What is Solar Wind?

The solar wind is a fast-moving stream of charged particles (plasma) that emerges from the sun. It travels around the solar system, carrying with it the magnetic field of the sun.

Figure 1: The solar wind interacts with Earth’s magnetosphere

The solar wind is a major factor affecting the space environment around the Earth and other planets. On Earth it causes phenomena such as auroras, geomagnetic storms, and radiation belts.

• The solar wind's plasma consists mostly of electrons (~47%), protons (~47%), and alpha particles (~5%). It also includes tiny amounts of heavy ions and atomic nuclei of elements like carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, iron, phosphorus, titanium, chromium, and nickel's isotopes.
• Different parts of the Sun produce solar wind at different speeds. Coronal holes, found near the Sun's poles, create fast solar wind, moving at 500 to 800 kilometers per second. The equator produces slower solar wind, moving at about 400 kilometers per second.
• Far from the Sun, the solar wind reaches speeds of 250–750 km/s and is "supersonic," meaning it moves faster than fast "magnetosonic waves." It slows down at the termination shock near Earth. The solar wind causes phenomena like the aurora (northern and southern lights), comet tails that always point away from the Sun, and geomagnetic storms that can change magnetic field lines.
• The solar wind varies in density, temperature, and speed over time and across solar latitudes and longitudes. Its particles escape the Sun's gravity because of their high energy from the corona's high temperature, resulting from the coronal magnetic field.
• When solar activity is low, the solar wind and its current sheet (a thin, wide sheet of slow wind) are flat. When solar activity increases, the wind forms a spiral with varying speeds and densities, like a "twirling ballerina's skirt".
  
  Figure 2: The Interplanetary Magnetic Field (IMF)—The Heliospheric Current Sheet (HCS) 🗗
• Fast wind catches up to slower wind, creating areas with dense and strong magnetic fields called corotating interaction regions.
• The Sun rotates every 27 days, affecting the solar wind. As the Sun turns, different regions send out varying wind speeds, creating a complex pattern.
• Earth's position in this "ballerina skirt" of solar wind affects space weather.
• Fast winds cause geomagnetic storms, while slow winds bring calm conditions. Monitoring and forecasting the solar wind helps predict space weather impacts on Earth.
• The solar wind causes phenomena like the aurora (northern and southern lights), comet tails that always point away from the Sun, and geomagnetic storms that can change magnetic field lines.

Discover how the solar wind affets skywave propagation.
See also an index of terms for HF Radio propagation.