Differences between CME‐driven storms and CIR‐driven storms

Twenty one differences between CME‐driven geomagnetic storms and CIR‐driven geomagnetic storms are tabulated. (CME‐driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; CIR‐driven includes driving by the associated recurring high‐speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME‐driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR‐driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR‐driven storms than it is prior to CME‐driven storms. CME‐driven storms pose more of a problem for Earth‐based electrical systems; CIR‐driven storms pose more of a problem for space‐based assets.