Currents associated with abnormal quiet days in Sq(H)

Abstract

Summary Declination data have been analysed on NQDs and AQDs for the years 1963-64-65. Such an analysis indicates that there is a larger southward current in the morning and a larger northward current in the afternoon on NQDs than AQDs in both the northern and southern hemispheres. The strength of this current is found to be IMF-dependent. Taken in conjunction with the previous analyses of the H-data it is concluded that on AQDs the Sq(H) amplitude is affected by a reduction in the current of a large current vortex which extends over both hemispheres and is part of the normal Sq(H) current system. Such a current is driven by diurnal winds, variations in the strength of the wind thus contributing to the day-to-day variability of the Sq(H) amplitudes. AQDs therefore represent days of small amplitude in the general day-to-day variability. The IMF-dependence arises due to complicated current systems that flow on AQDs and which are associated with high latitude phenomena and generally have their focus at latitudes 60°, similar to those found by Takeda & Araki.