P R O T O N C Y C L O T R O N ECH O
— a P h en om en on o f W ave-W ave and W ave-P article
In teraction s in T opside Sounding o f th e Ion osp h ere
-A C C E P T B D A D issertation Subm itted in P artial Fulfilment of the FACULTY OF GRADUATE STUDIES Requirem ents for th e Degree of
D O C T O R O F PH ILO SO PH Y
Dr- R.E. ITorita (D ept, of Physics and Astronom y), Supervisor
Dr. J.B, T atum (D ept, of Physics and Astronom y), D epartm ental M ember
Pr./)D.A. Van den Berg (Dept, o f Physics and Astronomy), D ep artm en tal M ember
— ; **--- ’— ;
---Or. G.G. Miller (D ept, of M athem atics and Statistics), O utside M em ber
Dr. M.B. Hocking (D ent. of C hem istry), O utside M ember
Dr. 'T. W atanabe (U niversity of B ritish Colum bia), E xternal Exam iner
(c) Guang-Ming Chen, 1993 University of V ictoria
All rights reserved. D issertation may not be reproduced in whole or in p art, by mimeograph or other means, w ithout the permission of the author.
by
Guang-Ming Chen
B.Sc., University of Science and Technology of C hina, 1963 M.Sc., University of A lberta, 1987
L»EAN in
UEAN in th e D epartm ent of Physics and A stronom y
We accept this dissertation as conforming to the required stan d ard
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Department, of Physics and Astronomy University of Victoria
Victoria, B.C., Canada V8W 3P6 ' Fax: (604)721-7715
Tel: (604)721-7727
September 16, 1993
Terra Scientific Publishing Company (TERRAFUB) 2-24-302 Midorigaoka, Meguro-ku, Tokyo 152, Japan Fax: 81-3-3718-4406
Tds 81-3-3718-4403
Dear Sir:
I have adopted a figure in my dir/sertation from C. T. Russell (1987), The magnetosphere, in The Solar Wind and ihe Earih, edited by S.-I. Akasofu and Y. Kamide, Chapter 5,, p.80, Figure 8. Could you kindly give a written permission as soon as possible? I am looking forward to hearing from you. Thank you.
Sincerely,
G.-M. Cheu
D ear Dr. Chen:
’ Thank you for your Fax. as above, i would like to perm it to use your proposed m aterial(s).
Y ours sincerely,
K eiji Oshida
P ublisher, TERRAPUD
D epartm ent of Physics and Astronomy U niversity of Victoria
Victoria, B.C., C anada V8W 3P6
A ugust 24, 1993
T h e Johns Hopkins University Press 701 W est 40th Street
B altim ore, M aryland 21211
D ear Sir:
I have adopted a figure in m y dissertation from A. T. Y. Lui (1987), R oad m ap to m agnetotail domains, in MagneLotail Physics, edited by A. T. Y. Lui, p. 5, P late 1.1. Could you kindly give a w ritten permission as soon as possible? I am looking forward to hearing from you. T hank you.
Sincerely,
G.-M. Chen
PERMISSION GRANTED:] ,
J t e l a n e W. S u l l i v a n , A o e i t i t a n t t o U i ^ i x i o t o v
Mghtv
& P e r j n i e s i o n o .D atef
■Jo-THE JOHNS HOPKINS UNIVERSITY PRESS
2 7 1 5 N. C toflos S treet SaltlPjora, MD 2 1 2 1 8 4 3 1 9
= 6 SEP, 1993
D epartm ent of Physics and Astronomy University of Victoria
V ictoria, B.C., C anada V8W 3P6
August 24, 1993
Gordon and Breach, Science Publishers Ltd. 41/42 W illiam IV Street
London W .0 .2
D ear Sir:
I have adopted a figure in m y dissertation from M. D. Papagiannis (1972), Space Physics and Space Astronomy, C hapter 2, p. 41, Figure 2.5-1. Could you kindly give a w ritten permission as soon as possible? I am looking forward to hearing from you. Thank you.
Sincerely,
G.-M. Chen
Permission granted in so fa r as
w", aro the 'copyright holder -and
p r o v id e d su itm ’b le r e f e r e n c e i s
g iv e n atnd 'm a te r ia l i s ress?l.
Publisher
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i 6 SEP. 1993
^ 2o.' ^ S k A < X A/.M . A P f W A DEPARTMENT o f e l e c t r i c a l e n g i n e e r i n g a n d e l e c t r o n i c s
I v n U U T
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f u r o - c h o , c h i k u s a - k u , n a g o y a 4 6 4 j a p a nUNIVERSITY
PHONE 052-781-5111 FACSIMILE 052-782-1992Septem ber 3, 1993
Mr. G.-M. Chen
D epartm ent of Physics and Astronomy University of V ictoria
V ictoria, B. C., C anada V8W 3P6
D ear Mr. Chen;
I received your le tte r of A ugust 24, 1993, I herewith perm it you to reproduce a figure in your dissertation from my paper: Excitation of electrostatic ion cyclotron waves by a pow er-m odulated transversely excited atm osphere (TEA) CO2 laser, Phys, Fluids, IJ<%
p.1155, Figure 1 (1993).
It should be noted th a t the copyright of the above paper has been transferred to the American In stitu te of Physics. Accordingly, it may be necessary to receive the permission of ‘She AIP to use th e figure in your dissertation.
I hope you get your Ph.D . successfully!
Sincerely yours,
Dr. G.-M. Chen
D epartm ent of Physics ancl Astronomy University of V ictoria
Victoria, B .C ., C anada VSW 3P6
September 23, 1993
American In stitu te of Physics 335 East 45th Street
New York, NY 10017-3483
D ear Sits:
I would like to notify you th a t I have adopted a figure in m y dissertation from th e article of Sasaki et al, (1993): E xcitation of electrostatic ion cyclotron waves by a pow er-m odulated transversely excited atm osphere (T E A ) C 0 2 laser, Phys, Fluids, B 5, p.1155, Figure 1. and Dr. Sasaki has kinndly given his permission for my use. T hank you very much.
Sincerely,
SUPERVISOR: PRO FESSO R ROBERT E. HO RITA
A b stra c t
Proton cyclotron echoes are phenom ena related to the proton cyclotron fre quency discovered On topside sounder swept-frequency ionograms from the Cana dian satellite Alouette II in 1969. Subsequent studies were also lim ited to the use of th e swept-frequency ionograms and devoted only to these so called regu lar proton cyclotron echoes. The regular proton cyclotron echoes occur on the swept-frequency ionograms at constant apparent ranges predom inantly at fre quencies below th e electron plasm a frequency /iv, and slightly above th e electron cyclotron frequency ///. In this dissertation over 2000 topside sounder iono gram s (b o th swept-frequency mode and fixed-frequency mode) obtained from th e A louette II, ISIS I and II satellites of th e A louette-lSlS program are used to investigate proton cyclotron echoes in detail.
Exam ination of the combined swept-frequency and fixed ionograms indicates th a t the proton cyclotron echoes are also observed on the fixed-frequency iono grams, In addition to some features, such as constant apparent ranges and higher order m ultiple echoes, which have been already observed on th e swept- frequency ionograms and also occur on the fixed-frequency ionograms, under some Conditions non-constant apparent ranges and modulations in intensity of th e proton cyclotron echoes on the fixed-frequency ionograms are observed.
Usually the proton cyclotron echoes on the fixed-frequency ionogram can be observed for a much longer tim e than on th e swept-frequency ionograms due to th e fixed sounding frequencies. A proton cyclotron echo can be under observation for several spin periods of the satellite if the plasm a param eters encountered by th e sounder are appropriate, The m odulation in intensity of the
proton cyclotron echo by antenna orientation is evident. In term s of analysis of th e combined swept-frequency and fixed-frequency ionograms, and th e satellite orbital param eters and spin axis a ttitu d e , effects on proton cyclotron echoes of an ten n a orientation with respect to th e e a rth ’s m agnetic field are exam ined. It is found th a t higher intensity and higher harmonics of proton cyclotron echoes occur when the sounding antenna is parallel to th e e a rth ’s m agnetic field.
A new class of proton cyclotron echoes was discovered, which occur on elec tro n plasm a resonances. The proton cyclotron echoes on th e / / / , n f n (n — 2, 3, 4), / q3 and f o have been observed- The first th re e are checked in m ore detail.
T h e proton cyclotron echoes observed on th e / / / , 4 ///, / q 3 and f o resonances
exhibit doublet:. on the 2 /// resonance triplex and on 3 f n resonance single while th e regular proton cyclotron echoes are always single. A frequency difference of about 5 — 10 Hz exists between subechoes in a doublet or triplex. T he regular proton cyclotron echo seems to correspond to th e first echo of th e double or trip le proton cyclotron echoes. No echo minus exists and m ost proton cyclotron echoes on th e electron plasm a resonances are observed at dip angles whose m ag nitudes are less than 8°, This new class of proton cyclotron echoes is attrib u te d to th e results of nonlinear interactions of ion and electron B ernstein waves or ion B ernstein waves and DKO mode electrom agnetic waves (for th e f n resonance). A bsorption phenom ena on th e 3/h, 4 /// and / q 3 resonance spikes near the pro
ton cyclotron period on swept-frequency ionograms are observed occasionally, b u t no t yet understood.
A theory based on nonlinear interaction of two waves is suggested to interpret proton cyclotron echoes. Many observational features of proton cyclotron echoes can be interpreted by this nonlinear interaction model of two waves.
Examiners:
Dr. R.E. Ilo rita (D ept, of Physics and Astronomy), Supervisor
Dr. J.B. T atu m (D ept, of Physics ancl Astronomy), D epartm ental Member
_______________________________ _______ _
Dr.JD.A. A'andenBerg (Dept, of Physics and A stronom y), D epartm ental M ember
Dr. G.G. M ilter (D ept, of M athem atics and Statistics), O utside M ember
Dr. M.B. Hocking (D epu of C hem istry), O utside M ember
C on ten ts
T itlep a g e
i
A b s tr a c t
ii
C ontents
v
List of Tables
viii
List of F igures
xix
Acknowledgem ents
xx
Dedication
xxi
C h a p te r X
I n tro d u c tio n
1
1.1 T h e-M ag n eto sp h ere . . ... 2
1.1.1 M agnetic Field Structures . ... 5
1.1.2 Plasm a Structures ... 7
H igh-Latitude B oundary Layer (H L B L )... 8
Low-Latitude B oundary Layer ( L L B L ) ... 8
Polar C usp ... 9
M agnetotail . ... 9
P la s m a s p h e r e ... 10
Iting C urrent ... io 1.1.3 Bow Shock and M agnetosheath ... 11
1.2 The Ionosphere ... . 12
1.2.1 S tructure of the I o n o s p h e r e ... 13
1.2.2 Layer Form ation of the Ionosphere . . . 15
1.2.3 Difference between the Ionosphere and th e M agnetosphere 16
C h a p te r 2
Topside Sounding o f t h e Ionosphere
18
2.1 G round Observations of the Io n o s p h e re ... 18Contents
,____________
_ _,______ „___ ____
Yl,2 .2 .1 Early Experim ents , •... .... . 22
2.2.2 A louette I (launched Septem ber 29, 1962) 23 2.2.3 Explorer XX (launched August 25, 1 9 6 4 ) ... , 24
2.2.4 A louette II (launched November 29, 1965) . ... 24
2.2.5 ISIS I (launched January 30, 1 9 6 9 ) ... 25
2.2.6 ISIS II (launched April 1, 1971) , . ... » , , , 26
2.2.7 Sum m ary ... 27
2,3 O bservations of P lasm a Resonances or Waves Phenom ena . , , . 27 C h a p t e r 3 T h e B a s ic T h e o r y o f W av e s in H ot, M a g n e to p la s m a 31 3.1 I n tr o d u c tio n , . 31 3.2 T h e Main E q u a t i o n s ... 32 3.2.1 M axwell’s E q u a t i o n s , . 32 3.2.2 T he Vlasov E q u a tio n ... 34 3.2.3 The Wave E q w t i o n ... 34
3.3 T h e Dispersion R elation of Waves in H ot M agnetoplasm a , , , , 35 3.3.1 Solution of th e Vlasov E q u a tio n ... 35
3.3.2 Calculations for M obility tensor M J" and Dielectric Tensor K ... , 39
3.3.3 Dispersion Relation of Plasm a Waves 41 3.3.4 Dispersion Relation of E lectrostatic Wave,-3 41 3.4 S u m m a r y ... . 43 C h a p t e r 4 O b s e r v a tio n s o f t h e P r o t o n C y c lo tro n E c h o e s o n F ix e d - F r e q u e n c y I o n o g r a m s 414 4.1 In tro d u ctio n ... , 44 4.2 O b serv atio n s. ... . 47 4.3 Sum m ary ... 53 C h a p t e r 5 E ffe c ts o n P r o t o n C y c lo tr o n E c h o e s o f A n te n n a O r ie n ta t io n w ith R e s p e c t t o t h e E a r t h ’s M a g n e tic F ie ld 58 5.1 Intro d u ctio n . , 58
5.2 E lectrom agnetic Wave in the I o n o s p h e r e ... 60
5.3 O bservations ... 64
5.4 C oordinate Systems ... , , . , ... 73
5.4.1 T errestrial Coordinate System ... 73
5.4.2 Celestial Coordinate S y s te m ... 73
5.4.3 Geomagnetic Coordinate System , . 74
Vll
5.6 S u m m a r y ... . ... 82
C h a p te r 6 P r o to n C y c lo tro n E ch o es on / g n R eso n a n ce s 87 6.1 In tr o d u c tio n ... 87
: 6.2 Electron B ernstein Waves ... 89
6.3 f q n R e s o n a n c e s ... 92
6.4 Observations of Proton Cyclotron Echoes a t /g „ Resonances . . 93
6.5 Sum m ary ... . 103 C h a p te r 7 P r o to n C y c lo tro n E c h o es on // / o r
n fa
R e so n a n c e s 106 7.1 In tr o d u c tio n ... 106 7.2 Observations of th e / « and i i f n R e s o n a n c e s ... 107 7.3 Full-wave Dispersion C u r v e s ... I l l 7.4 Explanations of the n f n and / / / Resonances ... 1147.5 Proton Cyclotron Echoes on the n f u and f u Resonances . . . . 118
7.6 Sum m ary ... 130
C h a p te r 8 G e n e ra tio n M ech an ism o f P r o to n C y c lo tro n E c h o es 133 8.1 In tr o d u c tio n ... 133
8.2 Analysis of th e Observational M eth o do lo g y ... 133
8.3 Ion Bernstein Waves ... 139
8.4 G eneration of Ion B ernstein Waves ... 143
8.5 M F Waves (A'm) 145
8.6 Discussion . . . . ... 146
C h a p te r 9
C o n c lu sio n s 152
L ist o f T ables
5.1 Some Experim ental and O rbital D ata of Two ISIS Satellites . . 65 5.2 P a rtia l O rbital D a ta of th e ISIS II Satellite for May 31, 1972 from
th e World M a p ... 86
6.1 D a ta of proton cyclotron echoes scaled from Figures 6,2 - 6.6 . . 102 6.2 D a ta of proton cyclotron echoes normalized by R regu . . . 102
L ist o f F igu res
1.1 N oon-m idnight m eridian cross-section of th e m agnetosphere. The
th e solar wind flow. The shocked flow, deflected, slowed and h eated , flows around the magnetopause in th e region called the m agnetosheath. A small portion of th e solar wind plasm a enters th e m agnetosphere through th e polar cusp. Some of this entering p lasm a forms a boundary layer called the plasm a m antle, and some of this drifts down to th e region of th e neutral point where it is accelerated to form the plasm a sheet. A fter R ussell\19S7). 3 1.2 A three-dim ensional of the magnotosphere, exhibiting the plasm a
dom ains w ithin. A fter Lui (1987)... ... 4 1.3 A typical daytim e profile of th e ionosphere and the plasm asphere.
Modified from Papagiannis (1972) . 14
4.1 ISIS I combined fixed-frequency (0.25 MHz) (left portion) and swept-frequency ionogram (right portion) illu stratin g proton cy clotron echoes on b oth m odes... ... 48
4.2 ISIS I Combined fixed-frequency (0.25 MHz) (left portion) and swept-frequency ionogram (right portion) illustrating proton cy clotron echoes on b o th modes and a second m ultiple echo associ ated w ith th e fundam ental echo on th e swept-frequency m ode. . 51
C o n ten ts x
4.3 ISIS I combined fixed-frequency (0,25 MHz) (left portion) and swept-frequency ionogram (right portion) illustrating proton cy clotron echoes on both modes and th e non-constant apparent range on th e fixed-frequency m ode . . . ... 52 4.4 ISIS I combined fixed-frequency (0.25 MHz) (left portion) and
swept-frequency ionogram (right portion) illustrating proton cy clotron echoes on both modes and th e non-constant apparent range on th e fixed-frequency mode. . ... 54 4.5 ISIS I combined fixed-frequency (0.25 MHz) (left portion) and
swept-frequency ionogram (right portion) illustrating fundam en ta l proton cyclotron echo and its second m ultiple echo, and their non-constant apparent ranges on, the fixed-frequency m ode. . . . 55 4.6 ISIS I combined fixed-frequency (0.25 MIIz) (left portion) and
swept-frequency ionogram (right portion) illustrating th e funda m ental proton cyclotron echo and its second m ultiple echo, and th eir non-constant apparent ranges on the fixed-frequency mode. 56
5.1 P olarization of th e four principal waves th a t propagate parallel and perpendicular to the e a rth ’s m agnetic field B ; E is th e electric field vector of th e electrom agnetic Wave; k is the propagation vector; e is the electron charge and stands for an electron. . . . 63 5.2 Satellite orbital p aram eters... , 66 5.3 ISIS II Spin Axis A ttitu d e in 1972 ... 68
5.4 An ISIS II combined swept-frequency and fixed-frequency iono gram illu stratin g m odulation of the proton cyclotron echoes in intensity by an ten n a orientation. The ionogram was recorded at 0309/43 U T on M ay 31, 1972 ... 69
Q o n U n t s ________________ x i
5.5 An ISIS II combined swept-frequency and fixed-frequency iono gram illustrating m odulation of the proton cyclotron echoes in intensity by antenna orientation. The ionogram was recorded at
0308/56 UT on May 31, 1972 ... 70 5.6 An ISIS II combined swept-frequency and fixed-frequency iono
gram illustrating m odulation of the proton cyclotron echoes in intensity' by an ten n a orientation. The ionogram was recorded at 0310/28 UT on May 31, 1972 ... 71 5.7 An ISIS II5 Combined swept-frequency and fixed-frequency iono
gram illustrating m odulation of the proton cyclotron echoes in
intensity by an ten n a orientation. The ionogram was recorded be tween 1530:13 and 1536:49 UT on May 31, 1972 ... 72 5.8 The positions of the sun and ISIS II satellite on th e celestial sphere
on May &i, 1972 0309/43 UT and the orientation of th e spin axis of th e satellite. ... 77 5.9 The positions of the sun and th e ISIS II satellite on th e celestial
sphere on May 31, 1972 1536/16 UT and the orientation of th e
spin axis of th e satellite... ... . 81 5.10 ISIS II combined swept-frequency and fixed-frequency ionogram
illustrating m odulation of the proton cyclotron echoes in inten sity by antenna orientation and showing occurrence of th e pro ton cyclotron echoes on both swept-frequency an d fixed-frequency soundings. T h e ionogram was recorded a t 0257/42 U T on May 31, 1972... ... 84
C o n ten ts xij
5.11 ISIS II combined swept-frequency an cl fixed-frequency ionogram illustrating m odulation of th e proton cyclotron echoes in inten sity by anten n a orientation and showing occurrence of the proton cyclotron echoes on fixed-frequency Sounding only. T h e ionogram was recorded at 0258/27 UT on May 31, 1972. ... 85
6.1 Electron B ernstein wave dispersion relation, Modified from Craw ford (1965). ..., . >... ..., , . , 94 6.2 A typical exam ple of proton cyclotron echoes which occur a t the
/ < 3 3 resonance on an ISIS II ionogram taken at. 1653:23 U T on
May 15, 1972, a t the ground telem etry station in Santiago (SNT, 33.10# , 70.7°VU) when the satellite was located at 9.6°5, 78,9° W geographic coordinates and 1363 km altitude, and the dip angle was 5°. T he / q3 resonance appears at frequencies from 1,61 to
1.69 MHz and extends from zero to about 700 km apparent range. T he proton cyclotron echoes which occur at the fqa resonance are double: th e weaker one occurs at about 641 km apparent range with th e stronger one a t 664 km apparent range. Also the regular proton cyclotron echo is shown a t an apparent range of about 626 km a t frequencies between the f n and f o resonances and double proton cyclotron echoes occur on the fixed-frequency (0.48 MHz) ionogram a t apparent ranges of about 634 km and 660 km respectively. ... 95 6.3 Proton cyclotron echoes a t th e fq z resonance were observed on
an ionogram obtained 71 s following the one shown in Figure 6.2. T he satellite was located a t 13.4°$, 79.0°VU geographic coordi
Contents x u i« • •
6.4 Proton cyclotron echoes a t th e /g a resonance on an ionogram taken ju st 13 s later after the one shown in Figure 6.2. The satellite was located at 10,5°S, 78.9°IF geographic coordinates and 1364 km altitude, and the dip angle was 3°. Proton cyclotron echoes at th e / q 3 resonance similar to the ones shown in Figure 6.2 are observed. However, th e regular proton cyclotron echo extends over a wide frequency range, startin g a t 0.1 MHz, across f a and
f o (i.e., f a \ ) resonances, and approaching 2f a (0.9 MHz), and a
stronger spur is attached to the f a resonance. . ... 98 6.5 Proton cyclotron echoes a t the / q 3 resonance on an ISIS II iono
gram taken at 1653:45 U T on May 18, 1972 a t th e telem etry ground station in Santiago when th e satellite was located a t 12.2°S', 82.3°iy geographic coordinates and 1363 km altitude, and the dip angle was —1°. The proton cyclotron echo on th e / q3 resonance in this instance is different from th e previous exam ples since the weaker echo now occurs a t about 671 km apparent range below th e stronger one a t about 647 km apparent range. T he regular
proton cyclotron echo is a t an apparent range of about 633 km at frequencies between f a and f a resonances. . ... 100
C o n te n ts x i v
6.6 P roton cyclotron echoes located at b o th the fqa resonance and 4 /// resonance on an ionogram obtained 68 s following the one shown in Figure 6.5. T h e satellite was located a t 15.8°S, 82,5° IV geographic coordinates, and 1364 km altitude, and th e dip angle was —7°. B oth proton cyclotron echoes at the / q3 resonance and
th e 4 /// resonance are double. For th e proton cyclotron echoes at th e 4f n resonance, the stronger echo occurs at about 636 km ap p aren t range with th e weaker one a t about 657 km apparent range; for th e proton cyclotron echoes a t the fqa resonance, th e stronger echo has an apparent range of about 648 km with the
weaker one at an apparent range of ab o u t 672 km. T h e apparent ranges of th e corresponding proton cyclotron echoes a t the resonance are larger th an th e ones a t the 4f n resonance. T he stronger echoes at bo th the Jq3 resonance and the i f a resonance
have sm aller apparent ranges than the weaker ones, respectively. T he regular proton cyclotron echo occurs at an apparent range of ab o u t 636 km a t frequencies frorri /// to //y, and seems to link to th e sp u r... 101 6.7 O bserved f q n resonances w ith proton cyclotron echoes displayed
on a Ham elin diagram . The ordinate determ ines the decimal p art
fq n / f h r while its integer p a rt is determ ined by the num ber n of
each curve. T h e abscissa shows the ratio of //v //w - T h e Iiam elin diagram is modified from Belmont (1981). . ... . , . . 104
Contents
____________ _____ .__________________
xv
7.1 The high-resolution portion of an A louette II ionogram recorded »t th e Q uito Telemetry Station on M ay 4, 1967 (1214:22 UT; 25.2°5, 65.6°W’, 2612 km in altitude). T he heavy vertical traces* which are due to electrostatic waves of low group velocity in the Vicinity of th e sounder, are identified a t the top of th e ionogram; the weaker non vertical traces are due to the ionospheric reflection of electrom agnetic waves radiated by the sounder, A fter Benson
(1977)... • ... 108 7.2 An Explorer XX fixed-frequency ionogram showing th e m odula
tion of the fringe p a tte rn and antenna orientation effects at. the
3fir resonance (at -f 70° the antenna is parallel to the, e a rth ’s
m agnetic field and at —20°, perpendicular). A fter C alvert and
Contents xv i
7.3 Normalized dispersion curves for th e case where th e electron th er m al m otions are included, (but collisions neglected) with an am bient m agnetic field. T h e angular frequency is normalized by
th e angular electron cyclotron frequency and th e wave num ber is norm alized by l / R w here R — (« T /m e)1/,2/w c is the electron cyclotron radius («, IT, and m e are B oltzm ann’s constant, the electron tem p eratu re, and the electron mass, respectively). The electrom agnetic ordinary mode is designated by “0 ” while the ex traordinary m ode is designed by “X” (for the X branch) and “Z” (for the Z branch). The curves are presented for different angles
0 of k relative to B except for the electrostatic Bernstein modes
near th e harm onics of hujh which are presented for 0 = 90°. D ot ted area between k R = 9 x 10“ 2 and 4 X 10"1, where k = k^/sinO, indicates th a t th e waves propagating in oblique directions are sub
je c t to dam ping. The diagram corresponds to th e plasm a condi tions Jh/ Ih ^ 1*6- After Oya (1971b)..., . . . , 113 7.4 ISIS II ionogram obtained a t 1734:08 UT on May 4,1972, showing
th e proton cyclotron echo on th e 4/7/ resonance at an apparent range of about 650 km. The d a ta were collected a t th e Quito (QUI) ground station. Also observed are the regular proton cy clotron echoes w ith harmonics1 on the fixed frequency (0.25 MHz) ionogram on th e left and also on th e swept frequency portion a t frequencies above and below the electron cyclotron frequency ///. A fter Chen and H orita (1991). . . . . . . . ... 120
Contents xv ii
7.5 Proton cyclotron echo on th e 4 /// resonance on an ISIS II iono gram obtained a t 1734:53 U T on May 4, 1972. The d a ta were also collected at th e Quito (QUI) ground station. The regular proton cyclotron echoes are barely visible on th e fixed frequency ionogram and below th e / / / resonance on th e swept frequency portion. After Chen and Horita (1991)... 121 7.6 Proton cyclotron echo on th e 4fur resonance spike. The echo is
actually below the resonance spike a t an apparent range of about 1150 km. Note the regular proton cyclotron echo ju st above f n has some curvature. The ground station where th e d a ta were collected Was Ouagadougou (ODG). A fter Chen and H orita (1991), 123 7.7 Proton cyclotron echo on th e 3f n resonance spike at an apparent
range of about 550 km . The d a ta were collected at th e Santiago (SNT) ground station, After Chen and H orita (1991). . . . 124 7.8 ISIS I ionogram obtained a t 0916:41 U T on February 25, 1969,
showing th e proton cyclotron echo on the 3f n resonance spike. T h e echo is single w ith apparent ranges of about 771 km. T he regular proton cyclotron echo occurred a t frequencies between th e / / / and frj resonance spikes w ith an apparent range of about 787 ku;, exhibits curvature. The d a ta of this ionogram were collected
a t the Ouagadougou (ODG) ground station, 126
7.9 ISIS I ionogram obtained at 1713:03 U T on April 11, 1969, show ing the proton cyclotron echo on the 3 resonance spike. T he echo is single with apparent ranges of about 964 k~n. The regu lar proton cy clotron echo occurred at frequencies between th e f y and f n resonance spikes with an apparent range of about 952 km exhibits curvature. T h e d a ta of this ionogram were collected a t th e Ouagadougou (ODG) ground statio n ... 127
Contents x v iii
7.10 ISIS I ionogram obtained a t 1615:57 U T on April 23* 1969, show ing th e proton cyclotron echo on th e 2 /// resonance spike. The echo is triplex with apparent ranges of about 1316 km, 1345 km and 1374 km respectively. T he regular proton cyclotron echo just above the / / ; resonance spike with an apparent range of about 1331 km has some curvature. A spur related to the proton cy clotron echoes is. attached to the /jy resonance spike, The d a ta of this ionogram were collected a t th e Ouagadougou (ODG) ground s ta tio n ... , . 128 7.11 ISIS I ionogram obtained a t 1615:03 U T on April 23, 1969, show
ing th e proton cyclotron echo on th e 2 /« resonance spike. The d a ta were also collected at th e Ouagadougou (ODG) ground station, 129 7.12 ISIS II swept-frequency ionogram showing th e absorption on the
3/h spike. T h e d a ta were collected a t the Santiago (SNT) ground
station. ... , 131
7.13 ISIS I swept-frequency ionogram showing th e absorption on the 4Ih spike. T h e d a ta were collected at the Ouagadougou (ODG)
ground statio n ... 132
8.1 Exam ple of th e proton cyclotron echoes on both an ISIS I iono gram and an A scan observed at 0128:39 UT on February 27,1973 a,t K ashim a (KSH) ground telem etry statio n ... 135 8.2 G raphical representation of equally spaced pulse sequences and
th e ir Fourier transform s. Modified from Brigham (1974)... 137 8.3 Dispersion curves for pure ion B ernstein waves and neutralized
ion B ernstein waves for the same plasm a conditions: ojpi = 3wcl' and Te = T; and Tj| = IT . — (u^,- -f u ^ ) 1/ 2 is the lowest hybrid
8.4 Dispersion curves of neutralized ion Bernstein waves for different values of Te/T{, From Sasaki ei al. (1993). . . . 148 8.5 ISIS II Ionogram obtained on O ctober 26, 1971, a t 0659:30 UT
when the sounder is operating a t the fixed frequency of 1.95 MHz while th e receiver is swept from 0.1 to 20 MHz. Here f f refers to the 3-sec period when the receiver rem ains tun ed to th e fixed frequency. The reflection trace is visible when th e receiver fre quency is about equal to the tra n sm itte r frequency. From Palm er and B arrington (1973)... . 149 8.6 Sketch showing an electron electrostatic wave and a bunched pro
ton concentration produced by the sounding R F pulse a t tim e
t = 0 both m eeting a proton gyroperiod later a t / = Tp and being
involved in wave-particle interaction. These electron electrostatic waves presum ably receive energy from th e protons and are am pli fied, leading to th e 3 /// or 4f u proton cyclotron echoes observed at tim e / = 2p-f-A/ (not shown), while these electron electrostatic waves which missed the bunched proton concentration by passing through to the antenna before or after the protons had arrived produce the norm al resonance spike above and below th e echo.
XX
A ck n ow led gem en ts
I wish to express my sincere thanks to Professor R obert E. H orita for suggesting th is interesting topic for my dissertation and providing guidance and assistance. I value greatly his patience, support and encouragem ent throughout the course of this study.
I would like to th an k D. B. Muldrew of the Communications Research Centre, O ttaw a, for a com m ent in his communication to Dr. H orita which stim ulated us to studying effects on proton cyclotron echoes of an ten n a orientation with respect to th e e a rth ’s m agnetic field.
My th an k s are due to th e staff of th e D epartm ent of Physics and A stron omy, University of Victoria, for many instances of kind service and especially to M r. C. R. C ard, who spent much tim e scaling and labeling th e ionograms and provided th e excellent figures in this dissertation.
I thank th e W orld D ata C enter A for Rockets and Satellites a t the G oddard Space Flight Center, USA, and th e Communications Research C entre in O ttaw a, C anada, for providing the microfilmed A louette II and ISIS I and II satellite ionograms and World m aps for this research.
During th e course of this study, I was supported by the G raduate Teaching A ssistantship from th e D epartm ent of Physics and Astronomy, University of V ictoria, by th e U niversity of V ictoria Fellowship and by the G raduate Research A ssistantship from th e N atural Sciences and Engineering Research Council of C anada through research grants to Dr. R. E. Horita.
D ed ica tio n
This thesi$ is dedicated to
Chen Xuduan
Wang Deying
Chen Yufei
1
C h ap ter 1
In tro d u ctio n
A large variety of plasma-wave phenom ena in th e m agnetosphere and the iono sphere have been detected by ground-based facilities and by receivers on board spacecraft. The te rm ‘plasm a wave’ is used to denote all .,'aves which are generated in th e m agnetospheric and ionospheric plasm a or which have their wave characteristics significantly modified through propagation in th e m agneto
sphere and the ionosphere. These waves may be electrom agnetic or electrostatic. N aturally-occurring waves are generated by th e conversion of free energy w ithin plasm a in to wave energy through a Variety of wave-particle interaction processes. In turn, these waves may interact w ith the particles and modify the distribu
tio n function characteristic of the particle populations w ithin th e plasma. Thus w ave-particle interactions are very im p o rtan t in the m agnetosphere and the ionosphere and are believed to be responsible for the generation of waves, the pitch angle distribution and th e local acceleration of th e charged particles, the energy tra n sp o rt between particles and waves. Some electrom agnetic waves can propagate far enough from th eir source region so th at th eir observation provides inform ation on th e rem ote source region.
Besides th e n a tu ra l plasm a waves, plasm a waves are also stim ulated artifi cially by radio waves tran sm itted from spacecraft or from ground stations, and also by electron or ion beam s injected from sounding rockets or spacecraft. For exam ple, th e plasm a resonances observed in topside sounding o f th e ionosphere are explained to be a ttrib u te d to electrostatic waves stim ulated by the sounder pulse. T h e proton cyclotron echo observed in topside sounding of the ionosphere
1.1
The Magnetosphere2
is not quite understood yet. This dissertation is devoted to its investigation. In view of the above discussion, th e m agnetosphere and th e ionosphere are excellent laboratories for studying plasm a waves. The events we will deal w ith (proton cyclotron echoes and topside-sounder resonances) tak e place in this lab oratory. T h u s in this chapter we introduce our laboratory - the m agnetosphere and the ionosphere.
1.1
T he M a g n eto sp h ere
A m agnetosphere m ay be defined as a region in space created by th e interac tion between the intrinsic m agnetic field or ionized atm osphere of a celestial
body and a flowing m agnetized plasm a. Of th e eight p lanets visited by space craft, four (Merf/ury, E arth, Jup iter and Saturn) are known to have internally- generated m agnetic fields (Bagenal, 1985). Therefore, th e m agnetospheres for them are formed by th e outflowing plasm a from th e sun, th e solar wind, in te r acting with their intrinsic m agnetic fields. However, there are several objects (such as com ets, Venus, Mars and so on) in the solar system which are not m ag netized but nevertheless strongly interact with th e solar wind. So th e definition of a m agnetosphere is stretched to include them . Here we consider only th e interaction of the e a r th ’s m agnetic field with th e solar wind and therefore the m agnetosphere is referred to th e e a rth ’s magnetosphere. T h e e a rth ’s m agneto sphere has been surveyed in m ore detail than all other magnetospheres.
The m agnetosphere is th a t region of space determ ined by th e interaction of th e solar wind with th e e a rth ’s dipole-like m agnetic field. It extends to about 10 - 12 e arth radii (rjs ~ 6380 km) in th e sunward direction and to more th a n 1000 earth radii in th e anti-sunward direction from th e center of th e earth. It is shown schem atically in Figures 1.1 and 1.2. Figure 1.1 shows a noon-m idnight m eridian cross-section of th e m agnetosphere and Figure 1.2 a three-dim ensional
1.1
iVie
Magnetosphere 3 M a g n e t o p a u s e I n t e r p l a n e t a r y Medium /Polar
Cusp(North Lobe)
Neutral
Kigsfpa.
Solar WindPoint
N e u t r a l S h e e t Magnefotal) Bow S ho c k (S out h Lobe) P l a s m a s p h e r e M ag ne fo s he at hFigure 1.1: N oon-m idnight meridian cross-section of the magnetosphere. The solar wind flows from left and the bow shock stands in front of the solar wind flow. T h e shocked flow, deflected, slowed and heated, flows around th e magne topause in th e region called the m agnetosheath. A small portion of the solar wind plasm a enters th e m agnetosphere through, the polar cusp. Some of this entering plasm a forms a boundary layer called th e plasm a m antle, and some of this drifts down to th e region of the neutral point where it is accelerated to form th e plasm a sheet. A fter Russell (19S7).
1.1 The Magnetosphere
B ow shock
4 i> i "
pXo ^ Plasma, mantle v V%v .f $ M :
s i ’mM * $ $ $ $ $ ‘t&yr.*3, B o u n d a r y x« .« p la s m a /■pf\ ■-.'?I <ra SB Magnetic
;* M a a sn e ^ se
Ions from cleft ion fountain D etail o f g ra y area a b o v e ! S o lar e le c t r o n s & .' ■ s'* "■ .. ‘ W« . . . . I kVv^ .« L o c a liz e d t u r b u l e n c e region M agnetic island B o u n d a r y p la s m a s h e e t C e n tr a l p la s m a s h e e tFigure 1.2: A three-dim ensional of th e m agnetosphere, exhibiting th e plasm a domains w ithin. After Lui (19S7).
1.1
The Magnetosphere5
drawing of the m agnetosphere. T h e nam e “m agnetosphere” was introduced by Gold (1959), B ut under th e nam e “geom agnetic cavity” , it was discussed by C hapm an and Ferraro (1931b), and th e existence of such a cavity was anticipated by Birkeland (1908).
1.1.1 M ag n etic F ield S tru c tu re s
T h e m agnetosphere is bounded by the m agnetopause (see Figures 1.1 and 1.2), T h e location and th e shape of th e m agnetopause are determ ined prim arily by th e condition of pressure balance: th e total pressures (P lasm a plus m agnetic field) ju st outside and inside of th e m agnetopause should be equal, Thus we m ay have
+ f a = P m + 2^ ( U )
where subscripts sw and gm denote th e solar wind and the geom agnetic field. T h e pressure p,w exerted on th e m agnetopause depends on bo th the dynam ic pressure 2n m v 2cos2xp and th e therm al pressure n k T in the solar wind, Here
xj) is th e angle between the local norm al to th e m agnetopause and upstream
solar wind flow direction. Since the dynam ic pressure is ab o u t two orders of m ag n itu d e greater th a n th e therm al pressure, we may assume th a t
psiu = 2 n m v 2cos2xp (1,2)
Since p3W > B 2sw/2 p 0 and pgm < B 2gm/ 2//0, We obtain
B 2
2 n m v 2cos2xl/> = (1.3)
A t the geom agnetic equator, .
Bgm
where r e is th e equatorial distance of th e magnetopause from th e e a rth ’s center,
1.1
The Magnetosphere6
geomagnetic equator. However, B gm has aproxim ately twice its value due to the compression of th e solar wind so th a t many m ore m agnetic field lines is piled up near th e magnetopause. Also we assume t/; = 0 a t th e geomagnetic equator.
T hen combining (1.3) and (1.4) yields
MM
\2(ionmv2J Take v =300 km/s
m= 1.673 X 10"27 kg
n = 2 x 10°m"3
Bo= 0.3 X lO"4 tesla
p 0= 4tt X 10“7 henry/m
thus we obtain r e ft* 10r£ (1.6)This result is in good agreem ent w ith observations. T he geocentric average distance to th e subsolar point of th e magnetopause is 10 - 11 r# , b u t occasional extrem e excursions are reached as close as 6.6 r# or as far as 18 r # depending' on the solar wind dynam ic pressure 2 n m v 2.
On th e night side, the m agnetic field lines are stretched out along th e solar wind direction to form th e m agnetotail. Thus behind the e arth the m agne topause becomes a cylindrical surface. The radius of th e m agnetotail is about 40 7'e and rem ains th e sam e for a t least 100 r# . The m agnetotail extends for m ore than 1000 in space.
In the central p a rt of th e m agnetotail, close to th e anti-solar line, th e di rection' of th e m agnetic field reverses in a short distance along th e north-south direction. T he field lines in th e northern hem isphere are directed tow ards the e arth and th e ones in the southern hem isphere are directed away from th e earth.
1.1
The Magnetosphere 7T h e re is therefore a narrow zone w ith zero field. This neutral layer has a thick ness of about 1,000 km and is called the neutral sheet.
A t the interface between the day and night sides of th® m agnetosphere, there a re two regions, one no rth and one south, of th e m agnetic field lines with a funnel-shaped geometry, known as the clefts or polar cusps, T h e neutral points ex ist in th e polar cusps. The low m agnetic fields in these regions allow some p en etratio n of th e solar wind. T h e outer parts of th e m agnetotail, which include th e field lines th a t originate in th e polar caps are known as th e lobes.
Com plex m agnetic field structures, such as flux ropes and m agnetic islands, are occasionally observed. Flux ropes are associated with strong currents along
th e m agn etic field lines, giving rise to th e field lines spiraling like the fibers of a rope. M agnetic islands, in which the entrapped m agnetic field lines form closed loops, can be considered as a degenerate case of m agnetic flux ropes.
1 .1 .,2 P la sm a S tru c tu re s
W ith respect to plasm a, the m agnetopause behaves in a similar way as with resp ect to th e m agnetic field lines; it acts as a b arrier and forces th e solar wind p la sm a to flow around the magnetosphere. Thus th e m agnetopause may be re gard ed as a boundary th a t separates distinctly difFerent regions - the solar wind
p la sm a region and th e m agnetospheric plasm a region. T he average thickness of th e m agnetopause is about 600 - 800 km (Lundin, 1988). Interior to the m agnetopause lies th e boundary layer or plasm a boundary layer, The boundary layer is the m ajo r region of solar wind mass, energy and m om entum transfer into th e m agnetosphere (Burch, 1987; Lundin, 1988). Its characteristic feature is a m ix tu re of m agnetosheath and m agnetosphere plasm as flowing tailw ard. From a topological and phenomenological point of view the boundary layer may be
1.1
The Magnetosphere 8low -latitude boundary layer (LLBL). The HLBL and LLBL are topologically interfaced w ith the polar cusp.
H ig h -L a titu d e B o u n d ary Layer (H LBL)
T h e HLBL or the plasm a m antle is topologically th e boundary region connected to th e dayside polar cap ju st poleward of th e cusp. It is formed by the plasm a of predom inantly m agnetosheath origin flowing tailw ard along th e geomagnetic field lines a t a speed slightly less than the exterior m agnetosheath plasm a flow; T h e HLBL plays an im p o rtan t role in energy transfer. The solar wind mass and energy are transferred into th e inner m agnetosphere from it. The m agnetosheath p lasm a is also believed to be brought to th e central plasm a sheet from the HLBL (Cowley, 1980).
L o w -L atitu d e B o u n d a ry Layer (LLBL)
T h e LLBL is th e low -latitude portion of th e boundary layer which extends all th e way from local noon to far downtaij. It was also suggested by E astm an et al. (1976) th a t th e LLBL is the m ajor site of th e solar wind energy and m om entum transfer into th e magnetosphere. The plasm a flow in the sunward section of th e LLBL also has a considerable cross-field flow com ponent, as opposed to th e HLBL where th e plasm a flow is preferentially field aligned. T he LLBL is also believed to th e m ain source region for solar wind plasm a en try into the p lasm a sheet (E astm an et al., 1985). M agnetosheath plasm a would enter into th e central plasm a sheet along the flank of th e m agnetotail. This contrasts with th e H1BL where m agnetosheath plasm a enters th e central plasm a sheet through th e tail lobe.
1.1
The Magnetosphere0
P o la r C usp
A t th e m agnetic polar cusp, m agnetosheath plasm a extends So deep into th e m agnetosphere th a t the nam e “boundary layer” is not appropriate: The en tire funnel: of the field lines, down to th e upper atm osphere, is filled w ith m agnetosheath-like plasma. This region is referred to by some as the “polar cusp” or by others as the “m agnetospheric cleft” . Its outm ost p a rt, near the
m agnetopause, is called the “entry layer” , which is topologically connected to th e equatorw ard edge of the dayside m agnetic polar cusp. C haracteristic of the en try layer is a plasm a density almost as high as in th e exterior m agnetosheath b u t generally lacking the strong anti-sunw ard plasm a flow. It was believed to be th e m ain entry region of th e solar wind into th e magnetosphere.
M a g n e to ta il
A large portion of th e m agnetotail consists of two low plasm a density regions known as th e tail lobes, one in th e northern half of the m agnetotail and th e o th er in th e southern half. Particles populating this region include ions from th e polar cusp, ions from th e polar region a t low altitudes, and electrons from th e solar wind entered into th e tail lobe on open field lines.
Bordering the ta il lobe a t its lower latitud e interface is the plasm a-sheet boundary layer. T his region is often the m ost dynam ic plasm a domain of the m agnetotail, where ion beams coming from th e earth and from further down stream are often found. It is also where a lot of plasm a wave activities ate de tected , M agnetic field-aligned currents, flowing toward or away from the earth are often observed, These activities gradually decrease as one approaches the central plasm a sheet. The plasm a sheet as whole (i.e., the central plasm a sheet and th e plasm a-sheet boundary layer) is thin n est near the m idnight region and is ab o u t tw ice as thick near th e flanks of the m agnetotail. The plasm a energy
1.1
The Magnetosphere10
density is com parable to the m agnetic field energy density in th e plasm a-sheet
region,
In the middle of this reservoir of particles in th e plasm a sheet lies the neutral sheet, where the magnetic field is very weak (a few nanoteslas).
P la sm asp h ere
For all th e plasm a structures discussed so far, th e supplier of th e m ajor p a rt of th e plasm a population is ultim ately th e solar wind. It, however, is not th e sole source. A smaller b u t significant p art of th e plasm a sheet population comes from th e e a rth ’s ionosphere. There is also evidence for an ionospheric contribution to th e plasm a m antle (H ultqvist, 1982),
A region populated alm ost entirely by the plasm a from the ionosphere is the plasm asphere, located deep w ithin the inner m agnetosphere; it extends from the ionosphere outward to a relatively sh rrp boundary (called th e plasm apause), whose location is somewhat variable b u t typically coincides w ith a shell of m ag n etic fieid lines crossing the equator a t distance from 4 to 6 r# . The plasm a in this region is relatively dense and cold, with num ber densities ranging from > 10lo/m 3 ju st above the top of the ionosphere to values of th e order of 108/ m 3 near the plasm apause, with therm al energies of th e order of a few eV or less.
R in g C u rre n t
Finally, th e complex region generally nam ed the ring current forms th e interface between th e plasm asphere on th e inside and th e plasm a sheet on outside. A m ajo r source of plasm a for th e ring current is inward tran sp o rt of th e plasm a from the plasm a sheet, including both its solar wind and its ionosphere-source com ponents. Significant electric currents exist in this region. These currents
1.1
The Magnetosphere11
a ttrib u te d (C hapm an and Ferraro, 1931) to a “ring cu rren t” in space.
1.1.3 Bow Shock and M ag n eto sh eath
T h e bow shock and th e m agnetosheath lie to th e outside of th e m agnetopause b u t they are very im po rtan t and very closely related to the m agnetosphere.
In considering a flow at supersonic uniform velocity past an obstacle, no signal can oe propagated upstream . T h e flow ahead of th e obstacle has no way of knowing th a t th e obstacle exists, and therefore can not be modified by the presence of th e obstacle. However, th e flow can not reach the obstacle with the sam e uniform supersonic velocity because the boundary condition for th e mass flow requires th a t a t the surface of the obstacle th e normal com ponent of th e flow velocity should vanish. Hence the form ation of a “bow wave” is needed ahead of th e obstacle. T he bow wave is m athem atically described as a surface across which th e norm al com ponent of th e flow velocity, as well as th e density, the pressure and th e tem p eratu re, undergo discontinuous changes. Physically, the transitio n occurs though a layer of finite thickness. Conservation equations for m ass, m om entum , and energy are applied to determ ine th e velocity, th e density, th e pressure and th e tem p eratu re on one side of the bow wave in term s of these quantities on the other side. As the flow crosses th e bow wave, its velocity suddenly decreases while its tem p eratu re and density increase. The result is th a t th e velocity becomes subsonic, and may receive “inform ation” ab o u t the presence of th e obstacle.
T he above idea m ay be applied when th e supersonic solar wind m eets an obstacle, th e m agnetopause, in its path. Therefore, a bow wave (usually called th e bow shock) should be formed ahead of the m agnetopause. B u t more careful analysis reveals difficulties with th e above idea. All shocks m ust be dissipative
1.2
The Ionosphere12
of collisions. However, in th e solar wind collisions are often negligible, so th a t th e bow shock can not take th e form of such a collisional shock. The question of the “collisionless shock” in plasm a has been actively investigated (Colburn and Sonett, 1966; Schwartz, 1985), It has been suggested th a t m icroinstabilities and turbulence of various kinds may replace collisions as th e agency responsible for the dissipation (Tidm an, 1967; Schwartz, 1985), T h e bow shock has been observed by in situ spacecraft measurements.
The m agnetosheath is a transition region between th e bow shock and the m agnetopause, where the solar wind is slowed down to subsonic speeds and undergoes a deflection which causes it to envelop th e m agnetosphere.
1.2 T he Ionosphere
According to the IE E E Standard (1969) th e ionosphere is defined as “th a t p art of a planetary atm osphere where ions and electrons are present in quantities sufficient to affect th e propagation of radio waves” . Here we consider only the e a r th ’s ionosphere. T he ionosphere is a p a rt of th e e a rth ’s atm osphere extending from approxim ately 70 km to 1000 km in height above th e surface of the earth.
The existence of the ionosphere, as an electrically conducting region of the atm osphere, was first advanced by Stew art (1878). He suggested th a t the most probable cause of th e daily variations in th e e a rth ’s m agnetic field was the pres ence of electric currents flowing in th e upper atm osphere. M arconi’s successful experim ents in 1901 of radio communication across the A tlantic (Flem ing, 1902) prom pted Heaviside (1902) and Kennelly (1902) to suggest independently the existence of an electrically conducting layer at a height of the order of 100 km to explain th e reflection of radio waves. The final experim ental proof of the existence of the ionosphere was carried out by Appleton and B arn ett (1925) and by Breit and Tuve (1925).
1.2
The Ionosphere13
1 ,2 .1 S t r u c t u r e o f t h e Io n o s p h e re
T h e m ost im p o rtan t param eter in a description of the ionosphere is th e electron density. A typical electron density profile against height for daytim e is shown in figure 1.3. T he ionosphere is usually classified into D, E and F regions or layers. T h e lowest layer is called the D-layer which extends in height from about 60 to 85 km , It is present only during th e daytim e. The peak electron density of the D -layer occurs near 80 km and is of th e order of 3
X
109 eh'Ctroivs/vn3. T h e m iddle layer is called the E-layer. It extends from 85 km to about 150 km an d has a d aytim e m axim um electron density of about ~ 1 0 n electrons/m 3 at a height of around 115 km. Q uite often th e valley between th e D-layer and the E-layer is not very obvious. During the night th e electron density decreases by a t least tw o orders of m agnitude and th e E-layer disappears. Above the E-layer is th e F-layer. The F-layer is more heavily ionized. It extends from 150 to about 1000 km . T h e F-layer may be subdivided into th e Fi-layer and Fa-layer. T h e F i-lay er is present like th e D- and E-layers only during the daytim e. It extends from 150 to 200 km w ith a m aximum electron density of 2 x 10n eleetrons/rn3 a t a height of about 180 km. The F2-layer extends from 200 to roughly 1000k m and has a daytim e electron density m axim um near 250 km of about 5
X
1011 eiec tro n s/m 3. During the night the D-, E-, and Fi-layers disappear arid th e ionosphere takes the form of a single layer, called the F-layer, with a m axim um electron density of about 1011 electrons/m 3 in th e vicinity of 350 km.Above th e F 2-layer is the plasmasphere. T he plasm asphere basically follows th e ro tatio n of the e a rth and has th e shape of a doughnut, very much like th e volume form ed by th e lines of th e e a rth ’s m agnetic field which keeps th e plasm asphere ro tatin g with the earth, The boundary of the plasm asphere is called th e plasm apause, which at the equatorial, plane occurs at a geocentric distance o f 4 to 5 re- A t the plasm apause the electron densi ty drops sharply from
1.2
The ionosphere______________
rrrm
PL A SM A PA U SE A 10 PL A SM A SP H E R E r: 3 I O N O S P H E R E F t 2 10 JL L llii 2 3 ,4 5 ,6 10 10 10 10 10 10 E L E C T R O N D E N SI T Y N ( e l . / c m 3 )Figure 1.2: A typical daytim e profile of the ionosphere and th e plasm asphere. Modified from Papagiamiis (1972).
1.2
The Ionosphere15
~ 108 to ~ 106 electro n s/m 3. The plasmasphej ? is filled w ith therm al plasm a (a plasm a w ith a M axwell’s distribution of velocities and a tem p eratu re of a few thousand degrees Kelvin) which diffuses upwards from th e upper ionosphere.
1.2.2 L ayer F o rm atio n of th e Ionosphere
T h e ionosphere is created through th e photoionization process of th e solar ra diation. T h e rate of production of electron ion pairs per un it volume is given
by
Q = a n S (1.7)
w here a is th e effective ionization cross section of a given constituent gas, n its num ber density, and S th e local intensity of the ionizing solar radiation. Incom ing ultraviolet radiation and X-rays from th e sun ionize th e e a rth ’s atm osphere. A t great heights of th e order 1000 km or m ore the m edium is alm ost fully ion ized, but so tenuous th a t th e ion and electron densities are small. At lower levels th ere is m ore gas to be ionized so th a t the radiation is m ore strongly absorbed an d th e ion and electron densities are greater. At still lower levels the radiation has been used up so th a t th e degree of ionization is small again. The region where the ion and electron densities are greatest is the ionosphere.
T he layers in th e ionosphere are formed because the ionizing radiation from th e sun is n o t m onochrom atic and because the atm osphere consists of several different constituents which are ionized a t different wavelengths of the solar radiation spectrum . The height where m axim um ionization occurs depends on th e absorption of th e air for the ionizing constituent of th e solar radiation, and th e m echanism by which ions and electrons are removed. Different ionizing co n stitu en ts give m axim a a t different heights. Thus different ionospheric layers are formed. In th e D-layer cosmic rays and the Lym an—c* radiation (1216 A) ionize NO. In th e E-layer th e ionization is produced by solar X-rays in the
30-1.2
The Ionosphere16
100
A,
by soft X-rays and by ultraviolet radiation in the range between 100A
and the L ym an—(3 a t 1026 A. The m ain ions in th e E-layer are N O + and O j. In th e F-layer the principal ionizing agent is th e su n ’s ultraviolet radiation in th e 200 to 900A
range. The m ain atm ospheric constituent which is ionized is 0 2.1 .2 .3 D iffe re n c e b e tw e e n t h e I o n o s p h e r e a n d t h e M a g n e to s p h e r e
In th e F-layer the ion and electron density are only about 10-5 of th e density of neutral particles, and in th e E-layer th e figure is about 10-11. Thus gravity, acting m ainly on th e neutral particles, exerts a dom inating control on th e hy d rostatic configuration of th e m edium. Hence the ionized layers tend to keep horizontally stratified.
The e a rth ’s m agnetic field B is approxim ately th a t of a m agnetic dipole near th e e a rth ’s center. Its total field induction is given by
B = | | ( 1 + Zsin2<pfl2 (1.8)
w here M is th e dipole m om ent of the e a rth ’s dipole m agnetic field, r th e distance from the e a rth ’s center and <f> the geomagnetic latitude. A charged particle gyrating in the m agnetic field has th e m agnetic m om ent p = | m v 2j B and
hence feels a force, which is given by (Jackson, 1975; Nicholson, 1983)
F - —p s j B (1.9)
where m is mass of a charged particle gyrating in th e e a rth ’s m agnetic field and Uj. is the particle’s velocity com ponent perpendicular to th e e a rth ’s m agnetic field. The gravitational force per unit volume is pg where p is th e density of th e air and g is the gravitational acceleration. Note th e m agnetic force and the gravitational force have opposite directions. These two forces are about equal a t a height of 300 - 400 km. G ravity exerts a strong control up to heights of
1.2
The Ionosphere17
th e order of 1000 km . Above 1000 km th e stru cture of the atm osphere is mainly controlled by th e m agnetic field and hence is no longer horizontally stratified b u t more like the stru ctu re formed by th e e arth ’s dipole m agnetir field. This is th e m agnetosphere.
The m agnetosphere is a fully ionized ion plasm a and therefore a very good electrical conductor. In a perfectly conducting plasm a, m agnetic field lines be have as if they move with th e plasm a and hence this leads to th e concept of
“freezing in ” of th e m agnetic field. The shape of th e m agnetosphere is also in fluenced by th e solar wind. T he solar wind is also a fully ionized plasm a and a good conductor. T hey cannot quickly p enetrate into each other, because they are ‘frozen’. B ut th e solar wind distorts th e shape of the e a rth ’s m agnetic field so th a t th e m agnetosphere is of its unique shape.
s
18
C h ap ter 2
T opsid e Sounding o f th e Ionosphere
Since proton cyclotron echoes were first observed in topside sounding of th e iono sphere, here we introduce w hat is m ra n t by “topside sounding” of the ionosphere and describe th e instrum entation and the m ethod of observing proton cyclotron echoes. T he m ost im p o rtan t param eter in a description of the ionosphere is th e electron num ber density TV, and much effort has been devoted to its observation. P rior to about 1960 th e knowledge of the ionosphere was obtained only from ground observations by radio m ethods. From about 1960 onwards rockets and satellites began to be used and it becam e possible for th e first tim e to stu d y th e ionosphere at heights h above th e m axim um of N (h ) in th e F2 layer, th a t is the
region called th e topside of the ionosphere. T he ionosonde technique employed by a satellite above the F2 layer is similar to th a t used on the ground. This is
called topside sounding of the ionosphere. The topside sounding has proven to b e extraordinarily fruitful not only because of the inform ation obtained about th e stru ctu re of the topside ionosphere, bu t also because of th e discoveries of th e new phenom ena due to the sounder being em bedded in th e plasm a, such as proton cyclotron echoes, electron plasm a resonances and so on.
2.1
G ro u n d O bserv atio n s of th e Ionosphere
Ionospheric echo sounding was originally used in th e classical pulse sounding
experim ents of B reit and Tuve (1925, 1926). Short pulses of radio waves from a tra n sm itte r are sent vertically upwards and retu rn to a receiver on the ground
2,1
Ground Observations o f the Ionosphere19
after reflection in th e ionosphere. The tim e of travel t is m easured. T he combina tio n of a swept-frequency pulse tran sm itter and an autom atically tuned receiver is called th e ionosonde. This is the sam e as th e technique used in radar. If the pulse travelled entirely in free space it would have to go to a height h' — \c t called the equivalent or apparent height. In fact, the pulse speed slows in the ionosphere, and therefore th e apparent height is always greater than th e true height of reflection. T he apparent height is strongly frequency dependent. The apparent-height-versus-frequency record is called the ionogram.
Because of the e a rth ’s m agnetic field the ionosphere is birefringent with the result th a t a tran sm itted radio pulse splits into two modes which travel inde
pendently a t different group velocities and different polarizations. These are called the ordinary ( 0 ) and extraordinary (X) modes (or Waves), As th e sound ing frequency is increased, th e electron num ber density required to reflect the tra n sm itte d signal increases until reflection occurs at a height of m aximum elec tro n density. Above a critical frequency corresponding to the electron num ber density a t th e peak of the F 2 layer, reflection can no longer take place and the ionosphere becomes tran sp aren t to th e sounding signal.
For th e 0-Wave th e electron num ber density is given in SI units by
47r2eo m
N = T — / - 0.0124/ (2.1)
N = electron num ber density
/ = frequency of reflected sounding signal
eo = perm ittiv ity of free space
m = m ass of the electron
e = charge of the electron.
However considerable analysis is needed to obtain th e vertical electron dis trib u tio n , N ( h ) profile, from h '{ f ) curves, Since the pulse travels w ith th e group
