Deterministic and Stochastic Aspects of ENSO's Impact on Atlantic and Eastern North Pacific Tropical Cyclones

Monday, 18 April 2016: 2:45 PM
Ponce de Leon B (The Condado Hilton Plaza)
Christina M. Patricola, Texas A&M University, College Station, TX; and R. Saravanan and P. Chang

El Niño is characterized by equatorial sea surface temperature warming in locations varying from the east Pacific (“Cold Tongue El Niño”), to the central Pacific (“Warm Pool El Niño”). Observational studies differ in how El Niño's location impacts Atlantic tropical cyclone (TC) activity due to a short data record that is complicated by Atlantic SST variability. We address this question using large ensembles of channel model simulations forced with SST patterns that isolate El Niño's influence from the confounding effects of Atlantic SST. We find statistically significant reductions in seasonal Atlantic TC activity in response to both Warm Pool and Cold Tongue El Niño. Warm Pool El Niño, which has occurred more frequently and with increasing intensity in recent decades, is 50% and 150% as effective as Cold Tongue El Niño at suppressing Atlantic TCs for similar percentile-based (top 90th) and absolute (2.25 K) intensities of warming, respectively. This is because less warming is required near the warm pool to satisfy the SST threshold for deep convection, which leads to tropical cyclone suppression via vertical wind shear enhancements. We note the importance of stochastic atmospheric variability in contributing to variability in TC activity. Ensembles of channel model simulations forced with ENSO and the Atlantic Meridional Mode SST patterns produce a considerable range in accumulated cyclone energy, despite having fixed surface and lateral boundary conditions. The large stochastic variability may partially explain inconsistencies in observational analyses with limited sample size. This work implies that El Niño may become more effective at suppressing Atlantic TCs, if it intensifies and shifts towards the central Pacific in the future as some global climate models predict. However, implications are less optimistic in the eastern North Pacific, where Warm Pool El Niño is 130% as effective at enhancing TC activity compared to Cold Tongue El Niño of similar absolute intensity.
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