A worldwide disturbance in the Earth's magnetic field. These storms result from variations in the solar wind
that produce major changes in the currents, plasmas
, and fields in Earth's magnetosphere
. They can last from several hours to many days. The largest storms often result from coronal mass ejections
(CMEs), while coronal hole
high-speed streams (CH HSS) and co-rotating interaction regions
(CIRs) can also lead to periods of storming. Geomagnetic activity is normally measured by surface-based magnetometers
and quantified by several indexes to include the commonly used Kp index
and storm levels classified with use of the National Oceanic and Atmospheric Administration G-scale
GFZ German Research Centre for Geosciences, 2018: Frequently asked questions regarding geomagnetism: What is a geomagnetic storm? Accessed 14 August 2018. Available at https://www.gfz-potsdam.de/en/section/geomagnetism/data-products-services/frequently-asked-questions-faqs/#c14390.
Space Weather Prediction Center, 2018: Geomagnetic storms. Accessed 14 August 2018. Available at https://www.swpc.noaa.gov/phenomena/geomagnetic-storms.
Term edited 14 August 2018.