PC index as a proxy of the solar wind energy that entered into the magnetosphere: (5) verification of the solar wind parameters presented at OMNI website

Abstract

The polar cap magnetic activity (PC) index is regarded as a proxy for energy that input into the magnetosphere during the solar wind-magnetosphere coupling (Resolutions of XXII IAGA Assembly, 2013). The PC index variations usually follow the changes of the interplanetary electric field EKL, which is estimated by the solar wind parameters fixed in the Lagrange point and published in the OMNI database. However, the correspondence between EKL and PC is often violated under disturbed conditions. To reveal the regularity of violations, the correlation between the PC index and “estimated” EKL field was examined in course of magnetic disturbances, the magnetic substorms occurrence being regarded as independent evidence of the geoeffective solar wind affecting the magnetosphere. Analysis, carried out separately for PCN and PCS indices, showed that magnetic activity in the winter polar cap (PCwinter) ensures statistically more correct results than that in the summer polar cap (PCsummer). Correlation between the PCwinter index and “estimated” EKL field proved to be good (R > 0.5) in about 80% of the examined substorm events. In other 20% of events the correlation was poor or negative, even though the magnetic substorms occurred in evident association with the preceding PC growth. It implies that “estimated” EKL field did not impact on the Earth's magnetosphere in these cases. Thus, the PC index makes it possible to verify the actual EKL field affecting the magnetosphere, and to check, in such manner, whether or not the solar wind fixed in the Lagrange point (presented at the OMNI database) encountered the magnetosphere in actuality.