The Role of the Tropically Excited Arctic Warming Mechanism on the Warm Arctic Cold Continent Surface Air Temperature Trend Pattern

Concurrent with the rapid amplification of Arctic warming observed over the last several decades, a cooling trend has been observed over the continents, which has prompted studies into the question of whether continental cold extremes may be caused by Arctic amplification or sea ice decline. In this study we examine the December–February (DJF) surface air temperature (SAT) trend for all consecutive 20‐year time periods between 1979 and 2017, from which a transition from a cold‐Arctic‐warm‐continent toward a warm‐Arctic‐cold‐continent trend pattern is evident. We show that this transition toward a warm-Arctic-cold-continent SAT trend pattern is accompanied by a consistent transition in the sea level pressure trend pattern that supports warm air advection over the Arctic and cold air advection over the continents. Thus, in contrast with several previous studies, we argue that the circulation has contributed to the warm-Arctic-cold-continent SAT trend pattern observed in recent decades. Furthermore, following the finding that the SAT trend pattern strongly resembles the SAT response to La Niña-like tropical convection, we argue that the circulation driven contribution to the warm-Arctic-cold-continent SAT trend pattern is likely due to an increase in La Niña-like tropical convection.

The regression of the detrended DJF‐average SAT onto a detrended index, the P_sst index, defined to quantify the east‐west gradient of tropical Pacific sea surface temperature (SST) is characterized by a warm‐Arctic‐cold‐continent pattern much like the SAT trend pattern observed in recent decades. Pattern correlations show that the Arctic and midlatitude SAT trend patterns have become increasingly aligned with the SAT response to La Niña-like tropical convection, as measured by the P_sst index, and that this alignment is statistically unlikely to have happened by chance. A decadal timescale warming of the western tropical Pacific water has increased the east‐west gradient of tropical Pacific sea surface temperature, thus supporting the viewpoint that La Niña-like tropical convection has caused the circulation-driven contribution to the warm-Arctic-cold-continent SAT trend pattern.

An idealized model calculation is performed to further investigate the role that La Niña-like tropical convection has had on the warm-Arctic-cold-continent SAT trend pattern. This model calculation uses the DJF climatological wind, temperature, and pressure as a basic state and is forced by the anomalous tropical Pacific diabatic heating profile associated with days in which the P_sst index is anomalously large. The results of the idealized model calculation supports the notion that La Niña-like tropical convection can produce the warm-Arctic-cold-continent SAT trend pattern observed in recent decades.