Tropospheric scatter propagation and atmospheric circulations

Abstract

~r an s ho ri zoll vhf a nd uhf fi elds ex hi bit d e~p fa des o r la rge s ig nal enhance men ts of several hours .duratlOll, as the propagatlOll mec hams m a ltern ates between pa rtia l refl ectio n and scattenng caused by t urbulen t dielectri c fluctu ations in t he at mosph ere. Such a ltern ations occ ur when str ong refractIve layers de velop below 3,000 ft. Surface wind strea mlin e a na lyses s how ~hat mes? scale ce?ters of co nverge nce or dIv ergence cause local redis tribution of refractIve laye nng, tendmg to produce t he cha nge from on e mec ha ni sm to t he other.Current scatterin g t heory and t he empirical findin gs of others a re exam in ed to determin e ~h e gross meteorological factors t hat influence changes in scattered fi elds . Th e two vari ables 111 t he t urbulent scatterin g coeffi cients, t he scattering a ngle a nd t he in te ns ity o f di electri c fluctua t IOns at hI gh wave numbers, .are found to be d ependen t upon the refrac t ive laye rin g a nd the t h ermal s~a bllLty of t he a ll·mass . It h as bee n s hown elsewhe re that refr activ ity a nd s tablh ty are pnnClpally fun ctIO ns of the ver tical velocity in t he at mosphere. It is shown here that t he dIrectIOn a nd relatIve magn it ude of t he vertical velocity can be inferred f rom t he uppe r-troposp her:ic wind velocity diyerge.nce . R eceived scattere· d signa ls are found to be well co rrelated WIth co mputed velocIty divergence. I t IS s uggested t hat the va ri ations of scattered signal level or ra nge can be pred icted in a ro utIne manne r by r egul a r meteo rological p ersonn el usin g ordin a ril y available meteoro-logIcal d ata.

Transmission loss predictions for tropospheric communication circuits, Volume 1

“…Areas of divergence, usually favorable for elevated duct formation, appear to be most persistent over ocean areas from 10°to 40°n orth and south latitude, especially during winter months. [ Moler and Holden, I960;Randall, 1964] . Elevated ducts are usually less important for tropospheric propagation than those close to the surface.…”