Abstract 006

Abstract ID: 006

Subseasonal variability of the warm Arctic – cold North American pattern

Lead Author: Hai Lin
Environment and Climate Change Canada, Canada

Keywords: Subseasonal variability, Surface temperature, Teleconnections, Warm Arctic – Cold Continent pattern, Predictability

Abstract: Near surface air temperature variability over the North American sector displays a “Warm Arctic – Cold Continent” pattern (WACC) known as the Warm Arctic – Cold North America (WACNA). The WACNA is characterized by a pair of opposite surface air temperature anomalies over the high-latitude Chukchi-Bering Sea region and the North American continent. On the other hand, over the Eurasian sector the WACC pattern is denoted as Warm Arctic–Cold Eurasia (WACE). The WACC pattern has often been associated with the connection between Arctic sea ice reduction and cold weather over the middle latitude continents. Whether the existence of this pattern is due to variability of sea ice or is caused by atmospheric internal dynamics is subject to debate. In this study, we examine the variability of WACNA on the subseasonal time scale. It is found that a negative phase of WACE tends to lead a positive phase of the WACNA pattern by about 2 weeks. The WACNA pattern develops by interacting with the time-mean flow and synoptic-scale transient eddies. Two pathways of Rossby wave propagation are associated with WACNA. The northern pathway originates from eastern Siberia moving eastward across the Bering Strait to Canada, and the southern pathway is rooted in the subtropical waveguide propagating across the eastern North Pacific. The anomalous warm advection from the North Pacific and cold advection from the Arctic that follow the circulation anomalies lead to the development of the positive WACNA pattern. Our analysis suggests that tropospheric dynamics alone can generate the WACNA, and if its variability is essentially attributable to internal dynamics the predictability associated with this pattern is probably limited.

Bin Yu (Environment and Climate Change Canada, Canada)
Nicholas Hall (University of Toulouse, France)