The Influence of Atmospheric Cloud Radiative Effects on Annular Mode Persistence

Abstract:

The annular modes of eddy-driven jets are the leading source of weather variability at mid-latitudes. Annular mode persistence is important for mid-latitude weather predictability, and holds potential implications for the climate change response of the mid-latitudes. Previous work on annular modes has mostly focused on dry dynamics, and the influence of clouds on annular mode persistence has not been studied before. We use an idealized atmospheric model to investigate how the persistences of the barotropic and baroclinic annular modes are impacted by the atmospheric cloud radiative effects (ACRE) associated with each mode. The model does not explicitly simulate clouds, but represents ACRE as an imposed radiative heating whose sign and magnitude depends on the annular mode indices. We also test the sensitivity of our results to the structure and phase of the imposed radiative heating. These results deepen our understanding of the controls on annular mode timescales and provide potentially useful criteria for evaluating how mid-latitude clouds are simulated in comprehensive climate models.