[Seminar]

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Title: First detection of high-order azimuthal modes in sunspot atmosphere

Speaker: Yuan Ding

Affiliation: Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, UK

Time:  December 21, 2012 (Friday) 9:30 a.m.

Venue: Meeting Room 401 (Main Building)

Abstract:　

The 5-min oscillations inside sunspots appear to be the absorption of solar $p$-mode. It is a potential tool to probe the sunspot structure and the local plasma parameters. We study the power, phase and correlations properties of the 5-min oscillations and investigate its interactions with the sunspot magnetic field.  The azimuthal distributions of the phase and cross-correlation coefficient of the 5-min oscillations enclosing a sunspot are obtained with SDO/AIA images. Through non-linear fitting and periodogram analysis, the azimuthal mode are quantified and justified with significance tests.
　  The high-order azimuthal modes, analytically described as $\rho=\rho_1\cos(\omega t+k_z z+m\theta+\phi_0)$, in the lower atmosphere of sunspot were first detected in the phase and correlation distribution of the 5-min oscillations in sunspot AR11131 with AIA data in 1700 A, 1600 A and 304 A channels. The modes $m=2,3,4,5,7,8$ were detected in the sunspot magnetic field. Higher-order $m$ modes were detected in the upper atmosphere. One possible explanation is the modulation on the phase speed of 5-min oscillations by the slow MHD body mode with m>1 in sunspots.

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抚仙湖太阳基地
　　中国科学院天体结构与演化重点实验室
　　云南天文台学术委员会
　　2012-12-17