JOURNAL OF RESEARCH of the National Bureau of Standards- D. Radio Propagation Vol. 67D, No.3, May- June 1963

Effects of Radio Wave Propagation Through Mid-Latitude 6300 A Auroral Arcs

J. R. Roach 1

(R eceived No vembcr 20, 19(2)

Yery h igh frcq ucncy radi o sig na ls p rop agated from a pola r orbi t in g satclli tc Lh l'O ugh a sys tcm of mu lt iplc 6300 A red a uro ral a rcs a re s ho wn to be st rongly p ertu rbed by eacll a rc. Th e pcr Lurbat ions ar e ch aracteri zed by a mpli t ud e scintillat ion of the received sig nal. The scinti llat io n p O\\'er cOl'l'elates logari thmica ll y with tll e are photon flux, as dcri \'ed fro m th e photomctri c obser vat ion s . Thc rcd a rcs a nd radi o scin t ill ations were observed on tll C nigh t of J 2/ J :~ N' O\'cmbcr 19()O. during which a m ajor magnet ic storm was in p rocess . Sim ila r m casurcments on the quict m agneti c nig ht of 18/19 F ebru a ry J 961 , rcvcaled no apprecia ble radi o scin t ill at ion or red a re activity.

1. Introduction

R ecent rcscarch on l1lid-la tiLude 6300 A arcs has shown that t hey consist of a t ube of emission ori­ented along Jlh1gnetic isoclines and extending over considerable distances on the Earth's surface. Bar­bier [1958] and F . E . Ro ach and Marovich [1959] have presented observations of red arcs that have extended from Haute Provence, France to Fritz P eak, Colo . F . E. Roach, Barbier, and Duncan [1962] have discussed a red arc which appeared almost simulta­neously a t about the St,llle invariant latitude in the northern and southern henlisph eres, and separated by over 150 deg of longitude.

The height of red arc maximum intensity h as been est ablished on two occasions as approximately 400 km by F . E . Roach, Moore, Bruner , Cronin, and Silverman [1960]; and by Moore and Odenkran tz [1961]. Th e general cross section intensity profile has been determin ed by Tohm atsu and F. E. Roach [1962], based on observations of several red arcs a t Frit z P eak, Colo .; revealing a somewh at ellip t ical tube structure, with maximum intensity centered at 390 k111, ex tendin g down to 300 km and up to 750 km; and extending 400 km north and sou th of th e center .

These general large-scale characteristics of mid­lati tude 6300 A arcs are verified in this paper by independent photometric and radio telescope obser­vations. Photometric data of the 6300 A arc emis-

} sion were obtained at Fritz P eak, Colo ., during a period when observations of satellite signals were made at Van N uys, Calif. The radio signals were observed to be strongly pertUl'bed as a result of passage through a region in the ionosphere which corresponded in time and space with longit ude ex­t ensions of red arcs observed at Fritz P eak. The radio signal perturbation is shown to be logarith­mically proportional to th e arc photon flux .

Data are presented for several orbits on three differ ent nights, for which the magnetic K p index yaried from a maximum of 9° to a minimum of 2+.

I iVi'ember of Lhe Scientific Staff of Ba ll Brot hers Research Coq,oration, Boul· del' Colo.

Sevcre radio signal pCl' tm-bt1tions coillcident with 6300 A arcs OCCUlTed on the nig ht of 12/13 N O\'em­bel' 1960 following ,1 major solar fla,]'c event . In con t rast. t hc observat ion of a similar st1.telli te r adio signal on a gcomagnetically qui et n ight revealed vir tually no pcrt urbation, and no 63 00 A arcs were observcd.

2. Observational Techniques

The data discussed in this papcr wcre indepcnd­ent.ly obtain ed by the airglow photometers at Fritz P eak, Colo ., and by a radio telescope at Vt1.J1 N uys, Calif. The 6300 A photo mctric da ta were obtained with th e standard bil'cl'ri ngent ftl ter photometer, and t be measurcment techniques h avc been discussed by F . E. Roach and Marovich [1959 and 1960] in pre­vious publications. It need only be stated here t hat 6300 A data WCl'C ob tfl.in ed in almucantar sweeps of the photometer cvery 15 min at zenit h anglcs of 0, 40 , 60 , 70 , 75, and 80 deg .

The radio propagation data were obt.ained with a research radio t elescope which received signals from th e polar orbiting satellites . Th e signal source in the satellites was a VHF communications link u tiliz­ing a transmitting antenna with a gain of nomin al unity.

The radio telescope was located at the Lockheed Missile and Space Company facility, Van Nuys, CaliL , and the 6300 A photometer was loca;,ed at the National Bureau of Standards facility at Fritz P eak, Colo . The geodetic and geomagnetic cOOl'di­nates for these stat ions are given in t able 1.

The radio t elescope consisted of a trihelix array with a common ground plane, mounted on a servo-

l' ABL E 1. Coordinates of observing stations

Geodetic Geo· E levat ion Station magn et iC above

la ti tude sea·level T,at itudc Longitude

Van Nuys, Calif. -- - --- ----- - 1 34°13' N 118°29' \ ·V 41. 0° 213 m F ntz Peak, Colo ___ _______ _ ._ 39°j4' N 105°29' W 48. 7° 2740 m

263

I

I~~

driven pedestal. Th e trihelix array was con trollable in elevation and azimuth by means of a manually operated console. The receiving an tenna had a maximum gain of 19 db , itnd received the signals as circularly polarized componen ts. The effective ± 3 db antenn a bealllwidth was 15 deg.

Th e feeds from th e three helices were impedance match ed and coupled to a common feed at th e input to the preamplifier , mounted on the pedestitl. The preamplifi er had a gain of 23 db wi th a noise fi gure of 3.5 db . T he r eceiver was a N ems Clarke Model No. 1673 opera ted in the FM detection mode at a 300 kc/s IF bandwidth . The carrier signal frequency was in the cOlllmunications b and from 225 M c/s to 240 M c/s. The FM intelligence t hreshold of the receiver for the composite signal was 108 dbm .

The au tolll a tic gain control circui t of the receiver was modified to provide it linear ou Lpu t voltage for a logarithmic power input from ll5 dbm to 60 dbm. This AG C vol tage was monitored as it meitsure of the received signal strength in it 10 cis response circui t, which in turn modulated a voltage con trolled subcarrier . The sub carrier frequency was directly recorded on a channel of m agnetic tape alon g wi th a time standard. The resolution of this monitor was approximately ± 0.1 db .

The entire electronics system was calibra ted each orbit al acquisition by inserting the output of a standard signal generator in the preamplifier input . The composite FM-FM signitl was simulated by means of external oscillators modulating the signal generator carrier at the same deviation ratios as the satellite link. The trihelix array and ground plane were calibrated in a full-scale an terma range.

3 . Radio Propagation Data

The radio telescope was in opera tion during the p eriod, August 1960 to March 1961 , and obtained recordings of signals from several polar orbiting satellites. Data were selected for analysis during nighttime passages of the satelli tes that corresponded with pho tometric observations at Fritz P eak. Corresponding data were obtained for the nigh ts of 12/13 November 1960 and 18/19 F ebruary 1961. Radio propagation dat<t were also an alyzed for the nigh t of 7/8 D ecember 1960. The November nigh t was no table for a major geomagnetic storm, and th e respectiv e magnetic f{p indices 2 for each night are shown in table 2. Radio propagation da ta were also r eviewed for several other nights to es tablish that the normal characteristics of the received signals

2 The magnetic ]{ p index is th .:- geomagnetic p lanetary index.

T A B LE 2. Nl agnetic J( indires.

}{p Index

U ni versal Limes D ate

6:00 9:00 12:00 - - - -

12/13 November 1960 _____ 9- 90 90 7/8 December 1960 ________ 5+ 4- 40 18/19 February 1961. _____ 2+ 3+ 3+

264

were similar to those observed on the nigh t of 18/19 F ebruary 1961.

On each of the three nigh ts of interest in this p aper , r adio sign itls were ob titined for one orbit itl p ass east and one orbi titl pass west of the radio t elescop e. TIl e east and west orbi ts on eitch nigh t were in approxim ittely the same positions and passed the radio telescope durin g it 3-hr period followin g locitl l1lidnight. The orbi tal paths for these nigh ts are shown in geodetic latitude itnd longitude in figure 1. The respective satellite alti tudes and r anges from the radio telescope are shown in table 3.

Continuous recordin gs of th e r adio signals were ob tained for th ese orbi titl passes and por tions of the received signal stren gth for each p itSS are plo tted in fi gures 2 it and 2b . These plo tted data itre present ed for two time periods wh en the satellite r ange to the radio telescope WitS the sitme north of the telescope as sou t h of it . The ordin ate scales represen t the I

received power in decibels with resp ect to 1 j.J. V at the .50-ohm receiver input.

60 "' ,.

" r

~ 50

u '0

~ ~ "

20 ALL TI ME S ARE IN UNIV ERSAL TI ME

15 145 "0 135 130

LO NGITUDE

121 13 NO V EM BE R , 196 0 ORB IT n

125 120 11 5

IN DEGRE E S WE ST

"0

12/ 13 NOVEM BER ORBIT I

~18/1 9 FEBRU ARY, 1961 8:41 ORB IT TIl

'05 '00 95

F I GURE 1. Geodetic latitude and longitude projections of the Jive satellite orbital paths discussed in this paper.

Location indicated for Van Nll~'S , Californ ia. and Fr itz Peak , Colorado. Times ind icated on eac h projection arc Universal T illle.

T ABLE 3. Satellite altitudes and ranges

Orbit Univel'- Altitude R ange sal time

km km

1... _______ _ { 9:06 886 2026 9:10 830 879 9:15 735 2216

II _________ _ { 10:44 854 2957 10 :48 785 2610 10:53 690 3127

IlL _______ { 9:57 619 2554

10 :01 581 1842 10:06 520 2580

IV __ _______ { 8:32 565 1900 8:36 505 710 8: 41 430 2280

I 10 :08 550 2610 V __________ i 10 :12 490 1800

10 :17 415 2600

I >

V)

.J_ WVl III ::IE

16

12

8

~ 5 4 o

ORBIT I SOUTH OF VAN NUY S

>­r .J ,...0 <> >

~0~6~'O~2~~OL4~--~0~6~----0~8~'-----1~0----9-' -OL6-' 12----

z 0 wo: ~ ~ 16 V):E

.J­

" ~ 0 12 V) >-

o w w > >;: 8 w<f U-' WW a: 0:

4

ORBIT n SOUTH OF VAN NUYS

91430 32 34

OR81T NORTH OF VAN NUYS

ORBIT NORTH

36 38

n OF VAN NUYS

40 42 44

?0~'~4~4-4~2~~4~4~----'4~6------4L8----~5~0~---10-.~4-4-' 5-2- L----~1~0~'5~0~30~~3~2--~~3~4~--~3~6~--~3f8~----4-'-0-----4-L2------4L4-----10-L5-0-· ~46 U NIVE RSAL TIME

Vl -' W ID_

16

12

8

ORBIT m SOUT H OF VAN NUY S

l) (I) 4 ~~ 95~8~5~0--~5~2~--~5~4~----~56~----5~8~--~9~5~9-0-0--

o

~O on

8 :x: >->­<!>-' zO w> 0:: 0 >- 0:: 4 Vl~

::IE

-' ,, -

ORB IT IJ[ SOUT H OF VAN NUYS

~ 0 O·L-____ ~ ______ _L ______ L_ ____ ~~--~~---

en >- 832·12 14 16 18 20 B'32'22

Ow w>

ORBIT 3t SOU TH OF VAN NUYS

~ ~ 8 w" o .J ww a: a:

4

O ~~I ____ ~I~ __ ~I~ __ ~'~ __ ~'~~ 10'1000 02 04 06 08 10'10'10

UNIVERSAL

100402 0 4

1015'02 TiME

54

04

06

56

(0 )

ORB IT m NORTH OF VAN NUY S

0 8

OR BIT Ill:

10 12

NORTH OF VAN NUYS

58 02

ORBIT :IZ: NORTH OF VAN NUYS

06 08 10 12

(b)

14 16 10041B

04 06

14 16

F J(1 URE 2. Satellite radio wave 8ignal stTeng/.h Teceived at the Van Nuys radio telescope faT pOTtions of the orbits where the range from the satellite to Van Nuys was the same south as 1w1·th of the radio telescope.

(a) Orbits I and II; (b) Orbits III, IV, ancl V.

265

4 . Photometric Data

Photometric obsernl,tions of the 6300 A emission were obtain ed continuously throughout the night of 12/ ] 3 November] 960. No observations were m ade during the night of 7/8 D ecember 1960. T ypical almucan kn sweeps are presented in figure 3 for th e November night at the approximate tim es of the satellite orbital passes. During the F ebruary nio'ht the pho tometric ob.servations were termin ated pl~or to the satellIte orbItal passes. However, data were obtamed up to 7:00 u. t. , during which time the 6300 A inten sity never exceeded 125 r ayleighs. 3 There was no evidence of 6300 A arcs up to 7:00 U.t. in contrast to the well defined arc structure prior to the t ime on 12/ ]3 :Kovember 1960. This is consisten t with the rel~t~ve m agnetic activity for the two nights; high actiVIty seems to be required for the arc formation.

In figure 3, evidence for three red arcs is shown for 9:10 u.t. and 10:55 U.t. Arcs A and B were in a

3 T'ile rayle igh is de fined as a photometri c u n i t where: 1 raylcigh = 105 photons/­Cll1 2 (col umn) sec,

2.

~ 20

'" W -' >-~ 16

'3 " ~ 12

6300 A AL M UC AN TAR SWEEP AT 0 9 ·10 U T 12/13 NOVEMBER, 196 0 ZE N ITH ANG L E 75 OEG

2'

V> 20 I Q w -' ~ 16 or o -'

'" ' 2

" >­>-in 8 z w >-z

o

6300 & ALMUCANTAR SWEEP AT 10:55 U T 12/13 NOVEMBER,1960 ZEN I TH ANGLE 7 5 DEG

I' 0 E

~BACKGROUND 1300 I w

AZI M UT H ANGLE IN DEGRE E S

MAG. N MAG N

Or:------+----~E w I--""-----="~~_+-----

FIGUlm 3.

9:10 UT 10 ·55 UT

Photometric data of the 6300 .11 emission observed at F1'itz P eak.

li pper: 75 degree almucantar s\\'ee ps fa r the times af arbits I and II with the th ree arcs indicated ; Lower: circle )11ap presentation of arc indications for rach almucantar sweep at the times of orbits I and II. Data pOints represent the positions of relative peak intensities seen in the upper portion of fi gure. Sa w­tooth appea rance of d ata d ue to hysteresis in the photometer drive Jll C'char- islll . The circle diam eter is 1325 kilometers.

state of rapid evolut ion during t il e period around local 11lidnight. Tntensity and position variations were observed between successive 15-min intervals particula rly in t lle nortbern regioll s. Th e observed position and intensities of arcs A and B ar e shown in figure 4. The intensities were averaged for the ea,st and west observations on t he 75-deg ftlmucantal' . ' Arc r had relat ively Wefik in tensit,y n,nclIllO\'ed onlv slightly sout h during this period . "

It can be seen hom figure 4 tlhl,L, at the time of orbit I , the arc systems were to the north of Fritz Peak and at low peftk intensiLies . Between orbi t I :,nd orbit I! the arcs oscilhl, ted through a n in tensity 111Cl'ease of almost an order of lllagl1l tu cl e and migrated fftr to the so uth from their previolls posi­tions. At the time of orbit TT, arcs 0, B , and A were approximately 5 deg so uth, 1 deg south , and 3.5 deg north oJ Fritz Peak respectively. The rehl,tive in tensity of arc A was approximately t wice that of arc B, and arc B was approxinlately four times the intensity of arc O.

It should be noted th at arcs A , B, alld O luwe been described as monochrolllatic 6300 A emissions. The 5577 . A photometric data for the Stl,me night indicate t hat a green arc wa,s in evidence. This arc remained in t he gener al region of reel arc A throughout the time spanned by orbits T and IT (ass1llning a 400-km alti tude of Juaximulll intensity) . The green arc increased in in tensity in the same manner ftS the reel arcs at 9:40 u. t. Th e red arc emissions were gen erally l. 7 times as in tense as the 5577 A emission.

The occurrence of green arcs contiguous with reel arcs is so rare that lit tle is known of their altit ude or spatial distribution . Therefore, the green arc of 12/13 November 1960, is not included in the analysis presented in this paper, but is left for further investigation.

5 . Analysis of the Data

Scin tillation of I'adio signals propagated through the ionosphere is associated with variations in the electron distribution in the ionosphere. It h as been suggested by King and F. E. Roach [1961]' that the excitation of 6300 A is related to the electron con­cen tration in the F region . A search for a conela­tion between the two phenomena is therefore in order.

Arcs A, B , and C were extended from the Fritz Peak meridian, along lines of constant invariant latitude,4 to the longitude of the satelli te. The ( extended arcs are shown in figure 5, and it can be seen that the propagation path of the satelli te signal must p ass t hrough the arcs. The Fritz P eak meridian positions of both arcs were determined from the data presen ted in figure 4, for the times of i orbits I and II. The roo t-mean-square (rms) value of the logarithmic power amplitud e of the signal ~

4 Actually th o arCS are morc closel y alined ta paralie1, af eanstant sheet paramo etor L t.h a.n to magnetic i~oclines. rr'he invariant latitude is de termined from

the shee t parameter L as: COS2/\ =); where: /\ is the invariant: latitude; R is t he

equa.torial r3 (1i :lS of the E ar th ; and L is t he equatoria l radius of the line of force .

266

12/13 NQVEMBER, I960

6 _

z .. Q

"' w 4

" " .. ~ 2

N 0-

. . ...

~ 0 FRITZ P EAK

z a

L ATITUD E

II I I I \ ARC B

, I : ~~~~~?~y

• I

- I I I - e \ I I I I

1 • I i-t

I I • •••

1200 ~ " 07'n:OO;;--0~B;-;;0;;;-0 ---'0;!;9-,;COO;;--;!;,O "'0 0-----,':-;;' O~O -,-;;';;-,,--J

UNIVERSAL TIME

II II ORB IT I ORBIT II

30

'" I 25~

g '" a

20:1

'"

'" 15~

'" z W 0-

IO ~

~ 5 ~

~ w ;:

0

'" " Ii' 2

N 0-

n:: 0 FRITZ PEAK ~ LATITUDE z a

z -2 a ;::

'" a "- -.

12/ 13 NOV EMBER . 1960

AR C A

, . . , • POSIT IO N " INTEN SI TY

/ .

.-4 i 1'4 "

I ~ • ' . ,

i I

I I I I I I I 4 /

. /1

/ \ I \

• i I '. . \ . \ . .~

07 00 0600 0900 1000 1100 UNiVERSAL TIME

II II ORBIT I ORBIT IT

1200

30

'" I '-"

25 g ~ 3 i

20

F I r. e RE 4. Position and intensity oj red al'CS A and B during the local earl!J momillg oj 13 November 1960.

' I' ll(' lillie of s.:lt .. ' llite sigll a l rC'ccptio n at \ 'a n :--J u ys is indicated for orhits l and I L. T h e' d::sk'd li'll's mc fo r clarity.

with respect to t he average r eceived signf. l str ength Wfl,S used fl,S a stfl, tistical index of scin tillation. Th e I'l llS v fl,lu es were computed over 3-sec periods fl, nd included fl, fix ed sfl,mple size of 31 data poin ts. Th e fl,verage signfl,l level was ob tftin ed by means of fl, visual fairing of the plo tted signal strength. A nO lllin fl,l 2-sec time consLant Wfl,S applied du ring t he fairing to remove, as much as possible, t he m anmade vari ations fl,J 'isiu g from m fl,nm.l telescope tm ckin g and oscillation of the satelli te.

The rms scin tillation data are presented fl,S a Jun c­tion of tim e in figure 6 for t he orbi ts on the three nights . It should be Doted t hat the minimum rms valu e that co uld be resolved wi th the Illfl,llu al da t fl, processin g techniques used was 0.1 db . For t he nigh t of 18/ ] 9 F ebruary 196 ] , the l'nlS valu e exceeded 0.5 db fl,t only one time wh en i t r eached 0.7 db . However , on the nights of 12/13 N ovember fl,nd 7/8 D ecember , the rms values reached several significan t peaks. R estricti ng the fl, nfl,lys is for the present to th e nigh t of 12/13 N ovemb er , let us eXfl,lltin e these peaks.

During orbit I the rillS index reached maxim a of 0.55 db fl,t 909 .0 u.t.; 0.49 db at 912 .2 u.t .; 1.40 db at 914 .7 u.t. and of ] .80 db a t 915.1 u. t. These hfl,ve been identified as peaks ell, CI , bl , and a t r espec­t iv ely. M axim a reached durin g orbi t II were 1.40 db at 1047 .5 u .t.; 0.85 db at 1049 .0 u. t .; 2.60 db at 1050.7 u.t .; fl,nd 3.95 db fl, t 1052.4 u. t. identified as peaks d2 , C2, b2, and az r espec tively in figure 6.

The propfl,gation paths conesponding to four of these m axim a are proj ec ted on the lati tude-longitude plot of figure 7. The extended arcs A, B , and Care also shown . The two-dim ension al proper ties of the plo t are expanded to th e three-dimension al features of the satelli te orbi t, as well as the propagation paths and the red arcs, by also proj ecting the loci of COI1-

stant al t itude for t he propag,.tion pa t h, as lh e satelli te passes the mcl io Lelescope. Shown in fi gure 7 is the locus al t it ude of 400-klll only.

It is immediately obvious for orbi t JT tha t Lli ere is a spf\.Ce t im e coinc idence between the 400-klll reel arcs A , B , and C and th e 400-kmlocus of t he prop fl,gl t­t ion paths Jor pefl,ks (~2 , bz, and C2 . F or orbi t J, a simil ar coincidence ex ists for arcs .A, B , and (l wi t il peaks aI, bI, and eI, bu t i t is d ifFlcul t to see sin ce the proj ect ions n efwly overlap and th erefore is not showll .

20

.06

r~~:::::~;t::::::: ARC A

AR C AR C

AR C C

FR I Tl PEAK, COLORADO

1 ~ 4'':-' --:-"'""o---:,,:-:-,---:,':-:'o,-----:,,:-:-,--::,,'""o---:,,c:c, ---:,"'"'o---:,-:o:o,,----"',C:-o 0:---'::-:'---' LO N GITUDE IN DEGREES w EST

FIG U RE 5. Geodetic lati tude and lon(li tude p1'ojechons 0/ red arcs A, B, and C, extended from the F'1'it z P eak meridian position along parallels of constant sheet parameter L .

Arc pOsitions were c1cterrni ncd for t he t imes of orbil s I and II, and arc ShO\nl ex­tended to inclu de the longitude of both orbital passes.

267

12/1 3 NOVEWBER. 196 0

" OR BIT I b, I I. \ . ' .

d , <,

I I . .. ..... . . . ' . .......... .... .. .' 0 · · . · · · 9 : 07 !>08 9 :09 9 :10 9:11 9 :12 9 :13 9: 14 9'15 9 :16

" I 12113 NOVEMBER, 1960

" ORBIT n 0 br w 3

'" ~ '. ~

d, z I .. ~ <,

" I t- I -0

~ · . · · z 0 · <;! 10' 44 040 10'46 10'47 10'4B 10'49 10'50 10:51 10'52 10'5 t-

71 8 DEeE M BER. 1960 j

:t . "

~ ORBIT lII.

u :-............. .. . "' ..... . .

· : · · · . .. r . ' .. , , I

~ 9:57 958 9:59 IODO 10:01 10:02 10:03 10:0 4 10:05 10:0 6

18/19 FEBRUARY, 1961 J

J ORBIT IT

j ~

" . · · . . . . . . · ! · · . .

• , B'41 8 :32 8 -33 8 '34 8-35 836 837 838 839 840

J 18 /1 9 FEBRUARY, 1961

j ORBIT Jr

. · · . . . . . . . . . . , · · , , , , , . , , 10:08 1009 10'10 10=11 10:12 10'13 10 ' 14 10'15 10' 16 10'i7

UN I VERSAL TIME

FIGURE 6. Satellite radio signal perlU1'balion~ observed at Van N1!YS , f or each of the five orbits discussed in this paper.

Expressed as the root-mean-square sta tistic of the received signal logarithmic power <l IllJJEtude sci ntillatioll. Significant maxilna are indicated by lower case letters with a numericnl subscript design a.ting the respective orbit.

r t-

'"

60

55

~ 50

"' i:l 45 '" C>

~

;: 40

~ ~ 35 ;:: :3 u 30 ;::

§ C> 25

20

15

EXTENDED ARC A

'ZlFRITZ PEAK

145 140 135 130 125 120 115 tlO 105 100 LONGI TUDE IN DEGREES WEST

FIG URE 7. Geodetic latitude and longitude projections of: Ex­tended red arcs A, B, and C; orbit II ; the l'adio wave propa­gation path ;'00 km /OC1!8; and the mdio waI'e scintillation maxima propagation paths :12 , b2, e2, and d 2•

'1"'0 avoid confusion , the propagatio n path loci and sc intillation 11ll:lxilllH paths for orbit I are not shown.

268

On the basis of these six space-time cOlTelations it can be stated that the mdio signal scintillation is probably associated with a perturbing characteristic accompanying the red arcs .

Lookin g at the rlJ1S data for the night of 7/8 December 1960, three small maxima of 0.73 , 0.70, and 0.63 are seen at 1001.5 u.t ., 1002.4 u.t. , and 1004.2 u. t. respectively. Since no photometric data are available for this night, it can only be conjectured that on e or two of these maxima may be associated with red arcs . This seems reasonable since, from table 2, it can be seen that considerable llHtgnetic activi ty did occur on 7/8 December; but not as intense as on 12/13 N oveillber. It is consistent that the radio scintillations for orbit III would be less for the deCl'eased m agnetic activity. This argument can be extended to the night of 18/19 February 1961. During t his night the magnetic K p index: never exceeded 3+ , and it could be expected that the radio scintillations would be near a minimum. As shown in flgure 6 for orbits IV and V, the rms v[tlue is con­sistently less thall 0.5 db .

6. Further Analysis of the Results

In the preceding section it was shown that radio scin tillation peaks a, b, and c correlated with red arcs A , B , and C respectively for both orbits I and II. The positions of these three arcs are shown in table 4 in terms of the L parameter. Established by McIlwain [1961]' L defines the equatorial crossing of the magnetic shell that intersects the 400 km al titude at the [trc invariant latitudes. Two addi­tional arcs have been included in this table which require clarification.

Arc Z can be discriminated in figure 3 north of arc A. It has relatively low intensity and its position is difficult to determine accurately due to its distance from Fritz Peak. However, the position of arc Z was estimated from the almucantar data, and is shown in table 4 to extend the data of this multiple arc system.

TABLE 4.- A.1'c positions in te1'111 S of the sheet parameter J,

Orbit I Orb it II

Arc L L I I'.L

z ____________ 0. 85 ________ 0. 45 _______ _ ______________ ________ U. 45 ________ 0 .62 IL ___________ 0.2U ________ 2.80 _______ _ ______________ ________ . 4:3 ________ .5.\ H _ _______ ____ 2.77 ________ 2. 2, _______ _ ______________ ________ . 7li ________ .3 1

~::::::::-::: I --- ~- ~~ - ::::: 2~ : --- ; ~ ;~ - :::::: ~~

In addition, arc D has been included as a probable arc. The existence of arc D cannot be verified from the photometric data since it is positioned beyond the field of view of the Fritz Peak photometers. However, it was inferred fronl radio scin t illation peaks dl and d2 , on the basis of the excellent correla­tions betweell the arcs and the peaks discussed in

l 'I'

t he preceding section. The posi Lioll of arc D was ob­tained from t he invari ant ItLt iLude aL t he time of the maximum rms indication.

Included in table 4 is a tab ubLio ll of the separation in terms of L , between the a rcs . A definitive study of multiple arcs in general is plan ned.

Let us now examine the properLies of the signals propagated through the red arcs . The scintilla tion peaks were no t sharp, but increased to t he maximum, and then decreased over a considerabl e portion of the orbits. Recalling that Tohmatsu and F. E. Roach [1962] have shown that the red arcs extend with decreasing in tensity at least 400 km north and south of the center, and from 300 km to 700 km in alti tude, the broad scintillation peaks are consistent with the association between arcs and peaks emerging from this study.

In figure 8 t he red arc intensity profile has been projected on a latit ude-longitude plot, util izing t he propagation pat h loci to provide the altitude di­mension . Arc A and B slant profiles for orbit II are shown and it can be seen that t hey overlap in t he middle. To avoid confusion , t he slant profile for arc C was no t shown. Similarly, t he slant pro-

t, files for orbit I have been examin ed in detail, where the radio signal passed t hrough the arc nominally perpendicular to the tube structure. Each of these slant profiles was numerically integrated to yield the photon flux coincident with t he propagation paths.

The integra tions were based on tL lll tLximum in­tensity Jor the longest path length throu gh the center of intensity. Tbe maximum intensity was assum ed to be equal to the arc emission intensity observed at Fritz P e,) k. The zen ith angles of the photometer

VAN NUYS CALIfORNIA

)41 4rn--,!ro---".----.t''',--'''''',----m"O,-----;,=-----"h:-----."Ir----;\.,.-----irn-~.._--' LONGl r uDE IN DEGREES WEST

FJ(1 UHE 8. Geodetic latitude and long1:tude projections of: Orbit 11; extended arcs A, B, and C; the mdio wave propagation 1Jath loci; the radio wave scintillation maxima pl'opagalion paths; and the slant intensity profiles of arcs A and B.

Tho relative iniensities within the arc are inclicated fo r the profile of arc BJ with l ho m aximum relative intensity of 1 shown at the intersection of the extended arc with the 400 kill locus of t.he propagation path coincid ent with sc intillation IllClX iJl1 UIll b2.

axis were nearly the same as those of the radio telescope axis, so that this assumption is sufficiently accurate to provide an order of magnitude value for the number of column pho tons.

The number of photons along the propagation paths was computed according to the relative in­tensities within an arc and the integrated path lengths. These data are shown in figure 9, plotted with the amplitude scintillation rms data. The scin tillation data in decibels had a bitseline which varied between 104 dbm and 100 dbm throughout the region of the arc perturbation.

Since the profiles of al'C A , B , and C extend in to eitch other, the total integra,ted photon flux includes the sum of the contributions of each arc. It ell n be seen in figure 9 that the scintillation power, or the perturbation of the radio signal, W,lS covllriant with t he integrated photon flux throughout the three regions of arc activity.

A slant profile was also in tegrated for arc D ;Lt its deduced orbit II position, and Lhe co rrelation between scintillation peitk d2 and photon flux is shown in figure 9. The in tensity of the arc was

<D o

z • o :; -' -' ;::: , ~

<D

"

w

" ~ :::;

907 90B

~ 1 .. ..

ORB I T 1

ARCS A 8 B ... . . FLUX\ ..

. . SCINTILLAT ION \ ..

PEAK :~ \ P\AK ' I • • •

.... .. ...... .... ....... ..

z

" " -' o u

u w ~

N

" o ~ X ~ - z

o o :I: ..

909 9 10 91 1 91 2 9 13 9 14 9"15 916 UNIVER SAL TI ME

ORBIT IT

(A RC 0) ......

. ..

FLUX -..

ARC C

.... ..... ... .

ARC A .. AR C B

............... '. • PEAK .a ~

PEAK bz ..

.,

~SC INTIL lATION

..

o o

" " -' ~

104 4 10'45 10 ' 46 10'47 10'48 10'49 10'50 10'51 1 ()I 52 106 3

UHI V E RSAL TIME

FrOUHE 9. Satellite mdio wave scintillation and 6300 A arc column photon flux as a fttnction of the time of orbit 1 and II mdio reception at l' an Nuys.

The 6300 A photon flux was integrated for columns th rough the arcs accordi ng to tho slant inten sity profiles coincident with the scin tillation maxima, and from peak intensit ies observed at }'ritz Pea k.

269

inferred from the reb tionshi p between in tegra ~ed'pho­ton flux and scintillation power for the peaks comClde~t with arcs A, B, and C. Scintillation peak dz, IS

quite sharply defined but the photon :flux profile obtained was typically extended 400-lan north and south of the arc center. This lack of profile correla­tion may be attribu table to a mor~ confin~d .in­tensity gradient within the arc. That IS , the effectlVe north'and south ellip ticity of the tube may have been reduced by as much as a factor of two.

7 . Discussion

The perturbation of VHF radio signals propa­gated thl'ough a red arc, has been shown to correlate with the number of 6300 A photons created along the propagation path: It. is , t.herefore, in teresting to examine this relatlOnshlp wIth respect to other observations that have shown correlation with red arc phenomena.

King and F , E. Roach [1961] have r~ported a correlation between a red arc and oblIque IOnosonde echoes. They found that t]~ e foFz lW1,ximum fre­quency was lower ~n ~be. oblIque echo than m tbe vertical echo. Thls mdlcated that the electron density in the arc WflS less than i~ the vertical direction. Referring to figure 4 of Kmg and F. E . Roach [1961], King [1962] .reports that .front the apparent spread in the oblIque return, It can .be concluded that the irregularities in el.ectron den~lt~T in the arc were twice as intense as JJ1 tbe vertICal direction. King points out that th~s spread is typical of returns from red arcs. ~t IS , therefore , not surprising to find a clear correIa tIOn between red arcs and VHF scin tilla tion.

To aid in the quantitative evaluation of the possible electron structure within the arcs in relation to the 6300 A photon :flux, the data fro~11 figure. 9 . are cross plotted in figure 10 so a.s to p~'0V:lde ~he scmtIlla­tion rJ11S as well as the relatlVe scm tillatIOn power as a function of integrated photon :flux. The relative scintillation power is determined from the log­arithmic relationship of the decibel ratio , where the reference power was set equal to one. The func-

m o

z o

3 ~ z ~ 2

EQUATION (I):

Srms • 5.32 X LOG F · 0.66

VALUE OF ABS CISSA IS THE NUt.4BEA TIMES 109

EOUAT ION (21 '

SSP' 0 ,86 X ~.53 Z ./ 2.62 ,. ~

2.4 :5 22~ 20~

" g 1.6 ~

2 l4 •

FIGU R E 10. Satellite radio wave scintillation nns and relative power as a junction oj the integrated arc photon flux .

The correlation is indicated by the dashed line and eqs (1) and (2) ex press this relationship.

tional dependence of scintilla tion rll1 S on the ar ' ~ntegrated photon :flux, as obtained from these data IS:

S Tms= 5.32 X log F- 0.66 (1)

where: S rms is the scintillation rms in decibels, F is ' the arc integrated photon flux in 109 photons/cm2 sec (column) ; (kilorayleighs). Equation (1 ) can also be expressed as the dependence of relative scin tillation power on the arc integrated ' photon :flux:

Ssp= 0.86 X FO.53

where: SSIl is the relative scintillation power, F is tbe arc integrated photon flux in

(2)

109 photons/cm2 sec (column); (kilorayleighs). From (1) and (2), it can be seen that the radio

wave scintillation is logarithmically proportional to the integrated photon :flux within the 6300 A arc. It may be speculated that the electron irregularities within the arc leading to scin tillations, together with the decrease in electron density are due to a flow of electrons constituting an electric current. Such a flow of electrons might have the double effect of (a) introducing irregularities into the ionospheric plasma through curren t instabilities, and (b) enhancing the excitation of the oxygen atoms because of the elec­tron "heftting" resulting from the curren t.

The magnetic control of such a current may arise from the outer radiation (Van Allen ) zone, as evi­denced by the detection of narrow intense zones of radiation at 1000 km over a 6300 A arc, as reported by O'Brien , Van Allen, F . E. Roach, and Gartlein [1960]. The peak of the outer radiation zone does seem to move equatorward to the vicinity of L = 3 during times of magnetic activity, in apparent agree­ment with the southward movement of arcs A and B. It has been suggested by Stolov [1962J that mid­latitude 6300 A arcs are associated with the Ez branch of the outer zone, which remains at relatively con­stant position , similar to arcs C and D.

8. Summary

Very high frequency radio signals, propagated fr~m an orbiting satellite t hrough a system of 6300 A ll11d­latitude arcs, were shown to be considerably per­turbed, as measured by the amplitude scintillation of the receiver signal. Scintillation maxima occurred in space-time coincidence with three red arcs for two successive orbital passes of the satelli te . At the time of these correlations, the red arcs measured several kilorayleighs in brightness, as aprobable by-product of the major magnetic storm that reached a K p of 9. during this period.

The radio scintillation rms was shown to be co­varian t with the intensity gradients of five arc posi­tions. The intensity gradients of a sixth arc position, below the optical horizon of the Fritz Peak photom­eter, but inferred from a sharp increase in scintillation nns, probably occurred over a smaller geometrical tube,

270

The relaLive scintillation power associated with the arcs ,,,a hown to be logarithmi cally proportional to the colulllnar photon flux observed photometrically. The low frequency spread and the lower JoFz in the red-arc oblique echo observed in ionogram data can

! be consid ered with the scin tillaLion data presented her e, to indicate that considern,ble electron irregu­lari ties exis t wi thin a 6300 A arc.

It is suggested that red n,rcs may be due to cur­rent systems which redis tribute electrons irregularly aJong the arc tube to cause the illcreased scintilla­tion , as well fiB increase the temperature of the electrons to cause the enhanced 6300 A emission.

, The magnetic control of such a current may arise from the Ez and E3 branches of th e outer radiation zone.

I thank Dr. F . E. Roach of the Natio nfll Bure,LlI of Stn,ndards, Boulder, Colorado, for mflking the 6300 A photom eter data available for this analysis, find for his vahlflble counsel and advice in this problem. The rRdio propagation data were obtained under the Lockheed l\Iissile and SpftCe Company con tract AF 04 (647)-558. WIRny people assisLed in th e Rcquisition

I of the rHdio datn" and 1 would like to acknowl edge in particulm' the work of V. Beelik, V. Cou nter, D. Klein , H. LOll ch , F. Munson, and A. Palentonio . The bal an ce of the preparation of this pn,per was un­supported; bu t I would like to thank the Con 11'01 Data Corporf1tion , Denver office, for assisting in the programing and for providing computer time durin g

\ this analysis; as well as Ball BroLhers R ese1ll'ch Corporation 1'01' aiel in the graphic presen tation of the information ilnd for public,ltion services .

67 :2865 G:: - 2

9. References

Barbier, D. (1958), L'activite aurorale aux bases la t itudes' Ann. Geophys . 14, 334.

King, G. A. M. (25 Oct. 1962), Private communication . King, G. A. M ., a nd F. E. Roach (1961), Relationship between

red a urora l a rcs and ionospheric recombination, J . Res. N BS 65D, (Radio Prop.) No. 2, 129- 135.

McIlwain , C. E. (1961), Co-ordina tes for mapping the distri­bu t ion of magnetically trapped p a rticles, J . Geophys. Res. 66, 3681- 369l.

Moore, J. G., a nd F . K. Odenkrantz (1961) , The heigh t a nd geographical position of t he red a uroral ar c of April 1- 2, 1960, J . Geop hys. Res. 66, 2102- 2104.

O'Brien, B. J ., J . A. Va n Allen, F . E . Roach , and C. W . Gart le in (1960), Gorre lation of a n a uroral a rc and a sub­visible mon ochromatic 6300 A a re with outer-zone radiation on November 28, 195\), J . Geophys. Ros. 65, 2759- 276.5.

Roach, F. E., a nd K Ma ro vich ( l!l 59), A mono chrom aLic low lat it ude a urora, J. Res. N BS 63D, (R.adio Prop. ) No . 3, 297- 301.

Roach, F . E ., and E. Ma ro vich (\960), Aurora of OcLober 22- 23, 1958, at R apid City, Sou th DakoLa, J. Res. NB~ 64D, (Radio Prop. ) No.2, 205- 209.

Roac h, F . E., J . G. Moore, E. C. Brune r, H . Cronin , and S. M . Silverman (1960), The height of maximum lum.in osity in an a urora l a rc, J . Geo phys. R es . 65, 3575.

R oach, F. E., D. Barb ie r, a nd R . A. Duncan (1963), Obse rva­t ion of a 6300 A a rc in France , Uni ted f::ltates, and Austra li a, Ann. Geophys. (in press) .

~to l ov, H . L. (1962), Bifurcation of t he outer Van All en belt and re laLccl a uroral phenome na, J . Geophys. Re~. 67, 4QL1- 406.

Tohmats Ll , '1'. , and F. E. Roach ( ID62), The morphology of mid- lati tude 6300 Angst rom arcs, J. Geophys. Res . 67, 1817- 1821.

(Paper 67D3- 261 )

271