Plasma flows and sound-speed perturbations in the average supergranule

Supergranules create a peak in the spatial spectrum of photospheric velocity features. They have some properties convection cells but their origin is still being debated literature. The time-distance helioseismology constitutes method that suitable for investigating deep structure supergranules. Our aim to construct model flows average supergranular cell using fully consistent inverse methodology. We used Multi-Channel Subtractive Optimally Localised Averaging inversion with regularisation cross-talk. combined difference and mean travel-time averaging geometries. applied this methodology maps averaged over more than 10000 individual cells. These were detected automatically computed 64 quiet days around disc centre. ensemble allows us significantly improve signal-to-noise ratio obtain clear picture supergranule. found near-surface divergent horizontal which quickly monotonously weakened depth; they became particularly weak at depth about 7 Mm, where even apparently switched sign. To learn vertical component, we integrated continuity equation from surface. derived estimates flow depicted sub-surface increase 5 m/s surface 35 3 Mm followed by monotonous decrease greater depths. remained positive (an upflow) indistinguishable background 15 Mm. further systematic longitudinal direction. course agrees well solar rotation layers.