[SLS] Or Hadas (Weizmann Institute)

“Bridging Lagrangian and Eulerian Perspectives on Midlatitude Dynamics”

The midlatitude climate is driven by storms that shape weather variability and extremes. Research in this area has traditionally been divided between Eulerian studies of long-term local averages and Lagrangian analyses of individual storms. Here, we bridge these approaches by statistically analyzing thousands of storm tracks. Using a global 84-year storm catalog based on ERA5 data, we examine how Eulerian measures of storm activity, specifically the Eady growth rate, affect the Lagrangian growth of individual storms. We show that increasing baroclinicity generally enhances storm growth, whereas extreme jets suppress it. This non-monotonic behavior arises because strong jets promote rapid intensification while simultaneously limiting growth time, owing to their competing effects on available energy and storm vertical structure.

Building on these results, we address why Atlantic storms are more intense in winter than Pacific storms, despite the Pacific’s stronger jet stream. We identify a second key mechanism: jet orientation. The Pacific’s zonally elongated jet causes eastward- and poleward-propagating storms to exit the jet rapidly, whereas the Atlantic’s tilted jet aligns with storm trajectories, allowing longer residence times and greater growth. Together, these two mechanisms quantitatively explain the observed contrast in storm activity.

Finally, we examine the role of climate in storm variability. Using machine learning, we show that climate accounts for only a third of individual storm variability, although it accounts for over 90% of average storm activity. Further statistical analysis indicates that long-term climate trends account for only 0.1% of individual-storm variability, highlighting the challenges of attributing climate change impacts at the individual-storm level.

Sack Lunch Seminar Series —
Informal seminar series within PAOC (Program in Atmospheres, Oceans, and Climate) that focuses on more specialized topics than the PAOC Colloquium. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.

Contact: sacklunch-committee@mit.edu