Evolution of disturbance daily variation (DS) and interplanetary plasma parameters

The evolution of DS during the storms of February 7 and February 16, 1967 and October 31, 1968 is studied. It is shown that DS usually evolves as a morning maximum and a dusk minimum but not necessarily simultaneously. Also, the maxima and minima may shift to other LT sectors too. DS continues to be high even in the recovery phase and generally ends up as anoon-time decrease. DS seems to be related with solar wind parameters N and V but not with interplanetary magnetic field.