Uncertainty in TC Maximum Intensity with Fixed Ratio of Surface Exchange Coefficients for Enthalpy and Momentum

The classical tropical cyclone (TC) maximum intensity theory of Emanuel suggests that the maximum azimuthal wind of TC depends linearly on the ratio of surface exchange coefficients for enthalpy and momentum (C_k and C_d). In this study, a series of sensitivity experiments are conducted with the three-dimensional Cloud Model 1 (CM1), by fixing the ratio of C_k/C_d but varying the specific values of C_k and C_d simultaneously. The results show significant variations in the simulated TC maximum intensity by varying C_k and C_d, even if their ratio is fixed. Overall, the maxi-mum intensity increases steadily with increasing C_k and C_d when their value is smaller than 1.00 × 10⁻³, and then this increasing trend slows down with further increases in the coefficients. Two previous theoretical frameworks—one based on gradient wind balance and the other incorporating the unbalanced terms—are applied to calculate the maximum potential intensity (PI). The calculated value of the former shows little variation when varying the specific values of C_k and C_d, while the latter shows larger values with increases in both C_k and C_d. Further examination suggests that the unbalanced effect plays a key role in contributing to the increasing intensity with increasing C_k and C_d.