138:. Due to interactions with free electrons in the ionosphere, the waves becomes highly dispersive and like guided waves, follow the lines of geomagnetic field. These lines provide the field with sufficient focusing influence and prevents the scattering of field energy. Their paths reach into the outer space as far as 3 to 4 times the Earth's radius in the plane of equator and bring energy from lightning discharge to the Earth at a point in the opposite hemisphere which is the magnetic conjugate of the position of radio emission for whistlers. From there, the whistler waves are reflected back to the hemisphere from which they started. The energy is almost perfectly reflected from earth surface 4 or 5 times with increase dispersion and diminishing amplitude. Along such long paths the speed of propagation of energy is between c/10 to c/100 (where c is the speed of light) and the exact value depends upon frequency.
20:
1141:
1153:
304:, may escape the ionosphere and propagate outward into the magnetosphere. The signal is prone to bounce-mode propagation, reflecting back and forth on opposite sides of the planet until totally attenuated. To clarify which part of this hop pattern the signal is in, it is specified by a number, indicating the portion of the bounce path it is currently on. On its first upward path, it is known as a
142:
modulated. This conductivity modulation together with naturally occurring electrojet fields produces a virtual antenna which radiates at the modulation frequency. The HAARP HF heater array has been used to excite whistler-mode VLF signals detectable at the magnetic conjugate point, with up to 10 hops visible in the received VLF data.
141:
Modulated heating of the lower ionosphere with an HF heater array can also be used to generate VLF waves that excite whistler mode propagation. By transmitting high power HF waves with a VLF modulated power envelope into the D-region ionosphere, the conductivity of the ionospheric plasma can be
234:, but stood radio watch with Mallinckrodt until he heard the whistlers himself. Helliwell described these sounds as "weird, strange and unbelievable as flying saucers" in a 1954 article in the
316:. The + or - sign indicates either upward or downward propagation, respectively. The numeral represents the half-bounce currently in progress. The reflected signal is redesignated
105:. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers categorizes them into Pure Note, Diffuse, 2-Hop, and Echo Train types.
226:
in 1950. Mallinckrodt heard some whistling sounds and brought them to
Helliwell's attention. As Helliwell recalled in an article in the October 1982 issue of the
198:
668:
Inan, U. S.; Golkowski, M.; Carpenter, D. L.; Reddell, N.; Moore, R. C.; Bell, T. F.; Paschal, E.; Kossey, P.; Kennedy, E.; Meth, S. Z. (28 December 2004).
917:
379:, launched 1965, one of the earliest spacecraft to measure ionospheric and magnetospheric VLF waves, non-operational but still orbiting Earth.
807:
Smith, R.L.; Angerami, J.J. (Jan 1, 1968). "Magnetospheric
Properties Deduced from OGO 1 Observations of Ducted and Nonducted Whistlers".
134:
The pulse of electromagnetic energy of a lightning discharge producing whistlers contains a wide range of frequencies below the electron
260:
that was 13 miles (21 km) long. The antenna was used to transmit VLF radio signals into Earth's magnetosphere, to be detected in
69:
to 30 kHz, with maximum frequencies usually at 3 kHz to 5 kHz. Although they are electromagnetic waves, they occur at
1157:
240:. Helliwell tried to understand the mechanism involved in the production of whistlers. He conducted experiments at the VLF outpost
218:
is also known for his research into whistlers. Helliwell and one of his students, Jack
Mallinckrodt, were investigating lightning
264:. It was possible to inject these signals into the magnetosphere, since the ionosphere is transparent to these low frequencies.
434:
910:
885:
486:
794:
Melissae Fellet, "Robert
Helliwell, Radioscience and Magnetosphere Expert, Dead at 90," Stanford Report, May 20, 2011 at
191:
404:
280:, the observed characteristic of a whistler is that the tone rapidly descends over a few seconds—almost like a person
1179:
1145:
903:
150:
Whistlers were probably heard as early as 1886 on long telephone lines, but the clearest early description was by
1121:
877:
297:
1184:
1003:
505:"On estimating the amplitude of Jovian whistlers observed by Voyager 1 and implications concerning lightning"
370:
338:
333:
795:
740:
82:
1126:
1024:
863:
Geophysics and the IGY: proceedings of the symposium at the opening of the
International Geophysical Year
611:
Baumjohann, W.; Treumann, R. A.; Georgescu, E.; Haerendel, G.; Fornacon, K.-H.; Auster, U. (1999-12-31).
393:
155:
398:
852:
The INSPIRE Project - Exploring Very Low
Frequency Natural Radio (NASA educational portfolio program).
970:
175:
86:
58:
390:(MErcury Surface, Space ENvironment, GEochemistry and Ranging), launched 2004, decommissioned 2015.
926:
236:
670:"Multi-hop whistler-mode ELF/VLF signals and triggered emissions excited by the HAARP HF heater"
256:
of 10 kHz corresponds to a wavelength of 30 kilometres (19 mi)), Siple
Station had an
119:
known as "Jovian
Whistlers", supporting the visual observations of lightning made by Voyager 1.
1194:
1106:
1008:
343:
126:, where they are often called “lion roars” due to their frequencies of tens to hundreds of Hz.
1085:
1069:
965:
955:
858:
410:
816:
681:
624:
575:
516:
440:
19:
846:
8:
1189:
950:
945:
382:
309:
223:
171:
151:
135:
90:
34:
820:
685:
628:
579:
520:
1034:
1029:
960:
697:
650:
565:
478:
422:
54:
23:
612:
178:
lines. From this he deduced but was unable to conclusively prove the existence of the
993:
881:
642:
593:
534:
482:
446:
358:
353:
348:
301:
701:
654:
1090:
1059:
824:
689:
632:
583:
524:
470:
376:
231:
215:
167:
94:
78:
1111:
257:
245:
70:
1039:
732:
493:
Originally published by
Stanford University Press, Stanford, California (1965).
93:
of several kHz due to the slower velocity of the lower frequencies through the
74:
38:
637:
1173:
646:
597:
538:
416:
241:
187:
123:
102:
828:
431:(Solar TErrestrial RElations Observatory), launched 2006, still operational.
166:. Around the same time, Storey had posited the existence of whistlers meant
1116:
179:
895:
693:
277:
273:
208:
26:
796:
http://news.stanford.edu/news/2011/may/robert-helliwell-obit-052011.html
940:
669:
249:
195:
183:
98:
42:
529:
504:
1064:
588:
553:
387:
281:
253:
159:
112:
108:
62:
610:
570:
320:, until passing the geomagnetic equator again; then it is called
285:
201:—independently of each other, and the latter using data from the
116:
847:
A beginner's guide to natural VLF radio phenomena - second part.
419:(SOLO), Launched in February 2020, Operational in November 2021.
851:
766:
503:
Hobara, Y.; Kanemaru, S.; Hayakawa, M.; Gurnett, D. A. (1997).
428:
261:
203:
163:
115:
spacecraft detected whistler-like activity in the vicinity of
667:
502:
219:
769:. Engineering and Technology History Wiki. 29 January 2019
174:, and that it moved radio waves in the same direction as
66:
207:
spacecraft—experimentally proved the plasmasphere and
89:
lines from one hemisphere to the other. They undergo
85:
and return-path) where the impulse travels along the
296:
A type of electromagnetic signal propagating in the
469:
65:. Frequencies of terrestrial whistlers are 1
16:Very low frequency EM waves generated by lightning
790:
788:
786:
784:
552:Aplin, Karen L.; Fischer, Georg (February 2017).
73:, and can be converted to audio using a suitable
1171:
861:. In Odishaw, Hugh; Ruttenberg, Stanley (eds.).
800:
248:, which was active from 1971 to 1988. Since the
781:
661:
554:"Lightning detection in planetary atmospheres"
509:Journal of Geophysical Research: Space Physics
911:
806:
613:"Waveform and packet structure of lion roars"
211:'s existence, building on Storey's thinking.
551:
437:(TRACE), launched 1998, decommissioned 2010.
122:Whistlers have been detected in the Earth's
925:
726:
724:
722:
720:
718:
475:Whistlers and Related Ionospheric Phenomena
918:
904:
871:
413:(SMM), launched 1980, decommissioned 1989.
856:
730:
636:
587:
569:
528:
465:
463:
407:(SOHO), launched 1995, still operational.
715:
401:(SDO), launched 2010, still operational.
373:(ACE), launched 1997, still operational.
18:
1172:
761:
759:
757:
460:
435:Transition Region and Coronal Explorer
425:, launched in 2018, still operational.
364:
252:of VLF radio signals is very large (a
899:
443:, launched 1990, decommissioned 2009.
1152:
162:generated whistlers in his 1953 PhD
754:
449:, launched 1994, still operational.
276:radio operators. On the wide-band
13:
839:
405:Solar and Heliospheric Observatory
302:radio atmospheric signal or sferic
14:
1206:
230:, he initially thought it was an
222:at very low radio frequencies at
1151:
1140:
1139:
731:Gallagher, D. L. (27 May 2015).
272:Whistlers were named by British
809:Journal of Geophysical Research
291:
878:Radio Society of Great Britain
733:"Discovering the Plasmasphere"
604:
545:
496:
1:
859:"Whistlers and VLF Emissions"
857:Helliwell, Robert A. (1958).
453:
371:Advanced Composition Explorer
339:Electromagnetic electron wave
334:Dawn chorus (electromagnetic)
288:—hence the name "whistlers."
214:American electrical engineer
190:. In 1963 American scientist
37:VLF group's wave receiver at
741:Marshall Space Flight Center
674:Geophysical Research Letters
267:
59:electromagnetic (radio) wave
7:
1127:Charles Thomson Rees Wilson
1025:Upper-atmospheric lightning
394:Radiation Belt Storm Probes
327:
182:, a thin layer between the
156:Llewelyn Robert Owen Storey
154:in 1919. British scientist
10:
1211:
399:Solar Dynamics Observatory
298:Earth–ionosphere waveguide
145:
129:
1135:
1099:
1078:
1052:
1017:
986:
979:
933:
638:10.1007/s00585-999-1528-9
312:, it is referred to as a
33:wave, as received by the
1180:Atmospheric electricity
927:Atmospheric electricity
829:10.1029/ja073i001p00001
739:. Huntsville, AL: NASA
479:Dover Publications, Inc
77:. They are produced by
1107:Georg Wilhelm Richmann
1086:Electrodynamic tethers
971:Earth's magnetic field
344:Hiss (electromagnetic)
176:Earth's magnetic field
87:Earth's magnetic field
46:
29:of an electromagnetic
1070:Equatorial electrojet
966:Atmospheric chemistry
411:Solar Maximum Mission
308:. After passing the
22:
1185:Electrical phenomena
956:Atmospheric dynamics
737:Space Plasma Physics
694:10.1029/2004GL021647
441:Ulysses (spacecraft)
97:environments of the
951:Atmospheric physics
946:Atmospheric science
872:Romero, R. (2008).
821:1968JGR....73....1S
686:2004GeoRL..3124805I
629:1999AnGeo..17.1528B
617:Annales Geophysicae
580:2017Wthr...72...46A
521:1997JGR...102.7115H
471:Robert A. Helliwell
383:Helios (spacecraft)
365:Relevant spacecraft
310:geomagnetic equator
224:Stanford University
199:Konstantin Gringauz
152:Heinrich Barkhausen
136:cyclotron frequency
35:Stanford University
994:Radio atmospherics
961:Atmospheric dynamo
423:Parker Solar Probe
172:Earth's atmosphere
55:very low frequency
47:
1167:
1166:
1048:
1047:
1018:Optical emissions
987:ELF/VLF emissions
887:978-1-905086-38-2
865:. pp. 35–44.
623:(12): 1528–1534.
530:10.1029/96JA03996
515:(A4): 7115–7125.
488:978-0-486-44572-4
447:WIND (spacecraft)
359:Helicon (physics)
354:Radio atmospheric
349:Atmospheric noise
228:Stanford Engineer
79:lightning strikes
71:audio frequencies
1202:
1155:
1154:
1143:
1142:
1091:Magnetotellurics
1060:Solar irradiance
984:
983:
980:Electromagnetism
920:
913:
906:
897:
896:
891:
866:
833:
832:
804:
798:
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779:
778:
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749:
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665:
659:
658:
640:
608:
602:
601:
591:
589:10.1002/wea.2817
573:
549:
543:
542:
532:
500:
494:
492:
467:
323:
319:
315:
307:
216:Robert Helliwell
1210:
1209:
1205:
1204:
1203:
1201:
1200:
1199:
1170:
1169:
1168:
1163:
1131:
1112:Egon Schweidler
1095:
1074:
1044:
1035:St. Elmo's fire
1013:
975:
929:
924:
894:
888:
876:. Potters Bar:
842:
840:Further reading
837:
836:
805:
801:
793:
782:
772:
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729:
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546:
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489:
468:
461:
456:
367:
330:
321:
317:
313:
305:
294:
284:or an incoming
270:
246:West Antarctica
237:Palo Alto Times
170:was present in
148:
132:
17:
12:
11:
5:
1208:
1198:
1197:
1192:
1187:
1182:
1165:
1164:
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1136:
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1129:
1124:
1122:George Simpson
1119:
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1103:
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1067:
1062:
1056:
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1050:
1049:
1046:
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1043:
1042:
1040:Ball lightning
1037:
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39:Palmer Station
15:
9:
6:
4:
3:
2:
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1195:Space physics
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850:
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830:
826:
822:
818:
814:
810:
803:
797:
791:
789:
787:
785:
768:
767:"Owen Storey"
762:
760:
758:
742:
738:
734:
727:
725:
723:
721:
719:
703:
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417:Solar Orbiter
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355:
352:
350:
347:
345:
342:
340:
337:
335:
332:
331:
325:
324:, and so on.
311:
303:
300:, known as a
299:
289:
287:
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279:
275:
265:
263:
259:
255:
251:
247:
243:
242:Siple Station
239:
238:
233:
229:
225:
221:
217:
212:
210:
206:
205:
200:
197:
193:
192:Don Carpenter
189:
188:magnetosphere
185:
181:
177:
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153:
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137:
127:
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124:magnetosheath
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106:
104:
103:magnetosphere
100:
96:
92:
88:
84:
80:
76:
72:
68:
64:
61:generated by
60:
56:
52:
44:
40:
36:
32:
28:
25:
21:
1156:
1144:
1117:Nikola Tesla
1079:Applications
998:
874:Radio Nature
873:
862:
812:
808:
802:
771:. Retrieved
744:. Retrieved
736:
705:. Retrieved
677:
673:
663:
620:
616:
606:
564:(2): 46–50.
561:
557:
547:
512:
508:
498:
474:
295:
292:Nomenclature
271:
235:
227:
213:
202:
180:plasmasphere
164:dissertation
149:
140:
133:
121:
107:
50:
48:
30:
815:(1): 1–20.
278:spectrogram
274:World War I
209:plasmapause
194:and Soviet
27:spectrogram
1190:Ionosphere
1174:Categories
941:Geophysics
773:1 December
746:1 December
571:1606.03285
454:References
250:wavelength
196:astronomer
184:ionosphere
158:had shown
99:ionosphere
91:dispersion
83:intracloud
43:Antarctica
1065:Lightning
999:Whistlers
647:0992-7689
598:0043-1656
539:2156-2202
388:MESSENGER
282:whistling
268:Etymology
254:frequency
160:lightning
109:Voyager 1
63:lightning
1146:Category
707:20 April
702:16062416
655:11493967
473:(2006).
328:See also
232:artifact
81:(mostly
75:receiver
51:whistler
31:whistler
1158:Commons
1053:Sources
1030:Sprites
934:General
817:Bibcode
682:Bibcode
625:Bibcode
576:Bibcode
558:Weather
517:Bibcode
286:grenade
258:antenna
146:History
130:Sources
117:Jupiter
1100:People
1004:Chorus
884:
700:
680:(24).
653:
645:
596:
537:
485:
429:STEREO
262:Canada
204:Luna 2
168:plasma
95:plasma
57:(VLF)
698:S2CID
651:S2CID
566:arXiv
220:noise
53:is a
1009:Hiss
882:ISBN
775:2020
748:2020
709:2022
643:ISSN
594:ISSN
535:ISSN
483:ISBN
377:FR-1
186:and
111:and
101:and
825:doi
690:doi
633:doi
584:doi
525:doi
513:102
244:in
67:kHz
24:VLF
1176::
880:.
823:.
813:73
811:.
783:^
756:^
735:.
717:^
696:.
688:.
678:31
676:.
672:.
649:.
641:.
631:.
621:17
619:.
615:.
592:.
582:.
574:.
562:72
560:.
556:.
533:.
523:.
511:.
507:.
481:.
477:.
462:^
49:A
41:,
919:e
912:t
905:v
890:.
831:.
827::
819::
777:.
750:.
711:.
692::
684::
657:.
635::
627::
600:.
586::
578::
568::
541:.
527::
519::
491:.
322:2
318:1
314:1
306:0
113:2
45:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
