• Bhola N. Dwivedi

      Articles written in Journal of Astrophysics and Astronomy

    • Electron density and temperature measurements, and abundance anomalies in the solar atmosphere

      Anita Mohan Bhola N. Dwivedi Enrico Landi

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      Using spectra obtained from the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric Observatory), we investigate the height dependence of electron density, temperature and abundance anomalies in the solar atmosphere. In particular, we present the behaviour of the solar FIP effect (the abundance enhancement of elements with first ionization potential < 10 eV in the corona with respect to photospheric values) with height above an active region observed at the solar limb, with emphasis on the so-called transition region lines.

    • Solar Coronal Plumes and the Fast Solar Wind

      Bhola N. Dwivedi Klaus Wilhelm

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      The spectral profiles of the coronal Ne VIII line at 77 nm have different shapes in quiet-Sun regions and Coronal Holes (CHs). A single Gaussian fit of the line profile provides an adequate approximation in quiet-Sun areas, whereas, a strong shoulder on the long-wavelength side is a systematic feature in CHs. Although this has been noticed since 1999, no physical reason for the peculiar shape could be given. In an attempt to identify the cause of this peculiarity, we address three problems that could not be conclusively resolved, in a review article by a study team of the International Space Science Institute (ISSI) (Wilhelm et al. 2011):

      The physical processes operating at the base and inside of plumes, as well as their interaction with the Solar Wind (SW).

      The possible contribution of plume plasma to the fast SW streams.

      The signature of the First-Ionization Potential (FIP) effect between plumes and inter-plume regions (IPRs).

      Before the spectroscopic peculiarities in IPRs and plumes in Polar Coronal Holes (PCHs) can be further investigated with the instrument Solar Ultraviolet Measurements of Emitted Radiation (SUMER) aboard the Solar and Heliospheric Observatory (SOHO), it is mandatory to summarize the results of the review to place the spectroscopic observations into context. Finally, a plume model is proposed that satisfactorily explains the plasma flows up and down the plume field lines and leads to the shape of the neon line in PCHs.

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      Posted on January 27, 2016

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