Acoustic power mapping for active regions from MDI, HLH, and TON data

• Published in: Astronomy letters Vol. 28; no. 6; pp. 411 - 418
• Main Authors: Ladenkov, O V, Hill, F, Egamberdiev, Sh A, Chou, D Y
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 01-06-2002
• Subjects: Acoustics; Solar energy; Spatial distribution
• ISSN: 1063-7737; 1562-6873
• DOI: 10.1134/1.1484142

Based on the HLH and TON ground-based helioseismological projects and the SOHO/MDI spaceborne project, we obtained acoustic power maps of active regions averaged over 1 mHz intervals. These maps allowed the spatial and frequency distributions of acoustic power in an active region and its surroundings to be studied. The time step of the HLH data is 42 s, which makes it possible to investigate the acoustic power up to 11.9 mHz. Data in the Ca II K and Ni I lines, which originate in the middle chromosphere and the photosphere, respectively, give an idea of the height distribution of acoustic oscillation energy in the solar atmosphere. The acoustic halo produced by excess acoustic power around sunspots clearly shows up on acoustic maps in the Ca II K line and, to a lesser degree, in the Doppler Ni I line shifts. Ground-based observations also reveal a large enhancement of acoustic power inside sunspots. Our tests show that this effect results from the combination of a high intensity gradient in the data and atmospheric seeing. The latter was reduced by referencing each image to the sunspot. The spatial distribution of power inside the sunspot due to atmospheric seeing was found to depend on the exposure time of the data used. Excluding the nonsolar effects, a common property of all acoustic maps is the suppression of the solar-oscillation acoustic power in active regions.