Space Weather Monitoring on Ground-based Magnetic Observations (РС Index)

О. А. Troshichev and D. A. Sormakov

Polar cap magnetic activity (РС index) is an indicator of solar wind energy that enters the magnetosphere (Resolutions of XXII IAGA Assembly, 2013). Usually, the PC index follows changes in the interplanetary electric field EKL, that is estimated from measurement data on solar wind parameters at the Lagrange point L1 (available at the OMNI website). However, during the period of magnetic field perturbations, the correspondence between EKL and PC is often disturbed. To reveal the regularity of disturbances, the correlation was analyzed between the PC index and the computed field EKL during magnetic substorms, which are considered as an independent indicator of the impact of perturbed solar wind on the magnetosphere. The independent analysis for the PCN and PCS indices demonstrated that the magnetic activity in the winter polar cap (PCwinter) provides statistically more correct results than the magnetic activity in the summer cap (PCsummer). The correlation between the PCwinter and the computed field EKL (R > 0.5) was observed for ~80% of the analyzed substorms. In the other cases (20%), the correlation was low or even negative, even though substorms were evidently associated with the PC index growth. So, in these cases, the computed field EKL did not contact with the magnetosphere. Hence, the PC index allows verifying the real field EKL affecting the magnetosphere and checking in such way whether the solar wind registered at the Lagrange point contacted with the magnetosphere (data from the OMNI website).