Hurricanes were simulated for a range of drag and enthalpy coefficients using the axisymmetric model CM1. The model was initialized with the moist tropical sounding of Dunion with an SST of 29°C. Nine simulations tested the Emanuel MPI theory, with Ck/Cd ratios of 0.5, 1.0 and 2.0 for constant values of Cd of 1.5x10-3, 2x10-3 and 3x10-3. In addition, two simulations examined the effect of no-cap on Cd (i.e. increasing Cd with wind speed) and constant Cd (Cd = 2.4x10-3) with Ck held constant at 1.2x10-3 in both runs. All simulations used a horizontal turbulence length scale of 1000 m and vertical length scale of 50 m.
Unrealistically strong hurricanes resulted for Ck/Cd ratios of 1.0 and 2.0. A Ck/Cd of 0.5 produced the most realistic hurricanes and results consistent with Bryan (2012). In the case of capped versus no-cap Cd, stronger azimuthal and radial winds were present in the no-cap case. A comparison of structure for the Ck/Cd 0.5 cases shows for a larger value of Cd, the size of the radial flows increase, but between radius 20 40 km a weaker Cd produced a stronger azimuthal wind, and a greater radius of maximum winds. The change in momentum balance has implications for the consistency of the sensitivity of the CM1 model with MPI theory.