  We analyze spectral properties of solar convection in the range of depths
from 0 to 19~Mm using subsurface flow maps obtained by the time-distance
heiioseismology analysis of solar-oscillation data from the Helioseismic and
Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) from May 2010 to
September 2020. The results reveal a rapid increase of the horizontal flow
scales with the depth, from supergranulation to giant-cell scales, and support
the evidence of large-scale convection, previously detected by tracking the
motion of supergranular cells on the surface. The total power of convective
flows correlates with the solar activity cycle. During the solar maximum, the
total power decreases in shallow subsurface layers and increases in the deeper
layers.
