PA: Wikipedia says that an unstable atmosphere (lapse rate?) is necessary for hurricane development. When the lapse rate exceeds the MALR, then a parcel of air that rises, expands and cools will still be warmer and less dense than the surrounding air. That parcel will continue to rise. In regions above the boundary layer that are well mixed by convection, the lapse rate tends to be near the MALR on the average, but the lapse rate measured by radiosondes actually show large deviations at any moment due to weather and turbulence. In theory, convection will continue until enough heat has carried upward so that an unstable lapse rate no longer exists.
Everyone talks about the importance of SST to powering hurricanes, but no one pays any attention to the temperature difference that powers a hurricane’s heat engine. If SSTs and the upper atmosphere warm at the same rate, then that heat engine is operating with the same temperature difference (plus about 7% more latent heat per degC of surface warming). Do all hurricane reach the same height above the surface, possibly the tropopause, or do some get more power by reaching higher?
From Wikipedia, showing how lapse rate is ignored: “Dr. Kerry Emanuel created a mathematical model around 1988, called the maximum potential intensity or MPI, to compute the upper limit of tropical cyclone intensity based on sea surface temperature and atmospheric profiles from the latest global model runs. Maps created from this equation show values of the maximum achievable intensity due to the thermodynamics of the atmosphere at the time of the last model run (either 0000 or 1200 UTC). However, MPI does not take vertical wind shear into account.[8] MPI is computed using the following formula:
V = A + B * exp{C(T-T_0)}
Where V is the maximum potential velocity in meters per second; T is the sea surface temperature underneath the center of the tropical cyclone, T_0 is a reference temperature (30˚C) and A, B and C are curve-fit constants. When A = 28.2, B = 55.8, and C = 0.1813, the graph generated by this function corresponds to the 99th percentile of empirical tropical cyclone intensity data.”
