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Browsing by Author "Hasan, S. S"

Browsing by Author "Hasan, S. S"

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  • Spectroscopic Observation of Oscillations in the Corona During the Total Solar Eclipse of 22 July 2009 
    Singh, J; Hasan, S. S; Gupta, G. R; Nagaraju, K; Banerjee, D (Springer, 2011-05)
    We performed high resolution spectroscopy of the solar corona during the total solar eclipse of 22 July 2009 in two emission lines: the green line at 5303 Å due to Fe xiv and the red line at 6374 Å due to Fe x, simultaneously ...
  • Stability of cool flux tubes in the solar chromosphere Linear analysis 
    Hasan, S. S; Kneer, F (EDP Sciences, 1986-04)
    The linear stability of cool flux tubes in the solar chromosphere which are initially in radiative equilibrium is examined. Owing to the presence of carbon monoxide, there exists a narrow region near the temperature minimum ...
  • Stability of cool flux tubes in the solar chromosphere. II - Non-linear dynamical behaviour 
    Hasan, S. S; Kneer, F (The European Southern Observatory, 1990-06)
    A single vertical cool flux tube in the solar chromosphere is focused upon for stability studies. The analysis of a previous study by Hasan and Kneer (1986) is extended to the nonlinear regime with a view to examining the ...
  • Stokes Diagnostics of Magneto-Acoustic Wave Propagation in the Magnetic Network on the Sun 
    Vigeesh, G; Steiner, O; Hasan, S. S (Springer, 2011-10)
    The solar atmosphere is magnetically structured and highly dynamic. Owing to the dynamic nature of the regions in which the magnetic structures exist, waves can be excited in them. Numerical investigations of wave propagation ...
  • Structure of small-scale magnetic flux tubes and excitation of sausage mode oscillations 
    Hasan, S. S (Astronomical Society of India, 1998)
    The nature of small-scale magnetic fields in the solar atmosphere is discussed. In the first part of the review, equilibrium models for the structure of magnetic flux tubes are presented. It is shown that the thermodynamic ...
  • Three-dimensional simulations of magnetohydrodynamic waves in magnetized solar atmosphere 
    Vigeesh, G; Fedun, V; Hasan, S. S; Erdelyi, R (IOP Publishing, 2012-08-10)
    We present results of three-dimensional numerical simulations of magnetohydrodynamic (MHD) wave propagation in a solar magnetic flux tube. Our study aims at understanding the properties of a range of MHD wave modes generated ...
  • A time dependent model for spicule flow 
    Hasan, S. S; Venkatakrishnan, P (Kluwer Academic Publishers, 1981-09)
    A time dependent model for the flow of gas in a spicule is studied. In this model, the flow occurs in a magnetic flux sheath. Starting from hydrostatic equilibrium, the flux sheath is allowed to collapse normal to itself. ...
  • Time-dependent convective collapse of flux tubes 
    Hasan, S. S (D. Reidel Publishing Co, 1983)
    The time-dependent collapse of a slender flux tube extending vertically in the convection zone of the sun is modelled. Starting from an initial state in which the flux tube is in hydrostatic equilibrium, the non-linear MHD ...
  • Time-dependent interaction of granules with magnetic flux tubes 
    Venkatakrishnan, P; Hasan, S. S (Indian Academy of Sciences, 1981-06)
    The time-dependent interaction of the granulation velocity field with a magnetic flux tube is investigated here. It is seen that when a magnetic field line is displaced normal to itself so as to simulate thebuffeting action ...
  • Time-resolved spectral observations of spicule velocities at several heights 
    Hasan, S. S; Keil, S. L (American Astronomical Society, 1984-08)
    The vacuum telescope of the National Solar Observatory, Sacramento Peak was used to obtain H-alpha spectral observations of spicules. A set of spectra corresponding to five slit positions above the solar limb were recorded ...
  • Transient response of the solar wind to changes in flow geometry 
    Hasan, S. S; Venkatakrishnan, P (D.Reidel Publishing Co.,, 1982-10)
    An initial stationary flow in a configuration diverging as r-squared is assumed, a state corresponding to the normal solar wind solution. The effect on the flow through a tube whose area A(r, t) diverges faster than ...
  • Wave leakage in a magnetized isothermal atmosphere 
    Banerjee, D; Hasan, S. S; Christensen-Dalsgaard, J (Astronomical Society of India, 1996)
    The present investigation is a continuation of earlier work by Hasan & christensen-Dalsgaard (1992) and Banerjee, Hasan & Christensen-Dalsgaard(1995), where the interaction of various elementary modes in a stratified ...
  • Wave propagation and energy transport in the magnetic network of the Sun 
    Vigeesh, G; Hasan, S. S; Steiner, O (European Southern Observatory, 2009-12)
    Aims. We investigate wave propagation and energy transport in magnetic elements, which are representatives of small scale magnetic flux concentrations in the magnetic network on the Sun. This is a continuation of earlier ...
  • Wave propagation in multiple flux tubes and chromospheric heating 
    Hasan, S. S; van Ballegooijen, A; Steiner, O (Cambridge University Press, 2008-05)
    This investigation is a continuation of earlier work on the dynamics of the magnetic network. In a previous calculation (Hasan et al. 2005), we examined the response of a single flux tube to transverse motions of its ...
  • Wave propagation in sunspots 
    Hasan, S. S (International Astronomical Union, 1990)
    Wave propagation in sunspot umbrae is analyzed; the stratification in a typical umbra is approximated by a model atmosphere, extending vertically from a depth of a few thousand kilometers below the photosphere, to the ...
  • Wave propagation in the magnetic network on the Sun 
    Hasan, S. S; Vigeesh, G; van Ballegooijen, A. A (Cambridge University Press, 2006)
    Hasan et al. (2005) have recently presented 2-D dynamical calculations on wave propagation in in the magnetic network of the Sun. The latter is idealized as consisting of non-potential flux tubes in the quiet solar ...
  • Why Does the Sun Have Kilogauss Magnetic Fields? 
    Hasan, S. S; van Ballegooijen, A. A (Astronomical Society of the Pacific, 1998)
    Magnetic fields in the solar photosphere are concentrated in flux tubes with kilogauss field strength surrounded by nearly field-free plasma. Observations show that the flux tubes are located in convective downdrafts where ...

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