English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Observations indicate that in plage areas (i.e. in active regions outsidesunspots) acoustic waves travel faster than in quiet sun, leading to shortenedtravel times and higher p-mode frequencies. While it is clear that the ultimatecause of any difference between quiet sun and plage is the presence of magneticfields of order 100 G in the latter, the mechanism by which the magnetic fieldexerts its influence has not yet been conclusively identified. One possiblesuch mechanism is suggested by the observation that granular motions in plageareas tend to be slightly ``abnormal'', dampened compared to quiet sun.  In this paper we consider the effect that abnormal granulation observed inactive regions should have on the propagation of acoustic waves. Any sucheffect is found to be limited to a shallow surface layer where sound wavespropagate nearly vertically. The magnetically suppressed turbulence implieshigher sound speeds, leading to shorter travel times. This time shift Dt isindependent of the travel distance, while it shows a characteristic dependenceon the assumed plage field strength. As a consequence of the variation of theacoustic cutoff with height, Dt is expected to be significantly higher forhigher frequency waves within the observed regime of 3-5 mHz. The lower groupvelocity near the upper reflection point further leads to an increased envelopetime shift, as compared to the phase shift. $p$-mode frequencies in plage areasare increased by a corresponding amount, Dnu/nu = nu*Dt. These characteristicsof the time and frequency shifts are in accordance with observations. Thecalculated overall amplitude of the time and frequency shifts are comparableto, but still significantly (factor of 2 to 5) less than suggested bymeasurements.Comment: 18 pages, 5 figures. Solar Phys., in pres

The Effect of Abnormal Granulation on Acoustic Wave Travel Times and Mode Frequencies