Atmospherically driven polar amplification in the ERA-Interim reanalysis and CMIP5 historical and RCP8.5 experiments

Abstract:

We examine the control of intense moisture advection events on the temperature and sea-ice concentration trends north of 70N during boreal winter in both ERA-Interim and the CMIP5 historical and RCP8.5 experiments. We consider the mechanisms by which they warm the Arctic basin; finding that the structure of the warming associated with moisture intrusions is bottom amplified in the deep and marginal sea-ice zones. In the Barents Sea the minimum sea-ice concentration caused by intrusion occurs 5 days after the passage of the moisture in the reanalysis dataset. We find that the entire Arctic is in a state of cooling in the absence of a moisture intrusion event and that there is a positive trend in the number of these intrusion events crossing 70N during December and January; which has resulted in a significant trend of intense moisture fluxes over the Barents region in particular. We find that the trend in moisture intrusion events a can explain roughly 50% of the surface temperature and 40% of the sea-ice concentration trends in December and January. In general the CMIP5 datasets capture the impacts of these events quite realistically. There is a tendency for the moisture fluxes through 70N to be underestimated in most models. The factors that lead models to have quantitatively similar statistics to the reanalysis is also addressed.