Climate change-induced jet variability over the North Atlantic: Trends and drivers

Extreme weather in midlatitudes is strongly associated with extratropical cyclones, which propagate within preferred latitudinal bands known as the storm tracks. The position, orientation and intensity of storm tracks make a key contribution to regional climate variability and change. Therefore, understanding changes in storm track location and dynamics under the influence of anthropogenic climate change is crucial for quantifying the socioeconomic risks posed by their associated extreme events.

Deep tropospheric jets, which affect the entire depth of the troposphere are typically present over storm tracks and understanding their interactions and symbiotic life cycle is essential for quantifying trends and variability in regional climate in all regions affected by storm tracks. In this work, we analyse modifications in deep jet characteristics forced by anthropogenic climate change over the North Atlantic sector during the winter season (December-February) by using ERA5 reanalysis data and Community Earth System Model (CESM) simulations for historical and future periods.

Firstly, deep jets are separated into three regimes (southern, medium and northern) defined by different latitudinal positions and life cycle characteristics, such as Rossby wave breaking (RWB) type. Next, forced changes in regime frequency and life cycles are identified by applying machine learning techniques aimed at distinguishing anthropogenic forcing from natural variability. Further, the goal is to quantify the role of additional drivers, such as the Artic amplification, tropical amplification, polar stratospheric vortex or variations in El Niño Southern Oscillation for the observed change in jet regimes.

Preliminary analyses based on ERA5 indicate an increasing preference for cyclonic RWB and southern jet regimes, which favour the development of explosive cyclones. In contrast, anticyclonic RWBs, which are favoured in the northern regime and are linked to the presence of potential vorticity streamers and heavy precipitation over western Europe, tend to become less frequent.