Intensity change associated with concentric eyewall replacement

Tropical cyclone intensity changes associated with eyewall replacement cycles vary from case to case. To understand what controls the intensity change during an eyewall replacement cycle, two parallel experiments were conducted with identical initial conditions and model parameters, except a slight modification in microphysics scheme. The modification of the microphysics scheme results in systematic enhancement of cloud ice concentration. The storm in both experiments experiences a secondary eyewall replacement cycle, but in the experiment with the enhanced cloud ice concentration, the replacement lasts longer and the intensity change is more significant. Further comparison is conducted to understand the mircophysics effects on the eyewall replacement cycle and intensity change. The high concentration of cloud ice tends to enhance downdrafts in the outer region, which likely result to a weak outer eyewall and a clear moat with low entropy air. The weak outer eyewall has less ability to maintain a warm core in the original eye when the inner eyewall dissipates. The presence of low entropy air in moat adds additional load to the new eyewall. As a result, the storm experiences a notable weakening during the eyewall replacement.