Direct Mapping of Solar Acoustic Power

Details Direct Mapping of Solar Acoustic Power Direct Mapping of Solar Acoustic Power

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...415..847t&link_type=abstract

Astrophysical Journal v.415, p.847

Astronomy and Astrophysics

Astronomy

22

Sun: Oscillations

Scientific paper

We investigate the spatial distribution of acoustic power on the Sun as a function of both horizontal wavenumber, k, and temporal frequency, ν. Using time series of full-disk Ca II K line observations, obtained at the University of Hawaii's Mees Solar Observatory, we generated a set of six synoptic maps which represent the total acoustic power integrated over the three different frequency ranges; (a) 195.3 μHz ≤ ν ≤ 1790.4 μHz, (b) 1790.4 μHz ≤ ν ≤ 5501.3 μHz, and (c) 5501.3 μHz ≤ ν ≤ 8333.3 μHz, for values of k ≲ 0.25 Mm-1 and k ≳ 0.25 Mm-1. At high temporal frequencies we find "halos" of enhanced acoustic power surrounding active regions. The amount of enhancement is ˜10%±5% relative to the quiet photosphere. Both the high- and low-k maps exhibit the phenomenon. Our rather poor resolution in k does not allow a complete study of the spatial dependence of the halos, but there is some indication that their morphology may depend weakly on k. The halos extend several tens of Mm beyond the boundary of the plage as seen in the K line. These appear to be true solar features, and not an artifact of variable seeing. We also looked for evidence of subphotospheric magnetic structures, such as the "fingers" reported by Braun et al. We find one very faint, diffuse feature apparently connecting an active region in the southern hemisphere with one in the north. We hesitate to say that this is a true signature of a subphotospheric structure because of its very low signal level relative to the background. The high-k, p-mode map was examined for any evidence for an acoustic power deficit at the antipodal points of active regions. We estimate that any power deficit at active region antipodal points must be no more than ˜1%, and we therefore conclude that no strong deficit exists at the antipodes of sunspots. At low frequencies, both the high- and low-k maps show enhanced power at the locations of the active regions. This represents active region evolution.

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