  Cold pools (CPs) contribute to convective organization. However, it is
unclear by which mechanisms organization occurs. By using a particle method to
track CP gust fronts in large eddy simulations, we characterize the basic
collision modes between CPs. Our results show that CP interactions, where three
expanding gust fronts force an updraft, are key at triggering new convection.
Using this, we conceptualize CP dynamics into a parameter-free mathematical
model: circles expand from initially random points in space. Where two
expanding circles collide, a stationary front is formed. However, where three
expanding circles enclose a single point, a new expanding circle is seeded.
This simple model supports three fundamental features of CP dynamics:
precipitation cells constitute a spatially interacting system; CPs come in
generations; and scales steadily increase throughout the diurnal cycle.
Finally, this model provides a framework for how CPs act to cause convective
self-organization, clustering, and extremes.
