An Analysis of the Local Environmental Memory of Tropical Cyclone Passage

Recent research has suggested that changes in TC frequency, TC intensity, and TC lifespan are intimately tied to changes in tropical sea surface temperatures (SSTs; e.g., Webster et al. (2005), Emanuel (2005)). While theories exist that provide the physical basis for understanding trends in TC activity to a first order (e.g., maximum potential intensity theory), it remains plausible that the remaining variance in TC activity tendencies can be explained by the aggregate climate impact of TCs. However, this hypothesis cannot be fully addressed without first attempting to examine the mean spatiotemporal impact of one TC upon its local environment. Building upon the foundation provided by prior work (e.g., Sobel and Camargo (2005), Hart et al. (2007)), the following study will provide one of the preliminary attempts at objectively quantifying and analyzing the atmospheric and SST environmental memory of TC passage.

The crux of this study hinges upon the use of storm-relative composites of reanalysis data from the NCEP Climate Forecast System Reanalysis (CFSR) for TCs in the Western North Pacific (WPAC). Vertically integrated energy budgets are then used to attribute anomalies to specific physical processes. Results thus far have shown that TCs excite a significant response in the SST field for approximately four to six weeks following TC passage with maximum cross-track widths of approximately 1400 km. The significant spatiotemporal scales of these SST anomalies feeds back onto the atmospheric environment primarily through a cooling and drying of the lower troposphere. The TC-induced environmental stabilization is largely due to a significant reduction in surface latent heat fluxes as well as a low level flux divergence of total energy from the area surrounding the SST cold wake. In their totality, the spatially and temporally integrated impacts of these anomalies may suggest that TCs act as the tropical climate's thermostat during the late summer and early fall.