The role of Atlantic Multidecadal Variability in formation of seasonal temperature anomalies in the Northern Hemisphere estimated by model calculations
V.A. Semenov1,2,3, E.A. Shelekhova4,3, I.I. Mokhov1, V.V. Zuev4, K.P. Koltermann3
1A.M. Obukhov Institute of Atmospheric Physics Russian Academy of Sciences, Pyzhevsky 3, 119017, Moscow, Russia
2GEOMAR, Kil, Germany
3Lomonosov Moscow State University, 119991, Moscow, Lenin Hills, 1, Russia
4Institute of Monitoring of Climatic and Ecological Systems of the Siberian Branch of the Russian Academy of Sciences, 634055, Tomsk, 10/3, Academichesky ave
Keywords: Atlantic Multidecadal Variability, anomalous climatic regimes, climate models
Abstract
Atlantic Multidecadal Oscillation (AMO) is associated with variations of oceanic heat transport in the North Atlantic and the Atlantic Sectors of the Arctic. It has a significant impact on the climate of the Northern Hemisphere (NH). Since 1970s to the early 2000s there has been a positive AMO trend that coincided with the global warming trend. In order to estimate the AMO contribution to the seasonal temperature changes we employ the atmospheric general circulation model (ECHAM5) coupled to a thermodynamics mixed layer ocean model by using anomalous ocean heat convergence fluxes associated with the AMO. Relative contributions of the anomalous heat fluxes in the Atlantic and the Arctic sectors have been estimated. The results show that AMO can explain up to 40% of the observed winter and summer temperature changes over the last three decades. 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 at the surface in the high NH latitudes. AMO in the model leads to increased probabilities of extreme cold temperatures in February in some regions in Russia. This happens despite increase of the mean temperature. The probabilities increase for hot temperature extremes in July was also found in the European part of Russia. It is shown that the anomalous heat fluxes in the Arctic contribute a major part to the seasonal temperature changes related to the AMO. These fluxes are usually not taken into account when modeling the effect of North Atlantic Multidecadal Oscillation. The results obtained in the study indicate an important role of AMO in formation of weather and climate anomalies.
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