A Synoptic Analysis of Rapid Surface Warming during Arctic Spring Onset

During spring, the Arctic atmospheric circulation experiences a dramatic transition, which is dominated by a shift from the winter pattern to the summer pattern in the middle and upper tropospheric circulation and a rapid surface warming north of 75N. We apply a new technique to identify the spring onset in terms of local rapid increase in the surface air temperature for 32 years from 1979 to 2010. The spring onset date exhibits strong interannual variability but no significant trend. While the whole Arctic region warms rapidly during spring onset, a critical region to the north of Siberia experiences the most dramatic warming. A composite synoptic analysis shows that a circumpolar anti-cyclonic circulation anomaly transports cold air into the region upstream from the critical region; meanwhile, a cyclonic cell over the east Eurasian continent advects warm air into the critical warming region. The contributing factors for the rapid warming are investigated by decomposing local temperature tendencies in the thermodynamic equation into linear advection, non-linear contributions of baroclinic eddies, adiabatic warming/cooling, and diabatic processes. We find that the warming results from the net interplay among the four terms: The non-linear processes and diabatic heating are the primary drivers for the warming while the linear advection partially offsets the warming. A parallel analysis of storm track activity demonstrates the eastward propagation of baroclinic eddy activity from eastern Europe, leading to an enhanced Siberian storm track and northward transport of heat into the critical warming region.