A N O M A L O U S S H O R T - P E R I O D P U L S A T I O N S IN GOES
M A G N E T O M E T E R DATA BEFORE SOLAR P R O T O N EVENTS
D. Y. C H E N G
Institute of Space Physics, Chinese Academy of Sciences, Beijing, China
(Received 8 March, 1990; in reversed form 20 July, 1990)
Abstract. Through spectral analysis of GOES magnetometer data, we have found anomalous short-period pulsations occurring prior to solar proton events. The characteristics of these pulsations are: (1)both the H e (Earthward) and H n (eastward) components of the geomagnetic field show the occurrence of pulsations on the same day, and (2)the period of pulsation of H e and H n is greater than 48 s. For large events, this signature may occur up to 2 weeks prior to the solar proton event. It is suggested that this signature may provide a new tool in the forecasting of solar proton events.
1. Introduction
There have been a number of recent pulsation studies by Soviet scientists in search of improvement to the forecasting of solar flares, especially those producing proton events. These studies have examined: particle data from satellites (Libin et al., 1983), ground station cosmic-ray data (Starodubtsev, Filippov, and Chirkov, 1982), solar X-ray (Kobrin et al., 1983) and radio noise measurements (Kobrin et al., 1978), and ground-station geomagnetic data (Kobrin Malygin, and Snegirev, 1982). They variously report the occurrence of quasi-periodic pulsations in the ranges of 20 min and 60 to 120 rain, 2 to 3 days prior to solar proton events. This study of geomagnetic pulsations was therefore undertaken.
The NOAA Space Environment Laboratory has maintained magnetometers on board the GOES series of geostationary satellites, which provide observations of the geomagnetic field at geosynchronous orbit with a time-resolution of about 3.06 s, and an estimated absolute accuracy of 4 nT (Grubb, 1975). Data from these observations have been examined for a number of solar proton-event periods, as well as a cor- responding number of non-event periods (Solar-Geophysical Data, 1984-1989).
2. Data Coverage
The GOES magnetometers provide vector measurements of the geomagnetic field. The three field components are designated: Hp, parallel to the spacecraft rotation axis and approximately parallel to the Earth's rotation axis; He, toward Earth; and Hn, toward the east. An initial analysis of the three components of the GOES measured geomagnetic field was performed for the eight-day periods including and prior to the start of the seven solar proton events indicated in Table I.
Power spectrum analyses of the geomagnetic field data for six 8-day time periods that
Solar Physics 131: 395-406, 19910. �9 1991 Kluwer Academic Publishers. Printed in Belgium.
396 D . Y. C H E N G
TABLE I
Pre-proton-event data periods
Proton-event Peak intensity Magnetometer data start date (p cm- 2 s - 1 sr - ~ ) period
1984 Apr. 25 2500 Apr. 18-Apr. 25 1985 Apr. 24 160 Apr. 17-Apr. 24 1987Nov. 8 120 Nov. 1-Nov. 8 1989Mar. 8 3000 Mar. l -Mar. 8 1989 Aug. 12 9000 Aug. 5-Aug. 12 1989 Sep. 29 a 4800 Sep. 22-Sep. 29 1989 Oct. 19 a 7300 Oct. 12-Oct, 19
a Ground-level events; September 29 showed a 500 ~ cosmic-ray increase at Thule.
TABLE II
Non-proton-event periods
1985 Aug. 10-17 1986 Oc t 12-19 1987 June 5-12 1988May 4-11 1989 Jan. 10-17 1989 Jan. 18-25
Oct. 19: 2B solar flare
May 6: Magnetic storm, Ap = 106 nT
TABLE III
Pre-event extension periods
Magnetometer data Comments period
1984 Apr. 10-17 1985 Apr. 9-16 1987 Oct. 24-30 1989 Feb. 19-26 1989 July 28-Aug. 4 1989 Sep. 14-21
Prior to Apr. 25 event Prior to Apr. 24 event Prior to Nov. 8 event Prior to Mar. 8 event Prior to Aug. 12 event Prior to Sep. 29 event
we re n o t a s s o c i a t e d w i t h or fo l lowed b y a so la r p r o t o n e v e n t we re a lso p e r f o r m e d as
a con t ro l . T h e s e d a t a pe r i ods are i n d i c a t e d in T a b l e II .
F ina l ly , t he p r e - e v e n t e x a m i n a t i o n p e r i o d s were e x t e n d e d for t h e f irst six p r o t o n - e v e n t
p e r i o d s as s h o w n in T a b l e III .
ANOMALOUS PULSATIONS 397
3. Results
Each component of the GOES 3.06-s magnetometer data was spectrally analyzed for each day of the above data periods using a fast-Fourier-transform procedure described by Welch (1967). In all, 152 days' data were spectrally analyzed. Interesting results were found, which are summarized as follows:
(1) Among the 152 days' data, pulsations at some frequency were found to occur for about 61 days (40~o), 73 days (50~o), and 124 days (80~o), for the Hp, H e, and/4,
1/20 00:01:07,320 - t989 1/21 00:~:05,222 O. 154t0 ] ,20~E.04:
He
r l
1989 1/20 00:01:07.320 - - 1969 1/21 00:00:06,222 I .O0(E*04 O. 15410 I. ?TIE +03
~ . , H , '~ , ~ , . ~ . , ,o, 8, , , .~'.~.~, ,
0.00~*00 Frequency 1.634E-0[
Fig. 1. A representative spectral density profile: January 20, 1989.
398 D.Y. CHENG
components of the geostationary field, respectively. That is, pulsations of some duration occurred most of the time. The typical non-event power spectrum is represented by the
sample shown in Figure 1. (2) Analysis of the data periods indicated that solar pre-proton-event periods
demonstrated characteristic pulsations. These pulsations are characterized by (a) pul- sations occurring in both the H e and H, components on the same day and (b) pulsation periods greater than 48 s in H e or H,. Figure 2 shows an example of this characteristic spectrum, 4 days prior to the event of November 4, 1987. On the 152 days' data
>,
u~ g
r-1
G.. g,
1987 11/04 00:00:01.000 - 1987 t[/05 00:00:00.[05 8,854E*05 .O00E*04 O, 12102
l ~ . . . . so 4o, ~o 2o, i s to, ~, ~ ( ~ , )
Fig. 2.
.O00E§
g
Q_
g ..J
1987 11/04 O0:C~:Ol.O00 - O. 12102
I-In
1987 11/05 06:00:00.103 1.055E,02
10r 6 0 4 0 3 0 20 15 10 . . . . . i i i 81 T(ICM:. )
I O.O00E+~" ' Vreq'uency ' 1.634E-0{
GOES Maqnel Oala
Typical anomalous short-period pulsations associated with a proton event: November 4, 1987.
ANOMALOUS PULSATIONS 399
analyzed, only 26 days (16 % ) exhibit these anomalous pulsat ions; all these pulsat ions
occur within the 2-week per iod prior to the seven solar pro ton events,
(3) Table IV itemizes the principal features of the anomalous geomagnetic-field pul-
sations observed by G O E S prior to the solar proton-event per iods studied.
(4) The anomalous pulsat ions occur for at least 2 days of the pre-event per iod and,
for large events, may occur 2 weeks before the solar pro ton event. A representat ive
spectral response for the September 29 proton-event per iod is given in Figure 3.
(5) Spectral analysis of the six non-event -associa ted periods showed no anomalous
pulsat ion character is t ic of the pre-event periods, even in the case of the M a y 4 -11 , 1988
period, whichinc luded a strong magnetic storm. The October 12-19, 1986 per iod included
a non-par t ic le flare. While strong pulsat ions were observed 4 days earlier, they were not
of the appropr ia te frequency (see Figure 4).
TABLE IV
Characteristics of proton-event-associated pulsations
Proton-event Anomalous Pulsation period(s) Size class of date pulsation pulsation
date H e H ,
1984 Apr. 25
1985 Apr. 24
1987 Nov. 8
1989 Mar. 8
1989 Aug. 12
1989 Sep. 29
1989 Oct. 19
Apr. 10 60 60 obvious Apr. 12 60, 120 60 obvious Apr. 20 260 120 obvious Apr. 22 18 100 obvious
Apt. 10 100 32 weak Apr. 17 58 58 strong Apr. 22 53 I00 obvious Apr. 23 50 100 obvious
Oct. 25 80 90 weak Nov. 4 62 98 strong Nov. 7 120 70, 140 strong
Feb. 23 200 200, 98 strong Feb. 25 100 100 strong Mar. 1 90 15-30 obvious Mar. 2 Both had large fluctuations Mar. 4 100 110 obvious
July 29 I 10 40 weak July 31 48 48 obvious Aug. 8 150 60 weak
Sep. 17 150 82, 150 strong Sep. 23 150 95, 150 strong Sep. 24 100 100 strong Sep. 25 60 60 strong Sep. 28 140 100, 50 strong
Oct. 15 30 130 strong Oct. 17 15-100 15-100 obvious
4 0 0 D . Y . C H E N O
4. Preliminary Conclusions
In consideration of the above results, the following preliminary conclusions are reached: (1) Solar proton events are preceded by characteristic anomalous pulsations of the
geomagnetic field where (a)the pulsation period is greater than 48 s and (b)these pulsations are seen on both the H e and H. components of the geostationary field as observed by the GOES satellites on the same day.
t989 9/17 OO:O0:O0.OCO 1989 9/t7 25:59:59,102 ,00~,03 0.076[5 5,097E.02
He
zoo 60 i 4o 30 zo Is zo "I �9 �9 i i i 81 T ( S a c , )
1989 9/17 00:00:00.000 1989 9/17 23:59:59.10Z ] 1.000E*02 0.07615 2,,]21E,0!
1(~) 6 0 4 0 30 2 0 I~ 10 ~ T { S e C . ) . . . . . i i &
0.000s Frequency ;.634E-0[
Fig. 3a. Spectral density profile: September 17, 1989. Anomalous pulsations are observed here and on 5 of the 12 days (shown here as Figures 3(a), 3(b), 3(c), 3(d), and 3(e)) prior to the large, ground-level proton
event of September 29, 1989.
ANOMALOUS PULSATIONS 401
(2) Such anomalous pulsations occur for several days prior to a solar proton-event occurrence. The first occurrence of anomalous pulsations may be 2 weeks before the proton event, while the last occurrence is within 4 days of the solm" proton event.
(3) While only a small number of events have been analyzed, all seven proton events were preceded by the characteristic anomalous pulsations; none of the six background periods contained this signature. Occurrence of these characteristic pulsations may,
1989 9/23 O0:OO:O0.O00 - !989 9/23 23;59:59,102 .00~.03 0.07542 2,495[,02
He
-i
I~ 60 ~,0 30 20 15 I0 8 T(~c. )
.634E-01 O.O00E+O0 Frequency l
1989 9/23 O0:O0:O0.O00 - 1989 9/23 23:59:59.102 I.O00E+02 0,07542 3,773E,Ot
I00 60 AO 30 20 1~ lO 8 T ( ~ c , )
0.000E,00 Frequency 1,634E-0l
Fig. 3b. Spectral density profile showing anomalous pulsations: September 23, 1989.
402 D . Y . CHENG
therefore, provide for the prediction of solar proton events up to 2 weeks prior to their occurrence.
5. Discussion
Kobrin et al. (1978) suggested that quasi-periodic pulsation observations for forecast purposes may be significant because flares do not occur suddenly, but are preceded by a restructuring of the active region or development of a different kind of instability
] t989 9/24 00:06:14.320 - t989 9/25 00:0C:00.[03 . ] t .O00E,05 0.07544 2,061E,02
II
x
I
0.00~,00
'", ", '9 ',
Frequency
"t(~.)
1'.634E-0i
Fig. 3c. Spectral density profile showing anomalous pulsations: September 24, 1989.
A N O M A L O U S P U L S A T I O N S 403
caused by a flare trigger mechanism or pumping processes and energy accumulation in the active region. Reflecting the oscillations in the solar atmosphere with these processes, QPPs (quasi-periodic pulsations) may be an indicator of preflare instability. Miroshnichenko (1984) also related observed solar radio, solar X-ray, and magne- tospheric pulsations to pre-flare oscillations in the solar atmosphere.
It is unknown how processes on the Sun would produce anomalous pulsations of the geomagnetic field. From the analysis of the time period including the magnetic storm
t989 9/25 O0:~:Ol,CO] - 1989 9/25 ~ : ~ : ~ . I 0 3 �9 003s ,03 O. 07556 2,480E. 02'
t t c
.+
,~o,,o, , , ,o ,o ,o, ,+ ,o, +
1989 9125 O0:O0:O1.000 - 1989 9/26 00:00:00.103 1.000E+(TZ 0.07556 3,431E+Ot
10Q 60 44 :)O 20 15
O,(300E*O0 Frequency ],634E-Or
Fig. 3d. Spectral density profile showing anomalous pulsations: September 25, 1989.
404 b.Y. CHENG
and the non-particle flare, it seems that the observed anomalous pulsations reported here are not caused by high-speed streams emanating from coronal holes and that active region pre-flare processes for proton and non-proton solar flares are different.
This is an initial study of the relationship of fluctuations of the geostationary field to solar proton activity. Further analysis is required to reach more reliable conclusions and to provide results useful for forecasting of solar proton events.
[ 9,28 i
/
19e9 9/28 23:59:59.102 i 2,658E,021
"1
TC~le.)
1989 9/28 ~:00:O0.000 - [.00(3E*02 0.075~
tOO 60 ~ 30 20 15 tO 8
1989 9/28 23:59:59.1~ 3,102E,01
T ( ~ . )
0.00~*00 Frequency 1,634E-0t
Fig. 3e. Spectral density profile showing anomalous pulsations: September 28, 1989.
ANOMALOUS PULSATIONS 405
[ 1986 10/15 0(3:01:07.260 - I~15 10/16 O0:CO:02.[O] ~' 1, 000E.04 O. 12628 9,586E ,0~:
I
......... ." lg66 10/15 00:01:07.260 - 1986 10/16 00:C~:02..10I
[.0(X~,03 . 0.12628 61223E+02
O.O00E*CO ~ 1,634[-01
Fig. 4. Non-particle flare example. Short-period pulsations of 30 s duration occurred 4 days before the 2B flare on October 19, 1986.
A c k n o w l e d g e m e n t s
This work was supported by the Space Environment Laboratory. I would like to acknowledge the help of L. D. Lewis in providing the FFT code, L. Matheson in accessing the GOES magnetometer data, and useful discussions with R. Zwickl and H. Saner.
406 D.Y. CHENG
References
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Kobrin, M. M., Malygin, V. I., and Snegirev, S. D.: 1982, Geomag. Aeron. 22, 156. Kobrin, M. A., Korshunov, A. I., Arbuzov, S. I., Pakhomov, V. V., and Charikov, Yu. E.: 1978, Solar Phys.
56, 359. Kobrin, M. M., Malygin, V. I., Snegirev, S. D., Zhdanov, A. A., and Chariko, Yu. E.: 1983, in E. I. Molivesky
et al. (eds.), Solar Activity (Conf. Proc.), Nauka, Alma Ata, Moscow, p. 113. Libin, I. Ya., Lemberger, A. M., Blokh, G. M., and Kuzhevsky, B. M.: 1983, Proc. 18th Int. Cosmic Ray Conf.
3,15. Miroshnichenko, L. I.: 1984, in P. A. Simon, G. Heckman, and M. A. Shea (eds.), Workshop Proc., Meudon,
France, p. 244. Solar-Geophysical Data: 1984-1989, NOAA, Boulder. Starodubtsev, S. A., Filippov, A. T., and Chirkov, N. P.: 1982, Astron. Zh. 59, 1229. Welch, P. D.: 1967, IEEE Trans. Audio & Electroacoust., Vol. Au-15, No. 2, p. 70.
