Horizontal flows in active regions from ring-diagram and local correlation tracking methods

Abstract

Continuous high-cadence and high

spatial resolution Dopplergrams allow us to study subsurface dynamics that may be further extended to explore precursors of visible solar activity on the surface. Since the p -mode power is absorbed in the regions of high magnetic fi eld, the inferences in these regions are often presumed to have large uncertainties. In this paper, using the Dopplergrams from space-borne Helioseismic Magnetic Imager, we compare horizontal fl ows in a shear layer below the surface and the photospheric layer in and around active regions. The photospheric fl ows are calculated using the local correlation tracking ( LCT ) method, while the ring-diagram technique of helioseismology is used to infer fl ows in the subphotospheric shear layer. We fi nd a strong positive correlation between fl ows from both methods near the surface. This implies that despite the absorption of acoustic power in the regions of strong magnetic fi eld, the fl ows inferred from the helioseismology are comparable to those from the surface measurements. However, the magnitudes are signi fi cantly different; the fl ows from the LCT method are smaller by a factor of 2 than the helioseismic measurements. Also, the median difference between the direction

of corresponding vectors is 49 ° .