Linking upstream cold, continental air to the intensity of marine cold air outbreaks along the western boundary currents

The thermal contrast between cold land masses and warm oceans is an important contributor to extratropical circulation. During boreal winter, intense radiative cooling leads to the formation of extremely cold continental air masses at high latitudes over the land masses of Siberia and Canada. As these regions are located upstream of the Northern Hemisphere storm tracks, maritime cold air outbreaks (CAOs) originating from such regions may induce severe air-sea interaction and affect low-level baroclinicity, altering storm track activity. We refer to these two regions as the “Boreal cold air reservoirs” (BCARs) for the North Pacific and Atlantic storm tracks.

Starting from a case study of the January ’23 record-breaking cold air outbreak over eastern Russia, China and Japan, we revisit the connection between storm track activity and the strength of surface-based cooling over the upstream continents. Here, we link the CAO intensity to the presence and characteristics of upstream cold continental air using a backward trajectory analysis. Using backward trajectories initiated from 167 CAO events in the Japan Sea and 192 CAO events along the North American east coast, we then proceed to systematically link the CAO intensity to the presence and the characteristics of upstream, cold continental air. We show that the CAO intensity -measured by the associated surface sensible heat fluxes- scale with an increasing contribution of low-level, cold continental air to the total CAO air mass. The intensity of latent heat fluxes, on the other hand, scales with respect to the magnitude of the dry intrusion air stream in the extratropical cyclone usually associated with the CAO.