  The continuous high spatial-resolution Doppler observation of the Sun by
Solar Dynamics Observatory / Helioseismic and Magnetic Imager allows us to
compute helioseismic k-omega power-spectrum diagram using only oscillations
inside a sunspot. Individual modal ridges can be clearly seen with reduced
power in the k-omega diagram constructed by use of 40-hour observation of a
stable and round sunspot. Comparing with the k-omega diagram obtained from a
quiet-Sun region, inside the sunspot the f-mode ridge gets more power reduction
than p-mode ridges, especially at high wavenumber. The p-mode ridges all shift
toward lower-wavenumber (or higher-frequency) areas for a given frequency (or
wavenumber), implying an increase of phase velocity beneath the sunspot. This
probably results from acoustic waves' travel across the inclined magnetic field
of the sunspot penumbra. Line-profile asymmetries exhibited in the p-mode
ridges are more significant in the sunspot than in quiet Sun. Convection inside
the sunspot is also highly suppressed, and its characteristic spatial scale is
substantially larger than the typical convection scale of quiet Sun. These
observational facts demand a better understanding of magnetoconvection and
interactions of helioseismic waves with magnetic field.
