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 By 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 den- sity 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 receiv- ed 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 elect- ron 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 la- titude 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.