A Simple Method of Estimating Scalar Fluxes Over Forests   总被引：1，自引：0，他引：1  

Nelson Luis Dias  Jinkyu Hong  Monique Y. Leclerc  T. Andrew Black  Z. Nesic  P. Krishnan 《Boundary-Layer Meteorology》2009,132(3):401-414

A simple aerodynamic-variance method is proposed to fill gaps in continuous CO₂ flux measurements in rainy conditions, when open-path analysers do not function. The method requires turbulent conditions (friction velocity greater than 0.1 ms^–1), and uses measurements of mean wind speed, and standard deviations of temperature and CO₂ concentration fluctuations to complement, and at times replace, eddy-covariance measurements of friction velocity, sensible heat flux and CO₂ flux. Friction velocity is estimated from the mean wind speed with a flux-gradient relationship modified for the roughness sublayer. Since normalised standard deviations do not follow Monin-Obukhov similarity theory in the roughness sublayer, a simple classification scheme according to the scalar turbulence scale was used. This scheme is shown to produce sensible heat and CO₂ flux estimates that are well correlated with the measured values.  相似文献   

Gas-phase mean opacities for varying [M/H], N/O and C/O     

Ch. Helling  W. Lucas 《Monthly notices of the Royal Astronomical Society》2009,398(2):985-994

We present a set of gas-phase Planck mean and Rosseland mean opacity tables applicable for simulations of star and planet formation, stellar evolution and disc modelling at various metallicities in hydrogen-rich environments. The tables are calculated for gas temperatures between 1000 and 10 000 K and total hydrogen number densities between 10² and  10¹⁷ cm⁻³  . The carbon-to-oxygen ratio is varied from 0.43 to well above 2.0, the nitrogen-to-oxygen ratio between 0.14 and 100.0. The tables are calculated for a range of metallicities down to  [M/H]'= log  N _M/ N _H=−7.0  . We demonstrate how the mean opacities and the abundances of the opacity species vary with C/O, N/O and  [M/H]'  . We use the element abundances from Grevesse et al., and we provide additional tables for the oxygen abundance value from Caffau et al. All tables will be available online at http://star-www.st-and.ac.uk/~ch80/datasources.html .  相似文献   

Effects of tidal shallowing and deepening on phytoplankton production dynamics: A modeling study     

Lisa V. Lucas  James E. Cloern 《Estuaries and Coasts》2002,25(4):497-507

Processes influencing estuarine phytoplankton growth occur over a range of time scales, but many conceptual and numerical models of estuarine phytoplankton production dynamics neglect mechanisms occurring on the shorter (e.g., intratidal) time scales. We used a numerical model to explore the influence of short time-scale variability in phytoplankton sources and sinks on long-term growth in an idealized water column that shallows and deepens with the semidiurnal tide. Model results show that tidal fluctuations in water surface elevation can determine whether long-term phytoplankton growth is positive or negative. Hourly-scale interactions influencing weekly-scale to monthly-scale phytoplankton dynamics include intensification of the depth-averaged benthic grazing effect by water column shallowing and enhancement of water column photosynthesis when solar noon coincides with low tide. Photosynthesis and benthic consumption may modulate over biweekly time scales due to spring-neap fluctuations in tidal range and the 15-d cycle of solar noon-low tide phasing. If tidal range is a large fraction of mean water depth, then tidal shallowing and deepening may significantly influence net phytoplankton growth. In such a case, models or estimates of long-term phytoplankton production dynamics that neglect water surface fluctuations may overestimate or underestimate net growth and could even predict the wrong sign associated with net growth rate.  相似文献   

New 8–13 μm Si:Ga/DRO hybrid arrays for very large telescopes     

C. Lucas  Ph. Pantigny  D. Alloin  C. Césarsky  P. O. Lagage  H. U. Käufl  J. L. Monin 《Experimental Astronomy》1994,3(1-4):273-276

Since 1984, the CEA-LETI-LIR (Infrared Laboratory) has been involved in development of Si:Ga/DRO hybrid detector arrays dedicated to imaging of astronomical sources in the 8–13 m range. Successively, 32×32 element arrays were successfully manufactured for the ISOCAM camera and 64×64 arrays were fabricated for ground-based imaging. The latter detectors have been integrated in 3 cameras (C10, CAMIRAS and TIMMI for ESO) and have led to excellent astrophysical results since 1990.To equip instruments to be mounted on very large telescopes such as the European VLT at ESO, manufacture of new arrays has been undertaken and is currently under way at CEA-LETI-LIR. These new arrays will have a 128×192 format and will present the outstanding essential feature that their storage capacity will be able to be changed according to observation conditions (2 capacities will be implemented in the pixel).The main characteristics of these new detectors will be presented in this paper.  相似文献   

Forward-in-time and Backward-in-time Dispersion in the Convective Boundary Layer: the Concentration Footprint     

Xuhui Cai  Monique Y. Leclerc 《Boundary-Layer Meteorology》2007,123(2):201-218

The turbulence field obtained using a large-eddy simulation model is used to simulate particle dispersion in the convective boundary layer with both forward-in-time and backward-in-time modes. A Lagrangian stochastic model is used to treat subgrid-scale turbulence. Results of forward dispersion match both laboratory experiments and previous numerical studies for different release heights in the convective boundary layer. Results obtained from backward dispersion show obvious asymmetry when directly compared to results from forward dispersion. However, a direct comparison of forward and backward dispersion has no apparent physical meaning and might be misleading. Results of backward dispersion can be interpreted as three-dimensional or generalized concentration footprints, which indicate that sources in the entire boundary layer, not only sources at the surface, may influence a concentration measurement at a point. Footprints at four source heights in the convective boundary layer corresponding to four receptors are derived using forward and backward dispersion methods. The agreement among footprints derived with forward and backward methods illustrates the equivalence between both approaches. The paper shows explicitly that Lagrangian simulations can yield identical footprints using forward and backward methods in horizontally homogeneous turbulence.  相似文献   

Introducing a new learning method for fuzzy descriptor systems with the aid of spectral analysis to forecast solar activity     

Masoud Mirmomeni  Masoud Shafiee  Caro Lucas  Babak Nadjar Araabi   《Journal of Atmospheric and Solar》2006,68(18):2061-2074

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Further observations of IRAS 04302+2247     

P. W. Lucas  & P. F. Roche 《Monthly notices of the Royal Astronomical Society》1998,299(3):723-727

We present near-infrared broad-band and H₂ images of the quadrupolar source IRAS 04302+2247. High-resolution data at 3.8 μm show that the circumstellar envelope has a high degree of axisymmetry: the asymmetry at shorter wavelengths is almost certainly the result of extinction by dust in the cavity. Photometry of the flux peaks confirms that the source is variable but little change in appearance is observed between 1995 November and 1997 September. We report the first clear detection of the molecular outflow in H₂ at 2.1 μm, revealing discrete streams which are inclined to the axis of the cavity. The motion of knots in the outflow remains the most likely cause of the variability.  相似文献   

Fuzzy Logic System for Road Identification Using Ikonos Images   总被引：1，自引：0，他引：1  

Jalal Amini  Caro Lucas  Mohammad Saradjian  Ali Azizi  & Saeed Sadeghian 《The Photogrammetric Record》2002,17(99):493-503

Research into both extraction of man-made objects and automatic change detection from aerial and satellite images has made significant progress in recent years. This paper presents an approach, based on a fuzzy logic system, for the identification of suburban roads in Ikonos images. The linguistic variables are the mean and standard deviation (SD) of different objects with Gaussian membership function. After the roads have been identified provisionally and their skeleton extracted, the skeleton can be vectorised and then used as direct input to a GIS for further analysis. The method was tested on an Ikonos "Geo" image covering Bilesavar in north-western Iran. For the suburban area of Bilesavar, the results showed that grey scale values ranged from 20 to 190 for non-roads and 226 to 228 for roads, the optimum width of the Gaussian kernel function was 3 and the SD was 0.4. It was also found that about 91% of main roads with a width of 6 to 12 pixels could be extracted from high resolution satellite imagery by the algorithm. The computer program for this study has been developed in visual C++ based on Windows 98  相似文献   

Le ruissellement au spitsberg: le monde polaire face aux changements climatiques edited by Denis Mercier,Collection Nature et Sociétés,Presses Universitaires Blaise Pascal,Clermont‐Ferrand, 2001. Number of pages: 278. ISBN 2 84516 150 6.     

Monique Fort 《地球表面变化过程与地形》2002,27(10):1143-1144

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Marine nature reserves     

C.C. Lucas 《Marine pollution bulletin》1980,11(1):26-27

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