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Geomagnetic pulsations associated with sudden commencements and sudden impulses
Planet. Space Sci. 1967. Vol. 15. pp. 573 to 587. Pcr@mon Ptra Ltd. Printed In Northem Ireland
GEOMAGNETIC PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS AND SUDDEN IMPULSES TAKAO SAIT’O* and S. MATSUSHITAt High Altitude Observatory, National Center for Atmospheric Boulder, Colorado, U.S.A.
Research
(Read at the Inter-Union Symposium on Solar-Terrestrial Physics, Be&rade, 29 August to 3 September 1966. Received 29 November 1966) Abstract-Damped-type geomagnetic pulsations associated with both storm sudden commencements (ssc’s) and sudden impulses (sin) are studied for 388 events which occurred during the past 7 years from 1956 through 1962. Since the pulsations associated with ssc’s and with si’s usually showed very similar behavior, they are combined together under a notation, psc. These psc’s are class&xl into four groups according to period ranges in a similar way as pc’s: psc 1,0.2-5 xc; psc 2.3,5-30 set; psc 4,30-150 set; psc 5,150-600 sec. Predominant psc’s in middle and low latitudes, sub-aurora1 region, and auroral zone are psc 2.3, psc 4, and psc 5, respectively. Morphological behavior of p&s, such as daily variations of their amplitudes and periods, and patterns in their dynamic spectra show a remarkable similarity to those of corresponding period-range pcf. However, the psc’s show an interesting dependence on the range and duration of accompanying ssc’s. A brief discussion is given on these characteristics of PSC’S. 1.
INTRODUCTION
1.1. Previous works Many workers have previously reported that damped-type pulsations are often associated sudden commencements (ssc’s) and sudden impulses (G’s). Predominant periods of these reported pulsations seem to be at nearly 1 set, 20 set, 1 mm, and a few minutes. The pulsation with the predominant period of nearly one second was fist reported by Troitskaya et al. (1962) as being associated with ssc’s. Since that time, very few studies on this group of pulsations have been presented (Matsushita, 1962; Tepley and Wentworth, 1963 ; Heacock and Hessler, 1965). The damped-type pulsations with the predominant period of 20 set were reported almost 20 years ago by Utashiro (1948) and Kato (Kato and Utashiro, 1950a, b) who used induction magnetograms obtained at Onagawa, Japan. These pulsations were reported to have amplitude of the order of 0.1~ and decay time of several minutes, and were explained by an effect of a fluctuation of the ionospheric current at the time of ssc (Kato, 1951a, b; Kato and Tamao, 1956). A difference between the pulsating part and the gradual part of ssc on the disturbance hodographs was noticed by Kato et al. (1953). Separating the pulsating part from the gradual part, Kato and Saito (1958) proposed that the pulsation was caused by a hydromagnetic oscillation due to the ssc shock. Further morphological studies of this group of pulsations have been made based on data from many events recorded at one station; for example, the decay curve of their amplitudes with respect to the storm-time (Campbell, 1959a, b; Oshima, 1961), the diurnal variation in their periods (Kato and Saito, 1959; Bouxka, 1960, 1962), and the ratio of occurrence of ssc to the associated pulsation (Dubrovskiy, 1961). Morphological similarity
with storm
* Also ITSA-ESSA. On leave from Onagawa Magnetic Observatory, Geophysical Institute, University, Sendai, Japan. t Also ITSA-ESSA and the Department of Astro-Geophysics, University of Colorado. 573
Tohoku
574
TAKAO SAITO and S. MATSUSHITA
of ssc to si was noted and discussed in relation to their associated pulsations (Kate and Saito, 1958,1959; Yamaguchi, 1958; Matsushita, 1960,1962; Nishida and Jacobs, 1962). A solar cycle dependence on the occurrence of the sporadic storm following the pulsation in question and on the recurrent type storm without ssc was also studied (Saito, 1965a, b). The world-wide distribution of the pulsation stations during the International Geophysical Year brought a wider aspect of this group of pulsations. Based on the data at seven welldistributed U.S.A. stations, it was found that the negative impulse preceding ssc (MacUser, 1957) occasionally shows two or more oscillations (Mats~~~, 1960,1962). An apparent travel velocity of this group of pulsations was discussed by Berthold er al. (1960), Troitskaya (1961b), and Benioff (1963) based on the data from well-separated stations. Matsushita (1962,196s) suggested a possible close relation between the ionospheric oscillation associated with ssc and this group of geomagnetic pulsations, and advocated a probable important role of the ionosphere to these geomagnetic pulsations. No extensive report has been made on geomagnetic pulsations with the predo~nant period of approximately 1 min which are associated with ssc’s. However, it may be noteworthy in relation to this group of pulsations that a lengthening of the pc 4 period was reported at the time of negative si on 17 July 1958 (Veldkamp, 1960). Matsushita (1962) and Saito (1964a) asserted the existence of this group by showing examples of magnetograms. Damped-type pulsations associated with ssc’s, which have the periods of the order of a few minutes and the amplitudes of the order of 10 y, were reported after the analysis of IGY magnetograms (Sugiura, 1961; Wilson and Sugiura, 1961; Saito, 1961; Matuura, 1961; Wilson, 1962). Based on the spatial distribution of the rotation vector of the pulsations, it was interpreted that the primary effect of the impact of the magnetosphere generates a longitudinal hydromagnetic shock wave. A negative kick preceding the main pulse of ssc was interpreted as being a part of this damped pulsation. On the other hand, another theory was advocated that the negative kick was due to an effect of charged particles impinging into the high latitudes (Matsushita, 1957, 1960,1961, 1962). Further discussions were made on this problem (Wilson and Sugiura, 1963; Matsushita, 1963; Nagata et al., 1963; Sugiura and Wilson, 1964; Kato and Tamao, 1964; Hirasawa et al., 1966). Sudden increases (Matsushita, 1961, 1962) or concurrent pulsations (Sato, 1962b, 1964) of the cosmic noise absorption were reported in relation to the geomagnetic pulsation associated with ssc. Other morphological studies on the geomagnetic pulsations at the time of ssc were world-wide distribution of amplitudes of the pulsations (Sato, 1962a), latitude-diurnal effect of their amplitudes (Ohl, 1962), their rotation vector (Sano, 1963; Kato and Utsumi, 1964a, b), and their polar region effect (Sato, 1965). 1.2. De~ni~io~ and data used Since the pulsations associated with ssc’s and with si’s usually show very similar behavior (Kato and Saito, 1958,1959; Yamaguchi, 1958; Matsushita, 1962; Nishida and Jacobs, 1962), these pulsations are, hereafter, combined together under a notation, psc. Similarly, ssc and si are often combined together under the notation of ssc. Summarizing the individual works as reviewed in the previous section, these psc’s can be classified into four groups according to period ranges. They are called psc 1, psc 2.3, psc 4, and psc 5 in a similar way as geomagnetic continuous pulsations, pc’s (Jacobs et al., 1964) and are listed in Table 1. In the present paper all psc’s excluding psc 1 are discussed. Typical examples of psc 2.3, psc 4, and psc 5 associated with different ssc’s on different dates are shown in Fig. 1, and those associated with the same ssc on 11 July 1959 are shown in Fig. 2.
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS TABLE1. FOUR ORO~JPSOF TYPE
575
DAMPED-
PLRSATIONS As9ocIAlEDwrrH SSC AND Si
In spite of 4Osec for the boundary period between pc 3 and pc 4, which is recommended by IAGA (Jacobs et al., 19&I), 3Osec is applied here for the boundary period between psc2.3 and psc4, taking into consideration the solar cycle dependence on the boundary period (Kate and Saito, 1964)
Fl0.I
TYPE
Notation
Period range (set)
PSl psc 2.3
0.2-5 S-30 3LL150 150-600
TYPICAL
7: REMARK
MAONETOORAM N
j
A
P8C
lo*
2.3 02%n
u-1.
r 20n
6
ONAQAWA
7
FOR t.2oilas +--” 2’sm
S6C
FEB.25.
/
1858
FREDERICKSBURQ APR.27,
iaeo
i
HEALEY DEC. 12.
FIG. 1.
TYPICAL
EXAMPLES OF MAGNETOGRAM OF p&s DIFFERENT DATES.
1858
wrraar~naa WC’SOCC~RNDON
In the present analysis, studies were made of the horizontal component of psc’s associated with 388 events of ssc’s and si’s for the past 7 years from 1956 through 1962 as listed in Table 2. These ssc’s and si’s were se1ecte.d from the ZAGA Preliminary Report on Sudden Commencements when more than twenty stations reported the same event as ssc and more than ten stations reported the same event as si. All the events in the Preliminary Report were confirmed by referring to the magnetograms at well-distributed stations, such as Honolulu, Onagawa, Hermanus, and San Juan. References to the ZAGA Bulletin of Geomagnetic Indices K and C, Solar-Geophysical Data, Monthly Reports of the Onagawa Magnetic Observatory, Report of the Kakioka Magnetic Observatory, and other sources were
also made. Predominant psc’s are apparently psc 2.3 in middle and low latitudes, psc 4 in the subauroral zone, and psc 5 in the aurora1 zone. Rapid-run magnetograms at representative stations, Onagawa, Fredericksburg, and Byrd, were used for the study of psc 2.3, psc 4, and psc 5, respectively (see Table 3). The geographic and geomagnetic locations of these stations are shown in Table 4 together with other stations which are referred to in this paper.
No.
33: 34 35
; 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
: 4 5 6 7
1
YtXU
Jan. 21 1644 22 (1940) 27 O9OO 27 (1626) Feb. 11 0054 19 0221 19 (1443) 21 2002 22 0015 22 (1106) 25 0307 26 (0929) Mar. 02 2342 03 (0650) 19 0053 20 (1146) Apr. 15 (1628) 21 1101 25 (1133) 26 2110 28 1727 30 0137 May 11 (1807) 11 2342 16 O415 20 0638 21 (1817) June 05 (1512) 23 1806 July 08 0102 Aug. 09 lo41 10 (1310) 11 0043 21 0507 31 1015
1956
2o48 1136 (2332) 0822 2029 0340 0046 (1117) (2325) 0528
15 17 17 May 30 June 06 24 25 25 27 30
0714 (0519) 1344 (1457) 0419
Aug. 03 1557
;: %?
16 19 19 19 22
11 (0944)
05 0042
July“0; ‘;:;I
0910 125.5 1910 1313 1850 1807 1614 0023 0130 0336 1315 y$;;
1957
388 EWITE OF s%c’s (WITHOUT
P-
1642 0931 (1532) (1429) -1212 1540 (2253) 1247 (;;;;I
io907j
(2143) 1050 (0745) (0950) 1304 0125 (0555)
June 02 (0409) 07 0046 08 1728 14 1828 15 0509 19 (1600) 28 i)71328 1742 30 (0401) JuIy 03 (1603) 08 0748 12 (0112) 13 (2208) 17 (0930) 21 1637 21 (1926) 22 (1207)
Jan. 20 25 30 30 Feb. 04 11 12 12 16 Mar. 03 03 13 14 25 25 Apr. 26 May ;
1958 Jan. 02 1122 05 0136 09 1459 14 (0606) 16 0927 22 (0704) 25 0859 25 1125 26 0322 29 (212ti Feb. 08 i1321j 11 0318 11 0756 14 1142 16 (0649) 16 (0742) 16 (1734) 22 0046 22 1057 24 2319 25 (0215) 25 (0227) Mar. 02 (0824) 18 (2229) 22 2228 25 (1417) 26 0842 Apr. 09 1828 - 23 1036 29 11233) May 04 ‘2021’ 05 (1106) 08 (1636) 11 2328 12 (1537)
1959
Hour is indicated in universal time 1960
z %? 31 1511 Apr. 13 1450 May 22 0137 23 (0137) 25 (0211) 31 (0204) June 14 2335 20 1617 21 (0641) 21 (0818) 22 (1518) July 02 (2016) 13 1113 17 1825 20 0248 20 (2227) 26 1950 Aug. 26 (1320) 29 1709 Sep. 13 1554 20 (1608)
13 0253 16 0043 16 (0536) 17 (1400) 17 (1721) Mar. 09 1327
Jan. 08 1618 Feb. 03 0908 04 1331 04 1829 2 @$I
1961
lB) AND Sib (WITH PA-)
Jan. 05 0201 10 0718 13 1859 14 (0819) 16 2114 16 (2221) 18 0642 18 (073% 19 -2208 28 (1916) 29 ‘0205’ Feb. 05 (1134) 26 IO43 Mar. 16 (0847) Apr. 02 2313 - 03 (0855) 04 KUo3~ 05 {0842j 05 1300 06 (1628) 07 1511 10 0126 27 2000 30 0132 30 1213 May 07 (0927) 07 (1108) 08 0421 11 (0435) 15 (1009) 16 1351 16 (2036) 22 (1438) 28 2019 June 04 0248
WHICH ARE ANALYZED IN THIS PApER
AND HOUR OF THE
Jan. 02 21 24 29 Feb. 12 23 Mar.01 10 25 29 29 Apr. E
TABLB2. ‘~-HEDATE
Jan. 10 0213 10 (0939) 19 0113 Feb. O4 0930 05 (0315) 15 11855) 16 (0539) 22 0220 26 1233 26 (1533) 26 (1611) Mar. 03 (1311) 03 (1340) Apr. 20 (1535) 20 2356 25 1329 May 06 (0952) 27 0413 June 07 (0640) July 03 (1202) 31 (2322) Aug. 30 2338 Sep. 12 (0612) 19 (0221) Oct. 07 2026 Nov. 06 (0330) Dec. 04 0334 o4 (0710)
1962
Sep. 02 08 20 Oct. 26 26 Nov. 09 14 Dec. 24 25 27 30
0230 1006 0438 0026 1311 2030 0200 0148 0754 1503 0632
Dec.
Nov.
Oct.
Sep.
06 0508 09 1347 17 (1322) 18 (1016) 29 1920 30 (1628) 31 1812 02 0314 03 (0618) 03 (1047) 03 (1912) 04 1300 06 (0117) 06 1121 07 (0232) 13 0046 17 (2359) 21 1005 22 1345 23 0235 29 0016 14 0440 14 (1320) 14 (1608) 21 2241 06 1821 14 (0200) 18 (2204) 26 0155 29 (0225) 15 (1334) 19 0937 31 (0219) 31 (0321)
27 (1101) 27 (1122) 31 -1529, Aug. 17 0622 22 0227 24 0140 27 0303 Sep. 03 0843 16 0930 25 0408 30 1005 Oct. 22 0315 24 0730 27 1523 27 (1742) 27 (1826) 28 ‘065d 28 (1150) 31 (1613) Nov. 01 0959 01 (1451) 10 (1055) 11 0129 16 (0219) 16 (0433) 28 0109 Dec. 04 0035 13 0001 13 (1224) 14 (1308) 15 2022 17 1547 17 1817 25 (2330) 30 (1539)
12 (1658) 15 0703 24 0540 25 (0440) 30 (1412) June 03 (2313) 09 0016 11 O!m 27 (1348) 29 0728 30 0801 July 04 (1910) 11 1625 If 0803 17 1638 Aug. 16 0404 20 0412 20 (2037) 29 (0228) Sep. 03 1417 03 2159 05 (1956) 19 (04w 19 1128 20 1157 22 (0130) Oct. 21 (1605) 29 2347 Nov. 26 (2142) 27 2351 Dec. OS 0659 23 1525 21 30 Dec. 07 25
Nov.
Oct.
Sep.
Aug.
July
27 28 29 30 14 14 14 14 16 19 29 02 04 04 22 06 13 24 10 11 12 12 15
0145 (0521) 1939 1720 0447 1702 (2132) 1510 1409 1616 0022 1158 0230 (1145) 1404 0237 (2143) 1452 0718 0034 1349 1845 1304 0631 (2147) 1909 1804 2002
24 (1311) 24 (1400) 30 1847 30 2109 Oct. 11 (1220) 17 (2205) 26 1941 28 0810 Dec. 05 1358 27 0057
578
TAKAO
r15.2
TYPE
SAITO and S. MATSUSHITA
MA~NETO~RAM
A
3SC 2.3
0
DSC 4
c
QSC
ON JUtY
STATION
I I, IS5 Q
i
)I
ONAOAWA
FREDERlCUSSUf?0
5
BYRD
STATION
LJ
(08’ - Id
-
FIO. 2. AN BXAMPLBOF MAONETOCRM~~OF TEXRX ~F.Z SIhlULTANEOUSLY AT THB TiIB
OF psc’s WHICH 1959.
OCCURRED
OF THE SAME SSC ON 11 JULY
TABIJI 3. RXPRBSENTA‘~I~B STA’IION,MA~NETOORAMS, AND ANAtyzED yEARSFGREACripsc
Phenomenon
Representative station
Magnetograms main and (auxilii) Induction (La Cour, Ordinary) La Cour (Ordinary) LaCour (Ordinary)
Onagawa Fredericksburg
%=d
TABLE4. GBXRAPHIC AND GEOMAGNElTC wliIcH
ARE
No.
Station
Abbreviation
1 2
H&Y Fredericksburg San Juan Onagawa Honolulu Hermanus Byrd
He
: : 7
:; OU El BY
Anaiyzed
RE-
LOCATIONS
Y-
Jan. 1951%Dee. 1959 June 1957-Dec. 1962 Aug. 1957-Dec. 1959
OF THE
STATIONS
TOINTHISPAPER
Lat.
Geographic Long.
63B”N 38*12’=N 18*23”N 38*26”N 21.18”N 34.26”s 79.59”s
149*oo”w 77.22”W 66*07”W 141*28”E 158.06”W 19.14% 1206o”W
Geomagnetic Long. Lat. 63.6” 49.6 30.1 28.3 21.0 -33.3 -70.4
256.5% 349-9 032 2068 266.4 80.4 336.2
GEOMAGNETIC PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS 2. S-
579
BETWEEN psc’s AND pc’a
Diurnal variations of amplitudes of psc’s are obtained in relation to those of corresponding period ranges of pc’s. The amplitude of psc generally becomes larger for an ssc with a larger magnitude. To eliminate this effect, the double amplitude of each psc is divided by the range of each associated ssc; this is called a %ormalized amplitude”. The double amp~tude of the psc is read by the envelope method (Saito, 1961) to extract it from the superposing gradual part of ssc. Since the ssc range in the auroral zone is often indiscernible due to the large amplitude of the associated psc, the double amplitude of psc at Byrd is normalized by dividing it by the range of the corresponding ssc at a low latitude station, Hawaii, whose longitude is nearly that of Byrd. The diurnal variations in the normalized amplitudes for each psc are shown in Fig. 3B. The diurnal variations in the largest no~~zed amplitudes among these scattered points are shown by broken lines. Since no suitable data are available for the diurnal variation of amplitudes for PC’Sat the (A)
LOCAL
(El
PC
TIME
LOCAL
PSC
TIME
FIG. 3. DIURNAL VAIUATIONS IN THB AMPLITUDESOF pc’s (LEFT) AND psc’s (RIGHT) FOR THRJX PERIOD The
RANGES
ordinate of pc’s indicates the pulsation activity, namely a product of the amplitude aud duration of pc, and the ordinate of psc’s indicates the normalized amplitude.
580
TAKAO
SAITO and S. MATSUSHITA
stations which are being analyzed; and since both activity and amplitude of PC’S show almost the same diurnal behavior (Saito, 1966), the diurnal variations in the activities of PC’Sare shown in Fig. 3A as a substitute for those of pc amplitudes (Saito, 1964a). By comparing Fig. 3B with Fig. 3A, we may conclude that amplitudes of both psc’s and corresponding period-range PC’Shave fairly similar diurnal tendencies. 2.2. Diurnal variations of periods The periods of psc’s were obtained by averaging as many pulses with a uniform period as possible never more than ten of them for one sequence. However, pulsations containing
FK3.4. D~JRNAL VARIATIONS
IN THE PERIODS OF PC’S (SwmS B ON THE RIGHT).
A
ON THE LEFT) AND PSC’S (SERIES
(A,) pc 5 at Byrd after Saito (1964a); (AZ) pc 4 at Fredericksburg; one dot indicates one sequence of pc 4 for October 1-31, 1962; (As) pc 2.3 at Onagawa; the solid circles are after Kato and Saito (1959), the open circles are from magnetograms of pc 2.3 in Geomagnetic Rapid Variations Observed at the Onagawa Magnetic Observatory, Parts I and II; (B,) psc 5 at Byrd; (B*) psc 4 at Fredericksburg; (BJ psc 2.3 at Onagawa and Fredericksburg.
GEOMAGNETIC
PULSATIONS
ASSOCIATED
WITH SUDDEN
COMMENCEMENTS
581
various periods were excluded. The periods of psc’s thus obtained are plotted against local time in Fig. 4B and are compared with those of pc’s shown in Fig. 4A. A striking resemblance between the diurnal variations of the periods of pc’s and psc’s are seen in these Figures. Both pc 5 and psc 5 show the shortest period in the morning, pc 4 and psc 4 show the shortest period near noon, while pc 2.3 and psc 2.3 have the longest period near noon. The mean period of psc 4 is slightly longer than that of pc 4; this is probably caused by the secular effects on the periods of pc 4 and psc 4 as discussed in section 3.2. The present result on the diurnal tendencies of both pc 2.3 and psc 2.3 periods, which are longer in the daytime than at night (inverted-U type), is clearly seen in Figs. 1A and 2A but is apparently the reverse of the recent results on pc 3 period obtained by Christoffel and Linford (1966a, b) which are shorter in the daytime than at night (U-type). However, the present result agrees with previously obtained results (Utashiro, 1948; Kato and Utashiro, 1950a, b; Kato and Saito, 1958, 1959, 1962; Campbell, 1959a; Yanagihara, 1959; Saito, 1960, 1962, 1964a; Duncan, 1961, 1966; Ness et al., 1962; Kato, 1962; Prince et al., 1965; Kato and Sakurai, 1966). This controversy may be explained by an apparent solar cycle effect on the diurnal variation in the period of PC’Snear 30 set; the inverted-U type diurnal variation occurs in the sunspot maximum years, while the U-type variation occurs in the sunspot minimum years. This solar cycle effect can be caused by a combination of the following reasons: (1) the boundary periods shift gradually from 40 set in the sunspot maximum years to 30 set in the sunspot minimum years (Kato and Saito, 1964; Saito, 1962, 1964b); hence, the pc reported by Christoffel and Linford should probably not be classified as pc 3 but as pc 4 in the sunspot maximum phase: (2) the nighttime pc 2.3, whose period is near 10 set, tends to disappear near the sunspot minimum years (Kato and Saito, 1959; Yanagihara, 1959, 1960; Troitskaya, 1961a). 2.3. Dynamic spectra Saito (I 967) reported that a dynamic spectrum of psc shows a fairly coincidental pattern at a pair of nearly conjugate stations, Byrd and Great Whale River. Dynamic spectra of psc are compared with those of pc; one example at Byrd is shown in Figs. 5A, and Bz. The dynamic spectra of both pc and psc in these figures consist of a series of small patches which indicate that pc and psc show a similar series of patches with the exception of a small difference in the continuity of the series. From all the above-mentioned results we can infer a very close occurrence model of pc and psc. 3. CHARACTERISTIC
FEATURES OF psc’s
3.1. Effects of the steepness of accompanying ssc’s Characteristics of psc’s due to the accompanying ssc are discussed in this section based mainly on psc 4 data at Fredericksburg. The psc amplitude depends partly on the steepness of the accompanying ssc, where the steepness of the ssc is defined as the ratio of the range to the duration of ssc. Takahashi (1960) and BouEka (1962) reported a variety of the steepness. A dependence of psc 4 amplitude on the steepness of the accompanying ssc with respect to the local time of its occurrence is shown in Fig. 6A. In general, the small amplitude of psc 4, which is expressed by crosses and small circles, is distributed at the place where the steepness is nearly zero, and the large amplitude appears when ssc shows a sharp increase or decrease. The period of psc 4 is also plotted with respect to the steepness and local time of the
582
TAKAO SAlTO and S. MATSUSHITA
accompanying ssc as shown in Fig. 6B. It seems likely that the period of psc 4 becomes shorter when the ~rn~~g ssc has a larger positive steepness. 3.2. Eff’ecfsof the amplitude of accompanyingm’s As seen in Fig. 6, psc’s are associated with both positive and negative ssc’s. Figure 7 shows examples of psc 2.3, psc 4, and psc 5 associated with positive and negative si’s and an ssc. At high latitudes the amplitude of psc 5 is generally much larger than the range of si’s. In order to compare the two, si’s in low latitudes can be used as a reference of si’s at high latitudes. Thus, the rapid-run magnetogram of the psc 5’s at Byrd (Fig. 7C) is compared with the ordinary magnetogram of the si’s at a low-latitude station, HonoIulu (Fig. 7E), whose geomagnetic longitude is nearly that of Byrd. Several psc 5’s occurred at Byrd, the beginnings of which correspond to the positive and negative si’s at Honolulu near local noon. The periods of psc 5’s associated with the increasing phase of si’s are shorter than those associated with the decreasing phase of si’s, as seen by comparison of Fig. 7C with Fig. 7E. In order to understand the relation between the psc periods and the sign (including the range) of ssc’s, psc 4 periods, 7&., ‘s, shown in Fig. 6B and ranges of ssc’s, AH’s, observed at Fredericksburg were studied. Tpsc( can be equated as follows: Tpsc4
=fG
+fi
+fa
+fs + k(AH) =fl +fa + NW,
(1)
w&e f’ =fo + fI +fa fa = secular term fi = annual term =
(a&W
+ &I 4x3srgd+
A)
h= semi-annual term = (a2R(M) + b$ cos (g
d+t%)
f3 = diurnal term = a, ~0s (15”f + &) + b3 R(M) = monthly mean value of relative sunspot number M = phase of the solar cycle in the unit of month;
M = 1 starts from July, 1957.
d = day of the year started from 1 for the first of January t = local time at Fredericksburg k = coefficient of the ssc range, AH a,, b, = amplitude parameters, where i = 1, 2, and 3 PC= phase angle parameters, where i = 1,2, and 3. Since the periods of psc 4 and pc 4 show strikingly similar diurnal variations as mentioned in section 2.2,f’andf, of TP 4 are assumed to be the same asf’ andfo of T’ *, respectively, for simplicity. Observed values off ‘and f. of lpPO d at 12.5 hours local time at Fredericksburg are available in the form of monthly average (Kate and Saito, 1964; Saito, 1964b) and are listed in Table 5. The least square method of these values off’ and f. gives values of parameters a,, b,, PI, a,, b,, and /& as follows: f’ =fo + {0~0429R(M) + 3~38) cos (00986”d - 0.1”) -(O.O48OR(M) - 3*34) cos (1.97”d - 27*29).
(2)
FIG. 5. SPECTRA OF pc (SERIES A ON THE LEFT) AND psc (SERIES B ON THE RIGHT) AT BYRD. (Top diagrams shown by sub, 1). Amplitude spectra at the times indicated by the arrows below; (middle diagrams shown by sub. 2) dynamic spectra which consist of a series of small patches of the order of 10 min. (bottom diagrams shown by sub. 3). Chart records correspond to the dynamic spectra. The analysis of these was made possible through the courtesy of Dr. Wallace H. Campbell, ITSA-ESSA.
SR?
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS
I--
(B)
(4 . .
583
.
.
..
.
. -. *
!.
*
.
’ . :*
t
3
f
b
FIG. 6,
LOCAL
TIME
)%mx-s
OF
! 12 -
THE
“C
l
14 75’
16 18 20 W.M.T.
ssc
sTI~EPNBSS AT
22
24
(THE
0
RATIO
4
6 6 LOCAL
~ IO 12 I4 16 18 TIM1 c _. 750 W.M.T.
OF THE
RANGE
To
2
THE
*
.
.
DURATION
I
20
22
OF
THE
FRJZDEI~ICKSBURG:I!GRTHEAMPLWLJIX(LEFT)ANDTHEPWIOD (RImIT).
TYPICAL I
. a
psc4
ACCXXP~C+SSC)ON
.
~A9U~TO6RA~
REMARK
si
Si
A
/ ONAQAWA JUL27.1966 (iyf)
FIG.7. "hl?ICAL MAGNBXOGBAbi OF PSC'S ASSGcIA~
WITH PCBFEVE AND NEGATIW
NS
Si'SAND
A.N SSC.
(A) induction magnetogram; (B), CC), and (D) La Cour type rapid-run magnetograms; (E) ordinary magnetogram. Times are indicated by UT. (C) and (E) show the same event at Byrd and Honolulu, where the periods of pa 5’s at Byrd are longer at the time of negative si’s at Honolulu .
I
TAKAO SAITO and S. MATSUSHlTA
584
TABLE5. THE PERIODS
(SECONDS)
OF
pc
4
AT
12.5 HOURS
LOCAL
TMB
AT
FREDERICKSBURG (KATOANDSAITO,1964)
f’, monthly mean values; fO, secular values obtained by 11 2/2-month running average Month Jan. Feb. Mar. Apr. May June
JdY
Aug. %P* Oct. Nov. DeC
1957
f 44.9 48.5 55.1 79.6 77.2 71.0
fo
f’
-
65.2 65.5 76.7 68.7 53.3 48.1 47.2 52.6 63.5 68.6 727 70.3
6;9 62.9 62.9 62.9 62.9 62.9
1958
fo
f’
62.9 63.2 63.7 63.6 62.9 62.7 62.8 62.9 62.2 61.1 60.8 60.8
67.0 Es .
1959
62.0 53.1 47.2 z: . 57.6 57.5 58.4 57.4
fo
f’
60.7 60.3 59.9 59.3 58.3 57.1 56.3 56.0 55.8 55.2 54.3 53.6
59.6 64.7 58.9 47.8 44.6 402 42.3 44.9 53.0 50.2 51.9 51.9
1960
fo
f’
53.2 52.9 52.6 52.1 51.6 51.1 50.5 49.6 48.8 48.5 48.5 48,6
51.8 51.4 51.8 48.8 43.1 43.1 43.1 42.2 49.5 50.6 50.4 62.1
1961
fi 48.7 48.5 48.4 48.2 48.2 48.6 49.2 49.6 49.6 49.8 49.8 49.8
Root mean square of the deviation of the observed values from this formula is 3.25. Observed Tpsc 4 and thisf’ formula of TPc 4 substituted forf’ of T,,, 4 in (1) give actual values off, parameters and k by the least square method as follows: Tpec4 =f’
+fs
+ WW
= f’ + a3 cos (15’t + B3) + b, + k(AH)
=f’
+ 14.49 cos (15’t + 32.6’) + 11.09 - 0*127(AH) ’
The root mean square of the deviation in this calculation is 19.19. The obtainedf, in (3) should be almost the same asfs of Tw 4. The value of k was confirmed as follows: Tw 4 = f’ + f3 + kW0 =
(3) of Tpec4
+ WW
f’ + a, cos (15”t + /Q + b3 + k(AH) + k’(AH)a
(4)
The least square method to the observed values of Tpsc4 and f’ gives Tpat4 = f’ + 14.47 cos (15”t + 32.3’) + 11.15 - 0*142(AH) + 0X@022(AH)2
(5)
The root mean square of the deviation is 19.18. Since k’ is nearly zero and a,, ,!&,b,, and k in (5) are very close to those in (3), the formula (3) is valid without being affected by k’(AH)2. The relation between TpM:4 and AH is shown by the last term in (3). For example, when a positive ssc with a range of +lO y (a negative si with a range of -1Oy) is observed at Fredericksburg, the period of the associated psc 4 becomes shorter (longer) by 1.3 set than the expected period of pc 4 for the given year, month, day, and local time of the positive ssc (negative si) event. This result gives an explanation of the phenomenon mentioned by the comparison of Fig. 7C with Fig. 7E. 4. DISCUSSION AND CONCLUSION The analyzed results presented in the previous sections are summarized as follows: (1) The psc’s, whose periods range from 5 to 600 set, can be classified into psc 2.3, psc 4, and psc 5 in a similar way as the pc groups: pc 2.3, pc 4, and pc 5. (2) Diurnal variations in the amplitudes of psc’s are very similar to the corresponding PC’S: both psc 2.3 and pc 2.3 and both psc 4 and pc 4 show the maximum amplitude in the daytime; both psc 5 and pc 5 show the maximum amplitude in the morning.
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COM~N~ME~
585
(3) Diurnal variations in the periods of psc’s are also quite simiIar to the corresponding pc’s: both psc 2-3 and pc 2.3 show the longest period near noon; both psc 4 and pc 4 show the shortest period near noon; both psc 5 and pc 5 show the shortest period in the morning. (4) The dynamic spectra of psc’s have either a patch with a duration of about 10 min or a series of such patches in a similar way as the dynamic spectra of pc’s. (5) The ssc’s which have a rapid increase of geomagnetic H-component often accompany psc 4’s with large amplitudes and short periods. (6) The periods of psc 4 and psc 5 associated with positive ssc’s are shorter than those associated with negative ssc’s. The results (I) through (4) of the above six results indicate the similarity of the characteristics between psc’s and pc’s. When the Earth’s magnetosphere is assumed to contain resonance systems for hydroma~etic waves, psc’s and pc’s seem to occur being governed by these systems excited by the hydromagnetic waves due to the shock from outside the magnetosphere. The number of pulses contained in one psc event does not correspond to the same number of ssc shocks, or expansions and compressions of the magnetopause. In other words, even one shock of ssc on the magnetopause can generate a series of damped pulses of psc in the magnetosphere. The following three observational facts also support the present conclusion: (a) an ssc accompanies psc 2.3, psc 4, and psc 5 simultaneously; (b) damping ratios of the amp~tudes of psc’s are fairly constant during one sequence of the psc’s (Kate and Saito, 1958); (c) Periods of the pulses of psc’s are, in most cases, constant during one sequence of the psc’s. Results (5) and (6) show the relation between the sign of the accompanying ssc and the periods of psc 4 and psc 5. Many authors attributed pc 4 and pc 5 to transverse hydromagnetic waves propagating along the Earth’s magnetic field-lines (Kate and Watanabe, 1956; Obayashi and Jacobs, 1958). In the simplest ease, the period T of pc 4 and pc 5 can be expressed by the formula,
where, S, p, and H are respectively the path of hydromagnetic wave propagation, plasma density, and magnetic field intensity along the path. It is quite probable that this formula is applicable not only to pc 4 and pc 5, but also to psc 4 and psc 5 taking into consideration the present results on the similar behavior between psc and pc. In case the magnetosphere where the plasma is frozen is compressed at the time of a positive ssc or si (Nishida and Cahill, 1964), both d/2 - H-l and S decrease causing a decreasing of T. An expansion of the magnetosphere at the time of a negative ssc or si causes analogously an increase of T. This tendency of the period changes agrees welI with the present observationaf results on the modifi~tion of the periods of psc 4 and psc 5 at the times of ssc and si. Acknowledgements-The authors wish to express their sincere gratitude to Dr. Wallace H. Campbeh, ESSA, for his kindness in offering the frequency analyzer and the magnetic tape data of the geomagnetic pulsations recorded at the ESSA Byrd Statton which were used to obtain the dynamic spectra. The authors also wish to thank Professor Yoshio Kate, the Director of the Onagawa Magnetic Observatory, Tohoku University, for the valuable discussion. Thanks are also due to Mrs. Mary H&y and to Mr. Joe Oliger for their kind assistance throughout the ~rnp~~e~t of this work. BEMOPF,H. 1963. J. geophys. Res. 65,1413. BRRTHOIQW. K., HARRIS,A. K. and HOPE,3%J. X960.J. geephys. Res. 6!5,613. Bousrc~, 1. 1960, Studiageophys. geod. 4,280. BMJ%A,J. 1962. J. phys. Sot, Japan. Suppt. A-ZZ17,45.
586
TAKAO SAITO and S. MA’ISUSHITA
cM6pBELL,W. H. 195% Inst. Geophys. Univ. Cal6 Los Angdes Sci. Rep. 1,l. CAMPW. H. 1959b. J.geophys. Res. 64,1819. C~~~LQQFFEL, D. A. and L~NFQRD, J. G. 1966a J. geophys. Res. 71,891. Crnosrorrr?r-,D. A. and -RD. J. G. 1966b. J. geophys. Res. 71,47%. DUBRO~~K~Y, D. G. 1961. Rapid magnetic variations, JAGA BuZi, 16C, 57. DUNCAN,R. A. 1961. J.geopkys. Res. 66,2087. DUNCAN,R. A. 1966. J.geophys. Res. 71,470s. Geomagnetic Rapid Vartations Observed at the Gnagawa Magnetic Observatory during the International Geophysical Year, PartsI(1960) and II (1961). Sci. Rep. Toho&u Univ., Ser. 5, Geophys. 11 and 12, Suppl 1. HEA-, R. R. and HEALER,V, P. 1965. J. geophys. Res. 70,1103. -WA, T., N~~HIDA, A, and NAQATA,T. 1966. Rep. Zonospk Space Res. Jupan Ut, 51. IAGA Bulletin of Geomagnetic Indices K and C, (19561962). IAGA Pmliminary Report on Sudden Commencements. International Union of Geodesy and Geomagnetism (19561962). JACYXC~, 1. A., KATO,Y., MATSV~E~TA, S. and TROI‘IXKAYA, V. A. 1964. J. geophys. Res. 69,180. KAro, Y. 1951a Scl. Rep. Tohoku Univ., Ser. 5, Geophys. 3.40. KATO, Y. 1951b Rep. Zonosph. Space Res. Jupan $75. -1-0, Y. 1962. J. phys. Sot. Jupim, Suppl. A-ZZ 17,71. K&TO, Y., Ossrrrc~, S. and OKUDA,M. 1953. Sci. Rep. Tohoku Univ., Ser. 5, Geophys. S, 85. KATO, Y. and S~O, T. 1958. Sci. Rep. Tohoku Univ. Ser. 5, Geophys. 9,99. KATO, Y, and SAITO,T. 1959. J. Geomagn. Geoekect., Kyoto 10,221. KATO,Y. and S.uro, T. 1962. J. phys. Sot. Japan, Suppl. A-ZZ 17,34. KATO, Y. and Sm, T. 1964. Rep. Zonosph. Space Res. Japan 18,183. Kilo, Y. and SAKURAI, T. 1966. Private communication. J&x-o, Y. and TAMAO,T. 1956. Sci. Rep. Tohoku Univ., Ser. 5, Geophys. 7,147. KATQ Y, and TAMAO,T. 1964. Rep. Zo~sph. Space Res. Japan 18,213. ICATD,Y. and UT-O, S. 195Oa.J. Geomagn. Geoelect., Kyoto 2,71. tire, Y. and UT-O, S. 1950b. Sci. Rep, Tohoku Univ., Ser. 5, Geophys. 551. KATO, Y. and Un, T. 1964a. Sci. Rep. Tohoku Univ., Ser. 5, Geophys. lS,83. KATO,Y. and Urst_no,T. 1964b. Rep. Zonosph. Space Res. Japan 18,214. KA-Q Y. and WATANABE, T. 1956. Sci. Rep. Tohoku Univ., Ser. 5, Geophys. 8,ll. MAFBJSHITA, S. 1957. J. geophys. Res. 62,162. MATSUSHITA, S. 1960. J. geophys. Res. 6S, 1423. MAI-SUSHITA, S. 1961. J. geophys. Res. 66,3958. MA-IX-A, S. 1962. J.geophys. Res. 67,3753. MATSUSHITA, S. 1963. J. geophys. Res. 68,332O. MA-A, S. 1965. Radio Sci. J. Res. Nat. Bur. Stand./USNC-URSZ69Q 1149. MATUURA,N. 1961. Rep. Zonosph. Space Res. Japan 15, 192. Monthly Reports of the Onagawa Magnetic Observatory (1956-1959) 14. NAGATA,T., KO~QJBUN, S. and I~JXMA+ T. 1%3. J.geophys. Res. 68,4621. N, G. F. SCEAR~X, G. S. and H~FPNER, J. P. 1962 J. phys. Sot. Japan, SupZ& A-ZZ17,27. NESS,N. F., SNEXHXDA, A. and JACOES,J. A. 1962. J.geophys. Res. 67,525. NLWDA, A. and CAHIU, L. J., Jr, 1964. J. eophys. Res. 69,2243. OBAYASHI. I’. and JACOBS, J. A. 1958. Geop f ys. J. R. Astr. Sot. 1,53. OHL, A. M, 1962. J. phys. Sot. Jiqxm, SuppI. A-N 17,24. OEWDU, EL 1961. Mem. Kakioka Magn. Obs. 10,l. Pttmce, C, E., Jr., Bosx~, F. X., Jr. and Smrrx, H. W. 1965. J.geo hys. Res. 70,4%1. Report of the Kakioka Magnetic Observatory, Geomagnetism, (195dr 1959), NOS.2630. &TO, T. 1960. Sci. Rep. Tohoku Univ., Ser. 5, Geophys. 12,106. Qrro, T. 1961. J. Geomqgn. Geoelect., Kyoto 12,112. Sluro, T. 1962. Sci. Rep. Tohoku Univ., Ser. 5, Geophys. 14,81. Sm. T. 1964a J. Geomqn. Geoelect., Kyoto 16,115. Sm, T. 1964b Rep. Zonosph. S’e Res. Japan 18,197. Sm, T. 1965a. J. Geomqn. Geoelect., Kyoto 17,23. SNTO, T. l%Sb. Rep. Zonosth. Space Res. Japan 19.30. SAITO,T. 1966. NBS Techmcal Note. In press. Qrro, T. 1967. J. geophys. Res. In press. SANO,Y. 1963. Mem. Kakioka Magn. Obs. l&l. SATO,T. 1962a Rep. Zonosph. Space Res. Japan 16,295. SATO,T. 1962b Proc. Znt. Conf. Ionosphere p. 155. Physical Society, London. SATO,T. 1964. Rep. Zonosph. Space Res. Japan 18,173. SATO, T. 1965. Antarctic Research Series 4, Geomagnetism and Aeronomy (ed. A. H. Waynick). p. 173 American Geophysical Union.
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS
587
Solar-Geophysical Data, CRPL-F. Part B, Natl. Bureau of Standards, Boulder, Colorado. Res. 66,4087. R. 1964. J. geophys. Res. 69,121l. Tmm, I-L 1960. J. geophys. Res. 65,4206. TEPIJx, L. R. and WENIWORIH, R. C. 1963. J. geophys. Res. 68,3733. TRO~ISICAYA. V. A. 1961a. IAGA Bull. 16~. 130. TROITXAYA;V. A. 1961b. J. geophys. Res: 66,s. TROITSKAYA, V. A., ALPEROMCH. L. A., MELNIKOVA, M. V. and BULATOVA, G. A. 1962. J. phys. Sot. Japan, SuppI. A-II 17, 63. UT-O, S. 1948. J. Geomagn. Geoekct., Kyoto 1, 59. VELDKAMP, J. 1960. J. atmos. terr. Phys. 17,320. W-N, C. R. 1962. J. geophys. Res. 67,2054. W~SON, C. R. and SUGNRA. M. 1961. J.geophys. Res. 66,4097. Wnm~, C. R. and SUGIURA, M. 1963. J.geophys. Res. 68,3314. YUUCWCHI, Y. 1958. Mem. Kakioka Magn. Obs. 8.33. YANA~IIURA, K. 1959. J. Geomagn. Geoelect., Kyoto 10,172. YANA~HARA,K. 1960. Mem. Kakioka Magn. Obs. 9,15. SUONRA, ki: 1961. J. geophys. SUOIURA, M. and W-N, C.
Posnm~3aqxaxorqero Tma nynbcarluu, accoqmipyeme KaK c BkieaanHkam Aaqanam 6yp~ (B.H.~.), TaK u C BHeaanHbIm umy~bcabfu (B.U.), UccneRyIoTcH ua npeweT 388 mnendf, memuux MecTo Ha npoTmKeHuu nocne&tiux ‘7 neT, c 1956 ~0 KoHqa 1962. BBUJIJTO~O,VTO B.H.~.u B.U. 06arseo 06HapyNiBaJIUBecbMa~~0~HbIftpeWiM, ConpoBo~am~we EIX nynbcaquu CKOM6UHIipOBaIIbInon 06n~uu ria8BaEHetd n.B.H. ~TEI n.B.H. pacnpe~enmoTcfi no seTupear rpynnaw COrJIaCHO AJluTeJIbHOCTu n.B.H. 1, 0, 2-5 ceK; U.B.H. 2,3, 6-30 ce~; n.u.n. 4, 30-150 nepuoaoa, a memo: ceK; n.B.H. 6,16@-600 ceK. ~peo6na~amrqur.m n.B.H. Ha cpenfiefl a HU~KOR mupoTax, B noAnomipHofi o6nacTu a nonflpao~ aOHe HBJIRH)TCH U.B.H. 2,3, U.B.H. noosepenH0 4 u 5. OHarasa, @pe&iepuKcBypr u Bap~ CeneKquomposam B Karlem xapaKTepHbJXCTaHI,uft AJIH nOnOCbl Ka)KAOrO IIepUOsa. CyTowftde sapwaqnu B amnnurynax II nepuonax n.B.n. conocTamfnoTc~ c cy~oYHIJMU BapUa4uHMu COOTBeTCTBylOlWX U.H. CpaBueme TaKme npoeogmrcfi u Ann Auarpamf B AuHammqecKux cneKTpax n.B.H. u n.H. BaKnmsamT, STO o6a poAa nynbcaquft 09eHb CXOAHI~ no c13om oapnawwv n~Ha~mecKm cneltrpaar. IdayqaeTcu aro~u@uKaqm xapaKTepucTuKu n.B.H. pe3ynbTupyloQaR OT accoqm UpOBaHHbJX C HUMK B.H.~. i'f3-3aCBOeft 6onbmeB nO3UTHBHOi KpyTu3nbI (OTEO1[IeHue ahmnuTyAhl K npo~on~uTenbnocTu n.H.6.) m1.6. conpoeomAaeTcHn.a.H. 4, cHa6memianr 6onb~ei%aMnJIuTyJJOftU6o.leeKpaTKUMnepUO~OM. COrJlaCHO CTaTuCTuKe OmEAaeTCH, ST0 n.B.H. 4 yKOpaWiBaeTCH nyTebl0,127 CeK AlIfiB.H.~. C KamAbtM ly UpupaIUeHueM ropuaorrranbaott cocTaBnmo4e~ B @penepuKcmypre. BK.?WIaeTCH KpaTKOe 06CymAeHue 3TuX XapaKTepucTuK n.B.H.
GEOMAGNETIC PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS AND SUDDEN IMPULSES TAKAO SAIT’O* and S. MATSUSHITAt High Altitude Observatory, National Center for Atmospheric Boulder, Colorado, U.S.A.
Research
(Read at the Inter-Union Symposium on Solar-Terrestrial Physics, Be&rade, 29 August to 3 September 1966. Received 29 November 1966) Abstract-Damped-type geomagnetic pulsations associated with both storm sudden commencements (ssc’s) and sudden impulses (sin) are studied for 388 events which occurred during the past 7 years from 1956 through 1962. Since the pulsations associated with ssc’s and with si’s usually showed very similar behavior, they are combined together under a notation, psc. These psc’s are class&xl into four groups according to period ranges in a similar way as pc’s: psc 1,0.2-5 xc; psc 2.3,5-30 set; psc 4,30-150 set; psc 5,150-600 sec. Predominant psc’s in middle and low latitudes, sub-aurora1 region, and auroral zone are psc 2.3, psc 4, and psc 5, respectively. Morphological behavior of p&s, such as daily variations of their amplitudes and periods, and patterns in their dynamic spectra show a remarkable similarity to those of corresponding period-range pcf. However, the psc’s show an interesting dependence on the range and duration of accompanying ssc’s. A brief discussion is given on these characteristics of PSC’S. 1.
INTRODUCTION
1.1. Previous works Many workers have previously reported that damped-type pulsations are often associated sudden commencements (ssc’s) and sudden impulses (G’s). Predominant periods of these reported pulsations seem to be at nearly 1 set, 20 set, 1 mm, and a few minutes. The pulsation with the predominant period of nearly one second was fist reported by Troitskaya et al. (1962) as being associated with ssc’s. Since that time, very few studies on this group of pulsations have been presented (Matsushita, 1962; Tepley and Wentworth, 1963 ; Heacock and Hessler, 1965). The damped-type pulsations with the predominant period of 20 set were reported almost 20 years ago by Utashiro (1948) and Kato (Kato and Utashiro, 1950a, b) who used induction magnetograms obtained at Onagawa, Japan. These pulsations were reported to have amplitude of the order of 0.1~ and decay time of several minutes, and were explained by an effect of a fluctuation of the ionospheric current at the time of ssc (Kato, 1951a, b; Kato and Tamao, 1956). A difference between the pulsating part and the gradual part of ssc on the disturbance hodographs was noticed by Kato et al. (1953). Separating the pulsating part from the gradual part, Kato and Saito (1958) proposed that the pulsation was caused by a hydromagnetic oscillation due to the ssc shock. Further morphological studies of this group of pulsations have been made based on data from many events recorded at one station; for example, the decay curve of their amplitudes with respect to the storm-time (Campbell, 1959a, b; Oshima, 1961), the diurnal variation in their periods (Kato and Saito, 1959; Bouxka, 1960, 1962), and the ratio of occurrence of ssc to the associated pulsation (Dubrovskiy, 1961). Morphological similarity
with storm
* Also ITSA-ESSA. On leave from Onagawa Magnetic Observatory, Geophysical Institute, University, Sendai, Japan. t Also ITSA-ESSA and the Department of Astro-Geophysics, University of Colorado. 573
Tohoku
574
TAKAO SAITO and S. MATSUSHITA
of ssc to si was noted and discussed in relation to their associated pulsations (Kate and Saito, 1958,1959; Yamaguchi, 1958; Matsushita, 1960,1962; Nishida and Jacobs, 1962). A solar cycle dependence on the occurrence of the sporadic storm following the pulsation in question and on the recurrent type storm without ssc was also studied (Saito, 1965a, b). The world-wide distribution of the pulsation stations during the International Geophysical Year brought a wider aspect of this group of pulsations. Based on the data at seven welldistributed U.S.A. stations, it was found that the negative impulse preceding ssc (MacUser, 1957) occasionally shows two or more oscillations (Mats~~~, 1960,1962). An apparent travel velocity of this group of pulsations was discussed by Berthold er al. (1960), Troitskaya (1961b), and Benioff (1963) based on the data from well-separated stations. Matsushita (1962,196s) suggested a possible close relation between the ionospheric oscillation associated with ssc and this group of geomagnetic pulsations, and advocated a probable important role of the ionosphere to these geomagnetic pulsations. No extensive report has been made on geomagnetic pulsations with the predo~nant period of approximately 1 min which are associated with ssc’s. However, it may be noteworthy in relation to this group of pulsations that a lengthening of the pc 4 period was reported at the time of negative si on 17 July 1958 (Veldkamp, 1960). Matsushita (1962) and Saito (1964a) asserted the existence of this group by showing examples of magnetograms. Damped-type pulsations associated with ssc’s, which have the periods of the order of a few minutes and the amplitudes of the order of 10 y, were reported after the analysis of IGY magnetograms (Sugiura, 1961; Wilson and Sugiura, 1961; Saito, 1961; Matuura, 1961; Wilson, 1962). Based on the spatial distribution of the rotation vector of the pulsations, it was interpreted that the primary effect of the impact of the magnetosphere generates a longitudinal hydromagnetic shock wave. A negative kick preceding the main pulse of ssc was interpreted as being a part of this damped pulsation. On the other hand, another theory was advocated that the negative kick was due to an effect of charged particles impinging into the high latitudes (Matsushita, 1957, 1960,1961, 1962). Further discussions were made on this problem (Wilson and Sugiura, 1963; Matsushita, 1963; Nagata et al., 1963; Sugiura and Wilson, 1964; Kato and Tamao, 1964; Hirasawa et al., 1966). Sudden increases (Matsushita, 1961, 1962) or concurrent pulsations (Sato, 1962b, 1964) of the cosmic noise absorption were reported in relation to the geomagnetic pulsation associated with ssc. Other morphological studies on the geomagnetic pulsations at the time of ssc were world-wide distribution of amplitudes of the pulsations (Sato, 1962a), latitude-diurnal effect of their amplitudes (Ohl, 1962), their rotation vector (Sano, 1963; Kato and Utsumi, 1964a, b), and their polar region effect (Sato, 1965). 1.2. De~ni~io~ and data used Since the pulsations associated with ssc’s and with si’s usually show very similar behavior (Kato and Saito, 1958,1959; Yamaguchi, 1958; Matsushita, 1962; Nishida and Jacobs, 1962), these pulsations are, hereafter, combined together under a notation, psc. Similarly, ssc and si are often combined together under the notation of ssc. Summarizing the individual works as reviewed in the previous section, these psc’s can be classified into four groups according to period ranges. They are called psc 1, psc 2.3, psc 4, and psc 5 in a similar way as geomagnetic continuous pulsations, pc’s (Jacobs et al., 1964) and are listed in Table 1. In the present paper all psc’s excluding psc 1 are discussed. Typical examples of psc 2.3, psc 4, and psc 5 associated with different ssc’s on different dates are shown in Fig. 1, and those associated with the same ssc on 11 July 1959 are shown in Fig. 2.
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS TABLE1. FOUR ORO~JPSOF TYPE
575
DAMPED-
PLRSATIONS As9ocIAlEDwrrH SSC AND Si
In spite of 4Osec for the boundary period between pc 3 and pc 4, which is recommended by IAGA (Jacobs et al., 19&I), 3Osec is applied here for the boundary period between psc2.3 and psc4, taking into consideration the solar cycle dependence on the boundary period (Kate and Saito, 1964)
Fl0.I
TYPE
Notation
Period range (set)
PSl psc 2.3
0.2-5 S-30 3LL150 150-600
TYPICAL
7: REMARK
MAONETOORAM N
j
A
P8C
lo*
2.3 02%n
u-1.
r 20n
6
ONAQAWA
7
FOR t.2oilas +--” 2’sm
S6C
FEB.25.
/
1858
FREDERICKSBURQ APR.27,
iaeo
i
HEALEY DEC. 12.
FIG. 1.
TYPICAL
EXAMPLES OF MAGNETOGRAM OF p&s DIFFERENT DATES.
1858
wrraar~naa WC’SOCC~RNDON
In the present analysis, studies were made of the horizontal component of psc’s associated with 388 events of ssc’s and si’s for the past 7 years from 1956 through 1962 as listed in Table 2. These ssc’s and si’s were se1ecte.d from the ZAGA Preliminary Report on Sudden Commencements when more than twenty stations reported the same event as ssc and more than ten stations reported the same event as si. All the events in the Preliminary Report were confirmed by referring to the magnetograms at well-distributed stations, such as Honolulu, Onagawa, Hermanus, and San Juan. References to the ZAGA Bulletin of Geomagnetic Indices K and C, Solar-Geophysical Data, Monthly Reports of the Onagawa Magnetic Observatory, Report of the Kakioka Magnetic Observatory, and other sources were
also made. Predominant psc’s are apparently psc 2.3 in middle and low latitudes, psc 4 in the subauroral zone, and psc 5 in the aurora1 zone. Rapid-run magnetograms at representative stations, Onagawa, Fredericksburg, and Byrd, were used for the study of psc 2.3, psc 4, and psc 5, respectively (see Table 3). The geographic and geomagnetic locations of these stations are shown in Table 4 together with other stations which are referred to in this paper.
No.
33: 34 35
; 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
: 4 5 6 7
1
YtXU
Jan. 21 1644 22 (1940) 27 O9OO 27 (1626) Feb. 11 0054 19 0221 19 (1443) 21 2002 22 0015 22 (1106) 25 0307 26 (0929) Mar. 02 2342 03 (0650) 19 0053 20 (1146) Apr. 15 (1628) 21 1101 25 (1133) 26 2110 28 1727 30 0137 May 11 (1807) 11 2342 16 O415 20 0638 21 (1817) June 05 (1512) 23 1806 July 08 0102 Aug. 09 lo41 10 (1310) 11 0043 21 0507 31 1015
1956
2o48 1136 (2332) 0822 2029 0340 0046 (1117) (2325) 0528
15 17 17 May 30 June 06 24 25 25 27 30
0714 (0519) 1344 (1457) 0419
Aug. 03 1557
;: %?
16 19 19 19 22
11 (0944)
05 0042
July“0; ‘;:;I
0910 125.5 1910 1313 1850 1807 1614 0023 0130 0336 1315 y$;;
1957
388 EWITE OF s%c’s (WITHOUT
P-
1642 0931 (1532) (1429) -1212 1540 (2253) 1247 (;;;;I
io907j
(2143) 1050 (0745) (0950) 1304 0125 (0555)
June 02 (0409) 07 0046 08 1728 14 1828 15 0509 19 (1600) 28 i)71328 1742 30 (0401) JuIy 03 (1603) 08 0748 12 (0112) 13 (2208) 17 (0930) 21 1637 21 (1926) 22 (1207)
Jan. 20 25 30 30 Feb. 04 11 12 12 16 Mar. 03 03 13 14 25 25 Apr. 26 May ;
1958 Jan. 02 1122 05 0136 09 1459 14 (0606) 16 0927 22 (0704) 25 0859 25 1125 26 0322 29 (212ti Feb. 08 i1321j 11 0318 11 0756 14 1142 16 (0649) 16 (0742) 16 (1734) 22 0046 22 1057 24 2319 25 (0215) 25 (0227) Mar. 02 (0824) 18 (2229) 22 2228 25 (1417) 26 0842 Apr. 09 1828 - 23 1036 29 11233) May 04 ‘2021’ 05 (1106) 08 (1636) 11 2328 12 (1537)
1959
Hour is indicated in universal time 1960
z %? 31 1511 Apr. 13 1450 May 22 0137 23 (0137) 25 (0211) 31 (0204) June 14 2335 20 1617 21 (0641) 21 (0818) 22 (1518) July 02 (2016) 13 1113 17 1825 20 0248 20 (2227) 26 1950 Aug. 26 (1320) 29 1709 Sep. 13 1554 20 (1608)
13 0253 16 0043 16 (0536) 17 (1400) 17 (1721) Mar. 09 1327
Jan. 08 1618 Feb. 03 0908 04 1331 04 1829 2 @$I
1961
lB) AND Sib (WITH PA-)
Jan. 05 0201 10 0718 13 1859 14 (0819) 16 2114 16 (2221) 18 0642 18 (073% 19 -2208 28 (1916) 29 ‘0205’ Feb. 05 (1134) 26 IO43 Mar. 16 (0847) Apr. 02 2313 - 03 (0855) 04 KUo3~ 05 {0842j 05 1300 06 (1628) 07 1511 10 0126 27 2000 30 0132 30 1213 May 07 (0927) 07 (1108) 08 0421 11 (0435) 15 (1009) 16 1351 16 (2036) 22 (1438) 28 2019 June 04 0248
WHICH ARE ANALYZED IN THIS PApER
AND HOUR OF THE
Jan. 02 21 24 29 Feb. 12 23 Mar.01 10 25 29 29 Apr. E
TABLB2. ‘~-HEDATE
Jan. 10 0213 10 (0939) 19 0113 Feb. O4 0930 05 (0315) 15 11855) 16 (0539) 22 0220 26 1233 26 (1533) 26 (1611) Mar. 03 (1311) 03 (1340) Apr. 20 (1535) 20 2356 25 1329 May 06 (0952) 27 0413 June 07 (0640) July 03 (1202) 31 (2322) Aug. 30 2338 Sep. 12 (0612) 19 (0221) Oct. 07 2026 Nov. 06 (0330) Dec. 04 0334 o4 (0710)
1962
Sep. 02 08 20 Oct. 26 26 Nov. 09 14 Dec. 24 25 27 30
0230 1006 0438 0026 1311 2030 0200 0148 0754 1503 0632
Dec.
Nov.
Oct.
Sep.
06 0508 09 1347 17 (1322) 18 (1016) 29 1920 30 (1628) 31 1812 02 0314 03 (0618) 03 (1047) 03 (1912) 04 1300 06 (0117) 06 1121 07 (0232) 13 0046 17 (2359) 21 1005 22 1345 23 0235 29 0016 14 0440 14 (1320) 14 (1608) 21 2241 06 1821 14 (0200) 18 (2204) 26 0155 29 (0225) 15 (1334) 19 0937 31 (0219) 31 (0321)
27 (1101) 27 (1122) 31 -1529, Aug. 17 0622 22 0227 24 0140 27 0303 Sep. 03 0843 16 0930 25 0408 30 1005 Oct. 22 0315 24 0730 27 1523 27 (1742) 27 (1826) 28 ‘065d 28 (1150) 31 (1613) Nov. 01 0959 01 (1451) 10 (1055) 11 0129 16 (0219) 16 (0433) 28 0109 Dec. 04 0035 13 0001 13 (1224) 14 (1308) 15 2022 17 1547 17 1817 25 (2330) 30 (1539)
12 (1658) 15 0703 24 0540 25 (0440) 30 (1412) June 03 (2313) 09 0016 11 O!m 27 (1348) 29 0728 30 0801 July 04 (1910) 11 1625 If 0803 17 1638 Aug. 16 0404 20 0412 20 (2037) 29 (0228) Sep. 03 1417 03 2159 05 (1956) 19 (04w 19 1128 20 1157 22 (0130) Oct. 21 (1605) 29 2347 Nov. 26 (2142) 27 2351 Dec. OS 0659 23 1525 21 30 Dec. 07 25
Nov.
Oct.
Sep.
Aug.
July
27 28 29 30 14 14 14 14 16 19 29 02 04 04 22 06 13 24 10 11 12 12 15
0145 (0521) 1939 1720 0447 1702 (2132) 1510 1409 1616 0022 1158 0230 (1145) 1404 0237 (2143) 1452 0718 0034 1349 1845 1304 0631 (2147) 1909 1804 2002
24 (1311) 24 (1400) 30 1847 30 2109 Oct. 11 (1220) 17 (2205) 26 1941 28 0810 Dec. 05 1358 27 0057
578
TAKAO
r15.2
TYPE
SAITO and S. MATSUSHITA
MA~NETO~RAM
A
3SC 2.3
0
DSC 4
c
QSC
ON JUtY
STATION
I I, IS5 Q
i
)I
ONAOAWA
FREDERlCUSSUf?0
5
BYRD
STATION
LJ
(08’ - Id
-
FIO. 2. AN BXAMPLBOF MAONETOCRM~~OF TEXRX ~F.Z SIhlULTANEOUSLY AT THB TiIB
OF psc’s WHICH 1959.
OCCURRED
OF THE SAME SSC ON 11 JULY
TABIJI 3. RXPRBSENTA‘~I~B STA’IION,MA~NETOORAMS, AND ANAtyzED yEARSFGREACripsc
Phenomenon
Representative station
Magnetograms main and (auxilii) Induction (La Cour, Ordinary) La Cour (Ordinary) LaCour (Ordinary)
Onagawa Fredericksburg
%=d
TABLE4. GBXRAPHIC AND GEOMAGNElTC wliIcH
ARE
No.
Station
Abbreviation
1 2
H&Y Fredericksburg San Juan Onagawa Honolulu Hermanus Byrd
He
: : 7
:; OU El BY
Anaiyzed
RE-
LOCATIONS
Y-
Jan. 1951%Dee. 1959 June 1957-Dec. 1962 Aug. 1957-Dec. 1959
OF THE
STATIONS
TOINTHISPAPER
Lat.
Geographic Long.
63B”N 38*12’=N 18*23”N 38*26”N 21.18”N 34.26”s 79.59”s
149*oo”w 77.22”W 66*07”W 141*28”E 158.06”W 19.14% 1206o”W
Geomagnetic Long. Lat. 63.6” 49.6 30.1 28.3 21.0 -33.3 -70.4
256.5% 349-9 032 2068 266.4 80.4 336.2
GEOMAGNETIC PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS 2. S-
579
BETWEEN psc’s AND pc’a
Diurnal variations of amplitudes of psc’s are obtained in relation to those of corresponding period ranges of pc’s. The amplitude of psc generally becomes larger for an ssc with a larger magnitude. To eliminate this effect, the double amplitude of each psc is divided by the range of each associated ssc; this is called a %ormalized amplitude”. The double amp~tude of the psc is read by the envelope method (Saito, 1961) to extract it from the superposing gradual part of ssc. Since the ssc range in the auroral zone is often indiscernible due to the large amplitude of the associated psc, the double amplitude of psc at Byrd is normalized by dividing it by the range of the corresponding ssc at a low latitude station, Hawaii, whose longitude is nearly that of Byrd. The diurnal variations in the normalized amplitudes for each psc are shown in Fig. 3B. The diurnal variations in the largest no~~zed amplitudes among these scattered points are shown by broken lines. Since no suitable data are available for the diurnal variation of amplitudes for PC’Sat the (A)
LOCAL
(El
PC
TIME
LOCAL
PSC
TIME
FIG. 3. DIURNAL VAIUATIONS IN THB AMPLITUDESOF pc’s (LEFT) AND psc’s (RIGHT) FOR THRJX PERIOD The
RANGES
ordinate of pc’s indicates the pulsation activity, namely a product of the amplitude aud duration of pc, and the ordinate of psc’s indicates the normalized amplitude.
580
TAKAO
SAITO and S. MATSUSHITA
stations which are being analyzed; and since both activity and amplitude of PC’S show almost the same diurnal behavior (Saito, 1966), the diurnal variations in the activities of PC’Sare shown in Fig. 3A as a substitute for those of pc amplitudes (Saito, 1964a). By comparing Fig. 3B with Fig. 3A, we may conclude that amplitudes of both psc’s and corresponding period-range PC’Shave fairly similar diurnal tendencies. 2.2. Diurnal variations of periods The periods of psc’s were obtained by averaging as many pulses with a uniform period as possible never more than ten of them for one sequence. However, pulsations containing
FK3.4. D~JRNAL VARIATIONS
IN THE PERIODS OF PC’S (SwmS B ON THE RIGHT).
A
ON THE LEFT) AND PSC’S (SERIES
(A,) pc 5 at Byrd after Saito (1964a); (AZ) pc 4 at Fredericksburg; one dot indicates one sequence of pc 4 for October 1-31, 1962; (As) pc 2.3 at Onagawa; the solid circles are after Kato and Saito (1959), the open circles are from magnetograms of pc 2.3 in Geomagnetic Rapid Variations Observed at the Onagawa Magnetic Observatory, Parts I and II; (B,) psc 5 at Byrd; (B*) psc 4 at Fredericksburg; (BJ psc 2.3 at Onagawa and Fredericksburg.
GEOMAGNETIC
PULSATIONS
ASSOCIATED
WITH SUDDEN
COMMENCEMENTS
581
various periods were excluded. The periods of psc’s thus obtained are plotted against local time in Fig. 4B and are compared with those of pc’s shown in Fig. 4A. A striking resemblance between the diurnal variations of the periods of pc’s and psc’s are seen in these Figures. Both pc 5 and psc 5 show the shortest period in the morning, pc 4 and psc 4 show the shortest period near noon, while pc 2.3 and psc 2.3 have the longest period near noon. The mean period of psc 4 is slightly longer than that of pc 4; this is probably caused by the secular effects on the periods of pc 4 and psc 4 as discussed in section 3.2. The present result on the diurnal tendencies of both pc 2.3 and psc 2.3 periods, which are longer in the daytime than at night (inverted-U type), is clearly seen in Figs. 1A and 2A but is apparently the reverse of the recent results on pc 3 period obtained by Christoffel and Linford (1966a, b) which are shorter in the daytime than at night (U-type). However, the present result agrees with previously obtained results (Utashiro, 1948; Kato and Utashiro, 1950a, b; Kato and Saito, 1958, 1959, 1962; Campbell, 1959a; Yanagihara, 1959; Saito, 1960, 1962, 1964a; Duncan, 1961, 1966; Ness et al., 1962; Kato, 1962; Prince et al., 1965; Kato and Sakurai, 1966). This controversy may be explained by an apparent solar cycle effect on the diurnal variation in the period of PC’Snear 30 set; the inverted-U type diurnal variation occurs in the sunspot maximum years, while the U-type variation occurs in the sunspot minimum years. This solar cycle effect can be caused by a combination of the following reasons: (1) the boundary periods shift gradually from 40 set in the sunspot maximum years to 30 set in the sunspot minimum years (Kato and Saito, 1964; Saito, 1962, 1964b); hence, the pc reported by Christoffel and Linford should probably not be classified as pc 3 but as pc 4 in the sunspot maximum phase: (2) the nighttime pc 2.3, whose period is near 10 set, tends to disappear near the sunspot minimum years (Kato and Saito, 1959; Yanagihara, 1959, 1960; Troitskaya, 1961a). 2.3. Dynamic spectra Saito (I 967) reported that a dynamic spectrum of psc shows a fairly coincidental pattern at a pair of nearly conjugate stations, Byrd and Great Whale River. Dynamic spectra of psc are compared with those of pc; one example at Byrd is shown in Figs. 5A, and Bz. The dynamic spectra of both pc and psc in these figures consist of a series of small patches which indicate that pc and psc show a similar series of patches with the exception of a small difference in the continuity of the series. From all the above-mentioned results we can infer a very close occurrence model of pc and psc. 3. CHARACTERISTIC
FEATURES OF psc’s
3.1. Effects of the steepness of accompanying ssc’s Characteristics of psc’s due to the accompanying ssc are discussed in this section based mainly on psc 4 data at Fredericksburg. The psc amplitude depends partly on the steepness of the accompanying ssc, where the steepness of the ssc is defined as the ratio of the range to the duration of ssc. Takahashi (1960) and BouEka (1962) reported a variety of the steepness. A dependence of psc 4 amplitude on the steepness of the accompanying ssc with respect to the local time of its occurrence is shown in Fig. 6A. In general, the small amplitude of psc 4, which is expressed by crosses and small circles, is distributed at the place where the steepness is nearly zero, and the large amplitude appears when ssc shows a sharp increase or decrease. The period of psc 4 is also plotted with respect to the steepness and local time of the
582
TAKAO SAlTO and S. MATSUSHITA
accompanying ssc as shown in Fig. 6B. It seems likely that the period of psc 4 becomes shorter when the ~rn~~g ssc has a larger positive steepness. 3.2. Eff’ecfsof the amplitude of accompanyingm’s As seen in Fig. 6, psc’s are associated with both positive and negative ssc’s. Figure 7 shows examples of psc 2.3, psc 4, and psc 5 associated with positive and negative si’s and an ssc. At high latitudes the amplitude of psc 5 is generally much larger than the range of si’s. In order to compare the two, si’s in low latitudes can be used as a reference of si’s at high latitudes. Thus, the rapid-run magnetogram of the psc 5’s at Byrd (Fig. 7C) is compared with the ordinary magnetogram of the si’s at a low-latitude station, HonoIulu (Fig. 7E), whose geomagnetic longitude is nearly that of Byrd. Several psc 5’s occurred at Byrd, the beginnings of which correspond to the positive and negative si’s at Honolulu near local noon. The periods of psc 5’s associated with the increasing phase of si’s are shorter than those associated with the decreasing phase of si’s, as seen by comparison of Fig. 7C with Fig. 7E. In order to understand the relation between the psc periods and the sign (including the range) of ssc’s, psc 4 periods, 7&., ‘s, shown in Fig. 6B and ranges of ssc’s, AH’s, observed at Fredericksburg were studied. Tpsc( can be equated as follows: Tpsc4
=fG
+fi
+fa
+fs + k(AH) =fl +fa + NW,
(1)
w&e f’ =fo + fI +fa fa = secular term fi = annual term =
(a&W
+ &I 4x3srgd+
A)
h= semi-annual term = (a2R(M) + b$ cos (g
d+t%)
f3 = diurnal term = a, ~0s (15”f + &) + b3 R(M) = monthly mean value of relative sunspot number M = phase of the solar cycle in the unit of month;
M = 1 starts from July, 1957.
d = day of the year started from 1 for the first of January t = local time at Fredericksburg k = coefficient of the ssc range, AH a,, b, = amplitude parameters, where i = 1, 2, and 3 PC= phase angle parameters, where i = 1,2, and 3. Since the periods of psc 4 and pc 4 show strikingly similar diurnal variations as mentioned in section 2.2,f’andf, of TP 4 are assumed to be the same asf’ andfo of T’ *, respectively, for simplicity. Observed values off ‘and f. of lpPO d at 12.5 hours local time at Fredericksburg are available in the form of monthly average (Kate and Saito, 1964; Saito, 1964b) and are listed in Table 5. The least square method of these values off’ and f. gives values of parameters a,, b,, PI, a,, b,, and /& as follows: f’ =fo + {0~0429R(M) + 3~38) cos (00986”d - 0.1”) -(O.O48OR(M) - 3*34) cos (1.97”d - 27*29).
(2)
FIG. 5. SPECTRA OF pc (SERIES A ON THE LEFT) AND psc (SERIES B ON THE RIGHT) AT BYRD. (Top diagrams shown by sub, 1). Amplitude spectra at the times indicated by the arrows below; (middle diagrams shown by sub. 2) dynamic spectra which consist of a series of small patches of the order of 10 min. (bottom diagrams shown by sub. 3). Chart records correspond to the dynamic spectra. The analysis of these was made possible through the courtesy of Dr. Wallace H. Campbell, ITSA-ESSA.
SR?
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COMMENCEMENTS
I--
(B)
(4 . .
583
.
.
..
.
. -. *
!.
*
.
’ . :*
t
3
f
b
FIG. 6,
LOCAL
TIME
)%mx-s
OF
! 12 -
THE
“C
l
14 75’
16 18 20 W.M.T.
ssc
sTI~EPNBSS AT
22
24
(THE
0
RATIO
4
6 6 LOCAL
~ IO 12 I4 16 18 TIM1 c _. 750 W.M.T.
OF THE
RANGE
To
2
THE
*
.
.
DURATION
I
20
22
OF
THE
FRJZDEI~ICKSBURG:I!GRTHEAMPLWLJIX(LEFT)ANDTHEPWIOD (RImIT).
TYPICAL I
. a
psc4
ACCXXP~C+SSC)ON
.
~A9U~TO6RA~
REMARK
si
Si
A
/ ONAQAWA JUL27.1966 (iyf)
FIG.7. "hl?ICAL MAGNBXOGBAbi OF PSC'S ASSGcIA~
WITH PCBFEVE AND NEGATIW
NS
Si'SAND
A.N SSC.
(A) induction magnetogram; (B), CC), and (D) La Cour type rapid-run magnetograms; (E) ordinary magnetogram. Times are indicated by UT. (C) and (E) show the same event at Byrd and Honolulu, where the periods of pa 5’s at Byrd are longer at the time of negative si’s at Honolulu .
I
TAKAO SAITO and S. MATSUSHlTA
584
TABLE5. THE PERIODS
(SECONDS)
OF
pc
4
AT
12.5 HOURS
LOCAL
TMB
AT
FREDERICKSBURG (KATOANDSAITO,1964)
f’, monthly mean values; fO, secular values obtained by 11 2/2-month running average Month Jan. Feb. Mar. Apr. May June
JdY
Aug. %P* Oct. Nov. DeC
1957
f 44.9 48.5 55.1 79.6 77.2 71.0
fo
f’
-
65.2 65.5 76.7 68.7 53.3 48.1 47.2 52.6 63.5 68.6 727 70.3
6;9 62.9 62.9 62.9 62.9 62.9
1958
fo
f’
62.9 63.2 63.7 63.6 62.9 62.7 62.8 62.9 62.2 61.1 60.8 60.8
67.0 Es .
1959
62.0 53.1 47.2 z: . 57.6 57.5 58.4 57.4
fo
f’
60.7 60.3 59.9 59.3 58.3 57.1 56.3 56.0 55.8 55.2 54.3 53.6
59.6 64.7 58.9 47.8 44.6 402 42.3 44.9 53.0 50.2 51.9 51.9
1960
fo
f’
53.2 52.9 52.6 52.1 51.6 51.1 50.5 49.6 48.8 48.5 48.5 48,6
51.8 51.4 51.8 48.8 43.1 43.1 43.1 42.2 49.5 50.6 50.4 62.1
1961
fi 48.7 48.5 48.4 48.2 48.2 48.6 49.2 49.6 49.6 49.8 49.8 49.8
Root mean square of the deviation of the observed values from this formula is 3.25. Observed Tpsc 4 and thisf’ formula of TPc 4 substituted forf’ of T,,, 4 in (1) give actual values off, parameters and k by the least square method as follows: Tpec4 =f’
+fs
+ WW
= f’ + a3 cos (15’t + B3) + b, + k(AH)
=f’
+ 14.49 cos (15’t + 32.6’) + 11.09 - 0*127(AH) ’
The root mean square of the deviation in this calculation is 19.19. The obtainedf, in (3) should be almost the same asfs of Tw 4. The value of k was confirmed as follows: Tw 4 = f’ + f3 + kW0 =
(3) of Tpec4
+ WW
f’ + a, cos (15”t + /Q + b3 + k(AH) + k’(AH)a
(4)
The least square method to the observed values of Tpsc4 and f’ gives Tpat4 = f’ + 14.47 cos (15”t + 32.3’) + 11.15 - 0*142(AH) + 0X@022(AH)2
(5)
The root mean square of the deviation is 19.18. Since k’ is nearly zero and a,, ,!&,b,, and k in (5) are very close to those in (3), the formula (3) is valid without being affected by k’(AH)2. The relation between TpM:4 and AH is shown by the last term in (3). For example, when a positive ssc with a range of +lO y (a negative si with a range of -1Oy) is observed at Fredericksburg, the period of the associated psc 4 becomes shorter (longer) by 1.3 set than the expected period of pc 4 for the given year, month, day, and local time of the positive ssc (negative si) event. This result gives an explanation of the phenomenon mentioned by the comparison of Fig. 7C with Fig. 7E. 4. DISCUSSION AND CONCLUSION The analyzed results presented in the previous sections are summarized as follows: (1) The psc’s, whose periods range from 5 to 600 set, can be classified into psc 2.3, psc 4, and psc 5 in a similar way as the pc groups: pc 2.3, pc 4, and pc 5. (2) Diurnal variations in the amplitudes of psc’s are very similar to the corresponding PC’S: both psc 2.3 and pc 2.3 and both psc 4 and pc 4 show the maximum amplitude in the daytime; both psc 5 and pc 5 show the maximum amplitude in the morning.
GEOMAGNETIC
PULSATIONS ASSOCIATED WITH SUDDEN COM~N~ME~
585
(3) Diurnal variations in the periods of psc’s are also quite simiIar to the corresponding pc’s: both psc 2-3 and pc 2.3 show the longest period near noon; both psc 4 and pc 4 show the shortest period near noon; both psc 5 and pc 5 show the shortest period in the morning. (4) The dynamic spectra of psc’s have either a patch with a duration of about 10 min or a series of such patches in a similar way as the dynamic spectra of pc’s. (5) The ssc’s which have a rapid increase of geomagnetic H-component often accompany psc 4’s with large amplitudes and short periods. (6) The periods of psc 4 and psc 5 associated with positive ssc’s are shorter than those associated with negative ssc’s. The results (I) through (4) of the above six results indicate the similarity of the characteristics between psc’s and pc’s. When the Earth’s magnetosphere is assumed to contain resonance systems for hydroma~etic waves, psc’s and pc’s seem to occur being governed by these systems excited by the hydromagnetic waves due to the shock from outside the magnetosphere. The number of pulses contained in one psc event does not correspond to the same number of ssc shocks, or expansions and compressions of the magnetopause. In other words, even one shock of ssc on the magnetopause can generate a series of damped pulses of psc in the magnetosphere. The following three observational facts also support the present conclusion: (a) an ssc accompanies psc 2.3, psc 4, and psc 5 simultaneously; (b) damping ratios of the amp~tudes of psc’s are fairly constant during one sequence of the psc’s (Kate and Saito, 1958); (c) Periods of the pulses of psc’s are, in most cases, constant during one sequence of the psc’s. Results (5) and (6) show the relation between the sign of the accompanying ssc and the periods of psc 4 and psc 5. Many authors attributed pc 4 and pc 5 to transverse hydromagnetic waves propagating along the Earth’s magnetic field-lines (Kate and Watanabe, 1956; Obayashi and Jacobs, 1958). In the simplest ease, the period T of pc 4 and pc 5 can be expressed by the formula,
where, S, p, and H are respectively the path of hydromagnetic wave propagation, plasma density, and magnetic field intensity along the path. It is quite probable that this formula is applicable not only to pc 4 and pc 5, but also to psc 4 and psc 5 taking into consideration the present results on the similar behavior between psc and pc. In case the magnetosphere where the plasma is frozen is compressed at the time of a positive ssc or si (Nishida and Cahill, 1964), both d/2 - H-l and S decrease causing a decreasing of T. An expansion of the magnetosphere at the time of a negative ssc or si causes analogously an increase of T. This tendency of the period changes agrees welI with the present observationaf results on the modifi~tion of the periods of psc 4 and psc 5 at the times of ssc and si. Acknowledgements-The authors wish to express their sincere gratitude to Dr. Wallace H. Campbeh, ESSA, for his kindness in offering the frequency analyzer and the magnetic tape data of the geomagnetic pulsations recorded at the ESSA Byrd Statton which were used to obtain the dynamic spectra. The authors also wish to thank Professor Yoshio Kate, the Director of the Onagawa Magnetic Observatory, Tohoku University, for the valuable discussion. Thanks are also due to Mrs. Mary H&y and to Mr. Joe Oliger for their kind assistance throughout the ~rnp~~e~t of this work. BEMOPF,H. 1963. J. geophys. Res. 65,1413. BRRTHOIQW. K., HARRIS,A. K. and HOPE,3%J. X960.J. geephys. Res. 6!5,613. Bousrc~, 1. 1960, Studiageophys. geod. 4,280. BMJ%A,J. 1962. J. phys. Sot, Japan. Suppt. A-ZZ17,45.
586
TAKAO SAITO and S. MA’ISUSHITA
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