Definitions for "Geomagnetic storm"
When unusually strong surges of solar wind (charged particles from the Sun) hit the Earth. This effect causes variations in the magnetic field which surrounds the Earth. The result are visible aurora (Northern and Southern lights).
magnetic storms on earth caused by solar activity; they cause the auroras, surges in power lines, and interference of radio and TV signal transmissions
a disturbance in Earth's magnetic field triggered by solar activity. Aurorae, power outages, and satellite failures can all be caused by such storms.