  The heat engine model of tropical cyclones describes a thermally direct
overturning circulation. Outflowing air slowly subsides as radiative cooling to
space balances adiabatic warming, a process that does not consume any work.
However, we show here that the lateral spread of the outflow is limited by the
environmental deformation radius, which at high latitudes can be rather small.
In such cases, the outflowing air is radially constrained, which limits how far
downward it can subside via radiative cooling alone. Some literature has
invoked the possibility of `mechanical subsidence' or `forced descent' in the
storm outflow region in the presence of high inertial stability, which would be
a thermally indirect circulation. Mechanical subsidence in the subsiding branch
of a tropical cyclone has not before been observed or characterized. A series
of axisymmetric tropical cyclone simulations at different latitudes and domain
sizes is conducted to study the impact of environmental inertial stability on
storm dynamics. In higher latitude storms in large axisymmetric domains, the
outflow acts as a wavemaker to excite an inertial wave at the environmental
inertial (Coriolis) frequency. This inertial wave periodically ventilates the
core of a high-latitude storm with its own low entropy exhaust air. The wave
response is in contrast to the presumed forced descent model, and we
hypothesize that this is because inertial stability provides less resistance
than buoyant stability, even in highly inertially stable environments.
