Oceanic Influence on Seasonal Atlantic Tropical Cyclone (TC) Activity: Pacific vs. Atlantic

Tuesday, May 13, 2014 - 07:00
Add to Calendar

Tropical sea surface temperature (SST) variability in both the Pacific and Atlantic Ocean can influence seasonal Atlantic tropical cyclone (TC) activity. This study investigates this influence using a regional climate model. The focus of the investigation is on unresolved issues: 1) what is the impact of concurrent phases of ENSO and AMM on seasonal Atlantic TC activity, and how do ENSO and AMM together shape the atmospheric environment for Atlantic TCs? and 2) how does the location of maximum tropical Pacific warming during El Nino, which varies from the East Pacific to Central Pacific, impact seasonal TC activity and through what mechanisms? A large number of regional climate simulations are performed to shed light on these issues. The following findings emerge from this year: 1) ENSO and AMM can amplify or dampen the influence of one another on Atlantic TCs. In particular, strong La Nina and strongly positive AMM together produce extremely intense Atlantic TC activity, supported largely by above-average mid-tropospheric humidity. 2) Atlantic TC activity is relatively insensitive to the location of maximum tropical Pacific warming due to the existence of two thresholds, namely the SST threshold for deep convection and the vertical wind shear threshold for TC suppression. A statistically significant (5% level) reduction in Atlantic and increase in East Pacific seasonal accumulated cyclone energy (ACE) is simulated in response to both the East Pacific and Central Pacific El Nino SST forcings, while the response in seasonal ACE is insignificant in the West Pacific. These findings are useful in understanding future Atlantic TC changes in response to global warming.