Synoptic Variation of the Radio Refractive Index*

The synoptic variation of the atmospheric radio refractive index, evaluated from standard weather observations, is examin ed d uri ng an ou t break of polar continental air. It is found t hat t he reduced-t o-sea-Ieve1 value of t he r efractive index is a more sensitive synoptic parameter t han t he station value. The reduced valu e is quite sensit ive to the humidity and density structure of the storm under study while t he great station elevation d ependence of t he station value tends to mask synoptic changes. The reduced value changes systematically with t he approach and passage of t he polar front. The present system shows a consistent increase of t he reduced value in t h e warm sector of t he wave and a marked decrease behind t he cold front.