Search results for "Computational physics"
showing 10 items of 725 documents
Influence of atomic data on non-LTE chromospheric modelling
1997
Abstract The influence of various kinds of atomic parameters on computed Mg II h and k line profiles is studied. For this purpose, we have run a non-LTE code on several versions of a Mg II model atom differing from one another in the quality and source of the atomic data employed, while keeping fixed the underlying atmospheric structure. With this simple setup we show that employing good quality atomic data is a necessary condition to obtain reliable atmosphere diagnostics. This is of interest in many fields of stellar astrophysics, e. g. semi-empirical chromospheric modelling in our case, but also when modelling external velocity fields, circumstellar/interstellar absorption, etc. and so t…
Distribution of radiative energy in ground fog
1970
This study deals with the distribution of solar and infrared radiation in a multiple scattering and absorbing fog consisting of water droplets and water vapor. An iterative solution of the radiative transfer equation, as formulated by Chandrasekhar (1960), is presented here, which is utilized to obtain radiative intensities, fluxes and their vertical divergence for the entire infrared spectrum. A sufficient number of sample computations is carried out also in the solar spectrum such as to verify the applicability of the numerical procedure for the entire heat spectrum. All calculations are made for two fog models, representing low and high fog for a liquid cloud water concentration of 0.1 g…
Can turbulence within the field of view cause significant biases in radiative transfer modeling at the 183 GHz band?
2018
The hypothesis whether turbulence within the passive microwave sounders field of view can cause significant biases in radiative transfer modeling at the 183 GHz water vapor absorption band is tested. A novel method to calculate the effects of turbulence in radiative transfer modeling is presented. It is shown that the turbulent nature of water vapor in the atmosphere can be a critical component of radiative transfer modeling in this band. Radiative transfer simulations are performed comparing a uniform field with a turbulent one. These comparisons show frequency dependent biases which can be up to several kelvin in brightness temperature. These biases can match experimentally observe…
Calculations and measurements of the spectral radiance of the solar aureole
1968
The application of the theory of primary scattering to describe and interpret the spectral distribution of the sky radiance is discussed. It is shown that within the solar aureole the influence of the scattering of higher order can be neglected. Theoretical calculations of the spectral distribution of the sky radiance, carried out by Bullrich et al . (1965) based on an exponential aerosol size distribution with an upper limiting particle radius r = 10 ?, have been extended to r = 150 ?. The detailed study of the influence of these “giant” particles revealed that aerosol particles of r >30 ? have no effect on the sky radiation any more. Representative measurements taken at Mainz, Germany, at…
A fast approximate method for the calculation of the infrared radiation balance within city street cavities
1983
The approximate calculation method for diffuse solar irradiances in street cavities presented in an earlier paper is extended to include infrared flux densities. By expanding the infrared sky radiance as a truncated trigonometric series, it becomes possible to solve the integrals representing the obstruction of the sky analytically. An example is worked out to demonstrate the numerically very efficient calculation procedure.
Actinic Flux and Net Flux Calculations in Radiative Transfer—A Comparative Study of Computational Efficiency
2001
Abstract The accuracy and speed of three well-known computational techniques (DISORT, the δ–four-stream approximation, and the two-stream approximation), and the matrix inversion method, which is less well known, have been investigated. Results are presented for both broadband actinic and net fluxes over a range of parameters including solar zenith cosine, relative humidity, and altitude for two different surface/aerosol systems: terrestrial and oceanic. The matrix inversion method can only calculate actinic fluxes; therefore, this is the main focus of this paper. Investigations into the comparative accuracy of the four techniques for the oceanic model with and without a cloud layer include…
Collision efficiencies empirically determined from laboratory investigations of collisional growth of small raindrops in a laminar flow field
2007
In laboratory experiments at the vertical wind tunnel of the University of Mainz the collisional growth of drops with radii between 70 and 170 μm in radius were observed while the collector drop freely floated in a cloud of droplets with radii ranging from 1 to 7 μm. Previously existing tables with collision efficiency values were interpolated and completed in such a way that drop growth rates calculated with these collision efficiencies match with observed growth rates. These new tables provide collision efficiency values for a wide range of drop sizes and radius ratios p including those ranges where efficiency values missed so far. This is of high importance for small p-ratios where the c…
A Fast Solar Radiation Transfer Code for Application in Climate Models
1983
A method is presented for the calculation of solar heating rates in turbid and cloudy atmospheres. In contrast to other typical two-stream procedures, the system of differential equations describing the radiative transfer is decoupled through the application of a series expansion of the flux densities resulting in a single analytical expression for each flux. The present method (PM) yields a solution for the entire atmosphere instead of individual atmospheric layers. This procedure avoids as part of the solution scheme the inversion of a rather complex matrix thus resulting in high numerical efficiency. The model includes the absorption by atmospheric gases such as water vapor, CO2, O3 and …
Measurement of the Parity Violation in Quasi-Elastic Electroweak Electron-Scattering from 9Be
1986
In the energy range of about 300 MeV, available at the Mainz- Linac, quasi-elastic scattering dominates the total cross section at backward scattering angles. This process can therefore be detected efficiently by a gas Cerenkov-counter with large solid angle. This is a prerequisit for experiments on parity violation due to the very small asymmetry effect being of the order of 1|10-5 at these energies [1]. The counting system built, consists of 12 elliptical mirrors, imaging the Cerenkov photons seen in target direction onto photomultipliers. The mirrors cover the full azimuth for polar angles 115°≦ϑ≦145°, thus covering 20% of 4π (Fig. 1). The detector has been proved to yield a statistical …
Comparison between Theoretical Predictions and Legri Background Noise Experimental Measurements
2001
Trapped protons are responsible for the main component of LEGRI background. Detailed theoretical model has demonstrated that the proton-induced counting rate is two orders of magnitude larger than the counting rate of the diffuse gamma-ray flux. The continuous passes of LEGRI through the SAA (7 times everyday) makes very difficult the background modelling. Long and short lived isotopes contribute in very different time scales to the proton-induced background component. The goal of this paper is to present a comparison between the long-lived background noise theoretical predictions and the experimental data. The results show an unexpected good agreement between the predicted and the observed…