UCLA

In this study, we investigate the uncertainties mainly in the trends of frequency and shifts of ARs on the choice of AR detection algorithm and reanalysis data, and also analyze the causes of trends at various temporal and spatial scales using two ensembles from Community Earth System Model (CESM) simulations and decomposition covering the period of 1980-2016. Meteorological reanalyses show all-seasonal poleward shifts over the Pacific, in contrast to statistically insignificant equatorward shifts during MAM and SON over the Atlantic and Indian Ocean sectors throughout decades. The spatial patterns of intensification and shifts of ARs are largely driven by the changes in atmospheric circulation while anthropogenic forcing enhances the increase in moisture-driven AR frequency with nearly uniform warming over the Southern Ocean. Sea surface temperature (SST) variability characterized by the negative phase of the Interdecadal Pacific Oscillation (IPO) could generate dynamically-driven patterns of ARs to compensate for the poleward shift driven by thermodynamics.