MJO modulation on the cold extreme over the North America in a recent decade

Over the last decade, North American cold extreme events have exhibited a notable shift in timing, occurring more frequently in February rather than earlier in winter. This delayed-season tendency suggests a strong influence from intraseasonal climate variability. In addition we identify a pronounced warming trend in sea surface temperature (SST) over the equatorial Pacific warm pool region, with the warming signal becoming particularly distinct during the most recent decade. We examine a dynamical linkage between the Madden-Julian Oscillation (MJO) and cold extremes over the North America in late-winter. As the equatorial Pacific warm pool region shows a warming trend, the eastward propagation speed of the MJO tends to slow, resulting in increased residence time and a higher occurrence frequency of MJO phase 7 during February for a recent decade. Under these conditions, persistent convection over the equatorial western Pacific enhances diabatic heating and strengthens tropical thermal forcing. This sustained forcing excites Rossby wave responses, facilitating downstream wave propagation into the central North America region. The resulting MJO teleconnections favor the development of large-scale flow patterns conducive to cold extremes over North America, thereby increasing the likelihood of February cold waves.