The Simpson Symposium


Non-linear characteristics associated with the Atlantic tropical cyclone activity

Wilbur Y. Chen, NOAA/NWS/NCEP/CPC, Camp Springs, MD

Previous studies at the Atlantic tropical cyclone activity (ATCA) largely used linear analysis techniques. Our recent works suggest that non-linear behaviors are prominently associated with the ATCA. We would like to develop and test the non-linearity hypothesis as a necessary step to raise the prediction skill of the ATCA. Taking the ENSO impact for instance, an El Nino episode in the eastern equatorial Pacific extends its influence to the Atlantic TC prone sector while a La Nina event shows no such far-reaching impact. Our results show that the warm events are strongly related to a subdued season while the cold events are often not associated with an active season. The upper- and lower-level climate anomalies were investigated for active versus subdued Atlantic tropical cyclone seasons. For subdued seasons, the anomaly over the cyclone prone region is found to be a manifestation of a much larger global-scale variability, with its center located at the eastern equatorial Pacific and the variability resembles anomaly during El Nino boreal summers. On the other hand, for active seasons, the favorable climate anomalies are primarily confined to the lower troposphere in the western North Atlantic and appears to be associated with the local underlying warmer SST anomaly. Hence, there is a distinct pattern association of the active versus subdued TC season with a regional versus an El Nino type of global-scale climate anomaly. For other climate factors influencing ATCA, such as the underlying SST anomaly, local vertical wind shear strength, and the far-field sea-level pressure anomaly, a similar non-linear behavior is also explored.

Poster Session 7, Trpoical Cyclones: Large-scale Environment and Tropical Cyclones
Thursday, 13 February 2003, 9:00 AM-11:00 AM

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