Axisymmetric, Primitive Equation, Spectral Tropical Cyclone Model. Part II: Normal Mode Initialization

Abstract A three-layer, primitive equation tropical cyclone model is used to test the effect of nonlinear normal mode initialization (NNMI) in a tropical cyclone simulation. The model is solved using a spectral method with normal mode basis functions. Results from a six-day tropical cyclone simulation are used as initial data to test the NNMI. It is shown that Machenhauer’s NNMI scheme converges rapidly under tropical cyclone conditions when the dissipative and convective terms are not included in the nonlinear forcing (adiabatic initialization). When these terms are included (diabatic initialization), Machenhauer’s scheme no longer converges, but can still reduce the initial gravity mode time tendencies to an acceptable level. The radial winds produced by the diabatic initialization are qualitatively similar to those in the control simulation, but the positioning of the convective heating with respect to the radius of maximum wind is somewhat different. Because of this, the errors in the storm intensity ...