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Spectral analysis of the spatial structure of solar subphotosphericconvection is carried out for subsurface flow maps constructed using thetime--distance helioseismological technique. The source data are obtained fromthe Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory(SDO) from 2010 May to 2020 September. A spherical-harmonic transform isapplied to the horizontal-velocity-divergence field at depths from 0 to 19~Mm.The range of flow scales is fairly broad in shallow layers and narrows as thedepth increases. The horizontal flow scales rapidly increase with depth, fromsupergranulation to giant-cell values, and indicate the existence oflarge-scale convective motions in the near-surface shear layer. The results cannaturally be interpreted in terms of a superposition of differently scaledflows localized in different depth intervals. There is some tendency toward theemergence of meridionally elongated (banana-shaped) convection structures inthe deep layers. The total power of convective flows is anticorrelated with thesunspot-number variation over the solar activity cycle in shallow subsurfacelayers and positively correlated at larger depths, which is suggestive of thedepth redistribution of the convective-flow energy due to the action ofmagnetic fields.

Spatial Scales and Time Variation of Solar Subsurface Convection