Inference of magnetic fields in inhomogeneous prominences

Most of the quantitative information about the magnetic field vector in solar prominences comes from the analysis of the Hanle effect acting on lines formed by scattering. As these lines can be of non-negligible optical thickness, it is of interest to study the line formation process further. We investigate the multidimensional effects on the interpretation of spectropolarimetric observations, particularly on the inference of the magnetic field vector. We do this by analyzing the differences between multidimensional models, which involve fully self-consistent radiative transfer computations in the presence of spatial inhomogeneities and velocity fields, and those which rely on simple one-dimensional geometry. We study the formation of a prototype line in ad hoc inhomogeneous, isothermal 2D prominence models. We solve the NLTE polarized line formation problem in the presence of a large-scale oriented magnetic field. The resulting polarized line profiles are then interpreted (i.e. inverted) assuming a simple 1D slab model. We find that differences between input and the inferred magnetic field vector are non-negligible. Namely, we almost universally find that the inferred field is weaker and more horizontal than the input field. Spatial inhomogeneities and radiative transfer have a strong effect on scattering line polarization in the optically thick lines. In real-life situations, ignoring these effects could lead to a serious misinterpretation of spectropolarimetric observations of chromospheric objects such as prominences.Comment: 11 pages, 9 figure

A forth-and-back implicit λ iteration in the solution of radiative transfer in spherical media

Forth-and-back implicit Λ-iteration has been developed to solve radiative transfer (RT) problems with plane-parallel geometry in which there is a coupling of all RT equations by the scattering term included in the source function (Atanacković-Vukmanović, Crivellari and Simonneau 1997). Owing to the implicit representation of the source function in the computation of the mean intensities within a forth-and-back sequential treatment of the two intensities propagating in opposite directions, implicit Λ-iteration (ILI) appears to be a very efficient method in the solution of linear as well as non-linear transfer problems. In this paper ILI method is generalized and applied to radiative transfer problems with spherical symmetry. The results for the monochromatic radiative transfer in a spherical atmosphere are presented and compared to those of other authors obtained by the other methods

Clinical and ultrasonographic investigation of congenital hip dislocation: a retrospective study

Clinical and ultrasonographic investigation of congenital hip dislocation: a retrospective stud

Statistical Analysis of Langmuir Waves Associated with Type III Radio Bursts: I. Wind Observations

International audienceInterplanetary electron beams are unstable in the solar wind and they generate Langmuir waves at the local plasma frequency or its harmonic. Radio observations of the waves in the range 4--256 kHz, observed in 1994--2010 with the WAVES experiment onboard the WIND spacecraft, are statistically analyzed. A subset of 36 events with Langmuir waves and type III bursts occurring at the same time was selected. After removal of the background, the remaining power spectral density is modeled by the Pearson system of probability distributions (types I, IV and VI). The Stochastic Growth Theory (SGT) predicts log-normal distribution for the power spectrum density of the Langmuir waves. Our results indicate that SGT possibly requires further verification

Statistical Analysis of Langmuir Waves Associated with Type III Radio Bursts: I. Wind Observations

International audienceInterplanetary electron beams are unstable in the solar wind and they generate Langmuir waves at the local plasma frequency or its harmonic. Radio observations of the waves in the range 4--256 kHz, observed in 1994--2010 with the WAVES experiment onboard the WIND spacecraft, are statistically analyzed. A subset of 36 events with Langmuir waves and type III bursts occurring at the same time was selected. After removal of the background, the remaining power spectral density is modeled by the Pearson system of probability distributions (types I, IV and VI). The Stochastic Growth Theory (SGT) predicts log-normal distribution for the power spectrum density of the Langmuir waves. Our results indicate that SGT possibly requires further verification

Statistical Analysis of Langmuir Waves Associated with Type III Radio Bursts

International audienceInterplanetary electron beams, produced by CMEs and flares, are unstable in the solar wind and generate Langmuir waves at the local plasma frequency (f_p) or its harmonic (2f_p). Radio observations of the waves in the range 4 - 256 kHz from the WAVES experiment onboard the WIND spacecraft have been statistically analyzed. A subset of 36 events has been selected for this study. The background consisting of thermal noise, type III bursts and Galactic background has been removed and the remaining power spectral density has been fitted by Pearsons system of probability distributions. The coefficients of the probability distributions have been calculated by using two methods: method of moments and maximum likelihood estimation method. We have shown that the probability distributions of the power spectral density of the Langmuir waves belong to three different types of Pearsons probability distributions: type I, type IV and type VI. In order to compare the goodness of the fits, a few statistical tests have been applied, showing for all of the considered events that the Pearsons probability distributions fit the data better than the Gaussian ones. This is in contradiction with the Stochastic Growth Theory which predicts log-normal distribution for the power spectral density of the Langmuir waves. The uncertainty analysis that has been performed also goes in favor of the use of Pearsons system of distributions to fit the data

Statistical Analysis of Langmuir Waves Associated with Type III Radio Bursts

International audienceInterplanetary electron beams, produced by CMEs and flares, are unstable in the solar wind and generate Langmuir waves at the local plasma frequency (f_p) or its harmonic (2f_p). Radio observations of the waves in the range 4 - 256 kHz from the WAVES experiment onboard the WIND spacecraft have been statistically analyzed. A subset of 36 events has been selected for this study. The background consisting of thermal noise, type III bursts and Galactic background has been removed and the remaining power spectral density has been fitted by Pearsons system of probability distributions. The coefficients of the probability distributions have been calculated by using two methods: method of moments and maximum likelihood estimation method. We have shown that the probability distributions of the power spectral density of the Langmuir waves belong to three different types of Pearsons probability distributions: type I, type IV and type VI. In order to compare the goodness of the fits, a few statistical tests have been applied, showing for all of the considered events that the Pearsons probability distributions fit the data better than the Gaussian ones. This is in contradiction with the Stochastic Growth Theory which predicts log-normal distribution for the power spectral density of the Langmuir waves. The uncertainty analysis that has been performed also goes in favor of the use of Pearsons system of distributions to fit the data