Potential Precursors to and Implications of Tropical Cyclone Passage: A Regional Climate Perspective

One of the great remaining unanswered questions in meteorology is why there are approximately 90 tropical cyclones (TCs) globally per year. Understanding this conundrum as well as future trends in both TC intensity and frequency is seemingly tied to quantifying the interaction between TCs, atmosphere, and ocean. Specifically, what processes are responsible for making the environment both dynamically and thermodynamically more hospitable to a TC during its passage? What are the subsequent implications of the passage of a TC upon the atmosphere and ocean? The following study seeks to answer these questions in an effort to achieve a greater understanding of the interaction between TCs and the larger scale environment.

The main thrust of this study involves the use of 4-dimensional storm relative composited anomalies constructed from atmospheric reanalysis datasets. Preliminary results from these composites yield substantial anomalies in the temperature and moisture fields up to 2 months prior to the occurrence of a TC. These anomalies extend throughout the lower to middle troposphere growing in magnitude in the weeks prior to TC passage. The atmosphere responds to the passage of the TC by cooling and drying on a scale much larger than any forcing directly associated with the TC. In addition to this, a 20-30 day oscillation in the zonal wind field maximized at 100 hPa in the weeks prior to TC occurrence may be partially responsible for the large scale “preconditioning” of the atmosphere. The weakening of these anomalies after TC passage suggests a feedback between the TC and larger scale features and may explain the inability of the atmosphere to restore itself to its pre-TC state.