GEOMAGNETIC STORMS

GEOMAGNETIC STORMS

A geomagnetic storm is a significant disruption of the magnetosphere around Earth that happens when energy from the solar wind is efficiently exchanged into the space environment. These storms are caused by variations in the solar wind, which cause significant shifts in the Earth's magnetosphere's fields, plasmas, and currents. The solar wind conditions that are most effective in generating geomagnetic storms are high-speed solar wind that lasts for several to many hours and, most importantly, a magnetic field at the dayside of the magnetosphere that is directed southward, against the direction of Earth's field. Energy from the solar wind can be effectively transferred into Earth's magnetosphere under these conditions.

Largest storms resulting from these conditions are linked to solar coronal mass ejections (CMEs), in which Earth is visited by roughly a billion tonnes of plasma from the sun that has an embedded magnetic field. Although CMEs usually take several days to reach Earth, some of the strongest storms have been known to arrive in as little as 18 hours. A high-speed solar wind stream (HSS) is another solar wind disturbance that fosters the conditions necessary for geomagnetic storms. HSSs form co-rotating interaction regions, or CIRs, as they plunge into the slower solar wind in front. These areas are frequently associated with geomagnetic storms, which can deposit more energy in the Earth's magnetosphere over a longer period of time than CME storms, despite being less powerful.

Storms also cause intense currents in the magnetosphere, changes in the radiation belts, and ionosphere changes, which include heating of the ionosphere and upper atmosphere region known as the thermosphere. In space, a ring of westward current around Earth causes magnetic disturbances on Earth. The disturbance storm time (Dst) index, which measures this current, has traditionally been used to characterise the size of a geomagnetic storm. In addition, currents produced in the magnetosphere that follow the magnetic field, known as field-aligned currents, connect to intense currents in the auroral ionosphere. These auroral currents, known as auroral electrojets, also cause significant magnetic disturbances. All of these currents, along with the magnetic deviations they cause on the ground, are combined to create a planetary geomagnetic disturbance index known as Kp. This index serves as the foundation for one of three NOAA Space Weather Scales, the Geomagnetic Storm, or G-Scale, which describes space weather that has the potential to disrupt Earth's systems.

During storms, ionosphere currents and energetic particles that precipitate into the ionosphere add energy in the form of heat, increasing the density and distribution of density in the upper atmosphere and causing additional drag on low-earth orbiting satellites. Local heating causes significant horizontal variations in ionospheric density, which can alter the path of radio signals and cause errors in GPS positioning information. While storms produce beautiful auroras, they can also disrupt navigation systems like the Global Navigation Satellite System (GNSS) and cause harmful geomagnetic induced currents (GICs) in power grids and pipelines.