Strong Influence of Eddy Length on Boreal Summertime Extreme Precipitation Projections

Abstract Previous research has shown that projected changes in the horizontal eddy length of ascending anomalies likely drive subtropical changes in large‐scale ascent during extreme precipitation events ( extreme ascent ), which in turn strongly influence regional projections of extreme precipitation. Here we present evidence that this eddy length effect extends into the Northern Hemisphere extratropics during the summer season. This is shown by analyzing output from a large ensemble of the Canadian Earth System Model version 2 as well as models participating in the Coupled Model Intercomparison Project phase 5. As found previously, the changes in eddy length are associated with changes in an effective stability quantity that combines dry and moist effects. It is shown that the change of extreme ascent associated with a projected change of eddy length agrees with expectations based on analysis of internal variability of extreme ascent and eddy length during the historical period.