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Browsing by Author "Kalkofen, W"

Browsing by Author "Kalkofen, W"

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  • 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: 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 ...
  • Equilibrium structure of solar magnetic flux tubes: Energy transport with multistream radiative transfer 
    Hasan, S. S; Kalkofen, W (The American Astronomical Society, 1994-11)
    We examine the equilibrium structure of vertical intense magnetic flux tubes on the Sun. Assuming cylindrical geometry, we solve the magnetohydrostatic equations in the thin flux-tube approximation, allowing for energy ...
  • Excitation of Longitudinal Modes in Solar Magnetic Flux Tubes by p-Modes 
    Hasan, S. S; Kalkofen, W (Astronomical Society of the Pacific, 1998)
    This is a continuation of earlier work by Hasan (1997) on the interaction of longitudinal (sausage) waves in a slender flux tube with p-modes in the ambient medium. We use a realistic stratification for the flux tube and ...
  • Excitation of Oscillations in Photospheric Flux Tubes through Buffeting by External Granules 
    Hasan, S. S; Kalkofen, W (The American Astronomical Society, 1999-07)
    We examine the excitation of transverse (kink) and longitudinal (sausage) waves in magnetic flux tubes by granules in the solar photosphere. The investigation is motivated by the interpretation of network oscillations in ...
  • Excitation of Oscillations in the Magnetic Network on the Sun 
    Hasan, S. S; Kalkofen, W; van Ballegooijen, A. A (The American Astronomical Society, 2000-05)
    We examine the excitation of oscillations in the magnetic network of the Sun through the footpoint motion of photospheric magnetic flux tubes located in intergranular lanes. The motion is derived from a time series of ...
  • The Influence of Magnetic Flux Tubes on Their Environment 
    Hasan, S. S; Kalkofen, W (Astronomical Society of the Pacific, 1998)
    We present new calculations for model atmospheres in magnetic flux tubes extending vertically through the photosphere and convection zone of the Sun. This study is a continuation of earlier work by Hasan & Kalkofen (1994) ...
  • Kink and Longitudinal Oscillations in the Magnetic Network on the Sun: Nonlinear Effects and Mode Transformation 
    Hasan, S. S; Kalkofen, W; van Ballegooijen, A. A; Ulmschneider, P (The American Astronomical Society, 2003-03)
    We examine the propagation of kink and longitudinal waves in the solar magnetic network. Previously, we investigated the excitation of network oscillations in vertical magnetic flux tubes through buffeting by granules and ...
  • On the interchange instability of solar magnetic flux tubes. II. The influence of energy transport effects 
    Bunte, M; Hasan, S. S; Kalkofen, W (European Southern Observatory, 1993-06)
    We examine the interchange instability of thin photospheric magnetic flux tube models which satisfy both force and energy balance with their surroundings. The stability of the tubes is independent of the efficiency of ...
  • Results from a revisit to the K2V bright points 
    Sivaraman, K. R; Gupta, S. S; Livingston, W. C; Damé, L; Kalkofen, W; Keller, C. U; Smartt, R; Hasan, S. S (European Southern Observatory, 2000-11)
    We have used pairs of temporally simultaneous CaII K-line spectroheliograms and magnetic area scans to search for spatial correlation between the CaII K2V bright points in the interior of the network and corresponding ...
  • Spectral line radiation from solar small-scale flux tubes. II 
    Hasan, S. S; Kneer, F; Kalkofen, W (European Southern Observatory, 1998-04)
    We examine spectral line radiation from small-scale magnetic flux tubes in the solar atmosphere. This is a continuation of work by Kneer et al. (1996). The main difference with the previous investigation is in the choice ...
  • Spectral line radiation from solar small-scale magnetic flux tubes 
    Kneer, F; Hasan, S. S; Kalkofen, W (European Southern Observatory, 1996-01)
    We consider spectral line radiation from small-scale magnetic model flux tubes in the solar atmosphere. The structure of the tube is determined from the magnetostatic equations in the thin flux tube approximation. We assume ...

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