Satellite image of a cumulonimbus cloud
New research suggests that interactions between relatively small pools of cold air may play a crucial role in organizing hurricanes and other large-scale atmospheric events. Credit: NASA
Source: Geophysical Research Letters

In portions of Earth’s atmosphere, initially scattered thunderstorm clouds display a spontaneous tendency to cluster. Although this convective self-aggregation is believed to play an important role in the organization of squall lines, hurricanes, and the most important tropical weather cycle, the Madden-Julian Oscillation, the dynamics behind the phenomenon are still poorly understood.

Previous researchers have proposed that self-aggregation is due to differences in heat loss from cloudy regions compared to clear ones, but to date no direct correlation has been found. Now Haerter explores whether convective self-aggregation could instead result from interactions between cold pools, 10- to 100-kilometer-wide pockets of cold air that develop when evaporative cooling occurs beneath precipitating cumulonimbus and other convective clouds.

To further investigate the role of these small-scale interactions, the author developed a series of simple, conceptual models that treat cold pool–driven self-aggregation as a critical phenomenon. The findings indicated that collisions between multiple cold pools can lead to convective self-aggregation but that the triggering of a single cold pool does not.

By bridging the fields of statistical physics and atmospheric science, the author’s research offers novel insights into the potential linkage between small-scale interactions and universal behavior. The results offer a compelling mechanism for explaining how interactions between cold pools, rather than differences in radiation, ultimately organize large-scale, atmospheric phenomena. (Geophysical Research Letters,, 2019)

—Terri Cook, Freelance Writer


Cook, T. (2019), Can patches of cold air cause thunderstorms to cluster?, Eos, 100, Published on 15 May 2019.

Text © 2019. The authors. CC BY-NC-ND 3.0
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