Multi-Regime States of Arctic Atmospheric Circulation

The arctic circulation can develop multiple dynamical regimes, which has implications for the predictability of arctic weather. We use ensemble simulations of June – December 2007 by the WRF-ARW model to examine the development of multiple dynamic regimes in the arctic circulation, and to understand the differences in the atmospheric circulation caused by changes in sea ice and how it is represented. Simulations where grid-box sea ice is either 0% or 100% (binary) are compared to simulations where a grid box may be partially ice-covered (fractional) to determine when monthly mean differences that occur as a result of sea-ice treatment rise above nonlinear internal variability. For the simulations examined here, we find that the largest monthly mean differences occur in August and October, but they are governed only weakly by ice treatment. The differences are rather the result of the arctic atmospheric circulation developing multiple dynamical regimes, and ice-treatment ensembles, by chance, falling more into one regime than the other. Our results show that multiple regimes occur more (less) with greater (smaller) sea-ice area present, as the interactive ice surface allows the modeled atmosphere to have more freedom in its variability. The regime behavior as uncovered through this work has implications for the predictability of the future arctic circulation as summer ice cover wanes.