Day-to-day variation of geomagnetic H field and equatorial ring current

The paper describes the day-to-day fluctuations of the horizontal component of the geomagnetic field along Indo- Russian chain of stations during midday and midnight hours in relations to the corresponding variations of Dst index. The correlation between.H and Dst index is around 0.8 for all latitudes. The slope of the regression line is about 1.0 during daytime but during the nighttime hours the slope is only around 0.5. This suggests that the nighttime tail currents have almost equal contribution towards fluctuations of Delta H as due to the disturbance ring current. The equatorial electrojet current, designated by Delta H(TRD) - Delta H(ABG) has no correlation with Dst index because any variation of Dst are removed from Delta H at both stations and electrojet currents represents only the ionospheric current component.