Workings of solar wind flows
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma consists of mostly electrons, protons and alpha particles with thermal energy. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The solar wind affects other incoming cosmic rays interacting with planetary atmospheres. Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind. Earth itself is largely protected from the solar wind by its magnetic field, which deflects most of the charged particles; however some of the charged particles are trapped in the Van Allen radiation belt. A smaller number of particles from the solar wind manage to travel, as though on an electromagnetic energy transmission line, to the Earth's upper atmosphere and ionosphere in the auroral zones. The only time the solar wind is observable on the Earth is when it is strong enough to produce phenomena such as the aurora and geomagnetic storms.
A group of researchers from Physical Research Laboratory (PRL), Ahmedabad, have, for the first time, figured out the conditions under which certain types of solar storms can flow towards the earth and affect its atmosphere. This is important because such storms contain charged particles travelling at very high speeds and these can affect the electronics present on satellites in orbit around the earth.
Such solar storms have two causes: Coronal Mass Ejections (CME) and Corotating Interaction Regions (CIR). CMEs are huge explosions of charged particles extending beyond the sun’s corona or outer layer and can be visibly observed. CIRs are much more complicated and difficult to observe. CMEs can be detected by a coronagraph when they are ejected from the Sun. CIRs are generated in the interplanetary medium and there are no visual signatures for CIRs.
Charged particles are being spewed continually out of the sun’s corona, forming the solar wind. Some parts of these winds move faster than others. Since they contain charged particles in a plasma state, these different regions physically interact with each other to form wavelike disturbances called CIRs that emanate from the sun and spiral outwards. They are called “corotating” interaction regions as they rotate along with the sun, attached to it at one end.
The sun goes through cyclic variations with a period of eleven years during which sunspot activity increases to a maximum and then decreases.