The always changing sun constantly shoots solar material into space. The biggest of such events are massive clouds that erupt from the sun, called coronal mass ejections, or CMEs. These solar storms often come first with warning such as the bright flash of a flare, a burst of heat, or a flurry of solar energetic particles. But another kind of storm has puzzled scientists for its lack of typical warning signs as they seem to appear from nowhere, and scientists call them stealth CMEs.
An international team of scientists, led by the Space Sciences Laboratory at University of California, Berkeley, and funded in part by NASA, has created a model that simulates the evolution of these stealthy solar storms. The scientists relied upon NASA missions STEREO and SOHO for this work, fine-tuning their model until the simulations matched the space-based observations.
Compared to typical CMEs, which erupt from the sun as fast as 1800 miles per second, stealth CMEs move at a rambling gait between 250 to 435 miles per second. At that speed, stealth CMEs aren’t typically powerful enough to drive major space weather events, but because of their internal magnetic structure they can still cause minor to moderate disturbances to Earth’s magnetic field.
To discover the origins of stealth CMEs, the scientists created a model of the sun’s magnetic fields, simulating their strength and movement in the sun’s atmosphere. Central to the model was the sun’s differential rotation, meaning different points on the sun rotate at different speeds. Unlike Earth, which rotates as a solid body, the sun rotates faster at the equator than it does at its poles.
The model displayed differential rotation that causes the sun’s magnetic fields to stretch and spread at different rates. The scientists demonstrate this constant process generates enough energy to form stealth CMEs over the course of roughly two weeks. The sun’s rotation increasingly stresses magnetic field lines over time, eventually warping them into a strained coil of energy. When enough tension builds, the coil expands and pinches off into a massive bubble of twisted magnetic fields and without warning the stealth CME silently leaves the sun.