Water in a pot starts to bubble from the bottom before the whole thing boils. Steam bubbles rise from the base even though the stove hasn't fully heated up. The Sun's atmosphere behaves much the same way before a flare: streams of material surge upward from deep layers, even though the main heating source, according to previous ideas, hasn't switched on yet.
A solar flare is a sudden release of energy stored in the star's magnetic field. Previously, it was thought that magnetic field lines rearrange, accelerate electrons, and those electrons strike the lower atmosphere, heating it. The heated material rises, a process called chromospheric evaporation. But new observations from the stratospheric balloon Sunrise III show that upflows appear 5–10 minutes before the electrons arrive.
So, energy is delivered downward not only by electrons. It may also be carried by heat conduction or magnetic waves. This discovery changes our picture of how solar flares work and could help better predict space weather, which affects satellites and communications on Earth. Water in a pot boils not only from the stove below; sometimes heat comes from within the water itself.
The stratospheric observatory Sunrise III ascended to an altitude of 37 km, where the sky is 100 times clearer for ultraviolet light than at sea level. This allowed achieving a resolution of 59 km on the Sun, comparable to the size of a small city.
In Arthur C. Clarke's novel 'A Solar Storm', solar flares threaten Earth, but the mechanisms of their occurrence are described schematically. This work shows how much more complex the real physics is: even in the lower layers of a star's atmosphere, processes occur that we are only beginning to understand.