Caroline Muller breaks down the physics of big storms at the Global Km-scale Hackathon

At the recent Global Km-scale Hackathon, which took place between May 12-16th in the city of Hamburg, Professor Caroline Muller from the Institute of Science and Technology Austria delivered a compelling keynote on Mesoscale Convective Systems (MCSs). These systems represent a key element in understanding and predicting extreme weather and rainfall in a warming climate, hence accounting for a topic of high relevance within the nextGEMS community.

Mesoscale Convective Systems, explained

MCSs are large, organized clusters of thunderstorms that can span over 100 km and persist for hours, Prof. Muller explained. A familiar precursor to these systems is the so-called “popcorn convection”: scattered, isolated thunderstorms that resemble popcorn popping in the afternoon heat. However, when environmental and internal dynamics align, these scattered clouds can organize into powerful, long-lived systems.

Prof. Muller clarified these systems are central to global rainfall, especially in the tropics and subtropics. Furthermore, she emphasized their role in delivering intense precipitation events, making them highly relevant for climate models aiming to capture extreme weather patterns – such as those Earth system models used in nextGEMS.

What drives MCS development?

The keynote dissected the formation and evolution of MCSs, emphasizing both environmental and internal drivers. On the one hand, pre-storm environmental conditions play a key role in initiating MCS, such as atmospheric instability, vertical wind shear, moisture availability, and large-scale lift. However, internal dynamics are equally important in shaping their development, like cloud interactions, entrainment, cold pool dynamics, and self-aggregation mechanisms. 

Particularly, Prof. Muller focused on squall line regimes, referring to specific atmospheric conditions in which long and narrow bands of thunderstorms form and maintain themselves. These systems can stretch hundreds of kilometers and are associated with organized yet severe weather, including heavy rainfall, strong winds, and sometimes tornadoes. In squall line regimes the interaction between cold pools and wind shear is critical. This interaction helps transition disorganized storms into more organized and coherent mesoscale structures, enhancing the storm’s overall strength and longevity.

Insights from recent research and data-driven models

Another interesting aspect highlighted during Prof. Muller’s keynote was the increasing use of data-driven models to study these complex systems. One key research question was mentioned: Are environmental conditions or internal processes more critical for predicting MCS behavior?

Her conclusions suggest that internal feedbacks often dominate, especially in large systems exceeding 120 km. Nonetheless, she also pointed out the importance of neighboring systems to understand how MCSs don’t evolve in isolation; in fact spatial interactions and context matter significantly.

Prof. Muller’s keynote offered a rich overview of the physical mechanisms behind MCSs and posed important questions about how best to model and predict them. More specifically, her insights resonate with the broader goals of the diverse km-scale modelling communities attending the event: to capture the complex and multi-scale nature of convection in a changing climate.