Study of the long‐term variability of interplanetary plasma and fields as a link for solar‐terrestrial relationships

Abstract

Often the interplanetary parameters used for the study of solar‐terrestrial relationships are solar wind speed (V), the total interplanetary magnetic field (B), and the southward component of IMF (Bz). Both hourly and daily values of these parameters have usually been employed to associate with parameters defining terrestrial effects. For our study, we have used the daily values of the interplanetary indices (V, B, and Bz), as well as the daily values of the geomagnetic disturbance index Ap, for the years 1965–2007. The long‐term averages have been calculated for the days when simultaneous data are available for all the four parameters (V, B, Bz, and Ap). These include their yearly averages, as well as the averages on the basis of the phases of the solar activity cycle. The statistical relationship between them has been investigated on these long‐term averages, as well as on the day‐to‐day basis. These sets have been further divided and studied on the basis of days with Bz being <0 or ≥0. The results obtained can be summarized as follows: (1) the magnitudes of the values of Ap are observed to be always enhanced significantly for the case of Bz < 0, as compared to days with Bz ≥ 0, and (2) V versus Ap has always low values of correlation coefficient (r). (3) On the contrary, B versus Ap has high values of “r”; (4) the product of V and B versus Ap always yields much better correlations than for V or B alone, either on an average basis or on a day‐to‐day basis, and (5) although, the long‐term variations of V are not very significant, the variations of B follow solar activity cycle and has a continuously increasing trend during the solar cycles 20 and 21. The statistical results obtained here signify that the product of V and B is more significantly effective in producing large‐scale geomagnetic disturbances.