Predicted dependence of the cross polar cap potential saturation on the type of solar wind stream

We study estimations of the cross polar cap potential (CPCP) saturation during magnetic storms induced by various types of solar wind drivers. Using the model of Siscoe–Hill (Hill et al., 1976; Siscoe et al., 2002a,b, 2004; Siscoe, 2011), we evaluate the saturation parameter Q   and compare it with the criterion of the CPCP saturation in the main phases of 257 magnetic storms (Dstmin⩽-50Dstmin⩽-50 nT) induced by the following types of solar wind streams: magnetic clouds (MC), Ejecta, the compressed region, Sheath, before MC (ShMCShMC) and before Ejecta (ShEShE), corotating interaction regions (CIR), and indeterminate type (IND). Our analysis shows that expected number of events with CPCP saturation is higher for storms induced by ShMCShMC (80%) than for those driven by MC. It is also higher for storms induced by interplanetary coronal mass ejection (ICME) (13.2%) than for storms driven by CIR (3.5%) or by IND (3.5%). The estimated CPCP saturation criterion is satisfied more often for storms initiated by MC (25%) than by Ejecta (2.9%); it is satisfied for 8.6% of magnetic storms induced by the sum of MC and Ejecta, and for 21.5% magnetic storms induced by Sheath before them (sum of ShMCShMC and ShEShE). These results allow us to conclude that the rate of occurrence of CPCP saturation estimated in the main phase of magnetic storms depends on the type of solar wind driver.