Solar Wind

The solar wind is a continuous stream of charged particles (plasma) emitted by the Sun's atmosphere. When this stream reaches Earth, it transfers energy into the magnetosphere. It has two components: the properties of the plasma (speed, density, temperature) and those of the embedded magnetic field, the Interplanetary Magnetic Field. Geomagnetic storms are typically triggered by high-speed solar wind combined with a strong southward IMF — storm intensity increases as the Bz value becomes more negative. These measurements are captured by satellites stationed at the L1 Lagrange point, about 1.5 million km sunward of Earth, where they see the solar wind roughly an hour before it arrives. Current active satellites include NOAA's [SOLAR-1](https://www.nesdis.noaa.gov/our-satellites/future-programs/swfo/space-weather-observations-l1-advance-readiness-solar-1) and NASA's [IMAP](https://science.nasa.gov/mission/imap/).