Comparing eclipse observations of the 2008 August 1 solar corona with an MHD model prediction

Abstract

Context. The structure of the white-light and emission solar coronas and their MHD modelling are the context of our work. Aims. A comparison is made between the structure of the solar corona as observed during the 2008 August 1 total eclipse from Mongolia and that predicted by an MHD model. Methods. The model has an improved energy formulation, including the effect of coronal heating, conduction of heat parallel to the magnetic field, radiative losses, and acceleration by Alfvén waves. Results. The white-light corona, which was visible up to 20 solar radii, was of an intermediate type with well-pronounced helmet streamers situated above a chain of prominences at position angles of 48, 130, 241, and 322 degrees. Two polar coronal holes, filled with a plethora of thin polar plumes, were observed. High-quality pictures of the green (530.3 nm, Fe XIV) corona were obtained with the help of two narrow-passband filters (centered at the line itself and the vicinity of 529.1 nm background), with a FWHM of 0.15 nm. Conclusions. The large-scale shape of both the white-light and green corona was found to agree well with that predicted by the model. In this paper we describe the morphological properties of the observed corona, and how it compares with that predicted by the model. A more detailed analysis of the quantitative properties of the corona will be addressed in a future publication.

Flattening Index of the Solar Corona and the Solar Cycle

“…Note that another value of (a + b) index for the 2008 total solar eclipse, namely 0.29 (Rušin et al, 2010), and our value for the 2009 total solar eclipse (a + b = 0.24, see Table 1) led to higher amplitudes of solar cycle 24: 132 ± 76 and 109 ± 69 in terms of the smoothed monthly sunspot number, respectively. Nevertheless, we prefer the prediction based on our flattening index value for the 2008 total solar eclipse (Pishkalo and Baransky, 2009).…”

“…The index value decreases with the growth of daily or monthly sunspot numbers. As Koutchmy et al (1992) 11 Jul 1991 142.2 −0.73 0.503 0.00 Gulyaev, Vanyarkha, and Vanyarkha (1994) 0.00 Vanyarkha, Vanyarkha, and Gulyaev (1993) 0.00 Sýkora et al (1999) 03 Nov 1994 26.1 −0.25 0.832 0.13 0.14 Badalyan and Sýkora (2008) 0.27 Marková and Bělik (1995) 24 Oct 1995 13.4 −0.11 0.928 0.13 0.27 Marková et al (1996) 0.28 Rušin et al (1996) we noted above, the sunspot numbers were taken from the SIDC site. The monthly sunspot numbers were also smoothed using a 13-point running average and then interpolated to the time of total solar eclipse.…”

“…Under such an interpretation, it is natural that the observed structure of the solar corona during the total solar eclipse of 11 July 1991 (near the maximum of solar cycle 22) looks like a minimal corona rotated with respect to the solar equator (Gulyaev, 1992;Sýkora et al, 1999Sýkora et al, , 2003. It is significant that the shape and structure of the solar corona modeled in the potential-field approach or using magnetohydrodynamic (MHD) simulations (Altschuler and Newkirk, 1969;Riley, Linker, and Mikić, 2001;Sýkora, Badalyan, and Obridko, 2003;Wang et al, 2007;Pishkalo, 2010a;Rušin et al, 2010) are generally consistent with the observed ones for most of the total solar eclipses.…”

The Structure and Dynamics of the Corona—Heliosphere Connection

“…To answer this question we calculated with very high numerical resolution, the steady state MHD solution for the corona and wind during a Carrington rotation centered about the August 1, 2008 eclipse (Rušin et al 2010). Figure 2 shows the open and closed field distribution at the photosphere calculated from the model, along with the polarity inversion line slightly above the photosphere (for clarity).…”

The Sun's global magnetic field

“…A key emphasis of this area of research is on the direct comparison of the steady-state solutions with either white-light [70] or multi-spectral extreme ultraviolet (EUV) and X-ray observations [68,69]. Early global MHD models that used a simplified polytropic energy equation were able to produce a good representation of the Sun's large-scale magnetic field [71], but they were unable to reproduce realistic emission profiles in EUV and X-rays.…”