Diurnal Variability in the Energetics and Efficiency of the Tropical Cyclone Heat Engine

The oceanic tropical cyclone (TC) diurnal cycle includes oscillations in the total rainfall, boundary layer relative humidity, and boundary layer inflow. It is highly likely that a diurnal cycle also occurs in the efficiency of TC wind generation and related energetic variables, including the kinetic energy of the full TC wind field and the energy consumed by moist processes such as precipitation. However, the diurnal behavior of the full TC heat engine, including wind generation efficiency, has received little attention. Here, we use output from a hurricane nature run to investigate whether there is a diurnal cycle in the wind generation efficiency and energetics of TCs. We additionally examine whether the presence of the diurnal cycle rectifies this efficiency and energetics compared to a TC simulation with constant insolation. Preliminary results from the nature run are inconclusive regarding the existence of diurnal cycles in the efficiency, TC wind field kinetic energy, and other energetics. This may be due to the short time series of data available from the nature run. We compare the negative result in the highly realistic simulation to longer-lived, more idealized simulated TCs using the Bryan Cloud Model 1, where the diurnal cycle can be isolated from environmental shear and forward motion.