Role of storm track activity in the interannual seesaw of summer precipitation over northern Eurasia

Oscillation between relatively dry and wet extremes is a noteworthy characteristic of the interannual variability in summer precipitation over Siberia. Recently, we identified an out-of-phase relationship in the temporal signature of basin-scale precipitation between eastern and western Siberia (ES and WS). This east-west seesaw has been especially pronounced during the past 30 years. The spatial structure of large-scale precipitation and circulation anomalies associated with this east-west seesaw is characterized by an east-west dipole across northern Eurasia. We extended our work to investigate the important atmospheric processes involved in the dipole patterns of precipitation and large-scale circulation anomalies for the northern summers (June-August) of 1972-2001. In particular, this work focuses on the role of storm track activities associated with synoptic-scale (<10 days) eddies in producing the stationary waves that correspond to the precipitation anomaly dipoles. Linear regression and composite analyses of various eddy statistics are performed for two contrasting extremes in the Siberian summer precipitation seesaw. These two extreme phases are denoted ES-wet-WS-dry and WS-wet-ES-dry. The summer mean atmospheric anomalies related to the precipitation seesaw show stationary wavetrain patterns in conjunction with the precipitation dipole anomalies. The cold trough/warm ridge dipole corresponds to the relative wet and dry region. Analysis of storm track activity reveals similar east-west contrasting structures, meaning that the displacements associated with the anomalous storm tracks are accompanied by a phase reversal between the two extreme phases. An anomalous stationary trough (ridge) corresponds to the anomalous high-(low-)synoptic-scale-eddy-activity region in both ES and WS. The forcing by synoptic-scale eddies is examined to confirm the storm track feedback on the Eurasian stationary waves. The results show that barotropic feedback induced by synoptic-scale eddy vorticity fluxes is in phase with the Eurasian wave field. Cyclonic (anticyclonic) circulation forcing is collocated with the anomalous stationary trough (ridge). These spatially coherent relationships suggest that storm track feedback due to eddy vorticity fluxes helps to reinforce and maintain the Eurasian wave structure coupled with the precipitation dipole pattern of each phase. Consequently, the interannual variability of the Eurasian storm track intensity and location is a crucial factor in forcing the mean precipitation and circulation patterns between the two extreme phases.