Prediction of VLF diurnal phase changes and solar flare effects

VLF diurnal phase shift data are compared with predictions resulting from the waveguide equations for the first order mode. The effects of higher order mode energies appear to exist out to 2700 km, and may at times affect measurements beyond this range. A relation is given for the prediction of diurnal phase shift for 10–20 kc radio waves. Expressions are given for relating observed VLF phase perturbations caused by both small and large solar flares to the resulting apparent decreases in ionospheric reflecting height.