Journal of the Radio Research Laboratories September/ November Printed Printed in Tokyo, Japan Pp

Vol. Vol. 16 Nos. 87/88 Journal of the Radio Research Laboratories September/ November Printed Printed in Tokyo, Japan pp. 185-206 1969

UDC 510. 551. 535: 629. 783 ANALYSIS OF OBSERVATIONAL DATA OBTAINED BY ALOUETTE II

Il. Il. Structure of the Topside Ionosphere Deduced from Resonance Spikes on the Topside Ionograms

Nobuo MATUURA and Hisao INUKI

(Received (Received June 27, 1969)

ABSTRACT

Alouette Alouette II topside sounding data were recorded at Kashima Station, Radio Research Laboratories, and electron density distributions of the topside ionosphere obtained obtained on analysis of the topside sounding data for two years from October, 1966, to to September, 1968, are presented and also discussed from a theoretical point of of view. The plasma frequency at the satellite was determined from several characteristic characteristic frequencies of each topside ionogram obtained from Alouette II data. The average structure of the ionosphere was derived from plasma frequencies measured at various satellite positions over the data acquisition area of Ka- shima Station. The results are presented in terms of electron density distributions versus versus altitude and geomagnetic latitude for four half-year periods, and there is demonstrated clear seasonal e妊ect on the electron density, such as electron density sity in winter much less than that in summer, in high latitude and high altitude region. region. Some ionospheric parameters were determined by fitting theoretical electron-density electron-density profile to the observations. Theoretical electron-density profiles were obtained on the assumption of di 妊usive equilibrium condition above 600 km level level where the concentration of o+ and H+ are related with the concentrations of 0 and H at the level, and also a model of the neutral atmosphere in the region between 120 km and 600 km was derived including the e旺ects of thermal diffusion and escaping of H and He. The results show that the probable thermopause temperature temperature varies from about 1000 。K in the lower latitude region to about 1800°K in the higher latitude region, and, further, that the plasma temperature varies varies from about 1000°K in the lower latitude re~ion to about 2700°K in the higher higher latitude region.

1. 1. Introduction

Alouette II topside sounding'll data have been received at Kashima Station (36.0 。N, 140. 7°E), Japan, since the fall of 1966. Some preliminary results obtained by analysis of Alouette II topside ionograms recorded during the period from Octo- her, her, 1966, to September, 1967, have already been reported '2• 31. N(h) reduction is a successful tool to explore the structure of the topside ionosphere especially from

185 185 186 186 N. Matuura and H. Jnuk 1

Alouette Alouette I data, bu t sometimes N （的 profiles o btained from Alouette II ionogram s on th 巴 ass umpti on of simp ly vert ical propagation are l ess acc ura te w hen th 巴 satellite pos ition is hi gh er than about 2000 km . In the first part of the pr 巴sent paper is repor ted the ana lys is of A l ouette II ionograms by a re lative ly s imple method using resona n ce spikes . The electron densities in the sate lli te position we re determined from resonance spikes, and averaged latitudinal and altit udi na l distribution of the electron electron d巴nsiti es was obtained by accumulating the data on vario us Alouette II passes passes received at Kashima Station in each half-year period. In th巴 seco nd par t of the the present paper, electro n- density profi l es of th巴 topside iono sp he re under di 丘usiv e eq uilibrium condition ar 巴 th eoretica lly deri ved, and the physical structure of the tops tops id 巴 ionosp her巴 is discuss ed by compa ri son of obseτvat ions and the th eo ry.

2. Structure of the Topside Ionosphere from Alouette II Data

Analysis Analysis was made of A louette II tops id e so und ing data from 193 pa ss 巴S received at Kashima Station durin g the perio d from Octob er, 1966, to September, 1968. The data are di vid 巴d into fo ur groups belonging to two summer ha lf-year periods and two winter half- year periods, as desc rib ed b巴lo w, and the average el ectron dens it y di st ributi on was derived in each group: ( i ) October, 1966 ～March, 1967, 50 passes, (ii ) April,1967 ～September, 1967, 62 passes, iii) (iii) October, 1967 ～March , 1968, 32 passes, iv) (iv) Apri l, 1968 ～S eptember, 1968, 49 passes.

2.1 . Electron density at the satellite pos ition

An example of A l ouette II ionogram received at Kas hi ma Station is illustrated in Fig. 1, in which spikes of the electron gyro-resonance and its higher har moni cs (fu , 2fu, 3fu ), plasma resonance spike CfN), and upp er- hy brid resonance spike (f ト＝0 子工万2 ) are shown by arrows, and z巴ro range ec hoe s of Z trace Cf zs), 0 trace trace Cfo s= fN) , and X tra ce Cfxs) are also shown . T he electron densit y on the sa t ellite is given from the plasma frequency fN by th 巴 re lation N ,(c m -3) = 1.24 ×10 4 /;v2( MHz ). The plasma fr 巴quency on the satellite was determined dir ec tly from the

2£5“ ト6 wetteste も吋biE dMleS ，守川 x: x: 刷庁 ca内竜一角 4i 山内 is 。、ん刊 Z正部． 14 tgψF km 内j 舎 0 1000 1000

Fi g . 1. A louett 巴 II ionog ram rec eive d at Kas hi ma Station at at 1 5h 12m 42 s U T on Apr. 4, 1967 , and sate llit e pos ition in in latitud 巴 18 .5°N , longit ud e 121.3 °E, an d at alti tude 1825km. 1825km. Analysis Analysis of Observatio 河al Data obtained by Alouette II (II 〕 187

frequency of th 巴 plasma resonance sp ike f,v when the spike was clear ly identi 負ed, or or indirectly from thee l ectron gyro -resonanc 巴 freq uency /ff ( or its hi gh er harmonics), and the frequency of the extraord in ary trace at zero range fr s. T he upp 巴r-hybrid resonance frequencyβ ，w as u sed for increase in accuracy.

Fig. Fig. 2. Alouette II ionogram rec 巴ived at Kashima Station: at at 1711 Olm 59s UT on Jan. 5, 1968 , and sate ll ite position in in latit ud e 67.'1 °N, long itude 114 .4 °E, and at alti tude 2791 2791 km.

An examp le in Fig. 2 shows th巴 ionogram in which no plasma resonance spike is is see n b ecause the plasma frequency f,v is lower than the low 巴r limit of the swept frequency. frequency. In such a case, the va lu es of f,v calcu l ated from /H ，ん s or fトare quite erroneous erroneous be cause fu~ん ~fr s when /,v is much less than fH・ The lowest de- tectabl e frequency on the ionogram isa bout 0.1 5 MHz, and th e correspon ding electron den sit y is about 280 cm -3. So far as the above-m 巴nt ioned method is used for determining fN, the ca lcul ated electro n d ens ity l ess than 28 0 cm -3 is un c巴rtain . The el ectron dens iti 巴S l ess than 28 0 cm -3 were obta in ed in severa l ionograms as show n in in the results to b巴 described later on. For low electron densities, the frequency difference difference between close ly spaced /If and fr resona nces may be observed as a b eat or modulation pattern 山. Th e observable range in electron densities by this m et hod is is bet ween ab o ut 8 and 100 cm -3 . In the present ana lysis, the data of th 巴 very low elec tron densit y s uch as obta ine d from th e modu latio n pattern are n ot so mu ch and they are excluded.

2. 2. 2. Latitudinal distribution

The elec tron densiti es at var ious rnt e山 te positions were accumulated in each half-y ear period, and thee l ectron d ensities in tlu ・ee limi ted altitude ranges, 2800- 3000 3000 km, 2400 - 2600 km, and 1900 - 2100 km, are plotte d aga in st the g 巴omag netic latitude titude in Fig. 3. In this Figure the va lu es of in va riant latitud 巴（A) are show n b y ar rows in eac h altitude range, where the invariant latitude is averaged over the sate llit e pass longit ud e ( about 110 °E 160°E ). The curves in the Figure show the mean and smoothed latitudinal distribution of the 巴Jectron densiti es. In the r巴gion in in the altitude rang e 28 00 - 3000 km and in A> 60 °, the el ectron densities less than 280 280 cm → plott ed are see n, and the plotted va lu es sho uld rea d l ess than 280 cm -3 because of th eir un certainty as de sc rib 巴d a bove. In In Fi g. 4, the curves of the mean and smoothed latitudinal distribution for fo ur half -year per i ods are illustrat ed together. In th 巴 region A< 40 °, electron densiti 巴s ELECTRON －主ELECTRON Hg q. q. 弘三九% 電寸ー「 I 一寸・－ミ

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~ 10 ‘ ~』 103 103

102 102 L -'JU -'JU O' 主r 40 ・ 60 ・ GEOMAGNETIC LATITUDE

Fig. Fig. 4. Smoothed curves in Fig. 3 are illustrat 庖d together together at three altitude ranges, 1叩O～2100km, 2400 ～ 2600 km, and 2800 ～ 3000 km, for four periods, Oct. Oct. 1966 ～ Mar. 1967 （出 ick curves), Apr. 1967 ～ Sep. Sep. 1967 (thick broken curves), Oct. 1967 ～ Mar. 1968 1968 (thin curves) and Apr. 1968 ～ Sep. 1968 (thin broken broken curves). are are almost constant with the latitude and almost unchanged for two years, and in the the region A>40°, electron densities begin to decrease with the increasing latitude and they are especially low in the region 60° くA<70°, known as the trough region <5,5>. <5,5>. Though the low latitude boundary of the trough near 1000 km level is usually sharply sharply defined, the boundary shown in Figs. 3 and 4 is fairly smooth and broad. The smoothness of the boundary may partly come from averaging process. In the region region A>55° can be seen clear seasonal variations in the electron densities, such as as electron densities in winter (more precisely, in December, January and February) much less than those in summer, and it must be noted that the solar control over the the electron density is effective even in the trough region.

2. 2. 3. Altitudinal distribution

Charged particles in the topside ionosphere are easy to move along the geo ・ magnetic field lines, but not in the direction perpendicular to the field lines unless an electric field exists. Therefore, the altitude distribution of electron densities along along the field lines is physically more meaningful on the basis of dynamical beha・ vior vior than that in the vertical direction. The electron densities in the six limited invariant invariant latitude ranges, A<30°, 30°

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ELECTRON NUMB 回 DENSITY (cm-3) ELECTRON NUMBER DENSITY (cm-3)

Fig. Fig. 5. Electron densities are plotted against the altitude at six invariant latitude ranges, A<30 。， 30 。＜A<40°, 40 。＜ A

ELECTRON NUMBER DENSITY (cm・') Fig. Fig. 6. The best fitted theoretical profiles in Fig. 5 are illustrated together together in six invariant latitude regions, for four periods, Oct. 1966 ～ Mar. 1967 (thick curves), Apr. 1967 ～ Sep. 1967 (thick broken broken curves 〕， Oct. 1967 ～ Mar. 1968 (thin curves), and Apr. 1968 ～ Sep. 1968 (thin broken curves 〕．

In In the region イ＜ 55°, each profile has a deflection point near 1000 km level where the electron density scale height changes abruptly because the dominant ions change from O+ below the level to H+ above the level. In the region A>55°, it is seen seen from the electron density profiles that the transition level lies near 3000 km or higher, higher, and 0+ ions may be regarded as the dominant ions at least up to near 3000 km. Behaviors of the seasonal changes are also different between the region A<55° and 11>55°. In the region 11<55°, the seasonal variation, higher electron density density in summer and lower in winter, can be seen in the altitude region below about 1000 km where O+ ions are dominant, but no appreciable seasonal variation can be seen above about 1000 km where H+ ions are dominant. In the region イ＞ 55°, the seasonal change in the electron density, such as higher electron density in in summer than in winter, is remarkable in all altitude region where 0+ ions are dominant.

3. 3. Theoretical Model of the Topside Ionosphere

3. 3. 1. Chemical reaction in the topside ionosphere

Rocket observations 川町 show that the topside ionosphere consists of ionic species as as O+ ,N ヘHe+ and H+, and electrons. The influence of existence of N+ ions on the the electron density distribution may be regarded as unimportant, because the concentration centration of N+ is smaller than 0+ concentration by about an order of magnitude 192 192 N. Matuura and H. Inuki and further molecular weight of N+ is close to that of Q+, In the later discussions, the the existence of N+ ions will be neglected. Chemical reactions on o+ ions have been well studied to a great amount in relation relation to the problem of the F2 layer formation <9>. Photoionization of He is a major production source of He+ ions, and they are lost by the following charge transfer transfer reactions oo, 11>.

He++N2 ー→ He+N+N+ (la) He++N2 一一... He+N2+. (lb)

The reaction (la), as well as the dissociative photoionization of N2, plays the production production process of N+ ions<12>. The rate coefficient of the reactions(la, b) from laboratory laboratory experiments gives the value of about 1 × 10-u cm3 sec-1 <13>. From theoretical cal considerations of the observed He+ distribution, the rate coefficient of the reactions tions (la, b) is estimated less than 10-11 cm3 sec-1 by Bauer<10>, but Brinton, et al. ~~and Maier<11l gave the coefficient of about 10-9 cm3 sec →． The most important chemical reaction controlling H+ concentration is the following charge transfer reaction u4>.~~

~~Q++H ご H++O. (2)~~

The rate coe 血cient of this reaction is obtained as 4 × 10-10 cm3 sec-1 u51. The reaction reaction (2 ）・ acts both as a production and loss process for H 七 and H+ concentra- ti ti on in the chemical equilibrium state is given uoi by

~~nvELF「 E FaEH＋守 FILO＋『 lJ一一一。。司 EEJ 』－（め L~~

~~3. 3. 2. Transition from chemi 個 I equilibrium to diffusive equilibrium~~

Ionic Ionic and electron densities are governed by production process, loss process, and the the effect of dynamical density redistribution. Among the charged particle motions contributing contributing to the density redistribution, the influence of diffusion becomes more important important as the altitude increases. In comparatively low altitude region, the velo ・ city city of diffusion is much reduced by particle collisions, and hence the density distrbu・ tions tions for a steady state are in chemical equilibrium. In greater altitude region where particle collisions are less frequent, the influence of diffusion becomes more important important than that of production and loss process, hence the density distributions come to be in di 貧困ive equilibrium. The transition level from chemical equilibrium region region to diffusive equilibrium region can easily be recognized for Q+ ions at the F2 peak near 300 km. On the transition level for other ionic species, observational results results of the ion composition are useful. Altitude Altitude distribution of [H+]/[He+] obtained by rocket measurement on Wallops Island Island at 1240 LT, 10 October, 1961 <17>, shows that the influence of diffusion begins to to appear above 500 km, and that the di 貧困ive equilibrium region lies above the transition transition region between 500 and 700 km U 剖. Another rocket measurement on Wal- lops lops Island at 1300 LT, 2 March, 1966<0>, shows that the influence of diffusion begins Analysis Analysis of Observational Data obtained by Alouette II (II) 193

to to appear above about 400 km. Ion temperature near 400 km in the former observation tion was estimated at about 1235°K, and atmospheric temperature near 300 km in the the latter observation was estimated at about 850°K. Hence the difference in altitude tude of transition level in both cases might be due to the difference in atmospheric temperature. temperature. Distribution Distribution of H+ ions in diffusive equilibrium, when Q+ ions are dominant and H+ ions are minor component, is given by equation similar to Eq. (3) according to to Mange09>, if O ヘO and H are all in diffusiv 巴 equilibrium distribution and the atmosphere is in thermal equilibrium. Hence the chemical equilibrium equation(3) can well represent the H+ distribution even in the diffusive region so far as H+ ions are are minor constituent and Q+ ions are the dominant constituent. In the discussion to to be given below, the reference level is taken at an altitude of 600 km and it is assumed that Eq. (3) holds at the reference level and that ions and electrons are in in diffusive equilibrium above the level.

~~3, 3, 3. Density distribution of ions and electrons in diffusive equilibrium~~

Density Density distributions of ions and electrons which are in ambipolar di 笠usive equilibrium equilibrium along the geomagnetic field lines are determined by the following hydrostatic drostatic equations:

~~盟 L ＋「＿＿！＿＿＿立しト竺 lKsin I－~ lN;=O (For ions) (4a) at at L Tj at kTj kTj 」 J~~

~~空並＋「_L 空L__ ＋竺~sin I－~ lN.=0, (For electrons) (4b) at at I T. at kTe kTe 」~~

where the effects of flow and thermal diffusion are neglected, and suffixes j and e denote denote the quantities of ionic species j and electrons, respectively; N is the number density, density, T is the temperature, m is the particle mass, e is the particle electric charge, charge, k is Boltzmann constant, E11 is the field line component of the polarization electric electric field caused by am bipolar diffusion, g is the acceleration of gravity, I is the magnetic dip angle, and t is the distance along the field line reckoned upward from the the reference level. It It is assumed that the ion temperatures Ti are all the same and equal to Ti and that the electron temperature is related to the ion temperature by the relalion

~~Te/ 巴＝I' ニ constant. (5) Putting Putting electronic charge as - e, and ionic charge as e, the electrical neutrality of of the plasma gives the relation as follows:~~

~~Ne= I: N;-. (6)~~

~~Ion Ion and electron densities can be derived from Eqs. (4a, b) using the relation (5) (5) in the form : 194 194 N. Matuu1 ’a and H. Inuki~~

~~川＝ N;c （争）YPJX (7a)~~

~~Ne=Nec 待合 yμ.1px-11p, (7b) where suffix c refers to the quantities at the reference level (600km), and~~

~~X ＝悶［~；詫吋 (8)~~

~~Y=exp[-j ；静 in Idt] (9)~~

μ1=m1/mm μ.=m./m1r. (10) and mH is the mass of atomic hydrogen. Eliminating Eliminating the term including the electric field, X, from Eqs. (7a, b) using the the relation (6), the ion and electron densities normalized by the electron density at at the reference level, Nee, are given in the form:

~~叫凡＝ NJ*=N1c＊（号~） y<µh~~

~~N./Nec=N.* = ， ·~ι ）［~ Nkc*Y ＜ρ内 e>J I川 fil （日 b) ¥ 1 i I 恥~~

where N ＊三 N/N 仲 Thus, the ion and electron densities of the topside ionosphere in in the diffusive equilibrium are given by Eqs. (lla, b) with the aid of Eq. (9), if the the electron density Nee and ionic composition N1c* at the reference level, ion temperature perature Tt, and temperature ratio f3 are given. It It is assumed that the ion temperature increases linearly with the altitude as as represented by the form:

~~Ti(h) Ti(h) = Ttc-1-'~~

~~-ln Y= ¥1 ~sin I dl ＝他盟£...）＼＜＿佳一一 Jo Jo kTt ¥ kTtc /J1 ~2[1 ＋ ν （~－ 1)]~~

~~＝（鳴子）［ポ 021n （ν＋王子）＋ポ可（ i÷ ）］ (when νキ1) (13a)~~

＝（鳴子）限 J. (whenν ＝ l) （日 b) where sin I dl=dh, t;=r/r., rc=RE+hc, r=RE+h, ))=re-rt/Tic and RE is the earth ’s radius radius (6370km). Nighttime ion temperature distributions obtained by incoherent backscatter backscatter experiment at Arecibo (30°N)show the ion temperature of about 800 ～ Analysis Analysis of Observational Data obtained by Alouette II (II) 195

l000°K at 600km level and the ion temperature gradient of about 0.5°K/km in winter 捌. By the use of these values, the quantity 1.1 can be evaluated to about 3 to to 4. Neglecting Neglecting the existence of N+, ratios of the ion concentrations to the electron concentration concentration at the reference level are given

~~[O+]cf [O+]cf Nec= (1-C)/(1 ＋甲）~~

~~[He+]cf [He+]cf Nec=C (14)~~

~~[H+]c/Nec ＝甲（ 1-C)/(1 ＋守）， where the relation (6) is used and~~

~~万＝ [H+]c/[Q+]c ・~~

~~Densities Densities of ions and electrons obtained by Eqs. (lla, b) are determined by giving giving the values of the following parameters.~~

(i) Electron density at the reference level, Nee, (ii) (ii) He+ concentration at the reference level, i:;, (iii) (iii) Ion density ratio at the reference level ，守，（15) (iv) (iv) Ion temperature at the reference level, T;c, (v) Ion temperature gradient, r;, (vi) (vi) Ratio of electron temperature to ion temperature ，戸＝ T./T;.

~~3. 3. 4. Model of neutral atmosphere and ion density ratio~~

Ion Ion density ratio 守＝［ H+]c/[0 つe at the reference level is related with the density ratio ratio of neutral constituents [H]/[O] at the reference level by the relation given in in Eq. (3). A model of the neutral atmosphere is derived in this Section. [See also Appendix.] Appendix.] Analytical Analytical expression of ~~thermosphere temperature is given by Jacchia 121> in the form: form:~~

T(h) =Too ー（T ，，，一九） exp[ -s(h- h。）］ (16) where the suffix 0 refers to the quantities at the turbopause level, h0=120km, Too is is the thermopause temperature, and h is the altitude. Jacchia

~~ni=ni0yr1[y+a(l-y ）］ーu +r Jl (17) where the influence of thermal diffusion and escaping is neglected, and~~

~~y=exp[ -s(h-h0)]~~

~~(18) (18) r; ＝長失（手 r~~

α＝T=/To ・ For atmospheric constituents He and H, their density distributions are given by the the use of Eq. (16), inclusive of the influences of thermal diffusion and escaping, in in the form [Appendix]:

~~i-n W 「l+EJWidClid-h) l (19) - 10 Jl l+EiWJdhd J~~

~~where suffix d refers to the quantities on the base exospheric (taken to be 600km), and~~

~~WJ=yr1[y+a(l-y ）］ー(l+n ＋αTj) ん＝［。（与 )2 （舎）（ホ）（会） (20) (20) 島＝9E （た r~~

~~同＝ F-l!£;(1 ＋響） exp （－物）~~

The form of the effusion velocity 円 is given by Spitzer<22l ，αTJ denotes the coefficient coefficient of thermal diffusion, and the value of ー0.4 is used for both He and H <23l. Coefficient Coefficient of molecular diffusion Di for He and H is given in the form:

~~n 3 ./kT(mj ＋弱） 1 (21) (21) .VJ=lfc12・v .VJ=lfc12・v 27r:mJ~元・一面一，~~

where 弱 an n are the mean molecular mass and the total number density, respectively, vely, for the background mixed gas of 0, N2 and 02, and the collision diameter a is is taken to be 2 × 10-scm. When the upper atmospheric model is derived from Eqs. (17) and (19), the following following numerical values are used according to CIRA, 1965. h。＝ 120km T0=355°K [N2 ］。＝ 4 ×1011cm-a [02]0=7.5 × 1010cm-3 (22) [OJ 。＝ 7.6 ×101ocm → [He ］。＝ 2.4 ×107cm-3 [HJ 。＝ 2.0 ×10scm-s hd=600km Analysis Analysis of Observational Data obtained .by Alouette II (JI) 197

The value of [H]0 is taken from the model given by Kockarts and Nicolet t2s1, and this value gives the higher concentration of H than CIRA, 1965, model. How- ever, ever, the concentration of H obtained by rocket observation ts1 shows the value of about about 6 × 105cm-3 at 300km level, and the present model gives the value of H concentration centration of about 4 × 105cm-3 at the same thermosphere temperature of 850°K. Agreement is fairly good.

~~加7o".J~~

161 」旬。 800 1α)C) 臥)C) 向画面 1扇元一扇面200022( 渇 Thermopause Thermopause Temperature （・ K) Fig. Fig. 7. The ion-density ratio [H つ！［ O+] at the reference reference level. On 巴 is taken from Rush and Venkateswaran Venkateswaran [24], and the other from the present present model.

The ion density ratio 甲 obtained from the present model at various thermopause temperatures temperatures is shown in Fig. 7 together with the relation at 500km level given by Rush and Venkateswaran '241 summarizing various observational results. Both curves show similar thermopause temperature depend 巴nce except the difference between the the two altitudes where the relations were obtained.

~~3. 5. 5. 3. Examples of ion and electron density distributions~~

Distributions Distributions of ion and electron densities normaliz 巴d by the electron density at the the reference level are obtained from Eqs. (lla, b) by the values of the following parameters: parameters:

~~(i) He+ concentration at the reference level, t;;,~~

~~(ii) (ii) Thermopause temperatur 巴， T 向~~

~~(iii) (iii) Ratio of ion temperature to thermopause temperature ，α＝T;c/T. 町 (iv) (iv) Ion temperature gradient, r;, (23) ( v) Ratio of electron temperature to ion temperature, /3.~~

~~Mean ionic molecular weight, μ+=m+/mu, can be derived from Eqs. (lla, b) as 198 198 N. Matuura and H. Inuki~~

~~μ+= [,4 N;c*µjYlµ1+µ,>J ／［~ N;.*Y(μ1+μc>J. (24)~~

~~By differentiating the logarithms of both hands of Eqs. (lla, b) with the altitude, the reciprocals of scale heights for ion and electron density distributions are obtained in the form :~~

~~日＝ 1.0, X(H ぜ）： 0.0~~

~~。司コ主主《問問~~

~~1飢泊~~

~~500 500 。ね 1 10" i:r' 1 i:r2 xr' Nom 叫 ized Electron Density （的~~

~~日： 1.0, X(He+):0.1 国＝’ 2.0 km 3民加~~

~~2500 2500~~

~~2000 2000 τH ~ ; 1500~~

~~1000 1000 旬。。 1（）・ 1 10-2 10-1 1 10' ・2 10 ＇・ 1 Normalized Normalized Electron Density （紛~~

Fig. Fig. 8. Examples of the theoretical electron-density profiles of which values values are normalized to unity at the reference level, 600 km, are shown, when three values of a(=Ti/Too)=l.O, 1.5 and 2.0 were used, used, and {3( = Te/T;)=l.0. The continuous curves show the electron electron density profiles when the plasma temperature gradient, T;=O, T;=O, and the broken curves show the profiles when the plasma temperature temperature gradient, T;=0.5°K/km. Electron density profiles, (a 〕 when (=X(He+)=O, and (b) when (=X(He+)=0.1, are shown. Analysis Analysis of Observational Data obtained by Alouette II (II) 199

~~m;g {3 m+g oTi (ln (ln N;*) ＝ー 1 (25a) ah ah FI τ百王百五百 TI a瓦~~

三(lnN.*) ＝一＿！＿＿＿四＿ __! .i1l (25b) h (1+{3) kTi Ti oh where m+ is the mean ionic mass, and the relation μ1 》μ. is used. Examples of electron density distributions in various values of αand Too are shown in Fig. 8, where (a) {3=1 and C=O, and (b) {3=1 and C=0.1. In each case, electron electron densities are compared in both cases where the ion temperature is constant with the height, 'Z"i=O, and the ion temperature gradient exists ，向＝0.5°K/km. In Fig. Fig. Sa, it can be seen from the sharp deflection of the electron density profiles that that the scale heights of the electron densities increase abruptly at certain levels. Those deflection deflection points represent the transition levels from o+ dominant region below to H+ dominant region above, and the altitude of the transition level increases with the the thermopause temperature. When He+ concentration is effectively appreciable, the the deflection of the profiles becomes less abrupt as shown in Fig. Sb. The influence of inclusion of the ion temperature gradient appears at decrease in electron electron density for the H+ dominant region, and at increase in electron density for the the o+ dominant region as in the case of Too=1800°K in Fig. Sa. Such behavior can be understood by the following expression deduced from Eq. (25b).

~~ヰ（川＊） = -crl- 雨続・［ μ （川）長（完）］／［ 1＋長（h-hc)J. (26) (26)~~

~~From Eq. (26), increase or decrease in electron density scale height owing to inclusion inclusion of temperature gradient depends on the condition given by the following inequality: inequality:~~

~~・・目－－－~~

~~Fig. Fig. 9(a). Model neutral atmosphere is illus 位以ed in the the case where T 。。＝ 1200°K, and s=0.02km-1. 200 200 N. Matuura and H. /nuki~~

~~km l＼＼＼ ~JJ立－－－－－－‘us~~

阪拘

~~10"' 10"' 10・ 10 ’ 1面否古「－ I R・lotlve Ion ond Electron D・n・Illes Dis ，，』 bUll 。n.~~

Fig. Fig. 9(b). Model topside ionosphere is illustrated in the the case where Too=l200°K, Tic=1200°K, Te/Ti= 1, 1, ~＝ 0.01, and plasma temperature gradient, Ti=O (continuous (continuous curves) and Ti=0.5°K/km (broken curves). curves).

~~/kTic¥ /kTic¥ h-hc~ (1 吋）（広ジ (27)~~

~~so so far as i-i>O, the upper sign corresponds to increase in electron density scale height height and the lower sign to decrease, excluding the implicit effect of the temperature~~

gradient gradient on m ＋・ The right-hand side of Eq. (27) can usually be evaluated as several ral hundred km for the normal condition in Q+ dominant region, and as several thousand km in H+ dominant region. Thus, the electron density changes as described above. In In Figs. 9(a) and (b) are seen examples of neutral atmosphere model and topside ionosphere ionosphere model, where C=0.01, Too=l200 。K ，α＝1.0, and ,8=1.0.

~~4. 4. Comparison of Electron Density Profiles from Observations and Theory~~

Among five parameters given in (23) which determine the shape of the electron density density profiles, the thermopause temperature T 町 hence マ， gives the altitude of the deflection deflection point on the electron density profile, and this parameter can be fairly accurately accurately be determined, because the deflection points are clearly identified in the observed observed profiles as shown in Fig. 5. The parameterα ，hence Tic, as well as ion temperature gradient 'ri determines the scale height of the electron density profile except except the portion of profiles around the deflection point. It is not an easy task to distinguish distinguish the influence of 'ri from that of Tic because the influence of inclusion of i-i=0.5°K/km on the electron density profile is not so remarkable as seen in Fig. 8. The values of i-i=O in the region A<50° and 'ri=0.5°K/km in the region A>50° were adopted, because by these values somewhat better agreement between the ob- Analysis Analysis of Observational Data obtained by Alouette II (II) 201 servation servation and theory can be seen. It is assumed in the present comparison that /;=0, by reason of the fact that the influence of He+ in the case where I; is less than a few percent is not appreciable on the electron density distribution and also the fact that that the observed He+ concentration is less than a few percent in a wide altitude range <25・261. Further, it is assumed that {3=1 or Ti=1 ミeverywhere. The theoretical electron density profiles best fitted to the observations were chosen and are shown in Figs. 5 and 6. The appropriate parameters corresponding to to these profiles are listed in Table 1 and are also plotted against the geomagnetic latitude latitude in Fig. 10. A fairly similar latitude distribution can be seen between the plasma temperature determined from the present comparison and the nighttime electron electron temperature at lOOOkm from Explorer 22<211. Electron Electron density trough in the region A>55° was explained by higher thermopause temperature in that region, hence by lower ion density ratio [H つ／［ O+] there. there. Because of charged particle temperature also high in that region, some sort of of heating mechanism, for example, particle precipitations, may be operative in the trough trough region. On the other hand, mechanism of trough formation on the basis of the the idea of polar wind was suggested 印刷． Further study is needed for deciding which is the dominant mechanism, but whichever mechanism may be operative, the

~~国 d 帥・岨副 OAOAcpCPHRynk浦町官一帥問 brRben7。． 71 句” P36 ［伺 162 「 a 8 an・ 1♂ Hi'I Hi'I~~

~~Ne(cni')i Ne(cni')i 。． l ．‘ 105 105 ‘．‘ 1 ~ & ~ i 140m 内4r以。．． T Mnα） ’ぉ、副 . 』h 1 m ・。a4・ “ 1 :~~

~~Tp('K) 0・・ .~~

~~伊 30 ・ 60 。 90 ・ GEOMAGNETIC LATITUDE~~

Fig. Fig. 10. Probable physical parameters, the ion-density ratio ratio [H つ／［ 0 つat the reference level, 600 km, the electron electron density at the ref 巴rence level, Ne, the thermopause pause temperature, Too, and the plasma temperature, Tp （＝主（Ti+ Te)= Ti), are plotted against the geo ・ magnetic magnetic latitude. Nighttime electron temperature at about about 1000 km from Explorer 22 after Brace, et al. [27] [27] is also shown. 202 202 N. Matuura and H. Inuki

~~Table Table 1. Probable Ionospheric Parameters (Temperature (Temperature in °K, and Number Density in cm-3)~~

~~A<30° 130° ＜附O。14 代 A＜貯 Is 代 A ＜貯 Is 代的0° I 60 。＜A~~

Oct. Oct. 1966 T oo=lOOO T ~＝ 1000 Too=1600 T oo=l800 Tp=lOOO =1350 Tp=1500 Tp=1500 Tp=2400 Tp=2700 ～ Mar. 1967 Nec=l. 2× 105 =4. 5× 10' N ム＝ 6.0 ×10' Nec=6. 0× 10' Nム＝ 7.0 × 10• Nec=3. 0X104

Apr. Apr. 1967 T oo=l200 Too=l200 Too=llOO T oo=l200 Too=1600 Too=l800 Tp=1200 Tp=1200 Tp=1650 Tp=1800 Tp=2400 Tp=2700 ～ Sep. 1967 Nec=3. 5x 105 Nec=3. 0× 1Q5 Nec=l. 4× lQS Nec=l. 5 ×ms Nec=l. 5× lQ5 Nec=l.1X105

Oct. Oct. 1967 T 00=1000 Too= 900 Too=lOOO T 00=1000 Too=l400 Too=1600 Tp=lOOO Tp=1350 Tp=1500 Tp=1500 Tp=2100 Tp=2400 ～ Mar. 1968 Nec=l. 2× 1Q5 Nec=6. 0× 10' Nec=5.5 × 10' Nec=4. 0× 10' Nec=6.0 × 10' Nec=4.0 × 10'

Apr. Apr. 1968 Too=l200 T oo=l200 T 00=1600 T oo=l800 Tv=1200 Tp=1200 Tp=1800 Tp=1800 Tp=2400 Tp=2700 ～ Sep. 1968 Nec=3.0 × lQS N ム＝ 3.0 ×1Q5 Nec=l. 7× lQ5 Nec=l. 5× 10• N ム＝ 1. 3× lQ5 Nec=l. 0× 1Q5

~~existence existence of clear seasonal variation of the electron density in the trough region should should be taken into consideration.~~

~~5. 5. Conclusions~~

The average nighttime structure of the topside ionosphere over Japan during the period period from October, 1966, to September, 1968, was described by the use of Alouette II II data received at Kashima Station. The structure of the topside ionosphere differs much from the region where the invariant invariant latitude A<55° to the region where A>55°. In the region A<55°, the topside topside ionosphere is Q+ dominant below about lOOOkm level and H+ dominant above the the level. In the region A>55°, o+ dominant region extends up to near 3000km or higher, higher, and remarkable electron density reduction can be seen in this region, say, trough region. Clear seasonal variation such as higher electron density in summer and lower in winter can be recognized in the region where o+ ions are dominant. and on the other hand, no remarkable density variation can be recognized in th~ region region where H+ ions are dominant. The electron density at the reference level, the thermopause temperature, and plasma temperature can be fairly definitely determined by fitting the theoretical electron electron density pro 負les to the observations. Plasma temperature gradient and He+ composition composition were not definitely determined by this method alone. Comparison of electron density profiles between the observations and theory shows that the abrupt change of the topside ionosphere structure in d ～ 55° may be explained explained by an increase of thermopause temperature from about 10Q0°K in lower latitude latitude region to about 1800°K in higher latitude region. In higher latitude region where the temperature is high, the atomic hydrogen escaping from the exospheric Analysis Analysis of Observational Data obtained by Alouette II (II) 203 base base becomes intensive, and the reduction of atomic hydrogen density, hence the reduction reduction of atomic hydrogen ion density, becomes quite remarkable.

~~Acknowledgement~~

The authors wish to express their appreciation to the Members of the ISIS Working Group for placing the topside sounding data from Alouette satellites at the disposal disposal of Kashima Station, Radio Research Laboratories. Thanks are also due to Mr. Y. Ogata, technical liaison official of RRL to the ISIS Working Group, for his arrangement of the telemetry of Alouette satellites, and to Dr. I. Kasuya and Dr. K. Tao for their encouragement and support given in the data-reduction area. Thanks are extended also to Messrs. M. Kajikawa, 0. Ryuguji and C. Miki of Ka- shima Branch, RRL, who carried out the work of telemetry at Kashima Station, to to Dr. H. Hojo and Mr. T. Kaneko of the Information Processing Division for their their arrangement of information on the satellite orbital data, to Messrs. R. Nishizaki and M. Nagayama of Space Physics Section, Radio Wave Division, for their work of of ionogram reduction, and to Mmes. Negishi, Enjoji and Matono for their assi- stance stance in data analysis.

~~Referen 儲~~

( 1) Nelms, G. L., Barrington, R. E., Belrose, J. S., Hartz, T. R., McDiarmid, I. B. and Brace, L. L. H., Can. J. Phys., 44, 1966. 1419, ( 2) Ondoh, T., Matuura, N., Koseki. T., Nishizaki, R. and Kajikawa, M., J. Radio Res. Labs., 15, 59, 59, 15, 1968. ( 3) Matuura, N. and Ondoh, T., Space Research IX, p. 297, 1969, Proc. IEEE., 57, 1150, 1969. ( 4) Hagg, E. L., Can. J. Phys., 45, 27, 1967. ( 5) Muldrew, D. B., J. Geophys. Res., 70, 2635, 1965. ( 6) Thomas, J. 0., Rycroft, M. J., Colin, L. and Chan, ;K. L., Electron density profiles in ionosphere ionosphere and exosphere, Ed. J. Frihagen, North・ Holland Publish. Co., Amsterdam, p. 322, 1966. 1966. ( 7) Johnson, C. Y., J. Geophys. Res., 71, 330, 1966. ( 8) Brinton, H. C., Pharo III, M. W., Mayr, H. G. and Taylor, Jr. H. A., J. Geophys. Res., 74, 74, 2941, 1969. (9) Yonezawa, T., Space Sci. Rev., 5,3,1966. (10) (10) Bauer, S, J., J. Geophys. Res., 71, 1966. 1508, (11) (11) Maier II, W. B., Planet. Space Sci., 16, 477, 1968. (12 〕 McElroy, M. B., Planet. Space Sci., 15, 457, 1967. (13) (13) Ferguson, E. E., Rev. Geophys., 5, 305, 1967. (14) (14) Johnson, F. S., J. Geophys. Res., 65, 577, 1960. (15) (15) Hanson, W. B., Patterson, T. N. L. and Degaonkar, S. S., J. Geophys. Res., 68, 1963. 6203, (16) (16) Hanson, W. B. and Ortenburger, I. B., J. Geophys. Res., 66, 1425, 1961. (17) (17) Taylor, Jr. H. A., Brace, L. H., Brinton, H. C. and Smith, C. R., J. Geophys. Res., 68, 5お9, 1963. (18) (18) Bauer, S. J., J. Geophys. Res., 69, 553, 1964. (19) (19) Mange, P., J. Geophys. Res., 65, 3833, 1960. (20) (20) Prasad, S. S., J. Geophys. Res., 73, 6795, 19 槌． (21) (21) Jacchia, L. G., Smithsonian Institution Astrophys. Obs ・， Res. in Space Sci., Spec. Rept., 204 204 N. Matuura and H. Inuki

No. No. 170, Dec. 30, 1964. (22) (22) Spitzer, Jr. L., Chapter VII in The atmosphere of the earth and planets, Ed. G. P. Kuiper, Univ. Univ. of Chicago Press, 1952. 〈お〉 Kockarts, G. and Nicolet, M., Ann. Geophys., 18, 269, 1962, 19, 370, 1963. (24) (24) Rush, C. M. and Venkateswaran, S. V., Rev. Geophys., 3, 463, 1965. (25) (25) Maier, E. J. R., J. Geophys. Res., 74, 815, 1969. (2 め Hoffman, J. H., Proc. IEEE., 57, 1063, 1969. (2η Brace, L. H., Mayr, H. G. and Reddy, B. M., J. Geophys. Res., 73, 1印7, 1968. (28) (28) Banks, P. M. a凶 Holzer, T. E., J. Geophys. Res., 73, 6846, 1968.

~~Appendix~~

~~Thermosphere temperature above 120km level is approximately represented by the the following analytical form given by Jacchia <211 :~~

~~T(h)=Too 一（Too 一九） exp ［ー s(h-h 。）］， (Al)~~

~~where the su 血x0 refers to the quantities at the turbopause level h0=120km, and~~

T co is the asymptotic thermopause temperature. Jacchia 削 gave the coefficient s as a function of Too, but more detailed comparison between the thermosphere temperature ature given in CIRA, 1965, and that obtained by the analytical expression in Eq. (Al) suggests suggests that better agreement between them is attained by taking consideration of the the local time dependence of s. Resultant expression s can be given in the form:

~~s(t，九）＝ ex市（ t)+A 叫 T~K))] (A2)~~

~~and~~

T官（乙 M)=D （の＋C(t ）・M, (A3) where t denotes the local time (in unit of hour), M is the model number (1 ～ 10) given given in CIRA, 1965, and A, B, C and D are given as the functions of local time in in Fourier expansion series:

~~12 π nt¥ ..-. 12 π nt¥ A(t) = L: Un COS ｛ーァ）＋ :EαJ sin （ー－ l ¥ 24 I τ ＼ 24 I~~

~~B （叫んcos （警） + ~ ,Bn ＇蜘（警） (A4) (A4) 12 π nt¥ 12 πnt 、 cc の＝石川 OS ~五十~ Tn1 sin~五）~~

~~D(t ）＝子い OS （警）＋号 On1 sin （警）~~

The numerical values of coefficientsα 耐 αn1, etc. are given in Table Al for n= 0, 0, 1, 2, 3 and 4. Steady state density distributions of the major neutral constituents, 0, N2 and 02, 02, under diffusive equilibrium condition are determined by the following hydrostatic equation: equation: Analysis Analysis of Observational Data obtained by Alouette II (II) 205

~~Table Table Al. Numerical values of Fourier coefficients.~~

n 。 1 2 3 4 α，z -0.23463 一0.13103 -0. 00911 0.00288 0.00174 α，J 0.00000 0. 21187 0.02094 -0.01142 0.00449 Pπ Pπ -3. 98255 0.22247 -0. 00616 -0.02397 0.00429 ん’ 0.00000 -0. 09282 0.02605 -0. 01289 -0.00802 rn rn (°K) 109.128 -15. 850 -1.366 0.995 0.364 rn ’（ oK) 0.000 -18. 579 0.034 2.039 -0.327

~~On On (°K) 倒5.770 -137.136 31. 276 5.443 -6.108 ゐ’（ oK) 0.000 -27.140 13.943 2.989 0. 712~~

~~on ；上「 1 oT 上m;gl 剖ー＿n す瓦＇ Lr 百万一＇ /iT J,.1-v (A5)~~

where nJ and mi are the number density and the particle mass of j th species of the the neutral constituents, k is Boltzmann constant, g is the acceleration of gravity, and the thermosphere temperature T is given in (Al). The solution of (A5) is given: given:

~~日 Jo （争）叫－ ~：• .!f!/dh J~~

:::::nJ0yr1[y+a(l-y ）］ー（！＋ 71> (A6) where the height dependence of the gravitational acceleration is neglected as compared pared with the height dependence of the thermosphere temperature in the course of integration integration with the height, r is the radial distance from the earth ’s center, r=RE + h (R rc is the earth ’s radius), and

~~y=exp[-s(h-ho)]~~

~~r1 ＝笠 fK.q_( ..!'.!!) 2 skToo skToo ¥rl~~

a= Too/To ・ Steady state density distributions of the secondary neutral constituents, He and H, including the effects of thermal diffusion and escaping from the exospheric base are are determined by the following equation for j species according to Kockarts and

~~Nicolet 倒｝：~~

~~伽j ..I- 「旦土生ilR..1-'!!!l.ε1 叫， ..1-~ ｛引 2=0 (A7) 百万’ L T oh ' kT 」日 J ・ DJ¥ rl ’~~

where α TJ is the coefficient of thermal diffusion, DJ is the coefficient of diffusion, and Fd.J is the effusion flux at the exospheric base, rd. ・ The effusion flux Fd.J is given given by Spitzer<22> as follows: 206 206 N. Matuura and H. lnuki

.J =n .J kTa {l ＋盟生）e { m 判豆町riV;. (A め 'V 'V 2π m, ¥ kTa J xp ＼－~） where the su 缶x d refers to the quantities at the exospheric base, and Vi is the effusion effusion velocity. The solution of (A7) can be given in the form :

~~円附＇.＞［ 1ー（芳）E1h （の］ (A9) where~~

~~Wj(r) =yrJ[y+a(l-y)J-U+r1 句 Tj)~~

~~ん作j；閉会）（最）（わ (AlO)~~

~~E1 ＝咲（ど r The density at the exospheric base, n;ri, is given by (A9) as follows:~~

~~n1ri 判的［ i－（封切 rt]. hence~~

~~n1ri=n10W1ri/(l+EjW戸ha)• (All) Inserting Inserting (All) into (A9), we obtain~~

~~戸内W 「l+E;W 戸Chri-hll (A12) 1L 1L l+E1Widl~~