Mechanism of the wintertime subseasonal surface air temperature variability over Eurasia

Abstract

The formation mechanism responsible for the leading mode of the subseasonal variability of wintertime surface air temperature (SAT) over Eurasia is investigated. The leading SAT mode over Eurasia is characterized by a triple pattern with strong cold anomalies centered over northern Eurasia and weaker warm anomalies over the Arctic and East Asia, respectively, which has a deep barotropic structure and extends from the surface to the upper troposphere. It is tightly coupled to a wave-like atmospheric circulation, which stretches from the North Atlantic to East Asia and resembles the Scandinavia teleconnection pattern. Its formation mechanism is further revealed through the analysis of the temperature budget. The atmospheric circulation-induced horizontal advection is found to be the primary driver of the cold anomalies over northern Eurasia associated with the leading SAT mode in two steps. First, the advection of the climatological temperature by the mode-associated meridional wind anomalies triggers the cooling in the western part of Eurasia. Second, the advection of the above cold anomalies by background westerly winds from west Eurasia to the east further redistributes the cold anomalies. The meridional and zonal advection eventually causes the mode-associated strong cold anomalies over northern Eurasia.

Keywords

• subseasonal variability
• temperature advection
• circulation