Impacts of the North Atlantic Warming Hole on Atmospheric Circulation

Recent studies have documented the development of a warming deficit in North Atlantic sea surface temperatures (SSTs) both in historical observations and future global climate model projections.  This North Atlantic Warming Hole is deepest in May, when SSTs in the North Atlantic are projected by the Community Earth System Model rcp 8.5 scenario to decrease by 0.25°C in 2100 relative to historical period values.  During this same period, global mean SSTs are projected to increase by 3°C.  This study investigates the impact of this warming deficit on atmosphere circulation.  A series of large ensemble (30 member) experiments are conducted using the Community Atmosphere Model 5 forced with specified sea ice and SSTs for the mid (2050-2059) and late (2090-2099) 21^st century.  SST and sea ice fields from the Community Earth System Model – Large Ensemble experiment are used as boundary conditions for the control simulations.  Experiments with either a filled or deepened warming hole are conducted by adding a SST perturbation field to these time-varying SST boundary conditions. Filling (deepening) the NAWH results in a local increase (decrease) in temperature in the overlying lower troposphere relative to the control run.  The impacts of this altered boundary forcing on the North Atlantic storm track and its projection onto the North Atlantic Oscillation are investigated.  Furthermore, self-organizing maps are utilized to examine the impact on patterns of atmospheric circulation over Europe.