Enhanced levels of solar radiation can also cause heating and expansion of the neutral atmosphere and increase the amount of atmospheric drag that a satellite experiences in an unpredictable manner. Solar protons are accelerated to very high velocities in the explosive release of energy associated with a solar flare. These particles first make their way out of the corona. These field lines have a structure resembling the spiral traced out by a spinning lawn sprinkler, which is referred to as a Parker spiral. The largest space weather disturbances at Earth are produced by coronal mass ejections and fast solar wind streams emanating from coronal holes.
Coronal holes are the main source of recurrent solar activity.
They normally drive shocks ahead of them as they plow into the slower-moving solar wind streams. Vast quantities of high speed particles are born in these shock structures and speed ahead of the coronal mass ejection to impact the Earth before the CME itself makes an appearance. It is now believed that a large fraction of the solar energetic particles arriving at Earth were produced in these shocks rather than at flare sites on the Sun. CMEs are difficult to detect and, in fact, were not observed until coronographs were build and flow in space. Many of the CMEs that are blown toward the Earth never actually directly hit us.