Chromospheric seismology above sunspot umbrae

Snow, Ben, Botha, Gert and Regnier, Stephane (2015) Chromospheric seismology above sunspot umbrae. Astronomy & Astrophysics, 580. A107. ISSN 0004-6361

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Context: The acoustic resonator is an important model for explaining the three-minute oscillations in the chromosphere above sunspot umbrae. The steep temperature gradients at the photosphere and transition region provide the cavity for the acoustic resonator, which allows waves to be both partially transmitted and partially reflected.

Aims: In this paper, a new method of estimating the size and temperature profile of the chromospheric cavity above a sunspot umbra is developed.

Methods: The magnetic field above umbrae is modelled numerically in 1.5D with slow magnetoacoustic wave trains travelling along magnetic fieldlines. Resonances are driven by applying the random noise of three different colours -white, pink and brown - as small velocity perturbations to the upper convection zone. Energy escapes the resonating cavity and generates wave trains moving into the corona. Line of sight (LOS) integration is also performed to determine the observable spectra through SDO/AIA.

Results: The numerical results show that the gradient of the coronal spectra is directly correlated with the chromosperic temperature configuration. As the chromospheric cavity size increases, the spectral gradient becomes shallower. When LOS integrations is performed, the resulting spectra demonstrate a broadband of excited frequencies that is correlated with the chromospheric cavity size. The broadband of excited frequencies becomes narrower as the chromospheric cavity size increases.

Conclusions: These two results provide a potentially useful diagnostic for the chromospheric temperature profile by considering coronal velocity oscillations.

Item Type: Article
Uncontrolled Keywords: Sun: chromosphere, Sun: oscillations, magnetohydrodynamics, (MHD), sunspots
Subjects: F300 Physics
F500 Astronomy
G900 Others in Mathematical and Computing Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Gert Botha
Date Deposited: 09 Sep 2015 16:01
Last Modified: 01 Aug 2021 00:33

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