Impact of locally suppressed wave sources on helioseismic traveltimes

Shravan Hanasoge, S. Couvidat, S. P. Rajaguru, A. C. Birch

Research output: Contribution to journalArticle

Abstract

Wave traveltime shifts in the vicinity of sunspots are typically interpreted as arising predominantly from magnetic fields, flows and local changes in sound speed. We show here that the suppression of granulation related wave sources in a sunspot can also contribute significantly to these shifts, and in some cases, an asymmetry between ingoing and outgoing wave traveltimes. The tight connection between the physical interpretation of traveltimes and source-distribution homogeneity is confirmed. Statistically significant traveltime shifts are recovered upon numerically simulating wave propagation in the presence of a localized decrease in source strength. We also demonstrate that these time shifts are relatively sensitive to the modal damping rates; thus we are only able to place bounds on the magnitude of the effect of suppressed sources. We see a systematic reduction of 10-15 s in p-mode mean traveltimes at short distances (∼6.2 Mm) that could be misinterpreted as arising from a shallow (thickness of 1.5 Mm) increase (∼4 per cent) in the sound speed. At larger travel distances (∼24 Mm), a 6-13 s difference between the ingoing and outgoing wave traveltimes is observed; this could mistakenly be inferred as being caused by flows.

Original languageEnglish (US)
Pages (from-to)1931-1939
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume391
Issue number4
DOIs
StatePublished - Dec 1 2008

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shift
sunspots
sunspot
acoustics
wave propagation
homogeneity
travel
damping
asymmetry
retarding
magnetic field
magnetic fields
speed
sound
distribution
rate
effect

Keywords

  • Sun: helioseismology
  • Sun: oscillations

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Impact of locally suppressed wave sources on helioseismic traveltimes. / Hanasoge, Shravan; Couvidat, S.; Rajaguru, S. P.; Birch, A. C.

In: Monthly Notices of the Royal Astronomical Society, Vol. 391, No. 4, 01.12.2008, p. 1931-1939.

Research output: Contribution to journalArticle

Hanasoge, Shravan ; Couvidat, S. ; Rajaguru, S. P. ; Birch, A. C. / Impact of locally suppressed wave sources on helioseismic traveltimes. In: Monthly Notices of the Royal Astronomical Society. 2008 ; Vol. 391, No. 4. pp. 1931-1939.
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