Influence of the Eurasian Spring Snow Cover on Interannual Variations of Summer Zonal Dipole Pattern of Drought Conditions Over Northern Asia

This research investigates the linkages between spring Eurasian snow cover and summer drought conditions over northern Asia (N‐Asia) on interannual scale. The results show that the northern European snow anomalies significantly correlate with the second dominant pattern of summer N‐Asia drought conditions during 1955–2017. In addition, the snow anomalies occur in preceding winter and strengthen in spring, providing a possible predictor for N‐Asia summer drought conditions. The physical processes linking spring snow anomalies over northern Europe to summer N‐Asia drought conditions are as follows. Increased spring snow anomalies enhance the surface albedo and increase overall amount of snowmelt in early summer, which cool the local 2‐m temperature and increase the soil moisture in early summer. The increased soil moisture persists from early summer to late summer through positive soil‐precipitation feedback, consequently weakening summer surface sensible heat flux and decreasing air temperature over northern Europe. Then the decreased temperature strengthens the meridional air temperature gradients around 60°N, and further induces a cyclone anomaly over northern Europe by modulating the diabatic cooling and synoptic transient eddy activities, further triggering an eastward‐propagating Rossby wave train throughout Eurasia. This wave train results in a western Siberian anticyclone anomaly and an eastern Siberian cyclone anomaly. By adjusting the conditions of water vapor, dynamics, heat and radiation fluxes, the precipitation, and potential evapotranspiration conditions over N‐Asia are changed. Therefore, the pronounced atmospheric circulation pattern leads to less/more precipitation and more/less PET over western/eastern Siberia, favoring development of a zonal dipole pattern of N‐Asia drought conditions.