Persistent configurations of the North Atlantic jet stream from the perspective of large deviation theory

Unusual, long-lasting configurations of the North Atlantic jet stream affect the weather over Europe leading to persistent surface extremes. We study these persistent jet configurations in winter on intraseasonal and seasonal time scales using CMIP6 simulations, based on temporal averages of three jet indices: the jet latitude index, the jet speed index and the zonal jet index. We define these unusual configurations as long-lasting states, during which the jet stream is further south or further north, stronger or weaker, more split or more merged than usual. We estimate the probability of rare configurations, lasting at least 2 months, based on large deviation rate functions. The rate functions are asymmetric in case of the jet speed index, meaning that anomalously strong jet states are more persistent and more frequent than weak ones. Furthermore, we quantify the increased frequency of temperature and precipitation extremes over affected European regions. Here, we find a stronger link between jet events and precipitation extremes compared to temperature extremes. We observe the largest effects in case of precipitation extremes over the Mediterranean and Western Europe during anomalously strong jet configurations.