Vol. Vol. 21 No. 106 Journal of the Radio Research Laboratories 1974 Printed Printed in Tokyo, Japan pp. 311-340
UDC 523. 7: 525 “1972.08 ”
SOLAR-TERRESTRIAL DISTURBANCES OF AUGUST 1972
4. 4. SOLAR X-RAY FLARES AND THEIR CORRESPONDING SUDDEN IONOSPHERIC DISTURBANCES
By
Mitsuo OHSHIO
(Received (Received Feb. 22, 1973)
ABSTRACT
Four Four solar X-ray flares which occurred early in August, 1972, were large, being being inferred from sudden ionospheric disturbances caused by the pertinent flares. The time variations of the solar X-ray flux intensity observed could not be obtained obtained at the maximum stage of these four events owing to the artificial satel- lite lite eclipse and/or the saturation of the detector. Both of estimation from extra- polation polation in the shape of time variation and from the maximum phase deviation of of the normalized sudden phase anomaly (SP A) observed show that the maximum solar solar X-ray (1 ～8 A) flare flux intensities or the maximum enhanced ones for August August 4 and 7 were as large as to exceed 1 erg cm-2 s-1. Their decreasing stages stages were as long as to last more than half a day. The use of a flare model valid valid for the arrival of solar ionizing agents of the largest class during the pertinent pertinent period showed that the enhanced electron density in the ionosphere was larger larger than the quiet one by about two orders at the altitude of 70 km and by 2 to to 1 times at the altitude of 90 to 120 km. is It supposed that in these four events, particularly particularly in August 4 and 7 events, solar extreme ultraviolet ray flares also occurred occurred to cause all kinds of sudden ionospheric disturbances on their largest scale. scale.
1. 1. Introduction
Early in August, 1972, large-scale solar eruptions seen rarely occurred, also caused various large-scale disturbances both on the solar disk and in the earth ’S ionosphere and magnetosphere, and increased the cogmtion on the solar-terr 田 trial physics physics which had never been experienced hitherto. In this paper, the disturbed phenomena in the pertinent period are described in terms of solar X-ray fl.ares and sudden ionospheric disturbanc 白. Since the data on sudden ionospheric disturbances disturbances were limited to those observed at the Laboratories, the data could not help receiving restriction largely in space and in time, but the event on August 7 depended upon foreign data. In spite of many restrictions, the con- sideration sideration on the elongation of the relation of magnitude of sudden ionospheric
311 311 312 M. Ohshio disturbances disturbances to enhanced solar ionizing intensities which has been given by the author author and the estimation for the presumed maximum enhanced flux intensities of of solar ionizing agent owing to the saturation of the observed data and/or to the the artificial satellite eclipse are compared and investigated. Further, enhanced electron electron densities in the ionosphere are estimated by a flare model valid for the arrival arrival of solar ionizing agents of the largest class during the pertinent period.
2. 2. Data Used The data used on solar ionizing agents completely depended upon the results of of solar X-ray flux intensities with wavelength ranges, 1～ 8, 8～ 20, and 0.5rv3 A observed observed by solar X-ray monitoring satellites, SOLRAD 10-Explorer 44 and SOLRAD 9・Explorer 37, under the superintendence of R. W. Kreplin, U.S. Naval Research Laboratory. ci ＞～（ 8) Out of the data on sudden ionospheric disturbances observed at the Labora- tories, tories, the available radio wave propagational circuits and their geographical disposition disposition are shown in Table 1 and Fig. 1. Further, the event on August 7 depended upon the sudden phase anomalies (SPA's) on the circuits received in Sao Paulo and with small representative solar zenith angles.
K;ndof N。。 f SIO's SIO's C"c 凶IS Mo•ks ~Vl.i:. SPA 8(1 。INUBO) ー一一一－ －＼ SPA 1 (lo HIRAISO ）ー・－－－－－ ＼ SWF 4(1o HIRAISO) ---・
Fig. Fig. 1. Geographical disposition of radio wave propagational cir- cuits cuits received at the Radio Research Laboratories, available for detecting detecting sudden ionospheric disturbances. Out of the circuits shown, shown, those given in Table 1 are adopted. The Loran-C circuit, circuit, IWOJIMA-HIRAISO, and the SWF circuit, SHEP- PARTON-HIRAISO, PARTON-HIRAISO, are superposed each other on the map. Table Table 1. Available radio wave propagational circuits detecting sudden ionospheric disturbances.
Transmitting Site Receiving Site Distance along the LKαorロrmnDPnNhι Kind Call R11;dia Location Great Remarks Sign 向 gd ほ tion HV Circle of of Name 円し 剖 1 Frequency Name (Geographic or ∞ ノ Power (km) SID ’s Abbr・. (kW) Coordinate)
52°22'N 16. OkHz Fr 巴quency RUGBY GBR 001°1l'W 40 9550 Standard めと白培、・ NORTH 21°49 ’S WEST NWC 22. 3kHz 1000 6990 U CAPE 114°10 ’E S42寸 10.2kHz 35 。42 ’N Omega 21°24 ’N INUBO HAIKU・ HAIKU 12. 2kHz 2 140°52' E 6100 Navigation 町、足』 157°50 ’W 13. 6kHz SPA 44°39 ’N NV2Hhh CUTLER NAA 067°17'W 17.SkHz 1000 10640
『 JIM 48°12 ’N 18.6kHz 250 bbw CREEK NPG 121°55 ’W 7620 同門司旬。
qOpnunHu。。nJuqonLooNE H RA Y GU O h 24°4S'N A－ IWOJIMA 100 kHz 4000 司自ム組処 1290 Loran-C ． 141°20' E bNhhHaahbuwN
、111tilia 35°41 ’N 21MHz( 3-13) EJV TEHERAN Te 051°25' E lOMHz(13- 3) 7700
－－ t SHEPP AR- 36°20' s 、〆H官・ RA v－Qu O 36 。22'N i A A SWF Sh 18MHz( O・- 8) 100 ｝ ・s100 TON 145°25 ’E lht 140°38 ’E ’ 18MHz(20- 6) fll 12°03 ’S ト LIMA Li 15MHz( 6- 8) 10 tJ 15380 077°03 ’w llMHz( 8-13)
NOTES: 1. The value of Distance along the Great Circle (km) is rounded in the first place. 2. 2. The number within the parentheses successive to the frequency of SWF denotes time interval (U. T.) during during when the frequency had been transmitted in July and August 1972. ωHω 314 M. Ohshio
3. 3. Time Variations of Solar X-ray Flux Intensities There are shown in Fig. 2 the observed hourly average so!ar X-ray flux intensities intensities F (A.1 ～ん t) with wavelength ranges, A.=1 ～8 and 8～ 20 A from July 25 till till August 16, 1972. It is immediately noticed in the figure that there are four giant giant X-ray flares conspicuous in both ranges. Out of them, two, one, and one flares flares are situated on August 2, 4, and 7, respectively. Also on August 11 a 宜are with large F(S ～ 20 A ，の is recognized; however, the flare is indistinct in terms of F(l ～sA ，め. If the above-described four flares are paid attention to, each each F(l ～8 A) of these maximum values exceeds 10-1 erg cm-2 s一九 and conversely the the flares whose maximum values of F(l ～ 8 A, t) exceed 10-1 erg cm-2 s-1 are limited limited to the above-described four flares in the period shown in the. pertinent figure. figure. They have 1.72 ×10-1, 1.29 × 10 1, 3.43 ×10-1, and 4.56 × 10-1 erg cm-2 s-1 in their their maximum values in the order of time, even in their hourly average F(l ～ 8 A, t). It is conjectured, therefore, that these flares are still larger in their instantaneous instantaneous maximum flux intensities Fm(l ～ 8 A, tm). In this sense, so far as solar-terrestrial solar-terrestrial disturbed phenomena early in August, 1972, are discussed from the the point of view of solar X-ray flares, th 白 e will be called four giant solar X-ray 但ares worth noticing. They are named solar X-ray flare event Nos. 1. 2, 3, and 4 in the order of lapse of time. As seen in Fig. 2, the flux intensities at the starting time, t,, of these flares, F,(1 ～sA t，） ’s are as large as other flares existing actually to whose Fm(l ～ s A, t，） ’s the the values of F ,(1 ～ sA, t，） ’s correspond. <4J,<•J Especially, large are F ,(1 ～ sA, t，） ’s in in Event Nos. 2 and 1 and F,(8 ～20A, t，） ’s for 4 events. These values are difficult to to be recognized as the quiet values of flux intensities in terms of long-term variations variations of flux intensities. If t,(A.1 ～ん Event No. 1) is retroactive, F(A.1 ～ん， t) decreases decreases gradually as a whole including even flares with smaller hourly average maximum flux intensities than F ,(A.1 ～ん t,, Event No. 1). Though on July 28 a medium scale of flare occurs, F(A.1 ～－＜ u, t) still decreases, and on July 25 the mini- mum value which seems validly to have reached a quiet value is found out in terms of the whole tendency. The day when the flux intensities seem to have
reached reached their quiet value throughout the above 司 described four giant flares is August 16 especially in F(8 ～ 20 A，の. The 21 days of the period, therefore, will be discussed that the solar X-ray would have been in a disturbed period even if if no large flares had occurred. Thus, the minute observation of solar X-ray flux flux intensities will be an index to the prediction of solar disk disturbances. This This fact will be much clearer, on the other hand, if it is considered together that that each of the plage regions with direct relation to the occurrence of these four four giant flares is the identical McMath No. 11976 one (Event No. 2 may relate to to 11979 and 11974 regions), that the 11976 region is the most active also before and after the period of occurrence of these four giant flares, and that also the solar solar X-ray flux intensities have large values from the appearance of the pertinent region region on the solar disk till its immersion. Actually F(A.i ～ん t）’s increased after the the appearance of the 11976 region on July 28, on the day of the solar central meridian meridian passage of the pertinent region Event No. 3 occurred, two days before Event Nos. 1 and 2 did, and three days after Event No. 4 did. By the immersion ＼
nunuFIMO 0ZEO・ －h 山’ Z seq ロト由 』戸田町 eH 回口芝 ト hmFF Eυpo 由 mu mFF mFF u 一切白区－－「 FF ー－－ F{ B-20A, t) 玄n－ 一一 F{1-BA,t) （て コ－ LhoztzzhmMBcsc」門戸 』 EX め口町白司、・ o』 －omω00 MZ － ミ・ミ崎町立白 』 ω hb 〉《 なさ『 b 』コ。ェ FSR
リ窓口＼ 万 a由と ωω20 b 宮崎史的
104 104 HHUH 25 25 26 27 28 29 30 31 2 3 4 5 6 7 8 9 10 11 12 13
一同 July July August SOLRAD 9- Explorer 37 臼 LRAD 10 - Explorer 44 1972 Fig. Fig. 2. Time variations of observed hourly average solar X-ray flux intensity F （ん～ん， t) (erg cm-2 s-1) in the wavelength ranges of .t=l ～8 and 8～20 A from July 25 till August 16, 1972.(1),(2) It is shown that till July 31 31 and from August 1, SOLRAD 9・Explorer 37 and SOLRAD 10 ・Explorer 44 measured, respectively. From July July 28 till August 12, McMath plage region number corresponding to the X-ray flare is shown right above each flare<2>. flare<2>. The vertical lines and the arrows on July 28 and August 11 denote appearance and immersion of 11976, ωH respectively, respectively, and (CMP) on August 4 denotes its central meridian passage. 日 316 M. Ohshio of of the pertinent region on August 12, F （ん～ん t) especially F (I ～sA ，め decreases gradually. gradually. Accordingly, it will be discussed that so far as solar X-ray flar 田 are concerned, concerned, the four giant flares occurred mainly relating to the McMath plage region region No. 11976. How rarelly seen large area the pertinent region had will the X-ray heliograms tell. Cl),<2> Further, the solar activities in the pertinent period are discussed discussed in detail in another paper. cs>
4. 4. Presumption of Time Variations of Solar X ・ray Flare Flux Intensity
Since Since the solar X-ray flares are available in wavelength ranges of え＝ 0.5 ～3, 1～ 8, 8～ 20, and 1～5 A (the last one only is given by graphs'8'), A=l ～ sA is treated by the fact that the height distributions of local photoionization e伍ciency Y(x, z）’s (Fig. 3'7') of the photons corresponding to these wavelength ranges for a standard standard neutral atmosphere of the earth and the altitude of effective occurrence of of the available sudden ionospheric disturbances are considered together. The available data on the time variations of observed solar X-ray flux in-
180 180
150 150
100 100
~ 50 E 』園 E N
~ 0 コ ・4 ~＝ 90＇・ ・d <( 150
100 100
0.5 0.5 50 50
0 1Cf11 1Cf11 1（）＂咽 llf-I 168 167 166 165 16" 10'3
Local 問、 otoi ロniz ロ lion Efficiency , Y（首， z)(el 民 tron ・ion pairs 附咽 ton cm)"1) Fig. Fig. 3. Local photoionization efficiency Y （χ＝O & 90°, o孟z(km ）孟 180) 180) （ ~lectron-ion pairs (photon cm)-l)Cηfor the wavelengths of of l=0.5, 1, 3, 8, and 20 A. Sola れ Te ，γestrial Disturbances of August 1972 317 tensities tensities valuable for the study of sudden ionospheric disturbances brought no information information in the vicinity of each maximum flux intensity, because the pertinent four four giant flares were too large. This is considered to be due to artificial satel- lite lite eclipse and/or saturation of upper limit of measurement by detectors or their their insensitivity. ( i) Vicinity of the maximum value Time intervals on defective records due to saturation and/or artificial satel- lite lite eclipse were presumed by extrapolation especially in the vicinity of the maximum value. In this case, it was assumed that the aspects of F(I ～BA, t) before before and after the time interval of defective record were maintained as they were also in the very defective time interval. In In case of Event No. 1, as shown in Fig. 4 (a), there were presumed a curve elongating elongating the curve to bind points P1 and P2 (the elongated curve was nearly straight straight to the crossing point A or B) and two kinds of elongated curves, a point Pa Pa and the same time intervals recording the decreasing stages in other wave- length length ranges being considered. Accordingly, the two crossing points, A and B (FA> FB), were obtained. In case of Event No. 2, the values of F(I ～ sA, t) before before and after the time interval of defective records, i.e., the ending value at the the increasing stage and the starting one at the decreasing one are almost equal. equal. <3> The pertinent defective record may originate in an artificial satellite eclipse eclipse alone. In case of the pertinent event, as shown in Fig. 5 (a), there1were presumed a curve elongating the curve to bind points P1 and P2 and an elongated curve curve in which a point Pa and the same time intervals recording the decreasing stag 田 in other wavelength ranges were considered. Since both curves together had a curvature with convexity upwards, the extrapolated part was relatively little. little. In case of Event No. 3, as shown in Fig. 6 (a), there were presumed a straight straight line drawn from a point Pa parallel to the straight line to bind points P1 P1 and P2 (the line was in ~ood parallel relation to the straight lines to bind the respective respective corresponding points for A=l ～5 and O～3 A <3l) and an elongated curve in in which a point P4 and the same time intervals recording the decreasing stages in in other wavelength. ranges were considered. Since Event No. 4, as shown in Fig. Fig. 7 (a¥, had relatively a little increasing part and nothing to help presumption as as Event No. 3 had something, the presumption was most di 伍 cult for the in- creasing creasing stage. However, the starting point Pa 山 of the saturated value at its decreasing decreasing stage o妊ers the only help. That is, the increasing curve will not intersect intersect a segment P8P4. Therefore, the case where the increasing curve passes over over a point Pa will correspond to the case with the slowest 。increasing stage. In this this sense, the presumed maximum flux intensity Fm (I ～BA ，ん） will be to give its its lower limit. Hereupon, there were presumed an elongated curve passing over over points P1 and P2, passing through the record P1P2, and passing over a point Pa Pa and an elongated straight line to bind points P2 and Pa. On the other hand, there there was presumed an elongated curve in which a point P4 and the same time intervals intervals recording the decreasing stages in other wavelength ranges were con- sidered. sidered. Accordingly, two crossing points A and B (FA> FB) were obtained. (ii) (ii) Starting time As already described in Section 3, the starting times of the pertinent four 318 M. Ohshio flares, flares, i.e., the quiet time should be in common at least on July 25 in terms of long-term long-term variations of the flux intensities. Here, however, individual local starting starting times are given. In case of Event No. 1, the starting time was presumed to to be between points P1 and P4. In case of Event No. 2, the starting time was presumed to be between a point P 4 and a point (1923) ＜め where an artificial satel- lite lite eclipse started immediately before the point 巳. In case of Event No. 3, the starting starting time was presumed to be between points P1 and Ps or to be at a point P6 P6 itself. It is considered that local quiet values were lasting for several hours before before the occurrence of the pertinent event, so far as the recorded part existed. In In case of Event No. 4, it is difficult to assume that the starting time is at a point point P1, because of F(P1) :::::4 × 10-a erg cm-2 s-1. If the flux intensity is retro- active active from the point P1, it is considered that local quiet values were lasting for several several hours before the point Pe, so far as the recorded part existed. There- fore, fore, the starting time of the pertinent event is presumed to be between points Ps Ps and Pe. (iii) (iii) Ending time It It is a common concept that the ending time is most di 伍cult in its determin- ation ation as compared with the maximum time and the starting one. <4l Accordingly, an error of 0.5 ～1 hour in its determination is inevitable, and time as early as possible possible was adopted. In Figs. 4, 5, 6, and 7 (a), the time variation in their decreasing decreasing stage is ended at the presumed ending time. Conversely, F. is accompanied by not so large error in spite of so wide variations in determining t. ・
The above presumed values are tabulated in Table 2 in the lump. In the table, table, .tlFm was obtained from Fm-Fs ・ In spite of difficulty in determining t, and F,, since both Event Nos. 3 and 4 have relatively large F 叩’ s and have F ，’s considered considered to be valid, F. ’s did not influence the value of the third place in
.tlF 明、. Accordingly, in this accuracy L1F m is entirely equal to F 問 in both events.
Further, Further, the relative errors in case of substituting F 隅 for .tlF 悦 were less than about about 0.3 and 2 % in Event Nos. 1 and 2, respectively. Since F, is regarded as constant constant for a month or so, the presence of L1Fm cannot be neglected for smaller Fm, Fm, i.e., for smaller flare.<4l Also from the physical point of view, what corre- sponds sponds to an enhanced electron density produced by flare, .JN （χ，ふん～ん） is strictly strictly an enhanced flux intensity, L1F(J..i ～んふ It originates in the giant flares that that the above-described .t1 F. 畑、 are well approximated with Fm ’s, and they are exceptional. exceptional. It is for the shape of a flare on the graph showin~ the relation of its its flux intensity to time, however, that the determination of t, influences. Further, Further, though at the decreasing stage each of Event Nos. 3 and 4 seems to to have two or three minor peaks, cai each of the events is assumed to decrease uniformly uniformly from a viewpoint of the whole tendency. However, the inflexion of the the curve found out at the early period of their decreasing stage in Event Nos. 2, 2, 3, and 4 was reproduced faithfully.
5. 5. Properties of Solar X-ray Flares
As presumed in Section 4 and shown in Table 2, the pertinent four X-ray Table 2. Solar X-ray flares and their related observed sudden ionospheric disturbance phenomena
2
1972 1972 ~ug. 2 五ug. 2 Aug. 4 Aug. 7 Aug. 7 Aug. 7 三間 time (U. T.) ~ ・magnitude time 〔U. T.) magnitude time (U. T.) magnitude time (U. T.) magnitude time 尽 J. T.)magnitude time (U. T.) magnitude 一一一 1914 く t.< 1947
0623-06260 ー Te Te 32D SWF 0314-0328D-0535 D -0733 0253-0256-0315 0350-0403-0435 Sh Sh 32D 0622-06~~ D* 25D 23D" 0314-0333D-0448 0314-0333D-0448 0623-0637-0718D 0252-0256-0310 0356-0406- 0430 J~dB) Li 34D 48* 8 7 kA 宮内宮崎 NOTES: 1. As for P;, A, and B in the column of Flux Intensity, see Section 4 in the text and Figs. 4, 5, 6, and 7 (a). HhhM 2. 2. The blank in the columns of SPA and SWF denotes no ~henomenon. The mark, asterisk denotes a multi-peak phenomenon. D following a value indicates that the true value is greater than the listed value. 芯 3. 3. The last number on eacll__ circuit line in the column of SPA denotes an approximate value of representative solar zenith zenith angle on the circuit ，χ（。） at a time in the vicinity of tm (cf. captions of Figs. 4～7 (b) and 9 (a), (b)).. 4. 4. In Event No. 3, tm=0635 must be altered to h 孟0634, judged from available observed SPA ’s. Fm (1 ～s A, tm=0634)= 2.06 ×10°ergcm 2s 1 is presumed (cf. Section 6. (III) in the text). 5. 5. In Event No. 4, it should be minded that tm, u (both in (A) and (B)) gives the upper limit by the. presumption and that Fm, Fm, i accordingly L1Fm, i (both in (A) and (B)) giv~ the lower limit by the presumption. Judged from the SPA
自ares are indeed large-scaled and are as rare as one cannot easily experience. Especially, Especially, the fact that the maximum enhanced flux intensities, .dFm (1 ～sA ，九） in in Event Nos. 3 and 4, exceeded 10~ erg cm-2 s-1 (which was a presumed value thoroughly) thoroughly) is considered to be probably unprecedented, if a brief history of observation observation on solar X-rays<4l is read describing the qualitative discovery of solar solar X-rays in 1948, the quantitative detection of solar X-rays in quiet state in 1949, 1949, the photometrical detection of solar X-rays in disturbed state in 1949, the succ 白 S in the observation by means of the first solar radiations monitoring satel- lite lite in 1960, making public the r白 ults of observation by artificial satellites since 1961 1961 (completely continuous to the public since March, 1965, up to date), and so on. on. In In this sense, it seems to be significant that a glance is cast at the properties on shape of these four giant solar X-ray flares on the graph showing the relation of of their 宜ux intensity to time. Especially cognition will be physically important as as to if the pertinent giant 宜ares have quantitative extension of the properties which .dF 郁（ 0.5rv5 A, tm) （叫 or .dF, 間（ 1～s A, tm） 【 ~l-;§10-1 erg cm-2 s-1 indicated in the past, past, or have properties different from them. First, First, if F ,(1 ～8 A, t,) and F.(1 ～8 A, t.) are compared, F. ’s of each event have not not quiet values in a true sense, but have relative and local quiet values in the disturbed disturbed period, because the period of the starting times for the pertinent four flar 白 corresponds to a disturbed one of the sun as already described in Section 3. 3. Accordingly, indeed the values of F. (Even~ Nos. 1 and 2) are large as already d田 cribed in Section 4 or seen in Table 2, but the adoption ofF. for both events is not not so unreasonable from the point of view of validity that F. and F. of a flare are are nearly equal. The following are !Oughly d白 cribed compard with the study<4> of 35 events concerning concerning .dFm(0.5 ～5 A, tm). Though the absolute values of various physical quantities, quantities, especially of single quantiti 田（in the sense of fundamental unit) cannot cannot be directly compared each other because of discord of the wavelength ranges, ranges, the comparison of absolute values of physical quantities with the from of ratio ratio (in the sense of derived unit) will be valid. When d凡 is large, the dura- tion tion of increasing stage •1 and that of decreasing one rd are together large.
The of relation •1 to .d F, 明 seems to be on the elongation of the relation concern- ing ing .dF. 明（ 0.5 ～5 A, tm), but d.dFm/dr1 is smaller. The relation of •a to .dF. 鴨 is similar to to that of •1 to .dF, 和 Buf d'1Fm/dra is further smaller. The mean speed of in- creasing creasing and decreasing stag 白 of F, respectively si and sa, belongs to the medium or or the large groups, and the situation is quite usual. This originat 邸 in both larger larger '1F 幅 and longer duration required. As for the type of increase at increasing stages, Event No. 1 seems to belong to to pure rapid increasing type, Event Nos. 2 and 3 to quasi rapid increasing type, and Event No. 4 to rapid after slow increasing type. The increasing ratio of flux intensity, intensity, Fm/F, is quite usual in Event Nos. 1 and 2, while large in Event Nos. 3 and 4. This ori~inates in the fact that the former two events have relatively small small F 抗 and relatively large F, and that the latter two events vice versa. •a ’s have about 14.5, 13.0, 13.5, and 16.0 hours m the order of the events and are extremely extremely long, while the ratio of duration required of decreasing stage to that Solar-Terrestrial Solar-Terrestrial Disturbances of August 1972 321
of of increasing one, r:d/r:1, belongs also to the usual or the large groups. The
relation. relation. of r:d/r:1 to AFm is on the elongation of the relation concerning AF. 隅 .(0.5 ～5A ，ら）， if Event No. 4 showing rapid-after-slow-increasing-type is excluded. Since Since it is assumed that Fat the decreasing stage decreases uniformly, the dis- tinction tinction cannot be made ~etween monotonous and multi-stage decreases. The mean time constants of F, :r ’s, are 143, 189, 111, and 115 minutes in the order of events, events, and are extremely long. The relation of r to AFm seems to be on the elongation elongation of the relation concerning AF. 叩（ 0.5 ～5 A, tm), while dAFm/dris extremely small. small. Accordingly, Accordingly, the pertinent four events have extraordinarily large r:1, r:d, and r. r. These relations to AF, 隅 do not derive continuity to, discontinuity to, or qualita- tive tive difference from the usual flares in the past, because these relations are far apart apart from those. If the pertinent four events are assumed to come under the elongation elongation of the relation concerning AF, 隅（ 0.5 ～5A ，九） in the past, it is discussed that that the slopes of the above-described three quantities to AF. 醜 are far smaller than than those in the range to which these quantities in the past belonged. It It will justly be regarded that the descri~tion above depends thoroughly upon the presumed values which seem to be valid.
6. 6. Sudden Ionospheric Disturbances Observed The sudden ionospheric disturbances are described which were caused by the above-described above-described four giant solar X-ray fl 紅白 and which were observed at the Laboratories. Laboratories. The VLF radio wave propagational circuits appearin? in Table 1 are are not all the circuits to have observed them. As for Loran-C radio waves, the electric electric field intensities from the master and three slave stations are observed, and sudden field anomalies, SF A ’s, which were detected by means of them will be discussed in another paper. cs> (I) (I) Event No. 1 The sudden ionospheric disturbance phenomena, the disposition of the propaga- tional tional circuits, and the positional relation of the sun corresponding to the solar X-ray X-ray flare Event No. 1 are shown in Fig. 4(a), (b). The starting, the maximum, and the ending times and the maximum deviations are given in Table 2. Since the the pertinent event brought the smallest solar zenith angle χin Japan out of the the four giant flares as seen in Fig. 4 (b), there occurred large SPA ’s and SWF ’s respectively respectively exceeding the maximum SPA Aif>m=100° and the maximum SWF AEm=30 dB except Teheran-Hiraiso circuit. It is questionable why a clear SWF did did not occur, although Teheran-Hiraiso circuit was in the sunlit hemisphere over over the whole circuit and had never so large representative solar zenith angle χon the circuit. Indeed the pertinent event brought relatively small χ’s over all all the available circuits, but the magnitudes of SPA ’s and SWF ’s were in the ・second or the third rank and the second one out of the 4 events respectively because because the AFm was in the third rank out of the 4 events. Each of the disturbance phenomena occurred between P1 and P2 in Fig. 4(a). Since Since the arrival time lag of the maximum disturbed phenomenon from the presumed time of the maximum solar X-ray flare flux intensity, ti, m constitutes 322 322 M. Ohshio
Solar X- ray Flare Event No. 1 and 5.1.D.
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Solar Solar X-ray Fla 陪 Event No 目 1 1972 August 2
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乱
h （白刀｝凶 ↑二回2 曲一C ．〉〉． FcgLO － 凶一ロ」一 u －山一工恥 h－oZ
（乱，） (b) Fig. Fig. 4. (a) Observed and presumed time variations in solar X-ray flare flare flux intensity for Event No. 1, F(l ～8 A t). As for the method of presuming and the points Pt, A, and B attached to to the curve, see Section 4 in the text and Table 2. Observed available available sudden ionospheric disturbances corresponding to the F, F, SPA ’s (VLF), and SWF ’s (cf. Tables 1 and 2). (b) Geo- graphical graphical disposition of propagational circuits, of the subsolar point point (a circle), and of the day and night boundary line (a curve with oblique lines) at the altitude of about 90 km at 0358 (U. T.) in the vicinity of the presumed time of the maximum flux intensity ，向（ 1～ s A). Solar-Terrestrial Solar-Terrestrial Dzstz げ bances of August 1972 323 tz,m=3 tz,m=3 min. except uncertain SWF ’s, the presumed tπ ，＇ swill have been valid. On the other other hand, however, in case that an SPA to make the altitude z=70 ～ 70 km effec- tively tively occurring altitude, 11¢ has relatively small X, the follow of il Solar X- ray Flare Event No. 2 and 5.1. D. 1972 August 2 ...... 10ols . 1~ ~o .ベ 2. ~ と }n "iii 主 1o-l C 「~ n 向·~，出 ~Li:' lcf 守 MHAHIuH HU EBEE （ ghw －－ 』 。吉正0 8・ ）令 ow Sol ロ rX-ray Flare Event 1972 No:2 August 2 ．〉〉 dLJ Kind of No. of SfO's SfO's c;,.,,,15 Mα ＇＂ ・0OF SPA Sito INUBOI 一一－ SPA 1 (to HIR 刈SOI ーーーー－ 9・SWF 叫 to HIRAJSO ）一一ー 守 〉恥 EE4T4” ed ogu 正 NWC I 』申一回 ovmu（ 50 50 C ．〉〉・）凶 曲射「』】勺一山一 0 ZL。凶一ロ』一工 40 Shi: Shi: 0 工半。 50 50 h－ o・ 10 10 12 14 16 18 20 Time. Time. h( h,135EMI) （乱） （ゆ Fig. Fig. 5. (a) Observed and presumed time variations in solar X-ray flare flare flux intensity for Event No. 2, F(l ～8 A, t). As for the method of presuming and the points P; attached to the curve, see see Section 4 in the text and Table 2. Observed available sudden ionospheric disturbances corresponding to the F, SP A ’s (VLF), and SWF ’s (cf. Tables 1 and 2). (b) Geographical dis- position position of propagational circuits, of the subsolar point (a circle), circle), and of the day and night boundary line (a curve with oblique oblique lines) at the altitude of about 90km at 2045 (U. T.) in the the vicinity of the presumed time of the maximum flux inten- sity, sity, tm(l ～s A). Solar-Terrestrial Solar-Terrestrial Disturbances of August 1972 325 good follow already described in (I) is considered together, Fm (1 ～8 A, tm) of the pertinent pertinent event is considered not to have been acute but to have tended to have some duration. Since ti,m for Fm （ら） with some duration is generally larger than that that without any duration ，＜引 min t，，叩＝ 8 min. may suggest that the presumed tm tm is not so wanting in validity. The duration of decreasing stage rd of the pertinent SPA ’s was adopted to be longer than that of Event No. 1 (cf. Table 2). In this case, F(l ～8 A, t,, s) has an order of 10-a erg cm-2 s1 and is smaller than in the case of Event No. 1 by about about one order. This is considered on the ground that the inflexions at de- creasing creasing stage in both SP A ’s showed the distinct aspect different from the curve of of quiet daily variation in the pertinent time interval. At all events, the fact that that the ending time of sudden ionospheric disturbance phenomena, t,, 8, is earlier than than f, for several hours for the pertinent event to have [enhanced] flux intensity at at its ending time t. whose magnitude will be fully equal to the maximum flux intensities intensities of other X-ray flares will originate in the fact that the pertinent event had extremely long r as well as in the case of Event No. 1. (III) (III) Event No. 3 The sudden ionospheric disturbance phenomena, the disposition of the propa- gational gational circuits, and the positional relation of the sun corresponding to the solar solar X-ray flare Event No. 3 are shown in Fi~. 6 (a), (b). The starting, the maximum, and the ending times and the maximum deviations are given in Table 2. Since the pertinent event brought the second smallest χin Japan out of of the four giant flares as seen in Fig. 6 (b) and the event itself stood first or second second out of the four giant flares (cf. Table 2), sudden ionospheric disturbances occurred occurred with the utmost magnitude on the available whole circuits observed, although although all circuits from east presented in the dark hemisphere partly (HAIKU-, NAA-, and NPG-Inubo circuits) or mostly (Lima-Hiraiso circuit) in their circuit. The largest SP A amounted to d仲間＝ 237° (NWC- Inubo circuit) and the largest SWF L1Em=48 dB (Lima-Hiraiso circuit) (cf. Table 2). The magnitudes of SPA ’s and SWF ’s together stood first out of the 4 events. The starting times ts ’s of the 5 SPA events are scattered, and this fact originates originates in whether the phase variations of VLF radio wave circuits responded to to the enhanced flux intensity L1F(l ～8 A, t) of the subpeak in the pertinent event as as the multi-peak event or not. That is, because GBR-Inubo circuit as well as NAA-Inubo circuit described in (II) had small signal-to-noise ratio and because HAIKU-Inubo circuit encountered the transient phenomenon of daily variation where the phase was abruptly delayed at sunset, these three circuits showed no response response corresponding to the subpeak (cf. Fig. 6 (a)). However, NWC- and NPG- Inubo Inubo circuits showed their response. The subpeak would have existed on the saturated saturated part between P2 and Pa as seen in Fig. 6 (a). Out of both circuits, on NWC-Inubo circuit with smaller χ， the phase variation includes the F(l ～8 A, t) of of the unrecorded subpeak which will have existed, because the SPA occurred between P1 and P2 (tP1 =0519 and tP2=0531). Therefore, judging from the phase variation variation and a fairly good follow being considered already described in (I) and (II), (II), the subpeak in F(l ～sA ，の which will have existed is conjectured to have been small and not too acute. 326 M. Ohshio Solar X- ray Flα re Event No. 3 and S.I.D. 1972 August 4 1 2 4 6 8 10 12 （守的 10 『目 NM ？ と ‘‘‘‘弓 jellaPE’ UO h・ kmv 」申 一mCxv 曲 向．－－－ J ． vc『∞ 門 pl －SF ’d H P5 コ－）比 DrF L 00 （帥白山』切 NWC I! CHSコ ω 刀）円サ Solαr X-ray Flare Even! No.3 1972 August 4 ・〉〉． αL GBR Kind 。f Nl'.l OT I o SID' C"'"" Mo"' 0 色、 SPA 8(to !NU80 ）ーー－ ''" ''" 、、 SPA ¥(to HIRA(SO ！ー－ 」〉恥 ＼ SWF ゐ（ to HIRAISO ）一－ NAA r; j 子 NPG hzmcω ov ．〉〉．庄比工半 50 － ’nunυ c 。凶一 u －万一 『 UL b FD《 一工 Unu hh－o 16 16 18 20 22 0 2 4 6 Time tdh,135E.M.T.) （品） (b) Fig. Fig. 6. (a) Observed and presumed time variations in solar X-ray flare flare flux intensity for Event No. 3, F(l ～8 A, t). As for the method of presuming and the points P, attached to the curve, see see Section 4 in the text and Table 2 (especially NOTES 4.). The portion of F(t) =constant between P2 and P3 denotes the saturation. saturation. The presumed curve for the saturated portion is not not depicted. And observed available sudden ionospheric dis- turbances turbances corresponding to the F, SP A ’s (VLF), and SWF ’s (cf. (cf. Tables 1 and 2). (b) Geographical disposition of propaga- tional tional circuits, of the subsolar point (a circl 巴）， and of the day and night boundary line (a curve with oblique lines) at the altitude altitude of about 90 km at 0642 (U. T.) in the vicinity of the presumed time of the maximum flux intensity, tm(l ～s A). Solar-Terrestrial Solar-Terrestrial Disturbances of August 1972 327 The aspect of F(l ～8 A, t) at the increasing stage to the main peak between Pa Pa and P, is assumed that the aspect of increasing stage to the subpeak, p1 P2, is is maintained as it is in the slope. The semi-logarithmic linearity will be guaranteed guaranteed by the linear increases which observed available all the sudden iono- spheric spheric disturbance phenomena, especially the disturbance phenomena on Teheran- Hiraiso, Hiraiso, NWC-Inubo, and GBR-Inubo circuits with relatively small x displayed. Since, Since, however, the time when the above-described two SPA ’s with relatively small small x displayed ¥was tm, s =0634 ～ 35, tm should have been less than 0634 （ら， s’s on the three SPA circuits with χlarger than in these cases were not considered. cf. cf. Table 2). Accordingly, tm=0635 presumed mechanically in 4. (i) must be quickened quickened by more than one minute at least. If any circuit with smaller x had been available by the use of the world 司 wide data, the situation would have be- come clearer. In this connection, the chosen values of ordinary SPA 's ＜町 out of various various sudden ionospheric disturbances reported world-widely are 0635 and 0636 (the (the former and the latter are judged to be two kinds of reports based on ex- istence istence or non-existence of response corresponding to the subpeak, respective 司 ly disadvantage disadvantage to the detection of sudden ionospheric disturbanc 白． GBR-Inubo circuit circuit barely brought an indistinct SPA. Hereupon, Hereupon, three circuits of Cutler-Sao Paulo (NAA, 17.8 kHz, 7874.7 km), Jim Creek-Sao Creek-Sao Paulo (NLK, 18.6kHz, 10927.2km), and North West Cape-Sao Paulo (NWC, 22.3 kHz, 14554.1 km), each being located in the vicinity of the subsolar point point (16 。28' N, 50°30' W at 1528 U. T.), were utilized. <9J These three circuits brought brought exceedingly typical and large SPA phenomena. At the pertinent time corresponding corresponding to the maximum time of SPA on the first circuit described above, the the representative solar zemth angles on circuit ，χ’s which these three circuits showed, showed, and the magnitudes of SPA normalized to a distance 1 Mm, .dif>n ’s were χ＝ 21.5°, Llif>n=.29.8 。； χニ 38.0 。， L1¢>n=32.0 。； and χ＝ 103.6°, L1¢>n=9.0°, respectively. Solar Solar X- ray Fl are Event No. 4 and 5.1. D. 1・972 1・972 August 7 Time t (h,U.T.) 12 12 14 16 18 20 22 。 2 4 6 8 （ 101~ ’T凶 "' ~·E"' ...... u 話Z ，、 J ） LL 〉、 喝d ω 亡 。 Ps 噌d ヘ1( 中 c >< コ>< tι tι 10"" （凶 ωφ ~ 」mo a: a: Til 比」〉 刀） NAA nv －。OOFH 74Ti 半。。的。工仏。心コ GBR ハvq C 【 O NPG 申 KCov －的 （白℃）凶 cbvc ．〉〉． Li 50 g om －豆比工半 0 － U 50 2hL」－ Te O z 。 18 18 2 6 自 10 12 14 16 Time td h, 135EM.T.) (a) (a) Solar- Terrestrial Disturbances of August 1972 329 Solar Solar X-ray Flare Event No.4 1972 August 7 Klndof No.of 可肘 SID• c"'"'" Mo 『k• n SPA 8(1 。INUBO) ーーー－ 、、． SPA f(I 。HIRAI 由｝ーー一－ SWF 叫 to 附 RAJ 田｝一一－ ＼ ＼ ＼ ＼ 、止 449“‘u drJQ Am ワ ι’ （同 ，dp 凶ドF Fig. Fig. 7.(a) Observed and presumed time variations in solar X-ray flare flare flux intensity for Event No. 4, F(l ～8 A, t). As for the method method of presuming and the points P;, A, and B attached to the the curve, see Section 4 in the text and Table 2 (especially NOTES 5.). The portion of F(t) =constant in the isolated curves curves respectively including the points P5 and P8 denotes saturation. saturation. The presumed curves for the saturated portions are are not depicted. And observed available sudden ionospheric disturbances disturbances corresponding to the F, SP A ’s (VLF) and SWF ’s (cf. (cf. Tables 1 and 2). (b) Geographical disposition of propaga- tional tional circuits, of the subsolar point (a circle), and of the ・ day day and night boundary line (a curve with oblique lines) at the the altitude of about 90 km at 15.34 (U. T.) in the vicinity of the the presumed time of the maximum flux intensity t,,.(1 ～BA). Though the pr 白 umption of F （め at its increasing stage in the pertinent event was most di 伍cult as described already in 4. (i), the in 血ience of F （のbetween Ps and P1 in Fig. 7 (a) showing F(l ～sA ，の ~10-s erg cm-2 s-1 is considered to have appeared on the VLF phase variations, judging from the fact that the first circuit the the whole of which had been located in the sunlit hemisphere since 12h before at at least showed gradual increase of A\6~60 。 from about 12h till about 15h05 皿 and that that the aspects of variation of ¥6 （め’ s on the first and second circuits bore a close resemblance to each other from about 13h till about 1s~o5m, during which also the the whole of the second circuit was located in the sunlit hemisphere (the aspects did did not appear on the same time interval on August 8). The propriety of this consideration consideration will be more confirmed by verification with quiet daily variations of of the pertinent circuit. As described already in 4. (i), the presumption of F .，.（ 九） (cf. Table 2) gives the the lower limit. This fact produces the difference of 11 minutes between t町 s= 330 M. Ohshio 1528 1528 and min tm=1539 (case of A) even if which is adopted as shown in Table 2, because because the SPA on the only observed available circuit to Japan gives ら， s=1524 and sudden ionospheric disturbance phenomena which will have more advantage- ous ous conditions, probably an SPA cioi gives tm, s=1528.<1i,c 幻 Since the tm shown in Table 2 gave the upper limit, this large difference was unavoidable. In Fig. 7 (a), F 惜（ 1～s A, tm=1528)=3.96 ×10° erg cm-2 s-1 for tm=1528 on the elongation at the decreasing decreasing stage is presumed. This value implies 1.91 and 2.81 times as much as as the lower limits shown at respective points A and B by mechanical presump- tion tion (cf. NOTES 5. in Table 2). Even in these cases, the elongation at the de- creasing creasing stage and no duration at the maximum stage are assumed. That is, as long long as mechanical presumption is concerned, F(t) in the of vicinity Fm (tm) is acute acute at t=tm ・ However, rp （め on a circuit displaying relatively good follow to F （め and having having relatively small X: for example, the 引の on the fir 司 circuit out of the above-described above-described three ones, in the pertinent event, shows no acute maximum value value and is off the constant slopes at both stage from t:::::1520 at the increasing stage stage and till t:::::1530 at the decreasing stage. The second circuit also shows similar similar aspect. Accordingly, the pr 田 umption of F （めpassing over a point Pa in Fig. Fig. 7 (a) certainly express 白 the lower limit of the slope at the increasing stage and the presumption of F （めpassing over a point (t=1520, F=FPa) expresses the lower lower limit of the slope at the new increasing stage. On the other hand, if F(t) at at the decreasing sta~e is presumed from rp （の， Fm(l ～sA, tm 壬152 町is considered to to have to be approximately between 3.57 ×10° and 3.96 × 10° erg cm-2 s-1 on both conditions conditions that ゆ（t) is off the constant slope at the decreasmg stage till 1530 and has has its maximum value not acute at tm, s=1528 (this value quite coincides with the the above-d 田 cribed report. cii,<2> It is unknown whether the coincidence is acci- dental dental or results from nec 田 sary consequence in which the pertinent report depended upon the pertinent circuit ふ From the shape on the graph rp （の in the vicinity vicinity of the maximum value, F. 間（ 1～sA ，仏語 1528)=3.7 ×10° erg cm-2 s-1 is presumed. presumed. Thus, Thus, the time variation of unknown solar X-ray flare flux intensities con- versely versely can be presumed to some extent by the fact that the aspects of observed time time variations of sudden ionospheric disturbance phenomena are elucidated. 7. 7. Normalized Maximum SPA ’s and Maximum Enhanced Solar X-ray Flare Flare Flu 玄 Intensities (I) (I) The Basis of Relation between Both The presumed values of solar X-ray flare flux intensity F(l ～8 A, t) in the vicinity vicinity of its maximum value obtained by extrapolation on the graph showing the the time variation of flux intensity F(l ～sA ，め in Section 4, were corrected a little little in case of Event Nos. 3 and 4 in terms of correspondence to observed arrival arrival time of the maximum SPA values, tm, 8 discussed in Section 6. In these cases cases F(l ～8 A, t) was uniformly extrapolated thoroughly, and in case of Event Solar- Terrestrial of Disturbances August 1972 331 No. No. 3 no duration at the maximum stage was assumed. In In this section, the values in Section 4 or partly in Section 5 which were presumed quite independently by comparison and investigation of the relation between the maximum value of SPA, '1 • <5> When the flux intensities of ionoizing agents are larger than some degree, an SWF assum 田 the aspect of ZAN. In the correspondence between dゆand JF, however, however, as long as the observed SPA ’S available in this paper, each SPA dis- played played no saturation phenomenon (this is guaranteed in Event No. 3 which caused the the largest d九 available. cf. Table 2 and Fig. 6 (a)) in spite of arrival of large '1Fm '1Fm which had never been experienced. Therefore, the relation of '1Fm and '1 These available 21 events were observed from March 15 till April 12, 1966. The relation ＜町 between JF. 鴨（ 1～ sA ，ら） and '1 〔判bA｛ 60 600 za ｛L G4 ロロ乙 」〉｝ Number: Eve 同 N。． E・ 相：Estimated Solar 日。 dE dR 50 X-ray(l ・BA) 芝、 正凶． ＠ 凶 EE22 .Obser 時 d SPA(VLF) accc Eω自』 E :Observ 回 S同（ lOOkHz) コ コ 40 T23:>..:0.5 ・sA 400 E E －百三宮ESEdq － : >..: 1-BA E白書｝ 芝 ・＞..： 1・BA 30 初 0 EEEEd E －oE －uE 司 200 20 20 oZBEsao』 OZEEBao』 10 10 100 0 。1 (II) (II) Event Nos. 5 and 6 On the basis of the curve Ca obtained here, '1Fm (1 ～8 A, t,,,) is presumed from '1 Solar Solar X-ray Flare Event No 5 1972 August 7 s。lar X-ray Flαre Event No. 6 1972 August 7 "°'of "°'of "'°' ,wn ,wn s10, '""'' ，.，ニ；ニ ‘、． so~ 61:0 ＇・＇＂己 0) －ーーー 、、‘ SPA l!:C HiR 吋 oOI ーー '-・・ '-・・ SWF 4(:0 ーー －一－・－ー干 H!R,•oJJ ＼ 、ベ F ＼ ＼ ＼ F （品）（防 Fig. Fig. 9. Geographical disposition of propagational circuits, of the subsolar subsolar point (a circle), and of the day and night boundary line line (a curve with oblique lines) at the altitude of about 90km at at the presumed time of the maximum flux intensity ，九（ 1～ 8 A)=0253 and at 0350 (U. T.) in the vicinity of t抗（ 1～s A) for for the respective solar X-ray flare Event Nos. 5(a) and 6(b). Hiraiso Hiraiso circuit and non-observation on NWC- Inubo circuit. The SPA phenomena caused caused by both events are relatively small, therefore, their .d In In case of Event No. 5, good agreement between the presumed value .tlF., 問 (1 ～8 A, tm) (cf. Table 2) obtained by the same way as 4. (i) and .t1F,,, (1 ～s A, tm) inferred inferred conversely from .tl (1 ～s A, tm ）’s corresponding to both are apart although the maximum value of SPA with 100 kHz (cf. Table 1) has almost equal value to that of Event No. 5 as as seen in Fig. 8. Since the SPA ’s with 100 kHz occur on a single circuit in this this case, the di 妊erences of propagational distance D, used radio wave frequency, and geographical disposition of circuits do not intervene in d九問問、 to be com- pared pared with, therefore, the data ought to be pure. (Ill) (Ill) Event Nos. 1～4 Through Event Nos. 1～ 4, each of the presumed values by extrapolation on the graph showing the time variation of F(l ～8 A, t) (hereinafter tentatively referred referred to as '1F1) is larger than the presumed value from Llrfto, m, n (hereinafter tentatively tentatively referred to as LlF 世）.， Since the curve Ca also originates in the extra 同 polated polated value of the curve C1, each of them cannot be the standard to be stressed on. on. From Fig. 8, though '1F1 /LlF. 世：：：：： 2 was obtained in Event No. 1, LlF. 皿（ 1～s A, tm), accordingly accordingly F悦（ 1～8A,tm)z3 ～7×10-1<10° erg cm-2 s-1 will be presumed. In Event No. 2, '1F1/'1F9 王寺 l and the best approaching value out of the 4 events was derived. derived. This approach is conspicuous as well as that of Event No. 5. The good approach approach will originate in a little extrapolated portion, because both curves at the the increasing and decreasing stages have curvatures convex upward as described already already in 4. (i) and seen in Fig. 5 (a). In the pertinent event, '1Fm (1 ～sA ，ら）， accordingly accordingly F 悦（ 1～8 A, tm)z2 × 10-1<10° erg cm-2 s-1 will be presumed. In case that that the curve C1 in Fig. 8 is considered, the presumed values LlF. 明（ 1～s A, tm ）’s in in both events are included in the already analyzed '1Fm(0.5 ～5 A, tm) almost in Event No. 1 and completely in Event No. 2, if LlF was observed in the wave- length length range of 0.5 ～5 A. Consequently Event Nos. 1 and 2 cannot be called unprecedented unprecedented solar X-ray flares. Particularly, max LlF. 明（ 0.5 ～5 A, tm) was 1.496 × 10-1 10-1 erg cm 2 s-1 out of the individual events forming the foundation of the curve C1. C1. Therefore, the value corresponds to '1Fm (1 ～sA ，ら）＝ 6.96 ×10-1 erg cm-2 s-1 and will be discussed to include max '1F1 (1 ～s A, tm)=7.23 × 10-1 erg cm-2 s-1 (cf. Table 2) almost completely. In In Event No. 3, '1F.r/'1F 世与， 1.3 ～1.4 (1.4 originates in F 叩（ 1～s A, tm=0634)= 2.06 × 10° erg cm-2 s-1. cf. 6. (Ill) or NOTES 4. in Table 2) and an approaching value value good next to that of Event No. 2 was derived out of the 4 events. This will will originate in the fact that it was guaranteed that the mechanical elongation was not so wanting m propriety, being supported by the shape on record of corresponding corresponding SPA with relatively small χas already described in 6. (III), in spite spite of a long mechanical elongation at its increasing stage as was already des- cribed cribed in 4. (i) and seen in Fig. 6 (a). In the pertinent event, '1Fm (1 ～8 A, tm), accordingly accordingly Fm (1 ～s A, tm ）～1～ 2×10°;;;:; 10° erg cm-• s-1, will be presumed. In the pertinent pertinent event, min (LlFJi LlF 世） ， > LlF. 明（ 1～8 A, tm)=5.72 × 10-1 erg cm-2 s-1 (already described described in 7. (1)), consequently, this will be worthy of being called a really unprecedented unprecedented giant flare. In In Event No. 4, it is apprehended that the largest error out of the 4 events interven 白 in the presumption of LlF 1 as already described in 4. (i) and in Llrfto, m, n as as already described in 6. (IV) as long as the internal data. The utilization of SPA phenomena on the circuits with small x described in the latter half of 6. Solar-Terrestrial Solar-Terrestrial Disturbances of August 1972 335 (IV) (IV) wiped out the above-described apprehension. However, Ao,m,n=37 。， JJF 世＝， 7.6 × 10 1 erg cm-2 s-1, and 11F1 キF1"""3.7 ×10° erg cm-2 s-1 produce the result that ilF1/ilF 世＝， 4.9 made the largest discrepancy out of the 4 events. This discrepancy seems to be di 伍 cult of solution. It is considered that the '1n （χ ）distribution did not not show an ordinary distribution although the first and second circuits d田 cribed in in the latter half of 6. (IV) had not a wide difference in the used radio wave frequencies frequencies and that the presumed portion of F(l ～8 A, t) was too large at its increasing increasing stage. However, min (JFJ. JF 世）＝， JF ，世 still has magnitude not to be included included by the curve C1 in Fig. 8. On the other hand, the conjecture of 11F1 今F1<10° erg cm-2 s-1 is accompanied with many difficulties. Further, Further, what should be considered about this discrepancy is the propriety of of establishing the curve Ca in Fig. 8 and the possibility of realizing the satura- tion tion at maximum values of SPA. As for the former, indeed, in the remaining 5 events except Event No. 5 JF 世＜， 11F 1 holds. Accordingly, the curve Ca resulting resulting from the elongation of the curve C2, with the same property as the curve curve C1, is considered to have perhaps a smaller slope. It is, however, di 伍cult to alter alter the curve Ca judged from the presumed f1F1 's of the 2 events (Event Nos. 3 and 4) coming under JP, 明（ 1～sA ，ら）＞ 6.96 ×10-1 erg cm-2 s-1 (cf. the description of of Event No. 2 in 7. (III)) where the curve Cs really demonstrates its existence. This consideration will be naturally expected to the same kind of future data. As for the latter, from Fig. 3, Y （χ＝0。， A=l A) and Y （χ＝90 。， A=l A) have their effective effective bottom at altitudes of 40 and 50 ～ 60 km, respectively. Therefore, the decrease decrease of the altitude with constant electron density for the increase of JF(l A) becomes small as iJF(l A) becomes large, and an extremely large SPA is con- sidered sidered to have possibility to saturate at its maximum value (in this case, the follow follow of Since Since 11 Event Nos. 3, 1, and 5 or 6 will be to have given the relation between ilef>o, m, n for for the used radio wave frequenc~ ， 100 kHz, and ilF: 叩（ 1～sA ，ん） as well as the curves curves C1, C2, and Ca. In the pertinent curve and in the curve Cs, the propriety of of their existence will be determined by data to appear in future. 8. 8. Height Distributions of Electron Densities Produced by Giant So!ar So!ar X-ray Flares By the two methods of presumption in 7.(III), it was discussed that Event Nos. Nos. 3 and 4 would be really giant solar X-ray fl 紅白 almost regarded as satisfy- ing ing JF, 悦（ 1～8 A, tm) > 10° erg cm-2 s-1. There are calculated height distributions of electron electron densities produced by the arrival of such great quantities of ionizing agents. agents. Since at the maximum stage and at the increasing stage, F(l ～sA ，め is what was presumed, steady enhanced electron density at the maximum stage, ilNoo, is is calculated. In case of large JFm and small χ， since ilNoo gives good enough approximate value (electron production ratio JNm/ilNoo=0.9 ～ 1) compared with the actual actual maximum enhanced electron density ilN ムin spite of large acuteness of ilF(t) ilF(t) at its maximum stage, application to the pertinent giant flares will also have propriety to give a good approximate value. A model is set up to repr 白 ent giant X-ray flares. In this paper, although F(l ～8 A, t) is exclusively treated, it will be admitted that the general property of of good parallelism of flux intensities with adjacent wavelength ranges is also applicable applicable to the maximum stage of the pertinent flares by the aspects<3J of F （ん～ん t）’s at the observed time interval. The consequence of this admission will will be supported also by the report<1J,<2> that Fm(0.5 ～3 A, tm; Event Nos. 3 and 4）～ 10-1 erg cm-2 s1 while F 明（ 0.5 ～3 A, tm; Event Nos. 1 and 2）苫 10 2 erg cm-2 s-1. The increment of the giant flares at their shorter wavelength side is conspicuous. Hereupon, Hereupon, ilF, 刑（ 8 ～20 A ，ら）＝ I0-1 erg cm-2 s-1 ilF: 叫（ 1 ～8 A, tm)=10° erg cm-2 s-1 JFm(0.5 ～3 A, tm)=I0-1 erg cm-2 s-1 are are set up as a model. ilF: 悦（ 1～3A, t. 机） is calculated, being included in ilFm(l ～ 8 A, tm). By the adoption of values<•J of fundamental physical quantities which seem to be valid, the calculated JN 。。 Cx=O 。， 40 豆z(km 〕壬 1印， tm) is shown in Fig. lO(a) lO(a) and the calculated electron density at the flare maximum stage, Nq (quiet value)+JNoo value)+JNoo in Fig. lO(b). Fig. lO(a) shows that JN 。。（ χ＝0。， z, tm) surpasses Nq （χ＝ 0°, z) at the altitude range of 50 AF(8 ・201',tm )= to'1 org cm 勾4 150 トAF(l -81',tml=lO? .aF （，也 S-3A,tml=1C1 ・u ~ 100 N 。司コ＝ご《 0 1cr2 1cr2 1cr1 10° 101 102 103 104 105 106 Electron Electron Density N(el 町 trons cm・3) 150 150 E 三 100 N "' 司"' -コ 《 50 。 10° 10° 101 102 1c3 104 105 106 Electron Electron Density N(electronsα ぜ'3) Fig. Fig. 10. Height distribution of steady enhanced electron density in in case of solar zenith angle x=0° produced by a model of giant giant solar X-ray flares, L1Nro(x=0°, 40 壬z(km ）孟 150, t鴨） (electrons (electrons cm-8). The maximum enhanced solar X-ray flare flux flux intensity L1Fm （ん～ん， tm) is shown in Figure (a). L1F in Fig. Fig. (a) means L1Fm. Comparison of L1Nro(x=0°, z, t間） and a quiet quiet value Nq(x=O 。， z) (a), and comparison of Nq(x=O 。， z) and Nq （χ＝0。， z)+L1Nro （χ＝0°, z, tm)(b). In Fig. (a), L1Fro(x=0°, z, t":) in in cases of L1 F. 机（ 0.5 ～3 A, tm)=l0-1 erg cm-2 s_:i and 0 is shown shown (the former by solid and the latter by broken lines). produce differences in JJ 札（ χ＝0。， z<40km, lm ）’s larger than that at z=50 km, they they would not produce much di 任erence of influence on radio wave propagation on account of small absolute values of the electron density. Since Since the above-described consequence is based on the calculation of steady maximum enhanced electron densities atχ ＝0°, actual observations are conjectured to to indicate justly a value smaller than that. On the other hand, since a model is is adopted where wavelength ranges are restricted, the difference of .dFm （ん～んら） and the possibility that enhanced flux intensities with other wavelength ranges may influence actual electron density at a certain altitude make problems com- plicated. plicated. The state where SIF (sudden increase of /min) increases largely and where foFI and foF2 to say nothing of foE are blackout will be indicated in 338 M. Ohshio other other papers. <11>.<12> The occurrences of G. s. f. e. (geomagnetic solar flare effect) are are naturally expected, however, at Kakioka the G. s. f. e. ’s of H=+5 rat 0419, D= +3 r at 0423, and their ending time 似30 on August 2 were only detected. <13> However, the maximum time for H and D seems to be later than that for SPA and SWF as shown in Table 2. According to the world-wide report, <1≫<2> G.s. G.s. f.e. ’s occurred at 1838-1852 on August 2, at 0252-02 日 on August 7, and at 1513-1615 1513-1615 on August 7. These seem to come under Event Nos. 2, 5, and 4 in this this paper respectively, but they do not always accord with each other in time (cf. (cf. Table 2). The occurrence of such giant solar X-ray flares is su 伍dent to conjecture that that of solar E. U. V. ray flares. There seems to be no report on SFD,<1 ＞〆幻 but a conspicuous example is given, appearing in the trans-equatorial propagation of radio radio waves carried out at the Radio R 白 earch Laboratories, where the observa- tion tion at intervals of 30 min. of trans-equatorial propagation of VHF radio waves indicated indicated that the critical frequency of oblique incidence wav 回 increased from 23.8 23.8 to 34.8 MHz at 0800 U. T. on August 4. The continuous observation of electric electric field intensity in the identical experiment indicated that the intensity of blackout blackout till 0630 U. T. increased by 47 dB in its maximum value at 0830.<1 幻 This This is considered to be F2 region effect corresponding to solar X-ray flare Event Event No. 3. It It attracts great interest what 部 pects solar E. U. V. ray fl 紅白 assume early in in August, especially in cas 田 of pertinent 4 solar X-ray flares, but n,o informa- tion tion on those can be obtainable at all up to now. 9. 9. Conclusions (1) (1) Large solar X-ray flares occurred twice (Event Nos. 1and2), once (Event No. No. 3), and once (Event No. 4) on August 2, 4, and 7, 1972, respectively, in the period period of relative sunspot number of about 70 (in the 20th solar cycle it indicated 10 ～ 110). (2) (2) On the presumptions by extrapolation on shape on the graph showing the the relation of solar X-ray flux intensity to time and by the maximum phase deviation deviation of normalized observed SPA, the maximum X-ray flare flux intensity F,,.(1 ～8 A, t,,.) or the maximum enhanced one LIF,,.(1 ～8 A, t,,.) (since F,,. is large, it it can be regarded as LIF. 鴨） is given as follows : [Ll]F. 叩（ 1～8A, t，，. ～ 0331 U. T., Aug. 2, 1972 ）～ 3～7× 10-1 erg cm-2 s-1, [Ll]F,,.(1 ～8A, t明記2056 U. T., Aug. 2, 1972 ）～ 2× 10-1 erg cm-2 s-1, [Ll]F,,.(1 ～ 8 A, t,,.""'0634 U. T., Aug. 4, 1972 ）勾 1～2×10° erg cm-2 s一九 and [Ll]F. 情（ 1～8A, t，，. ～ 1528 U. T., Aug. 7, 197 劫～ 1～4×10° erg cm-2 s-1. The solar X-ray flares on August 4 and 7, 1972, were giant as their maximum solar solar X-ray (1 ～8 A) flare flux intensity exceeded 1 erg cm-2 s-1. (3) (3) In case of Event Nos. 3 and 4, large increment of flux intensity was observed observed also in the rang 田 of solar hard X-ray (0.5 ～1 A) and of solar r-ray (0.5 ～ 6.1 MeV=0.025 ～ 0.0020 A, observed by_an artificial~satellite, OSO ー7【14>). From large large increment of 宜ux intensity in solar soft X-ray ranges, large increment of Solar-Terrestrial Solar-Terrestrial Disturbances of August 1972 339 flux flux intensity in solar E. U. V. ray (100 ～1卯O A) ranges is conjectured. (4) (4) The enhanced electron density at the maximum time of X-ray flares in the ionospheric D and E regions is inferred to surpass or to be equal to those at quiet state in all 4 events. Especially, all kinds of sudden ionospheric dis- turbances in Event Nos. 3 and 4 are inferred to have been in the largest class. (5) (5) Even the conspicuous increment of solar hard X-ray flux intensity does not bring large influence effectively in terms of ionospheric radio wave propaga- hon. Acknowledgement The author heartily expresses his thanks to Professor P. Kaufmann and Dr. L. L. R. Piazza, Universidade Mackenzie, who readily consented to give the author the copy of record of VLF radio wave phase and amplitude received at Sao Paulo on August 7 and 8, 1972. The author thanks also Mr. T. Asakura, Chief of Inubo Radio Wave Observa- tory, tory, and Mr. T. Ishii, on the staff there, for putting the records of VLF radio wave phase during the period at the author ’s disposal. Further thanks are due to to Dr. R. Maeda, Chief of Upper Atmospheric Research Section, for the records of HF radio wave electric field intensity during the period. References References (1) (1) Solar-Geophysical Data (Prompt Reports), Nos. 338- & 337-Part I., U. S. Dept. of Com- merce, merce, N. 0. A. A., E. D.S., Oct. & Sep., 1972, respectively. (2) (2) World Data Center A for Solar-Terrestrial Physics, Preliminary Compilation of Data for Retrospective Retrospective World Interval July 26-August 14, 1972, Report UAG-21, U.S. Dept. of Commerce, N. 0. A. A., E. D.S., Asheville, N. Carolina, U.S. A., Nov. 1972. (3) (3) Solar-Geophysical Data (Comprehensive Reports), No. 342-Part II, U.S. Dept. of Com- merce, merce, N. 0. A. A., E. D.S., Feb. 1973. (4) (4) Ohshio, M., Ionospheric D region Disturbances Caused by Solar X-ray Flares, J. Radio Res. Res. Labs. (to be published). (5) (5) Ohshio, M., Nakajima, T., Tsuchiya, K., and Ishii, T., Results of Special Observations for for the Proton Flare Project 1969, IV. SPA ’S Observed During the PFP Interval, J. Radio Res. Res. Labs., 17, 33 48, 1970. (6) (6) Maeda, R. and Inuki H., Solar-terrestrial Disturbances of August 1972, 2. Development of of Solar Active Regions, J. Radio Res. Labs., 21, 291-301, 1974. (7) (7) Ohshio, M., Maeda, R., and Sakagami, H., Height Distribution of Local Photoionization Efficiency, Efficiency, J. Radio Res. Labs., 13, 245-577, 1966. (8) (8) Ouchi, C., Fujii, S, and Wakai, N., Solar-terrestrial Disturbances of August 1972, 14. Simultaneous Simultaneous Measurement of Intensities and Phas.'.! of Loran-C Waves, J. Radio Res. Labs., 21, 21, 443-450 1974. (9) (9) Private communication with Prof. Kaufmann and Dr. Piazza, Universidade Mackenzie. (JO) (JO) Solar-Geophysical Data, Descriptive Text, No. 330 (Supplem 巴nt), U.S. Dept. of Com- merce, merce, N. 0. A. A., E. S. D., Feb. 1972. (11) (11) Koizumi, T., Ohyama, H., Hiidome, S., and Echizenya, Y., Solar-terrestrial Disturbances of of August 1972, 8. General Feature of Ionospheric Disturbances Appeared in Vertical 340 340 M. Ohshio Sounding, Sounding, J. Radio Res. Labs., 21, 371-383, 1974, (12) (12) Yamaoka, M., Tanohata, K., and Tsuchiya, K., Solar-terrestrial Disturbances of August 1972, 1972, 11. Anomalous Propagation of VHF Waves in the Trans-equatorial Paths, J. Radio, Res. Res. Labs., 21, 405-422, 1974. U3) U3) Private Communication with Mr. M. Nagai, Magnetic Observatory, Kakioka. (151 (151 Chupp, E. L., Forrest, D. J., Higbie, P. R., Suri, A. N., Tsai, C., and Dunphy, P. P., Solar Solar Gamma Ray Lines observed during the Solar Activity of August 2 to August 11, 1972, 1972, Nature, 241, No. 5388, 333-335, Feb. 2, 1973.