Unified PCN and PCS indices: Method of calculation, physical sense, and dependence on the IMF azimuthal and northward components

摘要

The PC index estimates the polar cap magnetic activity generated by the solar wind and its embedded magnetic field. It shows a high degree of correlation with geophysical disturbance parameters characterizing the state of magnetosphere. After transition to 1-min PC index values, significant differences were revealed between the PCN and PCS indices, derived on the basis of magnetic data from Thule and Vostok stations, respectively. Differences in values of the 1-min PCN and PCS indices may give rise to discrepancy in results of various analyses and to quite erroneous physical conclusions. To eliminate any influence of the calculation technique on scientific results a unified method for derivation of the PC index was elaborated in the Arctic and Antarctic Research Institute (St. Petersburg) and Danish Meteorological Institute (Copenhagen), and new sets of the unified PCN and PCS indices were calculated. Under conditions of southward IMF the unified positive PCS and PCN indices are well consistent with one another in their value and behavior and linearly correlate with the solar wind merging electric field (MEF), irrespective of season. The IMF BY component is responsible for occurrence of the electric field MEF (and positive PC index) under conditions BZ > 0. Being proportional to MEF the PC index would be regarded as a measure of the interplanetary merging (geoeffective) electric field with the appropriate dimensionality of mV/m.