental data set. We present the diurnal variation, the most probable value of the diffusion coefficients and the seasonal evolution. The values obtained from Rn and ThB measurements have been compared.相似文献
7.
This paper is the second of a series devoted to the observation and analysis of coherent structures in the cloudy Atmospheric Boundary Layer (ABL) such as horizontal rolls or thermal cells. In the first paper, the TRAC (Turbulence Radar Aircraft Cells) experiment which is the observational support of this investigation based on coupled radar-aircraft measurements, was presented along with an overview of the main results of this campaign held in June 1993 in France. Here the analysis is focused on the spatial characteristics (length-scale, orientation ... ) of the coherent structures, their temporal evolution and vertical distribution deduced from the radar reflectivity fields acquired in clear air at several levels for five different ABLs. For that, an original and efficient image processing method able to extract the major mode of the organisation was developed. These characteristics are examined in relation to the dynamic and thermodynamic state of the ABL using mean and turbulent information as observed by the in-situ aircraft. These experimental results are the basis of a future Large Eddy Simulation modeling of an organised ABL which is in progress and will be the concern of the third paper in the series. 相似文献
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9.
We have studied the evolution of the planetary boundary layer using both oceanic and continental stations. This has been possible through the analysis of twice-daily temperature radiosondes at three different oceanic stations (Point A; Point K; and Azores) and also at three continental stations (Berlin, Trappes and Madrid) all situated in the Northern Hemisphere. We have studied the annual evolution of mixing layers and of temperature inversion levels; an annual evolution presenting a minimum in winter and a maximum in summer has been observed in the continental stations; the oceanic stations present a lesser variation and in the opposite sense. As for the elevated inversion layers, their maximum frequency can be observed in summer at the oceanic stations and in winter at the continental stations. We have shown that considering the studied stations, both the level and the frequency of the elevated inversion layers are similar at 00 h and at 12 h; such a result is important because these layers regulate the intensity of the exchanges between the ground and the free atmosphere. Using the equivalent coefficient, we have determined the annual variation of the vertical exchanges between the surface and different altitudes. At the continental stations, the vertical exchanges are more important in summer than they are in winter; the opposite behaviour occurs at the oceanic stations. 相似文献
10.
A comment is made on the Edmonds' study of the low-wavenumber power of solar granulation. It is concluded that its one-dimensional power spectrum is biased, and that the corresponding two-dimensional power spectrum shows negative parts. 相似文献