145-148The effect of vertical density gradients on the wave normal directions of down coming vlf waves is studied in the absence as well as in the presence of horizontal density gradients; It is shown that the vertical density gradients have no effect on the wavenormal directions of vlf waves in the presence of horizontal density gradients. The cause of increased rate of occurrence of whistlers and vlf emissions at low latitudes during the period of magnetic disturbances is also discussed in the light of this result
