Resonance of the space between earth and ionosphere

When noise radiation of roughly one or a few kilocycles per second is emi t ted in t he higher atmosphere, par t of it (an extraordinary wave) is p ropae;ated downward i nto t he space between ear th and ionosph ere. Hefiection a t t he eart h and ionosp here leads t hen to a standin g wave in t his space, whose intensity for a giv en inciden t power flu x va ries very mu ch wit h frequ ency . Maximum fi eld strength of t he standing wave is deri " ed for t he resonance freq uen cies of the space. The inciden t wave front s a re assumed to be horizontal. Only clearly defin ed wave fron t s being of a SLl ffi ciently wide extension a nd s llowing no noticeable irregulari ties will lead t o a defini t e resonance. The space between ea rth a nd ionosp here is compara ble to an air gap between t wo parall e l p lane r efl ecto rs. The lower ionosphere is however only a partial r efl ector, allowing radi ation to enter t he resona nce space and causing itt t he s" me t ime some loss of energy out of t he resona nce space (leakage) . Strat ifi cation of t he lower ionosphere has ome influence on t he resonance p henomena. Wit h a D layer, an addi tional resonan ce at a lower frequency is ob ta ined. It seems too early to dec ide whet her in any observed noises t he resona nce spectrum of t he space between eart h and ion osphere beco mes apparen t , but it is expected t hat noise spectra observed on t he groun d a re mod ifi ed by t he resonances. I n case of monoc hromatic emissions, the received in tensity depends on t he posi t ion in t he resonan ce pee t rum. The resonance spectrum should be received in case of emi sion of a whi te-noise spect rum, p rov id ed t he wave f ronts are appropria te.