Plasma and interplanetary magnetic field measured at L1, one minute apart.
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.