abdelatif

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Author name code: abdelatif
ADS astronomy entries on 2022-09-14
author:"Abdelatif, Toufik E."

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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.
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.

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Title: 3D Numerical Simulations of f-Mode Propagation Through Magnetic
Flux Tubes
Authors: Daiffallah, K.; Abdelatif, T.; Bendib, A.; Cameron, R.;
Gizon, L.
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.

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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.
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.

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Title: Helioseismic Effects of Magnetic Flux Tube: 3D Numerical
Simulations
Authors: Daiffallah, K.; Abdelatif, T.
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.

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Title: MAG Waves in Sunspots Umbrae: Slow Waves Leaking to the Corona
Authors: Yelles Chaouche, Lotfi; Abdelatif, Toufik E.
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.

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Title: New values of gravitational moments J2 and
J4 deduced from helioseismology
Authors: Mecheri, R.; Abdelatif, T.; Irbah, A.; Provost, J.;
Berthomieu, G.
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.

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Title: Solar oblateness induced by its differential rotation
Authors: Mecheri, R.; Provost, J.; Abdelatif, T.; Irbah, A.
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.

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Title: Mag Waves in Sunspot Umbra: Slow Mode Leaking to the Corona
Authors: Yelles Chaouche, Lotfi; Abdelatif, Toufik E.
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

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Title: Spectral Analysis of Irregulary Sampled Helioseismic Data
Authors: Seghouani, Nassim; Abdelatif, Toufik E.
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

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Title: Solar P-Mode and Sunspots Interaction: Effect of Shear Flow
Authors: Abdelatif, Toufik E.; Hughes, David W.
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

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Title: New Determination of Solar Gravitational Moments j2 and J4.
Authors: Mecheri, Redouane; Provost, Janine; Abdelatif, Toufik E.;
Irbah, Abdenour
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.

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Title: Astronomy in Algeria: past and present developments
Authors: Irbah, Abdenour; Abdelatif, Toufik; Sadsaoud, Hamid
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.

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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.
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.

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Title: Propagation of Gaussian Pulse in Inhomogeneous Dispersive
Plasma
Authors: Semmane, F.; Abdelatif, T.
1999ESASP.437..437S Altcode: 1999erbp.conf..437S
No abstract at ADS

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Title: Magneto-Atmospheric Waves
Authors: Abdelatif, Toufik E.
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.

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Title: Wave modes in thick photospheric flux tubes - Classification
and diagnostic diagram
Authors: Hasan, S. S.; Abdelatif, T.
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.

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Title: Transmission and Reflection of Compressive Waves at a
Nonmagnetic-Magnetic Interface
Authors: Abdelatif, Toufik E.; Thomas, John H.
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.

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Title: Surface and Body Waves in Magnetic Flux Tubes
Authors: Abdelatif, T. E.
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.

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Title: Sunspot Seismology
Authors: Thomas, J. H.; Lites, B. W.; Abdelatif, T. E.
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.

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Title: Heating of Coronal Loops by Phase-mixed Shear Alfven Waves
Authors: Abdelatif, Toufik E.
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.

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Title: The Interaction of Solar p-Modes with a Sunspot. II. Simple
Theoretical Models
Authors: Abdelatif, Toufik E.; Thomas, John H.
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.

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Title: Theoretical Models of the Interaction of Solar p-Modes With
a Sunspot
Authors: Thomas, J. H.; Abdelatif, T. E.
1987BAAS...19R.936T Altcode:
No abstract at ADS

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Title: The Interaction of Solar p-Modes with a
Sunspot. I. Observations
Authors: Abdelatif, Toufik E.; Lites, Bruce W.; Thomas, John H.
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.

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Title: Umbral oscillations as a probe of sunspot structure
Authors: Abdelatif, Toufik El-Hak
1985PhDT........85A Altcode:
No abstract at ADS

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Title: Umbral Oscillations as a Probe of Sunspot Structure
Authors: Abdelatif, T. E. H.
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.

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Title: Oscillations in a Sunspot and the Surrounding Photosphere
Authors: Abdelatif, T. E.; Lites, B. W.; Thomas, J. H.
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.

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Title: Oscillations in Sunspots and the Surrounding Photosphere
Authors: Abdelatif, T.; Lites, B. W.; Thomas, J. H.
1983BAAS...15R.719A Altcode:
No abstract at ADS