High-speed streams, coronal mass ejections, and interplanetary shocks: A comparative study of geoeffectiveness

Corotating high-speed solar wind streams, coronal mass ejections, and interplanetary shocks are common causes of geornagnetic disturbances in Earth's magnetosphere and ionosphere. This paper examines the geoeffectiveness of the different types of interplanetary structures. Several ionospheric electrodynamic parameters as well as geornagnetic indices are used to assess quantitatively the effectiveness of the various solar-driven interplanetary structures on the ionosphere and magnetosphere, including the polar-cap potential drop, Joule and auroral energy dissipation, and the AE and Dst indices. Epoch analysis is performed for three types of events associated with the different interplanetary structures, including 17 events of highspeed streams (HSSs), 18 events of shocks followed by complex ejecta, and 18 events of shocks followed by magnetic clouds. On average, the HSS events resembles a weak geomagnetic storm, with a minimum Dst value of -40 nT. The average behavior of the shock/ejecta and shock/cloud events displays the characteristics of a two-step main phase storm, showing the first Dst dip in the sheath region and the second Dst dip in the following cloud or ejecta. In addition to a positive excursion in Dst, solar wind dynamic pressure enhancement associated with interplanetary shocks also induces a prompt increase in ionospheric electric potentials, Joule heating, auroral precipitation, as well as the AE index. There are 8 superstorms with the minimum Dst < -250 nT amongst the events studied here. Four of them are caused by the sheath region and 4 by magnetic clouds and ejecta combined, making the sheath region as "geoeffective" as the cloud and ejecta in producing superstorms. The average ratio of the solar wind electromagnetic power as represented by the c parameter to the magnetospheric energy dissipation is 1.80 for the HSS events, 1.10 for the shock/ejecta events, and about 0.80 for the shock/cloud events. By comparison, the ratio of solar wind kinetic power to the magnetospheric energy dissipation is only around 0.05 for all types of events.