Polar vortices are a prominent feature in Titan's stratosphere. The
Cassini mission has provided a detailed view of the breakdown of the
northern polar vortex and formation of the southern vortex, but the
mission did not observe the full annual cycle of the evolution of the
vortices. Here we use a TitanWRF general circulation model simulation of
an entire Titan year to examine the full annual cycle of the polar
vortices. The simulation reveals a winter weakening of the vortices,
with a clear minimum in polar potential vorticity and mid-latitude zonal
winds between winter solstice and spring equinox. The simulation also
produces the observed post-autumn equinox cooling followed by rapid
warming in the upper stratosphere. This warming is due to strong descent
and adiabatic heating, which also leads to the formation of an annular
potential vorticity structure. The seasonal evolution of the polar
vortices is very similar in the two hemispheres, with only small
quantitative differences that are much smaller than the seasonal
variations, which can be related to Titan's orbital eccentricity. This
suggests that any differences between observations of the northern
hemisphere vortex in late northern winter and the southern hemisphere
vortex in early winter are likely due to the different observation times
with respect to solstice, rather than fundamental differences in the
polar vortices.