Quantifying Environmental Control on Tropical Cyclone Intensity Change
NAVAL RESEARCH LAB MONTEREY CA MARINE METEOROLOGY DIV
Pagination or Media Count:
Composite analysis is used to examine environmental and climatology and persistence characteristics of tropical cyclones TCs undergoing different intensity changes in the western North Pacific WPAC and North Atlantic ATL ocean basins. Using the cumulative distribution functions of 24-h intensity changes from the 2003-08 best-track data, four intensity change bins are defined rapidly intensifying RI, intensifying neutral, and weakening. The Navy Operational Global Atmospheric Prediction System daily 0000 and 1200 UTC global analysis and Tropical Rainfall Measuring Mission Microwave Imager data are then used as proxies for the real atmosphere, and composites of various environmental fields believed relevant to TC intensity change are made in the vicinity of the TCs. These composites give the average characteristics near the TC, prior to undergoing a given intensity change episode. For the environmental variables, statistically significant differences are examined between RI storms and the other groups. While some environmental differences were found between RI and weakeningneutral TCs in both basins, an interesting result from this study is that the environment of RI TCs and intensifying TCs is quite similar. This indicates that the rate of intensification is only weakly dependent on the environmental conditions, on average, provided the environment is favorable. Notable exceptions were that in the WPAC RI events occurred in environments with significantly larger conditional instability than intensifying events. In the ATL, RI events occurred in environments with weaker deep-layer shear than intensifying events. An important finding of this work is that SSTs are similar between intensifying and rapidly intensifying TCs indicating that the rate of intensification is not critically dependent on SST.