  We conduct a descriptive analysis of the multipolar structure of
gravitational-radiation waveforms from equal-mass aligned-spin mergers,
following an approach first presented in the complementary context of
nonspinning black holes of varying mass ratio [J.G. Baker et al. Phys. Rev. D
78 044046 (2008)]. We find that, as with the nonspinning mergers, the dominant
waveform mode phases evolve together in lock-step through inspiral and merger,
supporting the previous waveform description in terms of an adiabatically rigid
rotator driving gravitational-wave emission-an implicit rotating source. We
further apply the late-time merger-ringdown model for the rotational frequency
introduced in [J.G. Baker et al. Phys. Rev. D 78 044046 (2008)], along with an
improved amplitude model appropriate for the dominant (2, \pm2) modes. This
provides a quantitative description of the merger-ringdown waveforms, and
suggests that the major features of these waveforms can be described with
reference only to the intrinsic parameters associated with the state of the
final black hole formed in the merger. We provide an explicit model for the
merger-ringdown radiation, and demonstrate that this model agrees to fitting
factors better than 95% with the original numerical waveforms for system masses
above \sim150M\odot. This model may be directly applicable to
gravitational-wave detection of intermediate-mass black-hole mergers.
