Modulation of Quasi‐Biennial Oscillation on Wintertime Variability of Intraseasonal 2‐m Temperature Over Northern Eurasia and Its Potential Impact on Subseasonal Prediction in China

The mid‐high latitude intraseasonal oscillation (ISO) has remarkable impacts on the Northern Hemisphere. However, the interannual variance of the mid‐high latitude ISO and its underlying mechanism are rarely explored. Here, we find that the tropical stratospheric Quasi‐Biennial Oscillation (QBO) has notable impacts. A statistically significant contrast in the interannual variability of intraseasonal 2‐m temperature (T2m) over northern Eurasia is detected between the easterly (EQBO) and westerly (WQBO) QBO phase. The influence of the QBO could be attributed to the interactions of ISO perturbation and QBO‐related winter‐mean flow. Specifically, the ISO perturbation is more efficient in extracting kinetic and potential energy from the winter‐mean flow in EQBO. Additionally, the northern Eurasia ISO propagates southeastward and exert effects on China. Due to this, the subseasonal forecast system of NUIST (NUIST CFS1.1) displays higher skill in predicting the T2m in China during EQBO phase at 3, 4, and 5 pentads in advance. Plain Language Summary Extreme weather and climate in winter, such as cold waves, snowstorms, and prolonged low temperature, have severe impacts on the society, therefore it is of great value to improve subseasonal prediction of 2‐m temperature (T2m). In this study, we find that the variability of intraseasonal T2m over northern Eurasia varies from year to year during boreal winter, which is negatively correlated with the tropical stratospheric Quasi‐Biennial Oscillation (QBO). The variability of intraseasonal T2m is enhanced during QBO easterly phase (EQBO). In accordance with the higher variance of intraseasonal T2m, the extreme temperature events display higher frequency and stronger intensity in EQBO. We also find that the intraseasonal oscillation (ISO) in the northern Eurasia is not stationary, it often propagates southeastward, impacting the weather and climate in China. This has implications for the prediction of intraseasonal T2m in China. These results help understanding the relationship between the tropical QBO and mid‐high latitude ISO and provide a potential way to improve the subseasonal forecasts. Key Points The interannual variability of intraseasonal 2‐m temperature (T2m) is amplified during easterly Quasi‐Biennial Oscillation (EQBO) in winter The likelihood of extreme temperature events, particularly cold extreme events with intensified high‐pressure systems, is enhanced in EQBO The southeastward propagation of the intrasea