Representation of the wintertime Arctic Oscillation in a multi‐model ensemble

Abstract

AbstractThe Arctic Oscillation (AO) is a well‐known mode that affects climate variability in the Northern Hemisphere. The equal‐weighed multi‐model ensemble (MME) of six state‐of‐the‐art models from the Copernicus Climate Change Service (C3S) and Pusan National University (PNU) was analysed to understand the wintertime AO performance for the hindcast period December–February 1993/1994–2016/2017. The hindcasts were chosen with lead times of 1 and 4 months with respect to the initialization date (August and November, respectively). The spread of the AO prediction skills of the individual models was significant. In general, the MME demonstrates superior skill compared to the average of single‐model skills in representing the AO pattern at lead times of 1 and 4 months. The AO‐related vertical structure predicted by MME is similar to the observation, but the upper‐level structure is relatively poor compared to the structure of the hindcasted lower‐ or mid‐level atmosphere. Both observation and MME indicate that since the mid‐1990s, the relationship between the AO and East Asian winter monsoon (EAWM) has been weak compared to the connection between the AO and El Niño–Southern Oscillation (ENSO). Simultaneously, the North Pacific centre of the AO moved eastward during the observational period. The MME showed an AO pattern similar to that observed. The eastward shift of the North Pacific centre of the AO may contribute to deepening the Aleutian low and its effect on the tight AO–ENSO relation demonstrated in observations and MME. Strong AO–ENSO relations and weak AO–EAWM connections are found in both observations and MME model. The observation and MME represent the wave activity flux from 60°N to the equator in the troposphere; consequently, the wave activity flux may contribute to the AO and ENSO connection in both observation and MME.