Study of the phenomenon of whistler echoes

Abstract

In considering the propagation of lon g whistle rs and whistle r ec ho trains, the que stion ari ses about where the downcoming whistlers are refle cted. The se ve ral s uggestions that have bee n mad e include ground reflection and refl ection at the lowe r boundary of the ionosphere. In eithe r case, the ec ho of a daytim e whistle r would mak e se ve ra l more passes through the ab sorbing V region than the whi stle r itself, a nd we should expect whi stl e rs occurrin g a round noon to ha ve a much s maller probability of havin g ec hoes than whi stl e rs occurring at ni ght. An a nal ysis of se ve ral ye ars of data obt a ined a t the Da rtmouth Co ll ege whi stl e r stati on yield s the res ult , however, th at although th e a ve rage whi stl er rate is muc h hi ghe r a t ni ght than durin g th e da y, the proba bility of a whi stl e r having a n ec ho s hows littl e c ha nge fro m midni ght to midd ay. Co ns iste nt with thi s obse rva ti on a re th e res ults of ano th e r s tud y showing th at the diffe re nce in the inte nsity of a noo ntim e whi s tle r and its ec ho may be onl y a few decibe ls.If th e th eo reti cal predi cti ons a bout a bsorption of whi s tle r-mode waves a re even nearly correc t, our res ults on whi stl e r ec hoes a re in co mp a tible with the lo we r-bound a ry or ground·refl ec ti o n model. In no cases st udi ed by us has the whi s tle r echo bee n more inte nse th a n th e whi s tl e r itself, a nd we do not at prese nt favo r th e id ea th at whi stle r echoes a re a mplifi ed in th e magne tos ph er e. A mode l co nsis te nt with our results is one in whi c h a la rge fr ac tio n of the e ne rgy of a down co ming whi stl e r is refl ec ted above V·region heights . In thi s model a whi stl e r may be pi ctured as bounc in g bac k a nd forth betwee n th e ionosp heres of th e two opp os ite he mis pheres, with so me of th e e ne rgy " lea kin g through" to the ground a t one or both e nd s of th e pa th . Whi stle r obse rva tions could also be expla in ed by a model in whi c h t he daytime tra nsmiss ion loss fo r VLF e ne rgy is hi gh o nl y for th e firs t upwa rd pe ne trati on of th e ionosp he re, bu t s mall once th e e nergy is propagatin g in th e " whi stle r mode."

A new device for measurement of polarization and field intensity of low‐latitude whistlers

“…Therefore in measuring electric field, the cross-loop antenna gives less measurement e r r o r than the vertical antenna. (1) The polarization parameters of whistlers with incident angles less than 56" are p = -0.12 and v = 1.0 (circular polarization). Whistlers have some fluctuations in polarization around the circular polarization.…”