Geomagnetic Storms

摘要

Geomagnetic storms, in which the global geomagnetic field intensity decreases on the order of tens to hundreds nT, are phenomena that occur on the largest scale in the solar wind-magnetosphere-ionosphere coupled system. Geomagnetic storms develop when solar wind-magnetosphere couplings are intensified by solar wind disturbances (coronal holes and CME phenomena) that accompany southward IMF. Perturbations in the magnetic field are caused by geomagnetic storms and can be explained by the westward electric current along the geomagnetic equator (ring current). Such perturbations on the scale of 10~(15)-10~(16) J occur when the magnetosphere responds to the injections of energy during geomagnetic storms. Geomagnetic storms are generally believed to develop in association with an increase in magnetospheric convection. However, in contrast to magnetospheric convection development (which is saturated with strong solar wind electric fields), analysis of the correlation of solar wind parameters to magnetospheric convection and to geomagnetic storms has revealed that geomagnetic storm growth is not saturated with such electric fields. This indicates that geomagnetic field growth and magnetospheric convection growth may not correlate perfectly.