  The moist-air entropy can be used to analyze and better understand the
general circulation of the atmosphere or convective motions. Isentropic
analyses are commonly based on studies of different equivalent potential
temperatures, all of which are assumed to fully represent the entropy of moist
air. It is, however, possible to rely either on statistical physics or the
third law of thermodynamics when defining and computing the absolute entropy of
moist air and to study the corresponding third-law potential temperature, which
is different from the previous ones. The third law assumes that the entropy for
the most stable crystalline state of all substances is zero when approaching
absolute zero temperature.
  This paper shows that the way all these moist-air potential temperatures are
defined has a large impact on: (i) the plotting of the isentropes for a
simulation of the Hurricane DUMILE; (ii) the changes in moist-air entropy
computed for a steam cycle defined for this Hurricane; (iii) the analyses of
isentropic stream functions computed for this Hurricane; and (iv) the
computations of the heat input, the work function, and the efficiency defined
for this steam cycle.
  The moist-air entropy is a state function and the isentropic analyses must be
completely determined by the local moist-air conditions. The large differences
observed between the different formulations of moist-air entropy are
interpreted as proof that the isentropic analyses of moist-air atmospheric
motions must be achieved by using the third-law potential temperature defined
from general thermodynamics.
