مجال التميز | تميز دراسي وبحثي |
البحوث المنشورة |
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البحث (1): | |
عنوان البحث: | Magnetohydrodynamic Wave Modes of Solar Magnetic Flux Tubes with an Elliptical Cross Section |
رابط إلى البحث: | https://iopscience.iop.org/article/10.3847/1538-4357/abec7a |
تاريخ النشر: | 04/05/2021 |
موجز عن البحث: | The purpose of this paper is to study the behavior of magnetohydrodynamic (MHD) wave modes that propagate in compressible magnetic flux tubes with an elliptical cross section embedded in a magnetic environment. The dispersion relation that describes the behavior of MHD wave modes permitted in an elliptical magnetic flux tube is solved numerically. Distortion of the spatial structure of the purely real eigenmodes from the well-known circular flux tube model has been considered. It has been studied under both photospheric and coronal conditions. It has been shown that (i) solutions in the form of even Mathieu functions are more sensitive to the value of eccentricity than solutions with the form of odd Mathieu functions; (ii) if the ellipticity of the cross section of the magnetic flux tube increases, a sausage mode (m = 0) cannot be easily identified; (iii) even solutions that correspond to the fluting mode (m = 3) can be misinterpreted as a kink mode (m = 1) due to their similarities. In contrast to the fluting modes that are polarized along the major axis and strongly depend on the ellipticity of the magnetic flux tube, the kink and sausage surface modes are practically unaffected by ellipticity. Several examples of the spatial structure of the eigenmodes permitted in the pores and sunspots have been visualized. The solutions obtained in the approximation of cylindrical symmetry are in agreement with previous studies. |
البحث (2): | |
عنوان البحث: | A novel approach to identify resonant MHD wave modes in solar pores and sunspot umbrae: B − ω analysis |
رابط إلى البحث: | https://www.aanda.org/articles/aa/abs/2021/05/aa40429-21/aa40429-21.html |
تاريخ النشر: | 02/06/2021 |
موجز عن البحث: |
The umbral regions of sunspots and pores in the solar photosphere are generally dominated by 3 mHz oscillations, which are due to p-modes penetrating the magnetic region. In these locations, wave power is also significantly reduced with respect to the quiet Sun. However, here we study a pore where not only is the power of the oscillations in the umbra comparable to, or even larger than, that of the quiet Sun, but the main dominant frequency is not 3 mHz as expected, but instead 5 mHz. By combining Doppler velocities and spectropolarimetry and analysing the relationship between magnetic field strength and frequency, the resultant B − ω diagram reveals distinct ridges that are remarkably clear signatures of resonant magneto-hydrodynamic (MHD) oscillations confined within the pore umbra. We demonstrate that these modes, in addition to velocity oscillations, are also accompanied by magnetic oscillations, as predicted from MHD theory. The novel technique of B − ω analysis proposed in this article opens up an exciting new avenue for identifying MHD wave modes in the umbral regions of both pores and sunspots. |
المؤتمرات العلمية |
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المؤتمر (1): | |
عنوان المؤتمر: | AGU Meeying 2019 |
تاريخ الإنعقاد: | 12/12/2019 |
مكان الإنعقاد: | USA |
طبيعة المشاركة: | Poster presentation |
عنوان المشاركة: | New Elliptical Flux Tube Model to Explain Sunspot Oscillations |
ملخص المشاركة: | This work is motivated by elliptical sunspot oscillation data that cannot be explained by the standard cylinder model. We obtained a new numerical solution of the dispersion relation for a compressible magnetic flux tube with an elliptical cross-section embedded in a magnetic environment. We applied the bisection method to solve this equation and investigated the behaviour of oscillations which arise under both photospheric and coronal conditions. From our solutions we obtain an approximation of a circle like shape which is in perfect agreement with a previous well known results. Our model also explains a mode detected in an elliptical sunspot using the ROSA (Rapid Oscillations in the Solar Atmosphere) instrument based at the Dunn Solar Telescope. |
الرابط: | https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/539836 |
المؤتمر (2): | |
عنوان المؤتمر: | Theo Murphy scientific meeting: High resolution wave dynamics in the lower solar atmosphere |
تاريخ الإنعقاد: |
10/02/2020 |
مكان الإنعقاد: | Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell, Buckinghamshire |
طبيعة المشاركة: | Poster presentation |
عنوان المشاركة: | New Elliptical Flux Tube Model to Explain Sunspot Oscillations |
ملخص المشاركة: |
This work is motivated by elliptical sunspot oscillation data that cannot be explained by the standard cylinder model. Hence, in this work we describe a model that predicts the MHD wave modes that can be trapped and propagate in compressible magnetic flux tubes with an elliptical cross-section. We will discuss the resultant dispersion relations for body and surface modes, then show how the ellipticity of magnetic flux tubes affect these solutions (with specific applications to coronal and photospheric conditions). From a practical point of view the information from these dispersion diagrams do not show how these MHD modes will actually manifest themselves in observational data. Therefore, we have also prepared several visualisations of the eigenfunctions of these MHD wave modes to explain how the eccentricity affects each wave mode. In addition, the theory of MHD wave modes in cylindrical magnetic waveguides is well developed. However, realistic forward modelling of the observable signatures of such wave modes to compare them with high resolution data of the Sun’s atmosphere is still in its infancy. It is the purpose of this research to forward model how the actual integrated spectral line intensity and Doppler velocity of such MHD wave modes will appear in observational data depending on the particular wavelength used and the observer’s line of sight with respect to the magnetic cylinder axis. |
الرابط: | https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2020.0169 |
أنوار علي عبدالله الظفيري
دكتوراه
العلوم والتقنية
SHEFFIELD UNIVERSITY