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

We investigate the evolution of the horizontal flow field around sunspotsduring their decay by analysing its extension and horizontal velocity aroundeight spots using SDO/HMI Doppler maps. By assuming a radially symmetrical flowfield, the applied analysis method determines the radial dependence of theazimuthally averaged flow field. For comparison, we studied the flow insupergranules using the same technique. All investigated, fully fledgedsunspots are surrounded by a flow field whose horizontal velocity profiledecreases continuously from 881 m s$^{-1}$ at 1.1 Mm off the spot boundary,down to 199 m s$^{-1}$ at a mean distance of 11.9 Mm to that boundary. Once thepenumbra is fully dissolved, however, the velocity profile of the flow changes:The horizontal velocity increases with increasing distance to the spot boundaryuntil a maximum value of about 398 m s$^{-1}$ is reached. Then, the horizontalvelocity decreases for farther distances to the spot boundary. Insupergranules, the horizontal velocity increases with increasing distance totheir centre up to a mean maximum velocity of 355 m s$^{-1}$. For largerdistances, the horizontal velocity decreases. We thus find that the velocityprofile of naked sunspots resembles that of supergranular flows. The evolutionof the flow field around individual sunspots is influenced by the way thesunspot decays and by the interplay with the surrounding flow areas.Observations of the flow around eight decaying sunspots suggest that as long aspenumbrae are present, sunspots with their moat cell are embedded in networkcells. The disappearance of the penumbra (and consequently the moat flow) andthe competing surrounding supergranular cells, both have a significant role inthe evolution of the flow field: The moat cell transforms into a supergranule,which hosts the remaining naked spot.

Evolution of the flow field in decaying active regions, Transition from a moat flow to a supergranular flow