Reflection from a sharply bounded ionosphere for VLF propagation Perpendicular to the magnetic meridian

There is experimen tal evide nce t hat VLF signa ls propagating from west to east suffer less attenuation than fr om east to west. Earlier work t reating t he case of nonreciprocal propagation alo ng t he magnetic equator is extended in latitude. T he nonreciprocity sh own by I I RII for hi ghly o bliqu e propagation a lo ng t h e magnetic equator p ersists when t he refl ection point moves towards a magnetic pole, but at the pole itself II R II i reciprocal. To a first a pproximatio n .L R.L is reciprocal at a ll magnetic lati tudes. The conversion coe ffici e nts II a .L, .L a ll , are g reater for east-to-west propagation than for propagation in t h e opposite di rectio n, except at a magn etic pole where they are equal.