Helioseismology in Space Weather - National Solar Observatory

Emerging Active RegionsHelioseismic holography is applied tosamples of the two populations (preemergenceand without emergence), eachsample having over 100 members, whichwere selected to minimize systematic bias,as described in Leka et al.Birch, A. et al, 2012, ApJ, 762We find that there are statistically significantsignatures (i.e., difference in the means of morethan a few standard errors) in the averagesubsurface flows and the apparent wave speed thatprecede the formation of an active region. Themeasurements here rule out spatially extendedflows of more than about 15 m/s in the top 20Mm below the photosphere over the course of theday preceding the start of visible emergence.These measurements place strong constraints onmodels of active region formation.