Preface     

Ivan Pšenčík  Vlastislav Červený  Luděk Klimeš 《Pure and Applied Geophysics》1996,148(1-2):1-1

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Application of transilient turbulent theory to study interactions between the atmospheric boundary layer and forest canopies     

M. G. Inclán  R. Forkel  R. Dlugi  R. B. Stull 《Boundary-Layer Meteorology》1996,79(4):315-344

The new Forest-Land-Atmosphere ModEl called FLAME is presented. The first-order, nonlocal turbulence closure called transilient turbulence theory (Stull, 1993) is applied to study the interactions between a forested land-surface and the atmospheric boundary layer (ABL). The transilient scheme is used for unequal vertical grid spacing and includes the effects of drag, wake turbulence, and interference to vertical mixing by plant elements. Radiation transfer within the vegetation and the equations for the energy balance at the leaf surface have been taken from Norman (1979). Among others, the model predicts profiles of air temperature, humidity and wind velocity within the ABL, sensible and latent heat fluxes from the soil and the vegetation, the stomata and aerodynamic resistances, as well as profiles of temperature and water content in the soil. Preliminary studies carried out for a cloud free day and idealized initial conditions are presented. The canopy height is 30 m within a vertical domain of 3 km. The model is able to capture some of the effects usually observed within and above forested areas, including the relative wind speed maximum in the trunk space and the counter gradient-fluxes in the lower part of the plant stand. Of special interest is the determination of the location and magnitude of the turbulent mixing between model layers, which permits one to identify the effects of large eddies transporting momentum and scalar quantities into the canopy. A comparison between model simulations and field measurements will be presented in a future paper.  相似文献   

Natural and anthropogenic C2 to C6 hydrocarbons in the central-eastern Venezuelan atmosphere during the rainy season     

Loreto Donoso  Rodrigo Romero  Alberto Rondón  Emmanuel Fernandez  Pedro Oyola  Eugenio Sanhueza 《Journal of Atmospheric Chemistry》1996,25(2):201-214

The levels of low molecular weight hydrocarbons were measured at pristine sites and rural locations affected by hydrocarbon emissions from oil and gas producing fields in Venezuela. At the clean sites, lower concentrations of C₂ to C₆ alkanes were observed, whereas, in comparison with remotes sites, very much higher levels were measured at the polluted sites. Alkenes present relatively high concentrations, with isoprene being the most abundant, all over the study region. The main sources of alkenes are likely to be natural, mainly from vegetation. The levels of alkanes recorded at the clean sites and the alkene levels found everywhere in the region are in agreement with the values reported for other clean sites in the tropics. The increase of ozone production capacity due to the anthropogenic emissions of alkanes from oil and gas fields was estimated. Due to the presence in the atmosphere of important amounts of naturally emitted isoprene, ethene and propene, which makes a substantial contribution to the reactivity of the hydrocarbon mixture, a small increase (<5%) was estimated to occur in the capacity of the ozone production at a regional scale during the rainy season.  相似文献   

North-Eastward propagating 25–50-day mode and its link with Indian summer monsoon activity     

A. Ouergli  P. De Felice 《Meteorology and Atmospheric Physics》1996,61(3-4):127-135

Summary Spatio-temporal characteristics of the 25–50-day oscillations are investigated using the empirical orthogonal function (EOF) decomposition and spectral analysis with the Maximum Entropy Method (MEM). Daily pressure values over India during 1978 are used in this study. Power spectra of the temporal coefficients of the two leading EOFs show the existence of a low frequency oscillation with a period range 25–50-day over all India. An analysis using extended empirical orthogonal function (EEOF) indicates North-Eastward propagating 25–50-day mode. The analysis EOF has allowed to establish a relationship between the 25–50-day oscillation and the activity of the summer monsoon. The North-Eastward propagation of this mode is also confirmed by the simple EOF analysis.With 9 Figures  相似文献   

通辽CK－9井水位动态及影响因素的分析     

黄维有  王立海  德力格尔 《东北地震研究》1996,(1)

本文在对通辽ＣＫ－９井、水文地质条件和水动态特征初步分析的基础上，采用ＰＣ－１５００计算机，对该井的观测数据与气压、蒸发、降雨、开采、河水位、固体潮、地震波和潜水位等相互关系，进行了定量的相互分析．研究所得结果，对该井水位动态变化和影响因素的关系，提出了新的结论．  相似文献   

Temperature dependence of the 57Fe Mössbauer parameters in riebeckite     

A. Van Alboom  E. De Grave 《Physics and Chemistry of Minerals》1996,23(6):377-386

Mössbauer spectra for two riebeckite minerals were collected at temperatures in the range 4.2 to 500 K. The magnetic-ordering temperatures were found to be 33±1 and 31±1 K respectively. Fitting the paramagnetic spectra with a discrete number of doublets (three or four) did not lead to consistent results. Instead, a superposition of an Fe³⁺ (M2) doublet and one distributed ferrous component was found to produce adequate fits with reasonable parameter values. For both samples, a minor fraction of ferrous ions was observed to be present at the M4 sites and for one of the samples at the M2 sites as well. The temperature variations of the center shifts were well reproduced using the Debye model of the lattice vibrational spectrum to evaluate the second-order Doppler shift. The characteristic Mössbauer temperatures were calculated to be in the range 340–390 K for Fe²⁺, and 520 K for Fe³⁺. The temperature dependences of the various ferrous quadrupole splittings could not be explained in terms of the point-charge model and assuming a temperature-independent energy-level scheme for the ⁵D term. It is suggested that a gradual change with temperature of the orbital-level splittings takes place. All calculations yielded a positive sign for the principal component of the electric field gradient (EFG). The spectrum recorded at 4.2 K for one of the riebeckites was fitted with a superposition of an Fe³⁺ and a Fe²⁺ hyperfine-field distribution, the latter one primarily characterizing the Fe²⁺ (M1) cations. The following relevant hyperfine data were calculated: H _hf=161 kOe, ΔE _Q=3.11 mm/s, and V _zz<0, all referring to the maximum-propability values. For the second riebeckite at 4.2 K, an additional distributed ferrous component could independently be resolved. The two maximum-probability hyperfine fields were found to be 189 and 98 kOe and the corresponding ΔE _Q values 3.10 and 2.67 mm/s. Both components exhibit a negative V _zz. The subspectra were attributed to M1 and M3 sites respectively. The Fe³⁺ hyperfine fields are 548+-2 kOe for both riebeckites. The different values found for the Fe³⁺ quadrupole shift 2?_Q for the two samples is explained by a different angle between the hyperfine field and the EFG's principal axis. The magnetic spectra recorded at 15 K and higher, could not be reproduced adequately with reasonable parameter values.  相似文献   

Some observations from the data taken in and around Kharagpur during the onset of the monsoon, 1990     

R Pradhan  B Roy  U K De  D K Rakshit 《Journal of Earth System Science》1996,105(1):17-29

During MONTBLEX 1990, various observational platforms were operated at Kharagpur and the nearby Kalaikunda Air Base. Using the data from all the platforms, one can draw the following conclusions. The temperature and wind data obtained from various sensors have overall compatibility. Sodar wind data indicate the presence of a low level jet at around 300 m above ground. The inversion height may be evaluated from the vertical profile of the sodar back-scatter echo intensity. The sub-synoptic or synoptic scale convergence modulates the inversion height and the presence of cloud-base within the inversion height in turn modulates the sensible heat and momentum fluxes.  相似文献   

Statistical and spectral analysis of the wind regime in the area of Catalonia     

Jna. Gavaldà  J. Massons  J. Camps  F. Díaz 《Theoretical and Applied Climatology》1992,46(2-3):143-152

Summary This work presents a statistical study of the wind power potential of three stations in the Catalonia area (Spain) over the 1973–1982 period. These stations correspond to three airports (Barcelona, Palma de Mallorca and Girona), which obviously do not present a high wind power potential and are not the suitable locations for wind power utilization, but which have been chosen for the long record of data stored (10 years). The aim of this work is to provide a model of wind potential in terms of the speed and wind direction, which may be applied to other sites. The wind speed has been modelled by a Weibull distribution function and the wind direction by a normal two-dimensional function. A spectral analysis of both variables has also been carried out. The present study provides an evaluation of the local wind power in the geographic area of Catalonia.With 10 Figures  相似文献   

A contribution to the measurement of frequency dependence of electrical conductivity of rocks     

Marcela Laštovičková  Josef Bochníček 《Studia Geophysica et Geodaetica》1992,36(1):94-99

Summary Some errors of method occurring in A. C. measurements of the electrical conductivity of rocks are discussed. It is demonstrated that the difference between A.C. and D.C. conductivities, at given frequency, depends mostly on the magnitude of the D.C. conductivity and magnitude of the dielectric constant.  相似文献   

Improved indirect phase reflection height measurement at panská ves — method,equipment, evaluation     

Vladimír Fišer  Ivan Matys 《Studia Geophysica et Geodaetica》1992,36(3):269-279

Summary Indirect phase reflection height measurements have been performed at the Panská Ves Observatory, Czechoslovakia, for 30 years to monitor solar flare effects (SFA). Only after introducing the new receiver in May 1985, could the indirect phase height analysis (IPHA) method be applied to measurements along the Allouis — Panská Ves 162 kHJ measuring path. The IPHA method allows the electron density and pressure variability in the lower ionosphere to be studied, particularly near the 80 km altitude. This paper describes the theoretical background of the IPHA method, the measuring equipment used at Panská Ves, the method of evaluating records and checking of data, and the program package developed by us both for graphic and numerical processing, as well as our efforts to develop a homogeneous East European IPHA network. The IPHA method has been introduced succesfully at the Panská Ves Observatory.  相似文献