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Browsing by Author "Hasan, S. S"

Browsing by Author "Hasan, S. S"

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  • 2D radiative equilibrium models of magnetic flux tubes 
    Hasan, S. S; Kalkofen, W; Steiner, O (Kluwer Academic Publishers, 1999)
  • Acoustic Emission From Magnetic Flux Tubes in the Solar Network 
    Vigeesh, G; Hasan, S. S (IOP Publishing, 2013)
    We present the results of three-dimensional numerical simulations to investigate the excitation of waves in the magnetic network of the Sun due to foot point motions of a magnetic flux tube. We consider motions that typically ...
  • The Alfven-Carlquist double-layer theory of solar flares 
    Hasan, S. S; Ter Haar, D (Kluwer Academic Publishers, 1978-06)
    We use the Vlasov equations for ions and electrons to develop a theory of a double layer in which there are both free and trapped electrons and ions. We find the equations which replace the Langmuir condition and the Bohm ...
  • Chromospheric dynamics 
    Hasan, S. S (Elsevier Ltd, 2008=07)
    This review focuses on dynamics of the solar chromosphere, which serves as a good proxy for understanding processes in stellar chromospheres as well. In the quiet chromosphere it is useful to distinguish between the magnetic ...
  • Classification of Magnetoatmospheric Modes in Sunspot Umbrae 
    Hasan, S. S; Sobouti, Y (International Astronomical Union, 1990)
    We examine the wave modes in a sunspot umbra. Assuming stratification, based on a model atmosphere in a sunspot, the normal mode spectrum is determined. The modes are classified using a scheme based on a Helmholtz decomposition ...
  • Comment on the paper 'a new resonance in the solar atmosphere' by Joseph V. Hollweg 
    Venkatakrishnan, P; Hasan, S. S (D. Reidel Publishing Co., 1982-01)
    In the absence of genuine forcing terms, there is no resonance between linear fast mhd and gravito-acoustic waves.
  • Convective collapse and overstable oscillations in solar flux tubes 
    Hasan, S. S (European Space Egency, 1984-11)
    The collapse of solar flux tubes by a convective instability is investigated. At the initial epoch it is assumed that the flux tube is in hydrostatic equilibrium and that it has the same temperature as the ambient medium. ...
  • Convective Intensification of Magnetic Flux Tubes in Stellar Photospheres 
    Rajaguru, S. P; Kurucz, R. L; Hasan, S. S (The American Astronomical Society, 2002-02)
    The convective collapse of thin magnetic flux tubes in the photospheres of Sun-like stars is investigated using realistic models of the superadiabatic upper convection zone layers of these stars. The strengths of convectively ...
  • Development of Solar Differential Image Motion Monitor at IIA, for the NLST site characterization program 
    Hasan, S. S; Saxena, A. K; Bagare, S. P; Samson, J. P. A; Ismail, M. M; Rajendra, B. S; Aditya, T; Jabilullah, R. I; Tsewang, D (Indian Institute of Astrophysics, 2010)
    The Indian Institute of Astrophysics is planning to setup a 2 m National Large Solar Telescope (NLST) in India. In view of this, a site survey program was initiated. A Solar Differential Image Motion Monitor (SDIMM) unit ...
  • Dynamical Effects in Solar Photospheric Flux Tubes 
    Hasan, S. S (Kluwer Academic Publisher, 1996)
    The interaction of an intense flux tube, extending vertically through the photosphere, with p-modes in the ambient medium is modelled by solving the time dependent MHD equations in the thin flux tube approximation. It is ...
  • Dynamical phenomena in sunspots. I. Time dependent relaxation to equilibrium 
    Gangadhara, R. T; Hasan, S. S (European Southern Observatory, 1997-11)
    We have adapted a general purpose time-dependent 2-D code to study dynamical phenomena in sunspots. In the first part of our investigation, we numerically simulate the dynamical relaxation to equilibrium of a sunspot. ...
  • Dynamical Processes in Flux Tubes and their Role in Chromospheric Heating 
    Hasan, S. S (Indian Academy of Sciences, 2000-12)
    We model the dynamical interaction between magnetic flux tubes and granules in the solar photosphere which leads to the excitation of transverse (kink) and longitudinal (sausage) tube waves. The investigation is motivated ...
  • The DynaMICCS perspective. A mission for a complete and continuous view of the Sun dedicated to magnetism, space weather and space climate 
    Turck-Chieze, S; Lamy, P; Carr, C; Carton, P. H; Chevalier, A; Dandouras, I; Defise, J. M; Dewitte, S; Dudok de Wit, T; Halain, J. P; Hasan, S. S; Hochedez, J. F; Horbury, T; Levacher, P; Meissonier, M; Murphy, N; Rochus, P; Ruzmaikin, A; Schmutz, W; Thuillier, G; Vives, S (Springer Netherlands, 2009-03)
    The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative/convective zone interface ...
  • Dynamics and heating of the magnetic network on the Sun. Efficiency of mode transformation 
    Hasan, S. S; Ulmschneider, P (EDP Sciences, 2004-12)
  • The dynamics of the quiet solar chromosphere 
    Kalkofen, W; Hasan, S. S; Ulmschneider, P (Cambridge University Press, 2003)
    Wave propagation in the nonmagnetic chromosphere is described for plane and spherical waves, and excitation by means of impulses in small source regions in the photosphere; excitation for flux tube waves in the magnetic ...
  • Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere 
    Hasan, S. S; van Ballegooijen, A. A (The American Astronomical Society, 2008-06-20)
    We consider recent observations of the chromospheric network and argue that the bright network grains observed in the Ca ii H and K lines are heated by an as-yet-unidentified quasi-steady process. We propose that the heating ...
  • Dynamics of the Solar Magnetic Network: Two-dimensional MHD Simulations 
    Hasan, S. S; van Ballegooijen, A. A; Kalkofen, W; Steiner, O (The American Astronomical Society, 2005-10)
    The aim of this work is to identify the physical processes that occur in the network and contribute to its dynamics and heating. We model the network as consisting of individual flux tubes, each with a nonpotential field ...
  • Effect of Newtonian Cooling on Waves in a Magnetized Isothermal Atmosphere 
    Banerjee, D; Hasan, S. S; Christensen-Dalsgaard, J (Springer, 1997-05)
    We examine the influence of nonadiabatic effects on the modes of an isothermal stratified magnetic atmosphere. The present investigation is a continuation of earlier work by Hasan and Christensen-Dalsgaard (1992) and ...
  • The effect of p-modes on thin magnetic flux tubes 
    Hasan, S. S; Bogdan, T. J (Astronomical Society of India, 1996)
    We examine the effect of p-modes impinging on thin magnetic flux tubes. The aim of the study is to see whether global p-modes can excite wave motions of significant amplitude in a magnetic flux tube. For simplicity we treat ...
  • Energy transport in intense flux tubes on the sun. I - Equilibrium atmosphere 
    Hasan, S. S (The American Astronomical Society, 1988-09)
    Model calculations are performed to determine self-consistently the equilibrium atmosphere in an intense flux tube. The generalization of the Eddington approximation to three dimensions is used to develop a zeroth-order ...

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