The influence of diabatic processes on North Atlantic winter jet streaks and their extremes

The jet stream — the hemispheric-wide band of westerly winds that circles the mid-latitudes and shapes day-to-day weather by guiding large-scale flow features — has been a long-standing area of interest in atmospheric dynamics. Within this stream, jet streaks are regions of enhanced wind speed. These important features of atmospheric flow are frequently accompanied by clear-air-turbulence, affecting air travel flight times, comfort, and safety. 

Moreover, upper level divergence in the equatorward entrance and poleward exit regions couples jet streaks to surface weather via vertical motion. This links jet streaks to rapid cyclogenesis, intense precipitation, and extreme wind events. Extreme jet streaks are also often linked to poor performance of numerical weather prediction (NWP).  Understanding the dynamics of (extreme) jet streaks is hence important to further the mechanistic understanding of extreme weather events as well as error busts, and ultimately improving forecast quality.

Traditional tools, like the PV gradient and PV frontogenesis frameworks, have shed light on the dry dynamics of jet streaks. Similarly, the classical four-quadrant model explains their influence on surface weather. However, diabatic processes have been shown to play an important role in jet streak development. They are also key for the (mis)representation of jet streak in NWPs, warranting systematic and quantitative analysis. 

In this study, we explore the impact of diabatic processes on jet streak evolution using composite analysis and a Lagrangian PV-gradient diagnostic. It is based on ERA5 data from North Atlantic winters (DJF) spanning 1979–2023. We begin by characterizing the life cycle of jet streaks and extreme jet streaks and their relationship with Rossby waves and Rossby wave breaking.
Our findings show that stronger jet streaks tend to last longer, with their maximum wind speeds scaling with the PV gradient at their core. Extreme jet streaks frequently coincide with intense low-pressure systems, heavy precipitation, and upstream warm conveyor belts, indicating a heightened role of diabatic processes in their evolution. Using the Lagrangian PV gradient framework, we quantify the influence of diabatic processes, comparing extreme and non-extreme jet streaks. The results reveal a clear upward interaction between surface weather and jet streak development, with diabatic effects more pronounced in extreme cases.

Our findings underscore the need for further research into individual diabatic processes driving jet streak evolution. They also add to the growing evidence that extreme jet streak events may become more frequent in a warming climate.