Anomalous short-period pulsations in goes magnetometer data before solar proton events

Download Anomalous short-period pulsations in goes magnetometer data before solar proton events

Post on 06-Jul-2016

216 views

Category:

Documents

3 download

TRANSCRIPT

  • ANOMALOUS SHORT-PERIOD PULSAT IONS IN GOES

    MAGNETOMETER DATA BEFORE SOLAR PROTON EVENTS

    D. Y. CHENG

    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. CHENG

    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 Oct 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

    were not assoc iated wi th or fo l lowed by a solar p ro ton event were also per fo rmed as

    a contro l . These data per iods are ind icated in Tab le II.

    F inal ly, the pre-event examinat ion per iods were extended for the first six p ro ton-event

    per iods as shown in Tab le II I .

  • 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 60 40 30 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 pulsations; all these pulsations

    occur within the 2-week period prior to the seven solar proton events,

    (3) Table IV itemizes the principal features of the anomalous geomagnetic-field pul-

    sations observed by GOES prior to the solar proton-event periods studied.

    (4) The anomalous pulsations occur for at least 2 days of the pre-event period and,

    for large events, may occur 2 weeks before the solar proton event. A representative

    spectral response for the September 29 proton-event period is given in Figure 3.

    (5) Spectral analysis of the six non-event-associated periods showed no anomalous

    pulsation characteristic of the pre-event periods, even in the case of the May 4-11, 1988

    period, whichincluded a strong magnetic storm. The October 12-19, 1986 period included

    a non-particle flare. While strong pulsations were observed 4 days earlier, they were not

    of the appropriate 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

  • 400 D.Y . CHENO

    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 (Sac , )

    1989 9/17 00:00:00.000 1989 9/17 23:59:59.10Z ] 1.000E*02 0.07615 2,,]21E,0!

    1(~) 60 40 30 20 I~ 10 ~ T{SeC. ) . . . . . 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.

  • ANOMALOUS PULSAT IONS 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 ~:~:~. I03 9 003s ,03 O. 07556 2,480E. 02'

    t tc

    .+

    ,~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.

    Acknowledgements

    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

    Grubb, R. N.: 1975, The SMM/GOES Space Environment Monitor Subsystem, NOAA Tech. Memo, ERL SEL-42.

    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.

Recommended

View more >