In the solar corona, it rains from time to time — only not water, but plasma. The hot gas cools, clumps into blobs, and rushes downward along magnetic loops, like drops running down invisible gutters. Previously, it was thought that such rain required steady heating, but observations show too many droplets and symmetric drainage to both ends of the loop. Spectra reveal that heating is more impulsive than steady.
The authors of the new study tested what happens if a short, powerful heat pulse hits the corona. They ran a numerical model of a single magnetic tube and varied two parameters: how long the heating lasts and how strong the magnetic field is. They found that even a single pulse triggers condensation, but it needs ten times more energy than steady heating. If the pulse is shorter than the time it takes for the plasma to cool, rain flows to both footpoints of the loop at once.
The longer the heating and the weaker the field, the more readily rain forms. This explains why some loops have large, sparse droplets, while others have fine drizzle. Understanding such processes will help better predict space weather, since coronal rain affects the heating of the entire corona.
So a short pulse, like a lightning strike, scatters across a magnetic arc into a rain of plasma, and flows down both sides at once, like water from a gable roof.
Coronal rain falls at about 100 kilometers per second — faster than lightning.
In Stanislaw Lem's novel "Solaris," the ocean also spawns bizarre plasma structures reminiscent of coronal rain.