Interplanetary Magnetic Field -Solar Wind Coupling and Geomagnetic Response during Solar Cycles 23,24 and 25

Abstract

The present study investigates the variation in the geomagnetic storms, measured by Dst and Kp indices (with Kp scaled  as Kp ×10 for consistency) in relation to the southward component of the interplanetary magnetic field (IMF) Bz component, solar wind speed (V) and the product of the solar wind speed V and IMF Bz for the three consecutive solar cycles (SCs) 23, 24 and the rising phase of SC 25. The study enhances understanding of the dependency of geomagnetic activities on interplanetary parameters. From this study it is found that the product of V and Bz as the most geoeffective parameter and produces significant disturbance in Earth’s magnetospheric conditions compared to V or Bz alone, this is because  when solar wind speed V combines with southward magnetic field (Bz) it enhances the magnetic reconnection due to  which plasma flow speed suddenly increases and the induced electric field swaps the charge particles, which enhances  the geomagnetic activities. The study also determined the correlation coefficient between the Dst index and VBz for  these three SCs, which are (0.7, 0.65 and 0.5), and between the Kp index and VBz is (-0.7, -0.65 and 0.55), respectively.  The Kp index shows resemblance with the solar wind speed V, i.e. both these parameter reaches to its peak values corresponding to Dst minima. Furthermore, this study also investigated the variation of Dst and Kp index with solar  wind speed V and IMF Bz separately and found that the correlation between these parameters is moderate across all three 
SCs. This suggests that solar wind speed (V) or IMF (Bz) alone is not sufficient to produce intense geomagnetic storms. Additionally, there is an average time lag of 1 to 2 days between Bz minima and Dst minima, which indicates a complex mechanism involved in magnetic reconnection between Earth’s magnetosphere and IMF, the Dst and Kp indices found to vary inversely with respect to each other (during sharp dip in Dst Kp index reach to its peak value), also the geomagnetic activities during SC 23 and the rising phase of SC 25 is comparatively high and shows resemblance, which suggests  the same kind of variation may also be expected for the SC 25 as that of SC 23 which helps in predicting space weather conditions.