Author name code: abdelatif ADS astronomy entries on 2022-09-14 author:"Abdelatif, Toufik E." ------------------------------------------------------------------------ Title: MISOLFA: a generalized monitor for daytime spatio-temporal turbulence characterization Authors: Ikhlef, R.; Corbard, T.; Morand, F.; Renaud, C.; Fodil, M.; Ziad, A.; Borgnino, J.; Meftah, M.; Assus, P.; Chauvineau, B.; Hauchecorne, A.; Lesueur, P.; Poiet, G.; Ubaldi, F.; Hamadouche, M.; Abdelatif, T. Bibcode: 2016MNRAS.458..517I Altcode: 2016MNRAS.tmp...33I Ground-based solar observations are strongly affected by optical turbulence. The concept of a new instrument which allows one to measure both spatial and temporal parameters of atmospheric turbulence has been proposed in the late 1990s. The instrument MISOLFA (Moniteur d'Images Solaire Franco-Algérien) is based on this concept and has been developed over the past 10 years in the framework of a ground-based solar astrometry programme and in parallel to the development of several night time turbulence monitors at Calern Observatory, south of France. In this paper, we first describe its instrumental concept, the technical choices that were made to meet the specifications and discuss the difficulties encountered. Using numerical simulations, we present and test the methods that can be used in order to estimate the turbulence parameters from both MISOLFA image and pupil planes. The effect of finite outer scale on Fried parameter estimation from a simple estimate of the angle-of-arrival variance is clearly shown. Finally, we present the first results obtained with the instrument fully operating in its two observing planes. We obtained a mean value of angle-of-arrival coherence time of 5.3 ms, and good agreement is found between spatial parameters obtained with image and pupil planes. First estimates of the atmospheric structure constant Cn^2(h) and outer scale L0(h) profiles are also presented which illustrates the profiling capacities of the new instrument. Title: 3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes Authors: Daiffallah, K.; Abdelatif, T.; Bendib, A.; Cameron, R.; Gizon, L. Bibcode: 2011SoPh..268..309D Altcode: 2010SoPh..tmp..204D; 2010SoPh..tmp..228D; 2010arXiv1008.2531D Three-dimensional numerical simulations have been used to study the scattering of a surface-gravity wave packet by vertical magnetic-flux tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic atmosphere. The scattered wave has been found to consist primarily of m=0 (axisymmetric) and m=1 modes. The ratio of the amplitude of these two modes was found to be strongly dependent on the radius of the flux tube. The kink mode is the dominant mode excited in tubes with a small radius, while the sausage mode is dominant for large tubes. Simulations of this type provide a simple, efficient, and robust way to start to understand the seismic signature of flux tubes, which have recently begun to be observed. Title: VLF observations of ionospheric disturbances in association with TLEs from the EuroSprite-2007 campaign Authors: NaitAmor, S.; AlAbdoadaim, M. A.; Cohen, M. B.; Cotts, B. R. T.; Soula, S.; Chanrion, O.; Neubert, T.; Abdelatif, T. Bibcode: 2010JGRA..115.0E47N Altcode: 2010JGRA..11500E47N Two Very Low Frequency (VLF) AWESOME remote sensing systems located at Algiers, Algeria (36.45°N, 3.28°E) and Sebha, Libya (27.02°N, 14.26°E) monitor VLF signal perturbations for evidence of ionospheric disturbances. During the EuroSprite-2007 campaign a number of Transient Luminous Events (TLEs) were captured over the Mediterranean Sea by cameras at Pic du Midi (42.94°N, 0.14°E) and at Centre de Recherches Atmosphériques (CRA) in southwestern France (43.13°N, 0.37°E). The cameras observations are compared to collected VLF AWESOME data. We consider early VLF perturbations observed on 12-13, 17-18 October and 17-18 December, 2007. The data from the two VLF receivers confirm the association between TLEs and early VLF signal perturbations with the perturbations amplitudes dependent on the observation configuration i.e. whether the TLE is near the receiver, near the transmitter, or far from both and the scattering process. The results also reveal that the early VLF perturbations can occur in the absence of a TLE. Title: Helioseismic Effects of Magnetic Flux Tube: 3D Numerical Simulations Authors: Daiffallah, K.; Abdelatif, T. Bibcode: 2008ESPM...12..3.4D Altcode: Observations suggest clearly that there is a significant interaction between solar surface waves and magnetic flux tubes with specific helioseismic signature. Magnetic flux tubes permit the propagation of two types of magnetohydrodynamic waves: The longitudinal tube wave (sausage modes) and the transversal tube wave (kink modes).

The response of different magnetic flux tubes embedded in polytropic atmosphere to the propagation of surface gravity wave (f-mode) is studied numerically with the SLiM code (see Cameron et al. 2007). We find that the back scattering wave from different sizes of tubes reveals interesting information about which modes are excited in the tubes. The numerical calculations of the scattering effects (for different frequencies of the incident wave, different tube radius and values of plasma-beta) are compared with theoretical results obtained by Hanasoge et al. 2008. Title: MAG Waves in Sunspots Umbrae: Slow Waves Leaking to the Corona Authors: Yelles Chaouche, Lotfi; Abdelatif, Toufik E. Bibcode: 2005SoPh..229..255Y Altcode: 2005SoPh..229..255C The linear oscillations of a stratified atmosphere embedded in a uniform vertical magnetic field are studied here. We use a simple theoretical model, formed by the superposition of two isothermal layers, representing, respectively, i) the photosphere and the chromosphere, and ii) the corona. The bottom layer behaves, for some modes, as a resonant cavity where MAG waves are semi-trapped. We find the existence of two types of modes: 1) Fast modes which are trapped below the transition layer, 2) Mixed modes which are resonant modes in the first layer and leak part of the energy to the corona. These mixed modes have been found to be damped in the horizontal direction and can explain the observed slow modes in the corona. Title: New values of gravitational moments J2 and J4 deduced from helioseismology Authors: Mecheri, R.; Abdelatif, T.; Irbah, A.; Provost, J.; Berthomieu, G. Bibcode: 2004SoPh..222..191M Altcode: 2009arXiv0911.5055R By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole moments J2 and J4 were computed using a solar model obtained from CESAM stellar evolution code (Morel, 1997) combined with a recent model of solar differential rotation deduced from helioseismology (Corbard et al., 2002). This model takes into account a near-surface radial gradient of rotation which was inferred and quantified from MDI f-mode observations by Corbard and Thompson (2002). The effect of this observational near-surface gradient on the theoretical values of the surface parameters J2, J4 is investigated. The results show that the octopole moment J4 is much more sensitive than the quadrupole moment J2 to the subsurface radial gradient of rotation. Title: Solar oblateness induced by its differential rotation Authors: Mecheri, R.; Provost, J.; Abdelatif, T.; Irbah, A. Bibcode: 2003EAEJA....14676M Altcode: By using the theory of Solar gravitational figure, the solar quadrupole moment J2 was computed combined with a recent analytical model of differential solar rotation (Corbard et al. 2002) taking into account a near-surface radial gradient of rotation inferred and quantified from MDI f-modes observations. This value of J2 obtained permits to evaluate the solar oblateness and its induced latitudinal variation of solar diameter. This variation was compared to those obtained from observations. Title: Mag Waves in Sunspot Umbra: Slow Mode Leaking to the Corona Authors: Yelles Chaouche, Lotfi; Abdelatif, Toufik E. Bibcode: 2003IAUJD..12E..13Y Altcode: The linear oscillations of a stratified atmosphere embedded by a uniform vertical magnetic field are studied here. We use a simple theoretical model formed by the superposition of two isothermal layers representing respectively i) the photosphere and the chromosphere and ii) the corona. The bottom layer behaves for some modes as a resonant cavity where MAG waves are semi trapped. We find the existence of two types of modes: 1) Fast modes which are trapped below the transition layer 2) Mixed modes which are resonant modes in the first layer and leaking part of the energy to the corona. These last modes have been found to be damped in the horizontal direction and can explain the observed slow modes in the corona Title: Spectral Analysis of Irregulary Sampled Helioseismic Data Authors: Seghouani, Nassim; Abdelatif, Toufik E. Bibcode: 2003IAUJD..12E..26S Altcode: One of the problems often encountered in astronomical data analysis is the problem missing data or data with gaps. In Heioseismology as well as in Asteroseismology this problem is omnipresent in spite of the great networks present through the world (IRIS GONG Bison Title: Solar P-Mode and Sunspots Interaction: Effect of Shear Flow Authors: Abdelatif, Toufik E.; Hughes, David W. Bibcode: 2003IAUJD..12E..12A Altcode: Motivated by observations of field-aligned flows within sunspots we have analyzed in some detail the transmission and reflection of compressive waves at a plane interface between a magnetic and non-magnetic region in the presence of a shear flow. Many of the results are similar to the study done by Abdelatif and Thomas (1989). To these results new effects have been found: the asymmetry of the upward and downward propagating waves the modes can be advectively carried with the flow and slow modes can be excited in cool flux tube. These two effects have drastic consequences on the standing waves near sunspots and can lead to interesting effects. We suggest that running penumbral waves are not really eigenmodes of models with horizontal field but propagating p-modes that has been advectivelly carried by the Evershed flow. In the light of our study the absorption of p-mode as described by Braun et al (1987) can be interpreted in part as displacement of wave energy by upward or downward advection in and around the sunspot structure. We also have noticed that for large Mach number the presence of overreflection and the interface is subject to Kelvin Helmholtz instabilities Title: New Determination of Solar Gravitational Moments j2 and J4. Authors: Mecheri, Redouane; Provost, Janine; Abdelatif, Toufik E.; Irbah, Abdenour Bibcode: 2003IAUJD..12E..11M Altcode: By using the theory of Solar gravitational figure the solar quadrupole and octopole moment respectively J2 and J4 were computed using Nice Observatory solar model (P.Morel et al. (1997)) combined with a new analytical model of solar differential rotation (Corbard et al. 2002) taking into account a near-surface radial gradient of rotation inferred and quantified from MDI f-modes observations. The values of J2 and J4 obtained permit to evaluate the solar oblateness and it's induced latitudinal variations of solar diameter in order to compare them to those obtained from observations. We also use J2 to calculate its contribution to the advance of the perihelion of Mercury for which the found value is in agreement with the theory of General Relativity and the measurements of Mercury's orbit by means of planetary ranging radar. Title: Astronomy in Algeria: past and present developments Authors: Irbah, Abdenour; Abdelatif, Toufik; Sadsaoud, Hamid Bibcode: 2001IAUGA..24..171I Altcode: 2000IAUSS..24E..19I Astronomy studies have been developed in Algeria since 1890 when the Algiers Observatory was built. Several instruments were soon installed on the site and have contributed to many scientific projects such as the international sky-map program. However, the observatory activities were suddenly interrupted by the departure of all French astronomers in 1962. Twenty years were needed before new astronomy programs were developed at Algiers Observatory. They are principally based on imaging through atmospheric turbulence, solar physics and studies of pulsating variable stars. Only one observational program, however, has so far been developed. This consists of solar observations in the framework of an international program to survey the Sun's radius. The astronomers now form a relatively important team since more than twelve researchers have permanent status. This is a good start taking into account the fact that astronomy is not taught in Algerian universities. We will begin first by giving an overview of the history of Algiers Observatory, including its instrumentation. We will then present the existing Algerian team and all their current scientific work and proposed projects. Title: Analysis of Diameter Measurements Performed at Calern Observatory Astrolabe Authors: Moussaoui, R.; Irbah, A.; Abdelatif, T.; Fossat, E.; Borgnino, J.; Laclare, F.; Delmas, C. Bibcode: 2000SoPh..195..433M Altcode: Solar diameter measurements performed at Calern Observatory astrolabe during more than two solar cycles show variations at various time scales in a broad range. Due to seasonal effects and instrumental characteristics, the recorded data are not sampled uniformly and present some gaps during these years. This time series has been analyzed by means of a deconvolution of the window function, as an alternative method to the standard least square fits of harmonic functions. The results show an extremely important improvement of the power spectrum. Harmonic terms already found by other authors are confirmed but new frequencies are also revealed by this analysis. Title: Propagation of Gaussian Pulse in Inhomogeneous Dispersive Plasma Authors: Semmane, F.; Abdelatif, T. Bibcode: 1999ESASP.437..437S Altcode: 1999erbp.conf..437S No abstract at ADS Title: Magneto-Atmospheric Waves Authors: Abdelatif, Toufik E. Bibcode: 1990SoPh..129..201A Altcode: The nature and properties of magneto-atmospheric (MA) waves are discussed here. A simple model atmosphere, isothermal and permeated by a uniform vertical magnetic field, was used to find that there are two type of modes with avoided crossing of the eigencurves in a K - Ω diagram. The properties of these waves are found to be identical to the uncoupled fast and slow MA waves away from the crossings (specially for small horizontal wave number K ≪ 1). The energy density for the fast modes is found to vanish with height and is responsible for the 3-min umbral oscillations, while the slow mode energy density is harmonic. Title: Wave modes in thick photospheric flux tubes - Classification and diagnostic diagram Authors: Hasan, S. S.; Abdelatif, T. Bibcode: 1990GMS....58...93H Altcode: The nature of wave motions in thick photospheric flux tubes is analyzed. The aim of this investigation is to determine the normal modes of a stratified atmosphere with a vertical magnetic field and to discuss their properties. The results are displayed in the form of a diagnostic diagram. An interesting feature of the solutions is the existence of 'avoided crossings', which occur when adjacent order modes approach each other in the diagnostic diagram. In general, the character of a mode changes with height in the atmosphere. Results are applied to umbral oscillations, and it is found that the observed oscillations with periods in the range 2-3 min, correspond to low-order modes in these calculations. For low horizontal wave number K, the modes, in the photosphere, have almost equal contributions from longitudinal and transverse components. As K increases, the transverse component begins to dominate. In the chromosphere, the modes are essentially transverse and can be identified with slow modes. Title: Transmission and Reflection of Compressive Waves at a Nonmagnetic-Magnetic Interface Authors: Abdelatif, Toufik E.; Thomas, John H. Bibcode: 1989ApJS...70..239A Altcode: The transmission and reflection properties of compressive waves at a plane interface between uniform nonmagnetic and magnetic regions in the absence of gravity are examined. Using stereographic polar projection, these properties are presented as functions of the two angles determining the direction of incidence. It is shown that the reflection coefficient and the direction of propagation of the transmitted wave are dependent on the direction of propagation of the incident wave for several representative parametric values. It is found that the incident, reflected, and transmitted wavenumber vectors always lie in the same plane, although the group velocity of the transmitted wave does not always lie in this plane. When the transmitted wave is a fast mode, there is generally weak reflection. Title: Surface and Body Waves in Magnetic Flux Tubes Authors: Abdelatif, T. E. Bibcode: 1988ApJ...333..395A Altcode: The dispersion relation of surface and body waves in a magnetic flux tube is studied in detail. The properties of the fast and slow bodywaves are described in terms of the filtering characteristics of the flux tube. In addition to the axisymmetric and nonaxisymmetric distinction between the modes, an additional distinction is made between the fundamental mode and the rest of the modes. New results concerning the thin and large flux tube approximation are derived. The behavior of surface and body waves in the solar convection zone, photosphere, and corona is discussed. Title: Sunspot Seismology Authors: Thomas, J. H.; Lites, B. W.; Abdelatif, T. E. Bibcode: 1988IAUS..123..181T Altcode: The 5 minute oscillations in a sunspot umbra are the response of the sunspot to forcing by the 5 minute p-modes in the surrounding convection zone (Thomas 1981). This interaction of solar p-modes with a sunspot can be used to probe the structure of a sunspot beneath the visible surface of the Sun (Thomas, Cram, and Nye 1982). Here the authors report briefly the results of both an observational study and a simple theoretical analysis of this interaction. Title: Heating of Coronal Loops by Phase-mixed Shear Alfven Waves Authors: Abdelatif, Toufik E. Bibcode: 1987ApJ...322..494A Altcode: The dissipation of shear Alfven waves in a coronal loop driven externally by an incident wave in the subcoronal region is investigated. The phase mixing of these incident shear Alfven waves serves as the dissipation mechanism in the corona. The wave solution found by Heyvaerts and Priest (1983) for coronal holes is used to compute the total energy deposited in a loop. The energy deposited is shown to depend upon the magnetic diffusivity nu(m) and viscosity nu(v), contrary to the conclusion of authors who assumed that coronal loops are perfect resonators. The energy deposited in a three-layer model is computed for incident waves with periods of five minutes or five seconds. For a five-minute period, almost no energy is deposited, especially for small loops. For a five-second period, a substantial amount of energy is deposited in the loop, but not enough to account for the heating of small loops. Title: The Interaction of Solar p-Modes with a Sunspot. II. Simple Theoretical Models Authors: Abdelatif, Toufik E.; Thomas, John H. Bibcode: 1987ApJ...320..884A Altcode: The interaction of solar p-modes with a sunspot magnetic flux tube is investigated theoretically by means of two simple models. An increase in horizontal wavelength between the nonmagnetic and magnetic regions, due to the different characteristic wave speeds in the two regions, explains the corresponding observed wavelength shift of powe in the umbral k-omega power spectrum. The variation of the transmission coefficient with wavenumber along the p-mode diagnostic curves, due to resonant transmission, is responsible for the observed selective filtering of the p-modes by the sunspot. Title: Theoretical Models of the Interaction of Solar p-Modes With a Sunspot Authors: Thomas, J. H.; Abdelatif, T. E. Bibcode: 1987BAAS...19R.936T Altcode: No abstract at ADS Title: The Interaction of Solar p-Modes with a Sunspot. I. Observations Authors: Abdelatif, Toufik E.; Lites, Bruce W.; Thomas, John H. Bibcode: 1986ApJ...311.1015A Altcode: Time series of velocity maps of two isolated sunspots and their surroundings were recorded in the Fe I line and the umbral line Ti I. Both 3 and 5 min umbral oscillations were detected at photospheric heights. The 5 min oscillations have reduced amplitude in the umbra, which appears to act as a filter in transmitting selected frequencies in the power spectrum of 5 min p-mode oscillations of the surrounding convection zone. The k-omicron power spectrum of the umbral oscillations shows this selective transmission and also shows a shift of power to longer horizontal wavelengths. This behavior is exhibited by a simple theoretical model of the interaction of p-modes with a sunspot. The 3 min umbral oscillations are concentrated in the dark central part of the umbra. In both sunspots, the kinetic energy density of the 3 min umbral oscillation in the photosphere is much greater than the corresponding kinetic energy density at chromospheric heights measured in other sunspots. Title: Umbral oscillations as a probe of sunspot structure Authors: Abdelatif, Toufik El-Hak Bibcode: 1985PhDT........85A Altcode: No abstract at ADS Title: Umbral Oscillations as a Probe of Sunspot Structure Authors: Abdelatif, T. E. H. Bibcode: 1985PhDT.........2A Altcode: 1986DiAbI..46.2345A The interaction of the solar five-minute oscillations with a sunspot is thoroughly explored, both on observational and theoretical grounds. Simple theoretical models are developed in order to understand the observations of umbral oscillations. Observations made at the National Solar Observatory detected both the three-minute and five-minute umbral oscillations at photospheric heights. The three-minute oscillations were found to have a kinetic energy density six times higher in the photosphere than in the chromosphere and to be concentrated in the central part of the umbra, supporting the photospheric resonance theory for the three-minute umbral oscillations. The five-minute oscillations are attenuated in the umbra, which appears to act as a filter in selecting some of the peaks in the power spectrum of five-minute oscillations in the surrounding photosphere. The k-omega power spectrum of the umbral oscillations shows a shift of power to longer wavelengths. Theoretical models of the transmission of acoustic waves into a magnetic region explain both observed effects. The variation of the transmission coefficient of trapped acoustic waves along the eigenmode curves is responsible for the selection of the peaks of the five-minute oscillations. The wavelength shift, due to the different dispersion relations in the nonmagnetic region and the magnetic region, is responsible for the shift of power in the umbral k-omega power spectrum. Title: Oscillations in a Sunspot and the Surrounding Photosphere Authors: Abdelatif, T. E.; Lites, B. W.; Thomas, J. H. Bibcode: 1984ssdp.conf..141A Altcode: Velocity oscillations at photospheric heights in a sunspot and its surroundings have been measured. The average temporal power spectrum of oscillations in the sunspot umbra shows the five-minute oscillations splitting into several distinct modes and also shows the existence of the three-minute umbral oscillation at photospheric heights, with greater kinetic energy density than in the chromosphere. Title: Oscillations in Sunspots and the Surrounding Photosphere Authors: Abdelatif, T.; Lites, B. W.; Thomas, J. H. Bibcode: 1983BAAS...15R.719A Altcode: No abstract at ADS