Formation of Arctic summer circulation patterns: the role of synoptic cyclones under different phase of ENSO evolution

Abstract

We investigate the contribution of synoptic cyclones to the formation of summermean circulation patterns in the Arctic and then understand their linkage in terms of global teleconnection to different phases of El Nino-Southern Oscillation (ENSO) evolution. The optimal number of Arctic summer circulation patterns is obtained by the self-organizing maps (SOMs) applied to the daily mean sea level pressure in the Arctic domain (≥ 60°N). Three SOM patterns are identified: one with prevalent low pressure anomalies in the Arctic Circle (SOM1) and two opposite dipoles with primary high pressure anomalies covering the Arctic Ocean (SOM2 and SOM3). The relevant analyses with produced cyclone track data confirm the vital contribution of synoptic cyclones for all patterns. The overall Arctic cyclone activity is enhanced for the SOM1 because the meridionaltemperature gradient increases over the landArctic Ocean boundaries co-located with major cyclone pathways. The SOM1 is prevalent during the developing year of La Nina in following autumn and winter. In preceding spring, the snow extent anomaly is weakly negative over the surrounding land areas of the Arctic Ocean, leading to stronger baroclinicity along the pan-Arctic land-ocean boundaries in following summer. The SOM2 tends to occur during the decaying year of La Nina. The high-latitude land areas of northern Europe are more snow-covered in preceding spring, which results in weaker baroclinicity therin in following summer. The SOM3 is the prevalent pattern during the El Nino developing year. The northern mid-latitude Eurasia is less snow-covered in preceding spring, leading to more baroclinicity over northern Siberian continent. Though the springtime snow extent anomaly is negligible over the surrounding land areas of the Arctic Ocean, weaker baroclinicity is induced along the pan-Arctic land-ocean boundaries in following summer, which leads to the dominating high pressure anomaly over the central Arctic Ocean. Based on these relationships, we suggest that the ENSO-related evolution of the sea surface temperature in the tropical Pacific and continental snow cover extent could be used to outlook the summer-mean circulation pattern in the Arctic Ocean.