Improving AGCM Hurricane Structure With Two-Way Nesting

We demonstrate that two-way nesting significantly improves the structure of simulated hurricane in an atmospheric general circulation model. Two sets of 30-day hindcast experiments are conducted, one with the global-uniform-resolution (approximately 25-km nominal horizontal resolution) and the other with a regionally refined two-way nest (approximately 8 km over the tropical North Atlantic). The increase in the horizontal resolution on the nested grid improves the representation of storm intensity and intensification rate. When normalized by the radius of maximum wind (RMW), composite hurricane structures are generally similar in both simulations and compare well to observations. However, the hurricanes in the globally uniform configuration have much larger RMWs than observed, while those in the two-way-nested configuration have more realistic RMWs. We also find that the representation of the RMW has a critical impact on the simulation of inertial stability and boundary-layer convergence in the inner-core region. The more realistic inner-core size (indicated by RMW) and structure are possible reasons for the improved intensification rates in the two-way-nested configuration.