  Spectral proper orthogonal decomposition (SPOD) analyses are performed for
unstratified and stratified wakes of a circular disk at Reynolds number,
$U_\infty D/\nu = 50,000$, where $U_\infty$ is the freestream velocity and $D$
is the diameter of the circular disk. At $Re= 50,000$, three diameter-based
Froude numbers, $\Fro = U_\infty/ND = \infty$, $2$ and $10$ are analyzed. We
find that in the unstratified configuration, two modes: (i) the vortex shedding
(VS) mode ($m=1, \Str = 0.135$) and (ii) the double helix (DH) mode ($m=2, \Str
\rightarrow 0$) are the most dominant features. At far-downstream distances, DH
mode is dominant while at near and intermediate locations, VS mode dominates
the energetics. Reconstruction of TKE and Reynolds shear stresses are also
explored at near and far wake locations. In the stratified cases ($\Fro = 2$
and $10$), the vortex shedding mode (at $\Str \approx 0.13-0.14$) dominates the
wake. At intermediate to late streamwise locations ($x/D$), we establish
through pressure wave flux reconstruction that the VS mode is responsible for
the internal gravity wave (IGW) generation. A comparison between the SPOD
decomposition analyses between $Re =5000$ and $Re = 50,000$ is also performed
at $\Fro =2$. Preliminary results show that the low-$Re$ wake is also dominated
by the VS mode but exhibits more coherence, namely higher contribution of
leading SPOD modes, than the high-$Re$ wake.
