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Response of the low latitude geomagnetic field to the major proton event of November 2001
Advances in Space Research 36 (2005) 2434–2439 www.elsevier.com/locate/asr
Response of the low latitude geomagnetic field to the major proton event of November 2001 S. Alex *, B.M. Pathan, G.S. Lakhina Indian Institute of Geomagnetism, Plot No: 5, Sector 18, Kalamboli, New Panvel, Navi Mumbai, 410 218 Maharashtra, India Received 19 October 2002; received in revised form 6 November 2003; accepted 7 January 2004
Abstract A major solar flare eruption occurred at 16:20 UT on 4 November 2001, followed by strong solar radiation storm and proton event recorded by the SOHO and other interplanetary satellites. Coronal mass ejection associated with the flare event triggered an interplanetary shock, which impacted the geomagnetic field after about 33 h. The shock impact was quite intense to produce a SSC magnitude of 80 nT in the low latitude ground magnetic records followed by sharp and deep main phase (Dst 300 nT) in the first stage, following the density (Np) enhancement. High time resolution digital magnetic field data from the equatorial and low latitude stations in India are analyzed to study the influence of various IP parameters on the intensity and duration of the magnetic storm. A double step storm was found to be in progress caused by the multiple injections. During the period of recovery, after a period of 8 h, a third stage of depression in the ground magnetic field was set in, which corresponded to the southward directed Bz. The energy transfer processes associated with the event is presented. Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Solar flare; Proton event; Magnetic storm
1. Introduction Solar flares are the manifestations of the tremendous eruptions in the solar atmosphere, producing sudden energy release. The magnitude of the magnetic energy released in the solar chromosphere and corona during intense flares range at 1028–1034 ergs, energizing electrons and ions up to MeV and GeV/n respectively. During the high solar activity periods, active regions produce large fluxes of energetic flare particles to Coronal Mass Ejections (CME) related shocks, which can accelerate the Solar Energetic Particle (SEP) events (Webb, 1992; Feynman and Hundhausen, 1994). Joselyn and McIntosh (1981), Sheeley et al. (1983) and Hundhausen (1993) presented processes describing the associ*
Corresponding author. Tel.: +91 22 27480764; fax: +91 22 27480762. E-mail address: [email protected] (S. Alex).
ation of CME with flares and filament eruptions. Mass Ejections play a dominant role in driving large geomagnetic storms by causing sudden commencements on the magnetic records produced by transient IP shocks (Gosling et al., 1991; Tsurutani et al., 1992). Geoeffective nature of the solar disturbances and the energy transfer mechanism of the solar wind energy into the magnetosphere through the reconnection of IMF has been discussed in Burton et al. (1975), Gonzalez et al. (1994), Kamide et al. (1998a) and Tsurutani et al. (2003). Very energetic protons emitted during SEP events are reported to be of mainly two types, gradual events and impulsive events (Reames, 1999). A detailed study of the interplanetary response to the solar energetic particle acceleration in relation to Coronal mass ejection has been done extensively by various researchers (Burlaga et al., 1987; Gonzalez et al., 1994; Lario et al., 1998). The important interactive aspect of the association between the CMEs and SEP acceleration has been
0273-1177/$30 Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2004.01.026
S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
discussed by Kahler et al. (1984) and Gopalswamy et al. (2002). On November 4, 2001 an X1.0/3B, X-ray flare occurred in the active region AR9684, between 16:03 and 16:57 UT, GOES soft X-ray flux reported the peak emission at 16:20 UT. The flare was located at 7° South and 20° West. SOHO/LASCO observed a full Halo CME in C2 coronagraph at 16:35 UT as a very fast bright loop front over the west limb. This CME blasted off from the sun was measured at the plane of sky speed of the front area as 1620 km/s with discernible acceleratioa The flare of November 4, 2001 and the CME were accompanied by an energetic proton event. The present study mainly focuses on the geomagnetic signatures and the interplanetary parameters associated with the major proton event reported on November 4, 2001.
2. Results and discussions Solar cycle 23 witnessed three gradual polar events as reported by SOHO/CELIAS. Of the three events, the most intense event of November 4, 2001 was associated with a strong X-class flare type and an intense CME followed the event. Comparison of the three particle events reported by the CELIAS/MTOF instrument on the SOHO satellite demonstrated the event of November 4, 2001 as the largest in terms of the particles above
Fig. 1. Time since X-ray event (HR MNSS) (adapted from SOHO/ CELIAS).
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40 MeV. In Fig. 1 are reproduced the relative intensities of the three major proton events as recorded by the Proton Monitor on SOHO. The 00:00 time mark refers to the proton count with reference to the commencement of the X-ray event. Referring to the proton event of November 4, 2001, the, enhancement in the proton count persisted for almost 36 h, projecting a prominent peaking in the later half at the time of shock, which happened after almost 33 h of the commencement of the flare on November 4. In order to understand the emission features of the particle energy flux accompanying the solar energetic proton event of November 4, proton flux of various energy levels from the ACE and WIND are given in the topmost panel of Fig. 2. The time resolution of particle flux data for ACE satellite is 5 min and it is 1 min 32 s for the WIND data. Vertical dashed lines are marked against the recurring trend of enhancements in the particle flux densities during November 5–6. Following the strong X-ray flare at 16:20 UT on November 4, proton flux showed sharp increase at all the energy levels as observed by WIND and ACE satellites as shown in Fig. 2. A second increase was seen at 19:00 UT on November 5 too. The proton density (Np) as recorded by ACE satellite was considerably low on November 04 and a gradual increase in density was seen in the early hours of November 5. Around 19 UT a sudden jump in density was quite evident, coinciding with the second increase in proton flux density. Np remained at an enhanced level (80/cc) for a period of about 6 h from 19:00 to 01:15 UT on November 6. Due to spacecraft anomalies caused by the high rate of injection of energetic particles in the interplanetary medium, solar wind velocities from ACE/WIND satellites were degraded and could not be obtained during the peak of activity. However, SOHO/ CELIAS instruments detected the impact of the shock following the CME on November 4, 2001, and reported a steep increase in the solar wind velocity from 450 to 720 km/s at 01:15 UT on November 6, 2001 and the compressional effect of this shock was seen as a two step density enhancement at 01:15 and 01:55 UT. The magnitudes of interplanetary magnetic field components, By and Bz, were near zero and consistent on November 4 during the first particle event commencing from 16:15 UT as is evident from Fig. 2. These magnetic field components became oscillatory in nature from 12 UT on November 5, prior to the first density enhancement seen at 19 UT by ACE satellite. Simultaneous southward turning of the Bz with a magnitude of 15 nT is a dominant feature observed and the same trend in Bz persisted for almost 6 h from 19 UT. During this period, By was significantly positive. At the arrival of the shock at 01:15 UT, a further sudden decrease in the southward Bz by about 50 nT was a striking feature of complex nature of IMF during thisÕ event. Magnitude of By also followed negatively directed variations of nearly same
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Fig. 2. Proton Flux intensities, as recorded by the ACE and WIND, Proton density Np, Bz and the variation in the ÔHÕ component at the equatorial station, Tiruneveli (TIR) during 4–6 November, 2001. Three dashed vertical dashed lines shown represent the time corresponding to intense proton density enhancements.
magnitude as that of Bz, with a phase shift of an hour. The prominent magnitude of variations in the interplanetary magnetic fields, By and Bz from 19:00 UT on November 5 until 01:00 UT on November 6 and subsequent abrupt increase in the southward field associated with a magnetic cloud formation is a striking feature of the event. There was no high speed solar wind effecting the compression leading to the first event of density enhancement and southward turning of IMF. This event was probably a precursory event of non-compressional density enhancement type (Gonzalez et al., 2002, and references therein). Impact of the CME following the particle event on November 4 was seen as a shock at the magnetopause at 01:15 UT on November 6 and its influence on the ground magnetic records is evidenced from the strong storm sudden commencement (SSC) of 80 nT amplitude
in the ÔHÕ component at 01:50 UT, as recorded at equatorial elecrojet station Tirunelveli (TIR) and is shown in the bottom panel of Fig. 2. Ground magnetic records are time shifted by 35 min to consider the propagation time of the ejecta from satellite to the ground. A depression of about 80 nT observed in the horizontal component before this SSC could be associated with the precursory density enhancement and the dominant southward directed Bz between 19 UT of November 5 and 01:00 UT of November 6. Abrupt decrease in H component just after the SSC has coincided with the intense southward turning of Bz. The maximum in the main phase of the storm corresponded well with the significantly large Bz magnitude of 70 nT. Moreover the pre-shock conditions exhibited from the density fluctuations and the magnetic field seem to be an indicator of the precursory signature for an extreme case of Bz mag-
S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
nitude of 70 nT associated with the shock on November 06. Various authors had reported configuration of the complex structures of the solar ejecta and the magnetic field associated with it as a possible mechanism of magnetic cloud (Dal Lago et al., 2001 and Gonzalez et al., 2002). However, the event reported in the study differs from the classical structure of the magnetic cloud or the two-step storm feature described by Tsurutani and Gonzalez (1997), and Kamide et al. (1998b). Fig. 3 clearly brings out the shock effect and the magnetic storm characteristics as recorded from the interplanetary parameters by ACE and the ground digital magnetic data records from the equatorial, low and mid latitude locations for the two days November 5–6. The geographic and geomagnetic co-ordinates of the stations and the station abbreviations are provided in
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Table 1. In the bottom panels are shown the interplanetary parameters from the ACE/MAG. The shock effect in the interplanetary medium is evident as a significant enhancement in the total magnetic field, Bt, at magnitude of 80 nT on November 6, after 01:15 UT. The development of a strong southward component (Bz) of the interplanetary magnetic field of invariably large magnitude 70 nT persisting for almost 2 h is the unique feature of the interplanetary manifestation of the energetic particle event under study and thus favouring the onset of a severe magnetic storm. Corresponding to the negative Bz 15 nT for almost 6 h prior to the intense shock at 01:15 UT, shallow depression in the H component at all the locations is noticeable. The arrival of the shock is conspicuous at all the locations from the storm sudden commencement (SSC) magnitude of
Fig. 3. Shock effect in the equatorial, low and mid latitude digital magnetic records, seen as the sudden commencement (80 nT) at 01:50 UT on November 6. Formation of intense main phase corresponding to the large Bz of magnitude 70 nT is the salient feature of the event. Satellite data is time shifted by 35 min. The first vertical line corresponds to the SSC onset and the second one indicates the peak time of development of substorm.
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Table 1 List of magnetic observatories and their co-ordinates Station
IAGA code
Geographic
Geomagnetic
Latitude
Longitude
Latitude
Longitude
Tirunelveli Pondicherry Visakhapatnam Alibag Kakioka Ottawa
TIR PON VSK ABG KAK OTT
8.70° 11.92° 17.68° 18.63° 36.23° 45.4°
77.80°E 79.92°E 83.32°E 72.87°E 140.18°E 75.4°W
0.32° 2.70° 8.17° 10.02° 26.62° 56.37°
149.76° 152.13° 155.89° 145.97° 207.77° 354.11°
Fig. 4. UV images from the POLAR satellite on November 6, 2001, just before and after the intense shock impacted the magnetosphere at 01:15 UT. Auroral intensification prior to the shock at 01:00:11 UT is also evident. The intensified energy spectrum at 02:40:09 coincides with the peak Bz value of 70 nT and the first peak of the intense main phase as shown in Fig. 2.
80 nT, in the equatorial, low and mid latitude digital records. The ring current intensity parameter ÔsymHÕ (WDC, Kyoto) indicated that the symmetric component of the ring current, based on the low latitude magnetic records, had a maximum magnitude of the main phase intensity 300 nT. The magnetic variation at the mid latitude station Ottawa (OTT), given in the topmost curve, showed the maximum negative deviation of about 500 nT corresponding to the main phase period at the low latitudes. Second vertical dashed line shown at 06:20 UT of November 6, marks the second minima during the recovery phase, which has coincided well with the peaked positive value of 20 nT in By, with a lag of about 20 min. Auroral energy characteristics for selected time intervals during intense storm mainphase and substorm periods of the event are projected using the POLAR UV images in Fig. 4. The images chosen and shown correspond mainly to the time when the proton flux and magnetic field records presented intense activity. The predominantly energized spectrum (red) against the respective UT hours given coincides with the main phase intensifications. Auroral intensification prior to the shock at 01:00:11 UT is also evident. The intensified energy spectrum at 02:40:09 UT coincided with the peak Bz value of 70 nT and the first peak of the intense main phase as seen in Fig. 2. The extreme minimum seen
in the H field as a substorm feature for almost one hour, following the main phase, around 06:20 UT on November 6 could be attributed to the significant energy injection extending to lower latitudes, which is evident from the UVI image at 06:00:06 UT from the POLAR satellite on November 6.
3. Conclusions Shock wave associated with the CME on November 4, led to the compression of the magnetosphere on November 6, after about 33 h of the commencement of the flare/CME on the day, giving rise to an increase in the low latitude ÔHÕ component (SSC) to a magnitude of 80 nT. Subsequent to the compression and the enhanced energy flux into the ring current region, a strong main phase is set in with the magnitude of 300 nT, as is seen from the SYM ÔHÕ and the low latitude magnetic records (Fig. 3). Clear cut signature of an unexpected storm feature is evident from the low latitude ÔHÕ component of the magnetic field as emerged from the Bz magnitude of 15 nT correlating with the consistently increased peak in Np for about 6 h prior to the impingement of the shock at the magnetosphere and subsequent development of the geoeffectiveness, indicated by the large storm main phase on November 6. The storm
S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
manifestation following the reconnection of the interplanetary fields associated with the solar energetic particle event reported in the study seems to differ from the classical structure of the magnetic cloud or the two step storm feature described in the literature. The substorm like intense depression following the main phase could well be attributed to the impingement of high density solar wind streams as seen at WIND and ACE spacecrafts (Fig. 2), which resulted in the significant energy injection into the high latitude magnetosphere as seen in the UVI images around 06:00:06 UT (Fig. 4).
Acknowledgements The authors are thankful for the information provided in the Space Environment Center, Boulder, CO, National Oceanic and Atmospheric (NOAA), US Department of Commerce on the ACE, WIND, POLAR and GOES data. We extend our gratitude to the SOHO/ESA/NASA and WDC, Kyoto.
References Burton, R.K., McPherron, R.L., Russell, C.T. An empirical relationship between interplanetary conditions and Dst. J. Geophys. Res. 80, 4204–4214, 1975. Burlaga, L.F., Bahanon, K.W., Klein, L.W. Compound streams, magnetic clouds and major geomagnetic storms. J. Geophys. Res. 92, 5725–5734, 1987. Dal Lago, A., Gonzalez, W.D., Clua de Gonzalez, A.L., Vieira, L.E.A. Compression of magnetic clouds in interplanetary space and increase in their geoeffectiveness. J. Atmos. Solar Terr. Phys. 63, 451–455, 2001. Feynman, J., Hundhausen, A.J. Coronal mass ejections and major solar flares: the great active center of March. J. Geophys. Res. 99, 8451–8461, 1994. Gonzalez, W.D., Joselyn, J.A., Kamide, Y., et al. What is a geomagnetic storm?. J. Geophys. Res. 99, 5771–5792, 1994.
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Gonzalez, W.D., Tsurutani, B.T., Lepping, R.P., Schwenn, R. Interplanetary phenomena associated with very intense geomagnetic storms. J. Atmos. Solar Terr. Phys. 64, 173–181, 2002. Gosling, J.T., Mc Comas, D.J., Phillips, J.L., Bame, S.J. Geomagnetic activity associated with earth passage of interplanetary shock disturbance and coronal mass ejections. J. Geophys. Res. 96, 7831– 7839, 1991. Gopalswamy, N., Yashiro, S., Michalek, G., et al. Interacting coronal mass ejections and solar energetic particles. Astrophys. J. 572, 103– 107, 2002. Hundhausen, A.J. The size and locations of coronal mass ejections: SMM observations from 1980 and 1984–1989. J. Geophys. Res. 98, 13177–13200, 1993. Joselyn, J.A., McIntosh, P.S. Disappearing solar filaments: a useful predictor of geomagnetic activity. J. Geophys. Res. 86, 4555–4564, 1981. Kahler, S.W., Sheeley, N.R., Howard, R.A., et al. Associations between coronal mass ejections and solar energetic proton events. J. Geophys. Res. 89, 9683–9693, 1984. Kamide, Y., Baumjohann, W., Daglis, I.A., et al. Current understanding of magnetic storms: storm-substorm relationships. J. Geophys. Res. 103, 17705–17728, 1998a. Kamide, Y., Yokoyama, N., Gonzalez, W.D., Tsurutani, B.T., Daglis, I.A., Brekke, A., Masuda, S. Two step development of geomagnetic storm. J. Geophys. Res. 103, 6917–6921, 1998b. Lario, D., Marsden, R.G., Sanderson, T.R., et al. Ulysses and WIND particle observations of the November 1997 solar events. Geophys. Res. Lett. 25, 3469–3472, 1998. Reames, D.V. Particle acceleration at the sun and in the Helisophere. Space Sci. Rev. 90, 413–491, 1999. Sheeley Jr., N.R., Howard, R.A., Koomen, M.J., et al. Associations between coronal mass ejection events and soft events. Astrophys. J. 272, 349, 1983. Tsurutani, B.T., Gonzalez, W.D. The interplanetary causes of magnetic storms: a review. In: Tsurutani, B.T., Gonzalez, W.D., Kamide, Y., Arballo, J.K. (Eds.), Magnetic Storms. AGU, Washington, DC, pp. 77–90, 1997. Tsurutani, B.T., Gonzalez, W.D., Tang, F., Lee, Y.T. Great magnetic storms. Geophys. Res. Lett. 19, 73–76, 1992. Tsurutani, B.T., Gonzalez, W.D., Lakhina, G.S., Alex, S. A new appraisal of the geomagnetic storm of September 1–2, 1859. J. Geophys. Res. 108 (A7), 2003. Webb, D.F.. In: Svestka, Z., Jackson, B., Machado, M. (Eds.), The Solar Sources of Coronal Mass Ejections. Springer-Verlag, New York, p. 234, 1992.
Response of the low latitude geomagnetic field to the major proton event of November 2001 S. Alex *, B.M. Pathan, G.S. Lakhina Indian Institute of Geomagnetism, Plot No: 5, Sector 18, Kalamboli, New Panvel, Navi Mumbai, 410 218 Maharashtra, India Received 19 October 2002; received in revised form 6 November 2003; accepted 7 January 2004
Abstract A major solar flare eruption occurred at 16:20 UT on 4 November 2001, followed by strong solar radiation storm and proton event recorded by the SOHO and other interplanetary satellites. Coronal mass ejection associated with the flare event triggered an interplanetary shock, which impacted the geomagnetic field after about 33 h. The shock impact was quite intense to produce a SSC magnitude of 80 nT in the low latitude ground magnetic records followed by sharp and deep main phase (Dst 300 nT) in the first stage, following the density (Np) enhancement. High time resolution digital magnetic field data from the equatorial and low latitude stations in India are analyzed to study the influence of various IP parameters on the intensity and duration of the magnetic storm. A double step storm was found to be in progress caused by the multiple injections. During the period of recovery, after a period of 8 h, a third stage of depression in the ground magnetic field was set in, which corresponded to the southward directed Bz. The energy transfer processes associated with the event is presented. Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Solar flare; Proton event; Magnetic storm
1. Introduction Solar flares are the manifestations of the tremendous eruptions in the solar atmosphere, producing sudden energy release. The magnitude of the magnetic energy released in the solar chromosphere and corona during intense flares range at 1028–1034 ergs, energizing electrons and ions up to MeV and GeV/n respectively. During the high solar activity periods, active regions produce large fluxes of energetic flare particles to Coronal Mass Ejections (CME) related shocks, which can accelerate the Solar Energetic Particle (SEP) events (Webb, 1992; Feynman and Hundhausen, 1994). Joselyn and McIntosh (1981), Sheeley et al. (1983) and Hundhausen (1993) presented processes describing the associ*
Corresponding author. Tel.: +91 22 27480764; fax: +91 22 27480762. E-mail address: [email protected] (S. Alex).
ation of CME with flares and filament eruptions. Mass Ejections play a dominant role in driving large geomagnetic storms by causing sudden commencements on the magnetic records produced by transient IP shocks (Gosling et al., 1991; Tsurutani et al., 1992). Geoeffective nature of the solar disturbances and the energy transfer mechanism of the solar wind energy into the magnetosphere through the reconnection of IMF has been discussed in Burton et al. (1975), Gonzalez et al. (1994), Kamide et al. (1998a) and Tsurutani et al. (2003). Very energetic protons emitted during SEP events are reported to be of mainly two types, gradual events and impulsive events (Reames, 1999). A detailed study of the interplanetary response to the solar energetic particle acceleration in relation to Coronal mass ejection has been done extensively by various researchers (Burlaga et al., 1987; Gonzalez et al., 1994; Lario et al., 1998). The important interactive aspect of the association between the CMEs and SEP acceleration has been
0273-1177/$30 Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2004.01.026
S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
discussed by Kahler et al. (1984) and Gopalswamy et al. (2002). On November 4, 2001 an X1.0/3B, X-ray flare occurred in the active region AR9684, between 16:03 and 16:57 UT, GOES soft X-ray flux reported the peak emission at 16:20 UT. The flare was located at 7° South and 20° West. SOHO/LASCO observed a full Halo CME in C2 coronagraph at 16:35 UT as a very fast bright loop front over the west limb. This CME blasted off from the sun was measured at the plane of sky speed of the front area as 1620 km/s with discernible acceleratioa The flare of November 4, 2001 and the CME were accompanied by an energetic proton event. The present study mainly focuses on the geomagnetic signatures and the interplanetary parameters associated with the major proton event reported on November 4, 2001.
2. Results and discussions Solar cycle 23 witnessed three gradual polar events as reported by SOHO/CELIAS. Of the three events, the most intense event of November 4, 2001 was associated with a strong X-class flare type and an intense CME followed the event. Comparison of the three particle events reported by the CELIAS/MTOF instrument on the SOHO satellite demonstrated the event of November 4, 2001 as the largest in terms of the particles above
Fig. 1. Time since X-ray event (HR MNSS) (adapted from SOHO/ CELIAS).
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40 MeV. In Fig. 1 are reproduced the relative intensities of the three major proton events as recorded by the Proton Monitor on SOHO. The 00:00 time mark refers to the proton count with reference to the commencement of the X-ray event. Referring to the proton event of November 4, 2001, the, enhancement in the proton count persisted for almost 36 h, projecting a prominent peaking in the later half at the time of shock, which happened after almost 33 h of the commencement of the flare on November 4. In order to understand the emission features of the particle energy flux accompanying the solar energetic proton event of November 4, proton flux of various energy levels from the ACE and WIND are given in the topmost panel of Fig. 2. The time resolution of particle flux data for ACE satellite is 5 min and it is 1 min 32 s for the WIND data. Vertical dashed lines are marked against the recurring trend of enhancements in the particle flux densities during November 5–6. Following the strong X-ray flare at 16:20 UT on November 4, proton flux showed sharp increase at all the energy levels as observed by WIND and ACE satellites as shown in Fig. 2. A second increase was seen at 19:00 UT on November 5 too. The proton density (Np) as recorded by ACE satellite was considerably low on November 04 and a gradual increase in density was seen in the early hours of November 5. Around 19 UT a sudden jump in density was quite evident, coinciding with the second increase in proton flux density. Np remained at an enhanced level (80/cc) for a period of about 6 h from 19:00 to 01:15 UT on November 6. Due to spacecraft anomalies caused by the high rate of injection of energetic particles in the interplanetary medium, solar wind velocities from ACE/WIND satellites were degraded and could not be obtained during the peak of activity. However, SOHO/ CELIAS instruments detected the impact of the shock following the CME on November 4, 2001, and reported a steep increase in the solar wind velocity from 450 to 720 km/s at 01:15 UT on November 6, 2001 and the compressional effect of this shock was seen as a two step density enhancement at 01:15 and 01:55 UT. The magnitudes of interplanetary magnetic field components, By and Bz, were near zero and consistent on November 4 during the first particle event commencing from 16:15 UT as is evident from Fig. 2. These magnetic field components became oscillatory in nature from 12 UT on November 5, prior to the first density enhancement seen at 19 UT by ACE satellite. Simultaneous southward turning of the Bz with a magnitude of 15 nT is a dominant feature observed and the same trend in Bz persisted for almost 6 h from 19 UT. During this period, By was significantly positive. At the arrival of the shock at 01:15 UT, a further sudden decrease in the southward Bz by about 50 nT was a striking feature of complex nature of IMF during thisÕ event. Magnitude of By also followed negatively directed variations of nearly same
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S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
Fig. 2. Proton Flux intensities, as recorded by the ACE and WIND, Proton density Np, Bz and the variation in the ÔHÕ component at the equatorial station, Tiruneveli (TIR) during 4–6 November, 2001. Three dashed vertical dashed lines shown represent the time corresponding to intense proton density enhancements.
magnitude as that of Bz, with a phase shift of an hour. The prominent magnitude of variations in the interplanetary magnetic fields, By and Bz from 19:00 UT on November 5 until 01:00 UT on November 6 and subsequent abrupt increase in the southward field associated with a magnetic cloud formation is a striking feature of the event. There was no high speed solar wind effecting the compression leading to the first event of density enhancement and southward turning of IMF. This event was probably a precursory event of non-compressional density enhancement type (Gonzalez et al., 2002, and references therein). Impact of the CME following the particle event on November 4 was seen as a shock at the magnetopause at 01:15 UT on November 6 and its influence on the ground magnetic records is evidenced from the strong storm sudden commencement (SSC) of 80 nT amplitude
in the ÔHÕ component at 01:50 UT, as recorded at equatorial elecrojet station Tirunelveli (TIR) and is shown in the bottom panel of Fig. 2. Ground magnetic records are time shifted by 35 min to consider the propagation time of the ejecta from satellite to the ground. A depression of about 80 nT observed in the horizontal component before this SSC could be associated with the precursory density enhancement and the dominant southward directed Bz between 19 UT of November 5 and 01:00 UT of November 6. Abrupt decrease in H component just after the SSC has coincided with the intense southward turning of Bz. The maximum in the main phase of the storm corresponded well with the significantly large Bz magnitude of 70 nT. Moreover the pre-shock conditions exhibited from the density fluctuations and the magnetic field seem to be an indicator of the precursory signature for an extreme case of Bz mag-
S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
nitude of 70 nT associated with the shock on November 06. Various authors had reported configuration of the complex structures of the solar ejecta and the magnetic field associated with it as a possible mechanism of magnetic cloud (Dal Lago et al., 2001 and Gonzalez et al., 2002). However, the event reported in the study differs from the classical structure of the magnetic cloud or the two-step storm feature described by Tsurutani and Gonzalez (1997), and Kamide et al. (1998b). Fig. 3 clearly brings out the shock effect and the magnetic storm characteristics as recorded from the interplanetary parameters by ACE and the ground digital magnetic data records from the equatorial, low and mid latitude locations for the two days November 5–6. The geographic and geomagnetic co-ordinates of the stations and the station abbreviations are provided in
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Table 1. In the bottom panels are shown the interplanetary parameters from the ACE/MAG. The shock effect in the interplanetary medium is evident as a significant enhancement in the total magnetic field, Bt, at magnitude of 80 nT on November 6, after 01:15 UT. The development of a strong southward component (Bz) of the interplanetary magnetic field of invariably large magnitude 70 nT persisting for almost 2 h is the unique feature of the interplanetary manifestation of the energetic particle event under study and thus favouring the onset of a severe magnetic storm. Corresponding to the negative Bz 15 nT for almost 6 h prior to the intense shock at 01:15 UT, shallow depression in the H component at all the locations is noticeable. The arrival of the shock is conspicuous at all the locations from the storm sudden commencement (SSC) magnitude of
Fig. 3. Shock effect in the equatorial, low and mid latitude digital magnetic records, seen as the sudden commencement (80 nT) at 01:50 UT on November 6. Formation of intense main phase corresponding to the large Bz of magnitude 70 nT is the salient feature of the event. Satellite data is time shifted by 35 min. The first vertical line corresponds to the SSC onset and the second one indicates the peak time of development of substorm.
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Table 1 List of magnetic observatories and their co-ordinates Station
IAGA code
Geographic
Geomagnetic
Latitude
Longitude
Latitude
Longitude
Tirunelveli Pondicherry Visakhapatnam Alibag Kakioka Ottawa
TIR PON VSK ABG KAK OTT
8.70° 11.92° 17.68° 18.63° 36.23° 45.4°
77.80°E 79.92°E 83.32°E 72.87°E 140.18°E 75.4°W
0.32° 2.70° 8.17° 10.02° 26.62° 56.37°
149.76° 152.13° 155.89° 145.97° 207.77° 354.11°
Fig. 4. UV images from the POLAR satellite on November 6, 2001, just before and after the intense shock impacted the magnetosphere at 01:15 UT. Auroral intensification prior to the shock at 01:00:11 UT is also evident. The intensified energy spectrum at 02:40:09 coincides with the peak Bz value of 70 nT and the first peak of the intense main phase as shown in Fig. 2.
80 nT, in the equatorial, low and mid latitude digital records. The ring current intensity parameter ÔsymHÕ (WDC, Kyoto) indicated that the symmetric component of the ring current, based on the low latitude magnetic records, had a maximum magnitude of the main phase intensity 300 nT. The magnetic variation at the mid latitude station Ottawa (OTT), given in the topmost curve, showed the maximum negative deviation of about 500 nT corresponding to the main phase period at the low latitudes. Second vertical dashed line shown at 06:20 UT of November 6, marks the second minima during the recovery phase, which has coincided well with the peaked positive value of 20 nT in By, with a lag of about 20 min. Auroral energy characteristics for selected time intervals during intense storm mainphase and substorm periods of the event are projected using the POLAR UV images in Fig. 4. The images chosen and shown correspond mainly to the time when the proton flux and magnetic field records presented intense activity. The predominantly energized spectrum (red) against the respective UT hours given coincides with the main phase intensifications. Auroral intensification prior to the shock at 01:00:11 UT is also evident. The intensified energy spectrum at 02:40:09 UT coincided with the peak Bz value of 70 nT and the first peak of the intense main phase as seen in Fig. 2. The extreme minimum seen
in the H field as a substorm feature for almost one hour, following the main phase, around 06:20 UT on November 6 could be attributed to the significant energy injection extending to lower latitudes, which is evident from the UVI image at 06:00:06 UT from the POLAR satellite on November 6.
3. Conclusions Shock wave associated with the CME on November 4, led to the compression of the magnetosphere on November 6, after about 33 h of the commencement of the flare/CME on the day, giving rise to an increase in the low latitude ÔHÕ component (SSC) to a magnitude of 80 nT. Subsequent to the compression and the enhanced energy flux into the ring current region, a strong main phase is set in with the magnitude of 300 nT, as is seen from the SYM ÔHÕ and the low latitude magnetic records (Fig. 3). Clear cut signature of an unexpected storm feature is evident from the low latitude ÔHÕ component of the magnetic field as emerged from the Bz magnitude of 15 nT correlating with the consistently increased peak in Np for about 6 h prior to the impingement of the shock at the magnetosphere and subsequent development of the geoeffectiveness, indicated by the large storm main phase on November 6. The storm
S. Alex et al. / Advances in Space Research 36 (2005) 2434–2439
manifestation following the reconnection of the interplanetary fields associated with the solar energetic particle event reported in the study seems to differ from the classical structure of the magnetic cloud or the two step storm feature described in the literature. The substorm like intense depression following the main phase could well be attributed to the impingement of high density solar wind streams as seen at WIND and ACE spacecrafts (Fig. 2), which resulted in the significant energy injection into the high latitude magnetosphere as seen in the UVI images around 06:00:06 UT (Fig. 4).
Acknowledgements The authors are thankful for the information provided in the Space Environment Center, Boulder, CO, National Oceanic and Atmospheric (NOAA), US Department of Commerce on the ACE, WIND, POLAR and GOES data. We extend our gratitude to the SOHO/ESA/NASA and WDC, Kyoto.
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