Geoeffectiveness and efficiency of CIR, sheath, and ICME in generation of magnetic storms

摘要

We investigate the relative role of various types of solar wind streams in generation of magnetic storms. On the basis of the OMNI data of interplanetary measurements for the period of 1976-2000, we analyze 798 geomagnetic storms with Dst≤-50 nT and five various types of solar wind streams as their interplanetary sources: corotating interaction regions (CIR), interplanetary coronal mass ejection (ICME) including magnetic clouds (MC) and ejecta, and a compression region sheath before both types of ICME (SHE _(MC) and SHE _(Ej), respectively). For various types of the solar wind we study the following relative characteristics: occurrence rate; mass, momentum, energy and magnetic fluxes; probability of generation of a magnetic storm (geoeffectiveness); efficiency of the process of this generation; and solar cycle variation of some of these parameters. Obtained results show that in spite of the fact that magnetic clouds have lower occurrence rates and lower efficiency than CIR and sheath, they play an essential role in generation of magnetic storms due to higher geoeffectiveness of storm generation (i.e., higher probability to contain large and long-term southward IMF Bz component). Geoeffectiveness for all drives has the smallest value during a solar cycle minimum and increases at other phases of the cycle.