What is a geomagnetic storm?

A geomagnetic storm is a temporary but significant disturbance in Earth's magnetosphere. It occurs when a surge of solar wind, often from a coronal mass ejection (CME) or a solar flare, interacts with the Earth's magnetic field, causing it to fluctuate rapidly. During these events, the ionosphere becomes highly unstable. This instability heavily absorbs high-frequency (HF) radio signals rather than refracting them, leading to poor propagation conditions and sometimes complete radio blackouts. It is important to remember that this is a space weather phenomenon involving magnetic fields and charged particles. It has absolutely nothing to do with terrestrial tropospheric weather, such as rain or thunderstorms.