Idealized Numerical Simulations of Hurricane–Trough Interaction

Abstract

A three-dimensional, nonhydrostatic, fine-resolution model, with explicitly resolved convective processes, is used to investigate the evolution of (a) a hurricane in two sheared flows, and (b) a hurricane interacting with four different upper-level lows. The negative impact of vertical shear on hurricane intensification is confirmed. The hurricanes display asymmetries that are most pronounced in higher shear flow. In both shear cases, the hurricane asymmetries seem to be related to a single upper-tropospheric outflow jet forcing convective activity below its right entrance region. Weak subsidence is confined to only part of the eye. Less eye subsidence leads to less inner-core warming, and hence a smaller fall in central surface pressure. A hurricane in zero flow (control) displays subsidence in the entire eye leading to a symmetric storm with a deep, strong warm core temperature anomaly and lower central surface pressure. In the weak shear and control cases, the radius of maximum wind (RMW) contracts as the storms intensifies via the mechanism of ?symmetric intensification.? In the high-shear case the RMW and intensity remain almost steady. When hurricanes interact with troughs, asymmetries are evident in the hurricanes and their RMWs expand as the storms slowly intensify. During the interaction, the troughs are deformed by the hurricane flow. Remnants of the deformed troughs prevent an outflow channel from developing on the eastern side of the hurricanes, hampering storm intensification in three of the four cases. In the fourth case, a strong and shallow trough merges with the hurricane causing a three-dimensional split of the trough, reduction of vertical shear over the vortex, followed by rapid intensification and RMW contraction. This vortex reaches the highest intensity of all four trough-interaction cases and comes close in intensity to the comparable no-trough case.