Estimating Local Memory of Tropical Cyclones through MPI Anomaly Evolution

Abstract

This study examines the local memory of atmospheric and oceanic changes associated with a tropical cyclone (TC). The memory is quantified through anomalous maximum potential intensity (MPI) evolution for 20 days prior to the arrival of a TC through 60 days after the TC passage. The local MPI weakens and is not restored to the evolving climatology until well after the TC has departed. Stabilization occurs through warming of the atmosphere and cooling of the ocean surface on different time scales. The time scale of MPI stabilization following TC passage is approximately 30?35 days for a tropical storm to 50?60 days for a category 3?5 hurricane, with significant storm-specific and basin-specific variability. The atmospheric stabilization (warming with respect to SST) begins with TC arrival and continues for approximately 7?10 days after passage, when the troposphere cools below normal. The rewarming of SST and the subsequent rewarming of the atmosphere occurs within approximately 35 days for all intensities, despite a positive (weakened) MPI anomaly through two months. This suggests that the atmosphere retains anomalous warmth beyond what can be attributable to sensible heating from the rewarmed SST. The maintenance of a positive MPI anomaly beyond 35 days is thus attributed to a feedback on larger scales that requires considerable further research. A TC?s passage through a region does not always lead to a weakening of the MPI. In regions poleward of the sharp SST gradient, the MPI one month after TC passage is often several millibars stronger than climatology. There are also mesoscale regions of destabilization one month after TC passage that may result partially from salinity changes driven by oceanic mixing as well as changes in precipitation and evaporation.