Role of the Atlantic Multidecadal Oscillation in formation of seasonal air temperature anomalies in the Northern Hemisphere according to model calculations

Abstract

Atlantic Multidecadal Oscillation (AMO), associated with variations in oceanic heat transport in the North Atlantic and the Atlantic sector of the Arctic, influences appreciably the climate of the Northern Hemisphere (NH). From the 1970s to early 2000s, there was a growth in the AMO index, coinciding with the trend of global warming. To estimate the AMO contribution to the NH seasonal temperature changes, we analyzed the numerical experiments with the atmospheric general circulation model (ECHAM5) coupled to the thermodynamic model of the upper mixed ocean layer using anomalous ocean heat convergence fluxes associated with the AMO. As part of the research, we studied the relative contribution of anomalous heat fluxes in the Atlantic and the Arctic. It is shown that AMO can explain about 40% of the observed winter and summer temperature changes over the last three decades. The vertical structure of the AMO-related temperature changes has also much in common with empirical estimates. In particular, the model reproduces the Arctic amplification with maximum temperature trends near the surface at high NH latitudes. AMO in the model leads to more probable anomalously cold temperature regimes in February on the territory of Russia, despite the rise of the mean February temperature. Also, we indicated more a probable development of anomalously hot Julys, particularly in European Russia. It is shown that an important contribution to the seasonal variations comes from anomalous heat fluxes in the Arctic, which are generally disregarded when the effect of North Atlantic Multidecadal Oscillation in the Northern Atlantic is modeled. The results obtained indicate an important role of AMO in the formation of weather and climate anomalies.