Are the equatorial electrojet and the Sq coupled systems? Transfer entropy approach

Whether equatorial electrojet (EEJ) and solar quiet (Sq) are independent systems or not is a long standing question. Techniques such as correlation analysis, interpretation of the westward currents observed between EEJ and Sq focus, along with the simulation studies have been used to address this question, hitherto. In this article, we revisit this problem using a method based on transfer entropy that examines the relationship between day-to-day variability in EEJ and Sq during low solar activity period (year 2007-08). Magnetic field variations in the horizontal component from the geomagnetic observatory, Tirunelveli (TIR) from the Indian region are used as a proxy for EEJ currents. To represent variations of Sq current system, two stations outside the EEJ belt, Nagpur (NGP) and Jaipur (JAI) are analyzed. Our analyses clearly demonstrate that significant information is exchanged between EEJ and Sq variations, and hence they are in a cross-talk with each other, indicating EEJ and Sq are coupled systems. Variations of time scales less than 2 h appear at the equatorial station before Sq stations. Similar analyses carried out for the African sector also validate the above results.