Dynamical Simulations in North Atlantic Tropical Cyclone Activity using Observed Low Frequency SSTs Oscillation Imposed on CMIP5 Model SSTs

Tuesday, May 13, 2014 - 07:00
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The effects on early and late 21st century North Atlantic tropical cyclone statistics resulting from imposing the patterns of maximum/minimum phases of the observed Atlantic Multidecadal Oscillation (AMO) onto projected sea surface temperatures (SSTs) from two Coupled Model Intercomparison Project 5 (CMIP5) climate models are examined using a 100-km resolution global atmospheric model. The AMO is thought to alter North Atlantic tropical cyclone activity through changes in the magnitude of the SST gradient. By imposing the observed maximum positive and negative phases of the AMO onto two CMIP5 SST projections from the RCP 4.5 scenario this study places bounds on future North Atlantic tropical cyclone activity. During the early (2020-2039) and late (2080-2099) twenty-first century the positive AMO simulations produce a statistically significant increase in the mean number of named tropical cyclones (NTCs) compared to simulations using observed SSTs from 1982-2009. The increase is approximately 35%. The positive AMO simulations produce approximately a 68% increase in mean NTC count while the negative AMO simulations are statistically indistinguishable from the mean NTC count calculated from the 1995-2009 simulations. The maximum wind speeds increase by 6% in agreement with other climate change studies. Differences in the track densities show an increase in the number of landfalling storms along the east coast of the United States during the negative AMO phase; however, the positive AMO phase shows an increase in storms of higher intensity tracking closer to the U.S. coastline. Lastly, the NTC related precipitation is found to increase (approximately by 13%) compared to the 1982-2009 simulations.

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