• K. R. Sivaraman

      Articles written in Journal of Astrophysics and Astronomy

    • The two components in the distribution of sunspot groups with respect to their maximum areas

      M. H. Gokhale K. R. Sivaraman

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      From an analysis of the distribution of sunspot groups with respect to their maximum areas we find that this distribution consists of two distinct components. One component contributes to spot groups of all possible values of A* with a distribution density varying as ∼ exp (b1 á*1/2) with b1 nearly constant from cycleto cycle and having a mean value ∼10-4 km-1. The other component is predominantly responsible for spot groups withA* ≲, 30 *10-6 hemisphere but may provide a few spot groups even above 50 * l0-6 hemisphere. This component may follow a distribution density ∼ exp (-b2 A*). We also determine the widths of the latitude zones over which spot groups in various intervals of A* appear and study their variation with time. These widths and their variations indicate that the two statistical samples of spot groups may be produced by two families of flux-tube clusters as suggested earlier in a phenomenological model. Very thin flux-tube clusters in the statistical samples seem to be related to the ephemeral active regions and X-ray bright points.

    • Morphology of H-alpha filaments and filament channel systems

      V. I. Makarov M. N. Stoyanova K. R. Sivaraman

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      Ring-like filaments have been detected on the spectroheliograms in the H-alpha line. Inside these filaments the magnetic field flux has a predominant polarity. Some of the dark filaments are connected by filament channels which can be seen at the limb either as (a) weak prominences or (b) dense low chromospheric features or (c) multi-channel system of matter flow between two prominences or (d) common quiescent prominences. The filament and the filament channel together form a continuous closed contour and outline the region of thef polarity particularly at the beginning of the solar cycle. The change in sign of the polar field of the Sun is associated with the drift of the filament band to high latitudes.

    • Brightness, polarization and electron density of the solar corona of 1980 february 16

      K. R. Sivaraman M. Jayachandran K. K. Scaria G. S. D. Babu S. P. Bagare A. P. Jayarajan

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      During the eclipse of 1980 February 16 we photographed the solar corona at an effective wavelength of 6300 å. Using a quadruple camera we also obtained the coronal pictures in polarized light for four Polaroid orientations. We have used these observations to derive the coronal brightness and polarization and from these the electron densities in the corona out to a distance of about 2.5 R⊙ from the centre of the disc. The coronal brightness matches well with that of the corona of 1958 October 12.

    • Results from Kodaikanal synoptic observations

      K. R. Sivaraman

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      The synoptic observations of Kodaikanal form one of the longest unbroken solar data from the beginning of the 20th century to the present day, and consists of the white light and monochromatic images of the sun. In this review, I shall discuss the results of the investigations in two areas using these data: (i) Tilt angles of the magnetic axes of bipolar spot groups, and (ii) structure and dynamics of large scale unipolar magnetic regions on the solar surface.

      The observed properties and patterns of behaviour of the tilt angles can be used as effective diagnostics to infer the physical conditions in the subsurface layers of the sun, and thus get an insight into the physical effects that act on the rising magnetic flux tubes during their journey through the convection zone to the surface.

      The second topic of discussion here, namely, the studies of the dynamics of unipolar regions over several solar cycles, show that the global solar activity has a high latitude component which manifests in the form of polar faculae, in addition to the well known sunspot activity at the middle and low latitudes. This raises the question about the origin of this high latitude component.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

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