Origin of "very-low-frequency emissions"

Gallet, Roger M.; Helliwell, R. A.

doi:10.6028/jres.063d.007

Cited by 19 publications

(14 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The traveling wave tube amplification of incoherent signals which is proposed by Gallet and Helliwell [1959] seems improbable because a gain of several orders of magnitude is required.…”

Section: Vlf and Lf Emissionsmentioning

confidence: 99%

Radiation from electrons in magnetoplasma

Liemohn¹

1965

J. RES. NATL. BUR. STAN. SECT. D. RAD. SCI.

View full text Add to dashboard Cite

The radiation from an electron in a homogeneous magnetoplasma has some unu sual properti es as a consequence of the dispersive anisotropic nature of the medium. Attention is confine d to emi ssion in the ordinary (whistler) mode frequen cy band below the cyclotron resonance and the extraordinary mode frequency band around the plas ma freque ncy where the indices of refraction are ap preciably greater than one and vary signifi cantly. Due to the large indi ces, electrons can emit Cere nkov radiation over a limited band of nonrelativisti c e ne rgies . The cyclotron radiation which is generated by the gyration s of elec tron s is complicated also by thi s property of th e medium which permits both normal emi ssion due to "slower than li ght " moti on a nd a nom alous e mi ssion due to " fa ster than light" motion . In the ordinary mode, for example, th e anomalous cyclotron radi ation is emitted into the forward he misphere with res pect to the guiding ce nter motion of the electron wh ereas th e normal radiation is emitted into the backw ard he mi sph ere. In thi s paper th e freque ncy spectra and angular patterns of the average radia ted powe r are calcul ated by th e Ha milto nian method whi c h avoid s a direc t calc ulation of th e co mplicated electromagneti c fi eld vectors . The theory of e mi ssion in di s persive ani sotro pi c medi a with a hermiti an di electric te nso r by Kolomenskii and E idm an is th oroughl y re vie wed a nd exte nded to include relativi sti c e nergies; the co mpl icated anal yti c formulas for the power are evaluated for several spec ial cases; and th e res ults are appli ed to rece nt inte rpretations of ve ry low-freq ue ncy (V LF) and low-frequ e ncy (LF) emi ssions from elec trons in th e magnetos ph ere. The main co nclu sions of the work are as foll ows: (1 ) In th e ordin ary (whi stle r) mode mos t of the ene rgy is radi ated alon g wave normals at la rge angles to th e mag neti c fi eld at freque ncies othe r th an the rectilin early Dopp ler-s hifted fund a mental cyclotron harmonic whi ch is co ntrary to ass umptions of ce rtain VLF e mi ss ion theori es.(2) The reso nan ce s ingul ariti es in th e indi ces fo r a cold , colli sionless plas ma mu st be e liminated to ac hi e ve finit e power leve ls, but unfortunately the di electri c tenso r for th ermal motion is extre mely co mplex and for colli sions is non-hermiti a n; co nsequ e ntly, a n arbitrary upp er limit is imposed on th e indi ces in order to make a qu a ntitative es tim ate of th e powe r. (3) Based on th is approximation th e total power in the ordin ary mode is a slowl y varying fun ction of fr equ ency a nd electron energy with an average level of 10-30 W /(c/s) per electron. (4) This le vel is inadequate to exp lain observed VLF signals on th e bas is of in cohere nt emi ssion, but co herent e mi ssion from bunches of electrons can give th e obse rved power level of 10-14 W /c m 2 (c/s) above the ionos phere; he nce, the onu s of explaining the co mplex di spersion pattern s of VLF e mi ssions is l...

show abstract

“…The traveling wave tube amplification of incoherent signals which is proposed by Gallet and Helliwell [1959] seems improbable because a gain of several orders of magnitude is required.…”

Section: Vlf and Lf Emissionsmentioning

confidence: 99%

Radiation from electrons in magnetoplasma

Liemohn¹

1965

J. RES. NATL. BUR. STAN. SECT. D. RAD. SCI.

View full text Add to dashboard Cite

show abstract

“…To explain the discrepancy between observed and computed incoherent radiated power, Maggs (1976) suggested convective beam ampli®cation of the radiation as it propagated through the inhomogeneous ionosphere. Gallet and Helliwell (1959) and Dowden (1962) suggested travelling wave tube mechanism for the generation of VLF hiss. Swift and Kan (1975) studied beam ampli®cation of electrostatic whistlers and argued that the beam ampli®cation mechanism will produce VLF hiss from regions of low ionospheric plasma density at frequencies near the electron plasma frequency.…”

Section: Introductionmentioning

confidence: 99%

Two types of ELF hiss observed at Varanasi, India

Singh

Patel

et al. 1999

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. The morphology of ELF hiss events observed at low-latitude ground station Varanasi (L = 1.07, geomagnetic latitude 14°55¢N) are reported, which consist of two types: (1) events which propagated in ducted mode along the geomagnetic ®eld line corresponding to observing station Varanasi and (2) events which propagated in ducted mode along higher L-values (L = 4±6), after reaching the lower edge of ionosphere excite the Earth-ionosphere wave guide and propagate towards equator to be received at Varanasi. To understand the generation mechanism of ELF hiss, incoherent Cerenkov radiated power from the low latitude and middle latitude plasmasphere are evaluated. Considering this estimated power as an input for wave ampli®cation through wave±particle interaction, the growth rate and ampli®cation factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF hiss.

show abstract

“…5 long studied at lower frequencies, wave trains of slowly-varying frequency which resemble the "hooks" and other characteristic waveforms which have been studied at considerably higher frequencies ("VLF Emissions") 6 occur. Judging from the number of occurrences during the very limited intervals when observations of this type were made, such signals are not uncommon in the 1 to 50 cps range, and their study would be of considerable scientific interest.…”

Section: Analysis and Interpretation Of Datamentioning

confidence: 99%