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December 2006 solar extreme events and their influence on the near-Earth space environment: “Universitetskiy-Tatiana” satellite observations
Available online at www.sciencedirect.com
Advances in Space Research 43 (2009) 489–494 www.elsevier.com/locate/asr
December 2006 solar extreme events and their influence on the near-Earth space environment: ‘‘Universitetskiy-Tatiana” satellite observations I.N. Myagkova *, M.I. Panasyuk, L.L. Lazutin, E.A. Muravieva, L.I. Starostin, T.A. Ivanova, N.N. Pavlov, I.A. Rubinshtein, N.N. Vedenkin, N.A. Vlasova Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics, 1-2, Leninskie Gory, Moscow 119992, Moscow, Russian Federation Received 28 November 2007; received in revised form 17 April 2008; accepted 31 July 2008
Abstract The Russian microsatellite ‘‘Universitetskiy-Tatiana” was launched on Jan. 20, 2005 and was both a scientific and educational mission. Its two main aims were declared as: (1) monitoring of the energetic particles dynamics in the near-Earth space environment after solar events and during quiet times, (2) educational activities based on experimental data obtained from the spacecraft. In this paper observations acquired during Dec. 5–16, 2006, known as ‘‘Solar Extreme Events 2006”, were analyzed. The ‘‘Universitetskiy-Tatiana” microsatellite orbit permits one to measure both solar energetic particle dynamics, variations of the boundary of solar particle penetration, as well as relativistic and sub-relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. Both relativistic electrons of the Earth’s outer radiation and solar energetic particles are an important source of radiation damage in near-Earth space. Therefore, the presented experimental results demonstrate the successful application of a small educational spacecraft both for scientific and educational programs. Ó 2008 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Solar energetic particles; Outer belt of the Earth
1. Introduction It is now no well established that space weather effects can range from damage of space missions to disruption of power grids on Earth. The most important radiation damage is caused by solar energetic particles (SEPs) – protons and electrons. Direct measurements of SEP penetration boundary variations at low-Earth altitudes are very important for estimations of the local space weather conditions (e.g. Myagkova et al., 2007). Near-Earth space environment monitoring at low altitudes should be continuous, even during solar cycle minimum because anomalous solar extreme events sometimes do occur during this period of solar activity, for example the Dec. 5–16, 2006 event. *
Corresponding author. E-mail address: [email protected] (I.N. Myagkova).
The variations of the relativistic electrons in the Earth’s radiation belts (ERB) can play an important role in the near-Earth space environment too, especially during and after geomagnetic storms (e.g. Reeves et al., 2003; O’Brien et al., 2004). Relativistic electrons occurring during ERB enhancements cause volumetric ionization in the microcircuits of spacecraft, so the monitoring of relativistic electron flux dynamics at low altitudes is also important. Therefore, low-altitude polar satellites (in particular, small educational satellites such as ‘‘Universitetskiy-Tatiana”) can be useful for such measurements. 2. Experiment The ‘‘Universitetskiy-Tatiana” microsatellite was launched into a circular orbit with an inclination of 83° and with an initial altitude of about 1000 km on Jan. 20,
0273-1177/$34.00 Ó 2008 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2008.07.019
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2005 (during the occurrence of one of the most powerful solar flares of 2005). It operated until March 08, 2007. During Dec. 2006 its altitude varied in the range 910–980 km. It was made in the framework of the Space Scientific and Education project of Lomonosov Moscow State University ‘‘MSU-250”. This project was timed to the 250th anniversary of the University (Internet site of this project – http:// cosmos.msu.ru/eng/). Its main educational task is to develop the scientific potential of young scientists in Russia and other countries. The main scientific tasks of this satellite was monitoring of the radiation environment in the near Earth space (Sadovnichy et al., 2007). In this work we have used proton data with energies 2–14, 7–16, 15– 40 and 40–100 MeV and electron data with energies >70 keV, 300–600 keV, 700–900 keV and >3.5 MeV. The data was measured by two semiconductor detectors and one scintillation detector (for details see Sadovnichy et al., 2007). Due to the low polar orbit of the satellite SEP fluxes were measured on board the ‘‘Universitetskiy-Tatiana” microsatellite only in areas of open magnetic field lines (in the north and south polar caps) during 15–20min intervals every 50–55 min. The location of the solar proton penetration boundaries can be measured, as well as relativistic and sub-relativistic electrons of the Earth’s outer radiation belt, during each of the four crossings of the polar caps boundaries. 3. Solar extreme events in December 2006 Observed solar flare activity in the beginning of winter 2006 was rather unusual for this solar minimum period. In spite of relatively low values of sunspot numbers (59 and less, http://www.swpc.noaa.gov/ftpdir/indices/old_ indices/2006_DSD.txt) four solar flares of X-class in Soft X-Ray (SXR) emission were observed during the first half of Dec. 2006. Three of them were accompanied by a Coronal Mass Ejection (CME). Parameters of these solar flares (date, start-, maximum-, and end-time, solar coordinates, class in SXR, optical importance) and accompanying CMEs (linear speed and Position Angle (PA) measured from Solar North in degrees) are presented in Table 1 according with the data presented on http://www.swpc. noaa.gov/Data/index.html#reports (Solar Event Reports, 2006 year) on http://cdaw.gsfc.nasa.gov/CME_list. Produced in these solar flares, as well as by the associated CME driven shocks, SEPs were observed in near-Earth space by different scientific missions. Recent experimental results and theoretical studies show that
interplanetary shocks driven by CMEs play a major role in accelerating SEPs (e.g. Berezhko et al., 2001; Webb et al., 2001). In the next Section we present scientific results mainly related to the scientific goals of the ‘‘MSU-250” project. 4. Observations and data analysis 4.1. SEP dynamics It is well known that solar energetic particles (both protons and electrons) are very important source of radiation damage in the near-Earth space. Fig. 1 presents the time profiles of solar proton fluxes (left-hand panel) and electron fluxes (right-hand panel) in various energy ranges measured on board different satellites (‘‘UniversitetskiyTatiana”, ACE and GOES) during the time period Dec. 5–16, 2006. A good agreement in flux profile is found between similar energy ranges obtained by different spacecraft. As mentioned in Section 3, four X-class flares occurring during the first half of Dec. 2006 led to three powerful SEP events. After the first powerful flare (X9.0) on Dec. 5 only a small enhancement of solar protons was observed, and there were no solar electrons observed in the polar caps. It is possibly connected with the location of the first flare near the east limb (E68) or with the absence of a CME. The spectra of the solar particles (both protons and electrons) observed after the flares on Dec. 13 and 14 were significantly harder than after the Dec. 6 flare, especially before the arrival time of the CME. The fast arrival time of more energetic particles can be explained due to the central and West position (W23 and W46) of AR 0930 at the moment of these flares occurring. The maximum of low-energy protons observed in the evening of Dec. 15 was caused by the CME driven shock. 4.2. Solar proton penetration boundary variations The low polar Earth-orbit of the Universitetskiy-Tatiana” microsatellite permits us to measure not only the variations of the solar particle flux in the South and North polar caps every 50–55 min but also the location of SEP penetration boundary into the Earth’s magnetosphere during geomagnetic storms. Observations have demonstrated that for the estimation of possible SEP damage, both the intensity of energetic solar particles and the data about the boundaries of solar particle penetration in the Earth’s magnetosphere are very important (e.g. Leske
Table 1 Flare of X-class observed in AR NOAA0930 in Dec. 2006 Date Dec. Dec. Dec. Dec.
05 06 13 14
Flare time (UT) (start-maximum-end)
Flare coord.
SXR, class/importance
CME start time, UT
V_CME (km/s)
PA (deg)
10:18–10:35–10:45 18:29–18:47–19:00 02:14–02:40–02:57 21:07–22:15–22:26
S07E68 S05E64 S06W23 S06W46
X9.0/2N X6.5/3B X3.4/4B X1.5/–
– 20:12:05 02:54:04 22:30:04
– – 1774 1042
– 360 (Halo) 360 (Halo) 360 (Halo)
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Fig. 1. SEP variations from Dec. 5–16, 2006 in different experiments: (a) protons (ACE, 1.91–4.45 MeV – dotted line, GOES, 9–15 MeV – solid black line, 40–80 MeV – solid grey line, ‘‘Universitetskiy-Tatiana”, 2–14 MeV – open circles, 7–16 MeV – grey crosses, 15–40 MeV – squares, 40–100 MeV – black closed triangles); (b) electrons (ACE 53–315 keV – dotted line, 103–315 keV – solid line, ‘‘Universitetskiy-Tatiana”, >70 keV – open diamonds, 0.3– 0.6 MeV – open grey triangles, 0.7–0.9 meV – closed black squares).
et al., 2001). High-energy solar particle penetration in the polar caps during the main phase of magnetic storms is one of the important sources of radiation danger in the near-Earth space, especially for low-altitude satellites. The size of the solar particle penetration area depends on proton energy and on geomagnetic conditions. Following the solar flares occurring on Dec. 5 and 6 there were no observed significant magnetic storms (the maximal measured Dst was 134 nT) near noon on Dec. 6 and we could not measure deep SEP penetration boundaries in the Earth magnetosphere – location of SEP penetration boundary in the Earth’s magnetosphere during the main phase of the magnetic storm was about 58 degrees in the late evening MLT sector and about 60 degrees in the late morning one. The influence of the Dec. 13 and 14 flares on the Earth’s magnetosphere was more impressive due to two halo CMEs. In Fig. 2, variations observed in the SEP penetration boundary measured by ‘‘Universitetskiy-Tatiana” (protons with energies 2–14 and 40–100 MeV) during magnetic storms occurring in the time period Dec. 14–15 are presented. Different criteria for the analysis of the penetration boundary position exist. As was done in Kuznetsov et al. (2007b), in this work we used the next criterion - the boundary of proton penetration was determined for each polar cap region crossing when the intensity of the SEP flux was two times smaller than the maximal SEP flux in the nearest polar cap (within 15–20 min). In Fig. 2, values of penetration boundary obtained during the late morning magnetic local time (MLT), (MLT 7–10 h), are marked as open diamonds and circles, and during the late evening (MLT 19–22 h) as plusses and squares. For comparison, the time variation of the Dst-index is also shown in Fig. 2 as a full line. It is seen that the location of SEP penetration boundary in the Earth’s magnetosphere during the main phase of the magnetic storm was about
Fig. 2. SEP penetration boundary variations during the Dec. 14–15, 2006 geomagnetic storm. The Dst-variation is shown by the solid line.
55 degrees of invariant latitude K (where L = 1/cos2K) in the late evening MLT sector and about 57 degrees in the late morning one. Due to their higher rigidity the penetration of 40–100 MeV protons is found to go deeper than for 2–14 MeV protons both in the morning and evening sector. In the evening sector the SEP penetration is deeper and this result is similar to results published in earlier papers (e.g. Panasyuk et al., 2004; Yermolaev et al., 2005) regarding the Nov. 2001, Oct.–Nov. 2003 and Nov. 2004 solar events. Variations of SEP penetration boundaries are connected with the expansion of the polar cap size during the main phase of geomagnetic storms. The deeper penetration of SEPs in the evening sector could be connected with the fact that the magnetic field of the Earth has minimal value for late evening MLT – 22 h. It is possible that this allows
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solar particles to penetrate deeper in the Earth’s magnetosphere. The minimal latitudes of SEP penetration boundaries were found in the evening MLT in earlier experiments (e.g. Yermolaev et al., 2005; Myagkova et al., 2007). 4.3. Outer electron radiation belt variations Dynamics of Earth’s outer radiation belt, especially of relativistic electrons is one of the most important physical processes which influence the near-Earth space environment. The most dramatic variations of ERBs take place during magnetic storms. Fig. 3 shows the relativistic and sub-relativistic electron dynamics in the outer radiation belt during Dec. 2006 observed by the ‘‘UniversitetskiyTatiana” microsatellite. Due to the parameters of the orbit, the instruments on board ‘‘Universitetskiy-Tatiana” microsatellite could detect trapped radiation in the region of the South Atlantic Anomaly. In this work variations of the trapped electrons in the following energy ranges 300– 600 keV, 700–900 keV and >3.5 MeV were considered. Radiation belt variations during two time periods were analyzed: Dec. 5, near the weak magnetic disturbance near noon on Dec. 6 (Dst = 34 nT) caused by the first CME (see Table 1) and Dec. 12–16, during and after the magnetic storm with Dst = 144 nT which had the main phase at midnight from Dec. 14–15. It should be noted, that the >3.5 MeV electron channel is contaminated by protons when crossing the polar caps as it detects protons with energies of some tens MeV. However, in the outer ERB, where the protons of such energies are absent, measurements of this electron channel can be considered. The presented data indicate that the radiation belt dynamics during the Dec. 2006 storms was rather similar to dynamics observed during earlier strong storms (e.g. Panasyuk et al., 2004; Yermolaev et al., 2005; Kuznetsov et al., 2005, 2007a; Myagkova et al., 2005, 2007) namely: (a) the intensity of the flux of relativistic electrons decreased during the magnetic storm main phase, even for weak geomagnetic disturbances like Dec. 6; (b) during the recovery phase the intensity of the electron fluxes from the Earth’s outer radiation belt sharply increased, the electron belt significantly widened, and the belt maximum shifted to smaller L. Strong long-time variations of the relativistic and subrelativistic electrons in the outer ERB after the Dec. 15 geomagnetic storm at low (950 km) altitudes were measured by ‘‘Universitetskiy-Tatiana”. Prior to Dec. 15 a weak belt of electrons with boundaries L = 4–5 L was detected. Since Dec. 16 and up to the end of the month a strong belt of relativistic electrons was detected from L = 3 to L = 5.5–6 with maximum near L = 4. The most impressive variations of the 300–600 keV and 700–900 keV electron belts were observed on Dec. 15, when their intensity increased a half of magnitude and its maximum shifted from L = 5 to
L = 3.2–3.5. In according data presented on http://cdaweb.gsfc.nasa.gov/istp_public/, the strong variations of IMF parameters: B (from 5 to 17 nT), Bz (from 16 to 18 nT), solar wind (from 480 to 920 km/s) speed and plasma density (from 2 to 14 n/cc) took place from noon Dec. 14 to midnight between Dec. 14 and 15. In Myagkova et al. (2005) it was proposed that in some similar cases the observed relativistic electron flux variations can be explained by particle acceleration due to the radial diffusion and their scattering in the loss cone due to interactions with the whistler mode of electromagnetic waves. It is possible, that electron flux increases can be caused by diffusion on the cyclotron emission of the enhanced flux of some tens of keV protons (electrons can be in a parasitic resonance with the protons of much smaller energy). Some experiments permit to suggest that the relativistic electrons are scattered into the loss cone by electromagnetic ion cyclotron (EMIC) waves. In the anisotropic zone the ring current (RC) protons are unstable and can generate EMIC waves (Søraas et al., 2004). It is the agreement with the theory that suggested that ion cyclotron waves generated by the unstable proton population can precipitate relativistic electrons in the >1 MeV range (Thorne and Kennel, 1971). Important results of outer ERB studies were published by Reeves et al. (2003). They found that over a half of magnetic storms led to an increase of REB flux increase, however, for the other cases both decreases and absence of significant variations was still observed. Li et al. (1997) have shown that the solar wind speed is the leading controlling parameter on the variations of daily averaged energetic electron fluxes at geosynchronous orbit over a wide energy range: 50 keV to 6.0 MeV. Electrons with energy >1 MeV respond more to the solar wind speed but all the electrons in this energy range are well correlated with solar wind speed. Two possible interpretations for the enhancements of higher energy (>1 MeV) can be used: inward radial diffusion or in situ heating by ULF and VLF waves. However, the relative importance of these two mechanisms is still unknown. These electrons are sometimes named ‘‘killer electrons” as they are very dangerous to electronic devices, in particular the microcircuits that are used in spacecraft. Relativistic electrons of the outer ERB produce volumetric ionization in microcircuits of spacecrafts and breakdown their normal operation. Therefore, the measurement of relativistic electron dynamics is both of practical and scientific interest (e.g. Reeves et al., 2003; Kuznetsov et al., 2005; Myagkova et al., 2005, and references therein). We suggest that the high enhancements of relativistic electrons in the outer ERB observed by ‘‘Universitetskiy-Tatiana” microsatellite are useful for space weather studies. 5. Summary In this paper observational results obtained by the ‘‘Universitetskiy-Tatiana” spacecraft have been presented. The main results are:
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Fig. 3. Comparison of radiation belt particle flux profiles as a function of L-shell for electrons with energies of 300–600 keV, 700–900 keV and >3.5 MeV during Dec. 5–10, 2006 (left-side panel) and Dec. 12–16, 2006 (right-side panel).
1. ‘‘Universitetskiy-Tatiana” microsatellite observations during Dec. 2006 demonstrate that near-Earth space environment monitoring at low-altitude orbits is important during both solar maximum and minimum. 2. Monitoring of SEP penetration boundaries in the Earth’s magnetosphere is also useful during magnetic storms, since SEPs can penetrate deep into the Earth’s magnetosphere during the main phase of moderate
and even weak magnetic storms. In particular due to measurements of the SEP penetration boundaries one has the opportunity to estimate the radiation damage for space missions. 3. It is shown that the joint influence of the magnetic storm and the SEPs on the near-Earth environment is more significant due to SEP penetration into the Earth’s magnetosphere.
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4. The presented experimental results demonstrate the successful application of small educational spacecrafts ‘‘Universitetskiy-Tatiana” to be used for space weather studies.
References Berezhko, E.G., Petukhov, S.I., Taneev, S.N. Acceleration of solar cosmic rays by shock waves in the solar corona. Izvestiya RAN. Phys. Ser. 64 (3), 339–342 (in Russian), 2001. Kuznetsov, S.N., Kudela, K., Myagkova, I.N., Yushkov, D.Yu. Dynamics of the Earth’s radiation belts during the magnetic storm of November 6 2001. Adv. Space Res. 36 (10), 1997–2002, 2005. Kuznetsov, S.N., Myagkova, I.N., Yushkov, B.Yu., Denisov, Yu.I., Muravievs, E.A., Kudela, K. Dynamics of the Earth radiation belts during strong magnetic storms based on CORONAS-F data. Solar Syst. Res. 41 (4), 338–347, 2007a. Kuznetsov, S.N., Yushkov, B.Yu., Denisov, Yu.I., Kudela, K., Myagkova, I.N. Dynamics of the boundary of the penetration of solar energetic particles to Earth’s magnetosphere according to CORONASF data. Solar Syst. Res. 41 (4), 348–353, 2007b. Leske, R.A., Mewaldt, R.A., Stone, E.C., von Rosenvinge, T.T. Observations of geomagnetic cutoff variations during solar energetic particle events and implications for the radiation environment at the Space Station. J. Geophys. Res. 106 (A12), 30011, 2001. Li, X., Baker, D.N., Temerin, M., et al. Are energetic electrons in the solar wind the source of the outer addition belt? Geophys. Res. Lett. 24 (8), 923–926, 1997. Myagkova, I.N., Kuznetsov, S.N., Yushkov, B.Yu., Muravieva, E.A., Lemaire, J. Dynamics of the Earth’s radiation belts during time period April 14–24, 2002 – experimental data, in: Pulkkinen, T.L.,
Tsyganenko, N.A., Friedel, R.H.W. (Eds.), The Inner Magnetosphere: Physics and Modeling, Geophysical Monograf, 155. AGU, Washington, pp. 127–134, 2005. Myagkova, I.N., Kuznetsov, S.N., Kurt, V.G., Yushkov, B.Yu., Muravieve, E.A., Galkin, V.I. X-ray, gamma-emission and energetic particles in near-Earth space as measured by CORONAS-F satellite: from maximum to minimum of the last solar cycle. Adv. Space Res. 40 (2), 1929–1934, 2007. O’Brien, T.P., Looper, M.D., Blake, J.B. Quantification of relativistic electron microburst losses during the GEM storm. Geophys. Res. Lett. 31, L04802/1–L04802/4, 2004. Panasyuk, M.I., Kuznetsov, S.N., Lazutin, L.L., et al. Magnetic storms in October 2003. Cosmic Res. 42 (5), 489–534, 2004. Reeves, G.D., McAdams, K.L., Friedel, R.H.W., O’Brien, T.P. Acceleration and loss of relativistic electrons during geomagnetic storms. Geophys. Res. Lett. 30 (10), 1529, doi:10.1029/2002GL016513, 2003. Sadovnichy, V.A., Panasyuk, M.I., Bobrovnikov, S.Yu., et al. First results of investigating the space environment onboard the UniversitetskiyTatiana Satellite. Cosmic Res. 45 (4), 273–286, 2007. Søraas, F., Oksavik, K., Sandanger, M.I., Aarsnes, K.D., Greer, M.S., Cayton, T. Relativistic electron losses in regions of anisotropic proton precipitation. Geophys. Res. Abstr. 6, 04226, 2004. Thorne, R.M., Kennel, C.F. Relativistic electron precipitation during magnetic storm main phase. J. Geophys. Res. 76, 4456–4468, 1971. Webb, D.F., Crooker, N.U., Plunkett, S.P., St. Cyr, O.C. The solar sources of geoeffective structures, in: Song, P., Siscoe, G., Singer, H.J. (Eds.), Space Weather: Progress and Challenges in Research and Applications, Geophysics Monograph, 125. AGU, Washington, DC, p. 123, 2001. Yermolaev, Yu. I., Zelenyi, L.M., Zastenker, G.N., et al. A year later: solar, heliospheric, and magnetospheric disturbances in November 2004. Geomagnetism Aeronomy 45 (6), 681–719, 2005.
Advances in Space Research 43 (2009) 489–494 www.elsevier.com/locate/asr
December 2006 solar extreme events and their influence on the near-Earth space environment: ‘‘Universitetskiy-Tatiana” satellite observations I.N. Myagkova *, M.I. Panasyuk, L.L. Lazutin, E.A. Muravieva, L.I. Starostin, T.A. Ivanova, N.N. Pavlov, I.A. Rubinshtein, N.N. Vedenkin, N.A. Vlasova Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics, 1-2, Leninskie Gory, Moscow 119992, Moscow, Russian Federation Received 28 November 2007; received in revised form 17 April 2008; accepted 31 July 2008
Abstract The Russian microsatellite ‘‘Universitetskiy-Tatiana” was launched on Jan. 20, 2005 and was both a scientific and educational mission. Its two main aims were declared as: (1) monitoring of the energetic particles dynamics in the near-Earth space environment after solar events and during quiet times, (2) educational activities based on experimental data obtained from the spacecraft. In this paper observations acquired during Dec. 5–16, 2006, known as ‘‘Solar Extreme Events 2006”, were analyzed. The ‘‘Universitetskiy-Tatiana” microsatellite orbit permits one to measure both solar energetic particle dynamics, variations of the boundary of solar particle penetration, as well as relativistic and sub-relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. Both relativistic electrons of the Earth’s outer radiation and solar energetic particles are an important source of radiation damage in near-Earth space. Therefore, the presented experimental results demonstrate the successful application of a small educational spacecraft both for scientific and educational programs. Ó 2008 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Solar energetic particles; Outer belt of the Earth
1. Introduction It is now no well established that space weather effects can range from damage of space missions to disruption of power grids on Earth. The most important radiation damage is caused by solar energetic particles (SEPs) – protons and electrons. Direct measurements of SEP penetration boundary variations at low-Earth altitudes are very important for estimations of the local space weather conditions (e.g. Myagkova et al., 2007). Near-Earth space environment monitoring at low altitudes should be continuous, even during solar cycle minimum because anomalous solar extreme events sometimes do occur during this period of solar activity, for example the Dec. 5–16, 2006 event. *
Corresponding author. E-mail address: [email protected] (I.N. Myagkova).
The variations of the relativistic electrons in the Earth’s radiation belts (ERB) can play an important role in the near-Earth space environment too, especially during and after geomagnetic storms (e.g. Reeves et al., 2003; O’Brien et al., 2004). Relativistic electrons occurring during ERB enhancements cause volumetric ionization in the microcircuits of spacecraft, so the monitoring of relativistic electron flux dynamics at low altitudes is also important. Therefore, low-altitude polar satellites (in particular, small educational satellites such as ‘‘Universitetskiy-Tatiana”) can be useful for such measurements. 2. Experiment The ‘‘Universitetskiy-Tatiana” microsatellite was launched into a circular orbit with an inclination of 83° and with an initial altitude of about 1000 km on Jan. 20,
0273-1177/$34.00 Ó 2008 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2008.07.019
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2005 (during the occurrence of one of the most powerful solar flares of 2005). It operated until March 08, 2007. During Dec. 2006 its altitude varied in the range 910–980 km. It was made in the framework of the Space Scientific and Education project of Lomonosov Moscow State University ‘‘MSU-250”. This project was timed to the 250th anniversary of the University (Internet site of this project – http:// cosmos.msu.ru/eng/). Its main educational task is to develop the scientific potential of young scientists in Russia and other countries. The main scientific tasks of this satellite was monitoring of the radiation environment in the near Earth space (Sadovnichy et al., 2007). In this work we have used proton data with energies 2–14, 7–16, 15– 40 and 40–100 MeV and electron data with energies >70 keV, 300–600 keV, 700–900 keV and >3.5 MeV. The data was measured by two semiconductor detectors and one scintillation detector (for details see Sadovnichy et al., 2007). Due to the low polar orbit of the satellite SEP fluxes were measured on board the ‘‘Universitetskiy-Tatiana” microsatellite only in areas of open magnetic field lines (in the north and south polar caps) during 15–20min intervals every 50–55 min. The location of the solar proton penetration boundaries can be measured, as well as relativistic and sub-relativistic electrons of the Earth’s outer radiation belt, during each of the four crossings of the polar caps boundaries. 3. Solar extreme events in December 2006 Observed solar flare activity in the beginning of winter 2006 was rather unusual for this solar minimum period. In spite of relatively low values of sunspot numbers (59 and less, http://www.swpc.noaa.gov/ftpdir/indices/old_ indices/2006_DSD.txt) four solar flares of X-class in Soft X-Ray (SXR) emission were observed during the first half of Dec. 2006. Three of them were accompanied by a Coronal Mass Ejection (CME). Parameters of these solar flares (date, start-, maximum-, and end-time, solar coordinates, class in SXR, optical importance) and accompanying CMEs (linear speed and Position Angle (PA) measured from Solar North in degrees) are presented in Table 1 according with the data presented on http://www.swpc. noaa.gov/Data/index.html#reports (Solar Event Reports, 2006 year) on http://cdaw.gsfc.nasa.gov/CME_list. Produced in these solar flares, as well as by the associated CME driven shocks, SEPs were observed in near-Earth space by different scientific missions. Recent experimental results and theoretical studies show that
interplanetary shocks driven by CMEs play a major role in accelerating SEPs (e.g. Berezhko et al., 2001; Webb et al., 2001). In the next Section we present scientific results mainly related to the scientific goals of the ‘‘MSU-250” project. 4. Observations and data analysis 4.1. SEP dynamics It is well known that solar energetic particles (both protons and electrons) are very important source of radiation damage in the near-Earth space. Fig. 1 presents the time profiles of solar proton fluxes (left-hand panel) and electron fluxes (right-hand panel) in various energy ranges measured on board different satellites (‘‘UniversitetskiyTatiana”, ACE and GOES) during the time period Dec. 5–16, 2006. A good agreement in flux profile is found between similar energy ranges obtained by different spacecraft. As mentioned in Section 3, four X-class flares occurring during the first half of Dec. 2006 led to three powerful SEP events. After the first powerful flare (X9.0) on Dec. 5 only a small enhancement of solar protons was observed, and there were no solar electrons observed in the polar caps. It is possibly connected with the location of the first flare near the east limb (E68) or with the absence of a CME. The spectra of the solar particles (both protons and electrons) observed after the flares on Dec. 13 and 14 were significantly harder than after the Dec. 6 flare, especially before the arrival time of the CME. The fast arrival time of more energetic particles can be explained due to the central and West position (W23 and W46) of AR 0930 at the moment of these flares occurring. The maximum of low-energy protons observed in the evening of Dec. 15 was caused by the CME driven shock. 4.2. Solar proton penetration boundary variations The low polar Earth-orbit of the Universitetskiy-Tatiana” microsatellite permits us to measure not only the variations of the solar particle flux in the South and North polar caps every 50–55 min but also the location of SEP penetration boundary into the Earth’s magnetosphere during geomagnetic storms. Observations have demonstrated that for the estimation of possible SEP damage, both the intensity of energetic solar particles and the data about the boundaries of solar particle penetration in the Earth’s magnetosphere are very important (e.g. Leske
Table 1 Flare of X-class observed in AR NOAA0930 in Dec. 2006 Date Dec. Dec. Dec. Dec.
05 06 13 14
Flare time (UT) (start-maximum-end)
Flare coord.
SXR, class/importance
CME start time, UT
V_CME (km/s)
PA (deg)
10:18–10:35–10:45 18:29–18:47–19:00 02:14–02:40–02:57 21:07–22:15–22:26
S07E68 S05E64 S06W23 S06W46
X9.0/2N X6.5/3B X3.4/4B X1.5/–
– 20:12:05 02:54:04 22:30:04
– – 1774 1042
– 360 (Halo) 360 (Halo) 360 (Halo)
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Fig. 1. SEP variations from Dec. 5–16, 2006 in different experiments: (a) protons (ACE, 1.91–4.45 MeV – dotted line, GOES, 9–15 MeV – solid black line, 40–80 MeV – solid grey line, ‘‘Universitetskiy-Tatiana”, 2–14 MeV – open circles, 7–16 MeV – grey crosses, 15–40 MeV – squares, 40–100 MeV – black closed triangles); (b) electrons (ACE 53–315 keV – dotted line, 103–315 keV – solid line, ‘‘Universitetskiy-Tatiana”, >70 keV – open diamonds, 0.3– 0.6 MeV – open grey triangles, 0.7–0.9 meV – closed black squares).
et al., 2001). High-energy solar particle penetration in the polar caps during the main phase of magnetic storms is one of the important sources of radiation danger in the near-Earth space, especially for low-altitude satellites. The size of the solar particle penetration area depends on proton energy and on geomagnetic conditions. Following the solar flares occurring on Dec. 5 and 6 there were no observed significant magnetic storms (the maximal measured Dst was 134 nT) near noon on Dec. 6 and we could not measure deep SEP penetration boundaries in the Earth magnetosphere – location of SEP penetration boundary in the Earth’s magnetosphere during the main phase of the magnetic storm was about 58 degrees in the late evening MLT sector and about 60 degrees in the late morning one. The influence of the Dec. 13 and 14 flares on the Earth’s magnetosphere was more impressive due to two halo CMEs. In Fig. 2, variations observed in the SEP penetration boundary measured by ‘‘Universitetskiy-Tatiana” (protons with energies 2–14 and 40–100 MeV) during magnetic storms occurring in the time period Dec. 14–15 are presented. Different criteria for the analysis of the penetration boundary position exist. As was done in Kuznetsov et al. (2007b), in this work we used the next criterion - the boundary of proton penetration was determined for each polar cap region crossing when the intensity of the SEP flux was two times smaller than the maximal SEP flux in the nearest polar cap (within 15–20 min). In Fig. 2, values of penetration boundary obtained during the late morning magnetic local time (MLT), (MLT 7–10 h), are marked as open diamonds and circles, and during the late evening (MLT 19–22 h) as plusses and squares. For comparison, the time variation of the Dst-index is also shown in Fig. 2 as a full line. It is seen that the location of SEP penetration boundary in the Earth’s magnetosphere during the main phase of the magnetic storm was about
Fig. 2. SEP penetration boundary variations during the Dec. 14–15, 2006 geomagnetic storm. The Dst-variation is shown by the solid line.
55 degrees of invariant latitude K (where L = 1/cos2K) in the late evening MLT sector and about 57 degrees in the late morning one. Due to their higher rigidity the penetration of 40–100 MeV protons is found to go deeper than for 2–14 MeV protons both in the morning and evening sector. In the evening sector the SEP penetration is deeper and this result is similar to results published in earlier papers (e.g. Panasyuk et al., 2004; Yermolaev et al., 2005) regarding the Nov. 2001, Oct.–Nov. 2003 and Nov. 2004 solar events. Variations of SEP penetration boundaries are connected with the expansion of the polar cap size during the main phase of geomagnetic storms. The deeper penetration of SEPs in the evening sector could be connected with the fact that the magnetic field of the Earth has minimal value for late evening MLT – 22 h. It is possible that this allows
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solar particles to penetrate deeper in the Earth’s magnetosphere. The minimal latitudes of SEP penetration boundaries were found in the evening MLT in earlier experiments (e.g. Yermolaev et al., 2005; Myagkova et al., 2007). 4.3. Outer electron radiation belt variations Dynamics of Earth’s outer radiation belt, especially of relativistic electrons is one of the most important physical processes which influence the near-Earth space environment. The most dramatic variations of ERBs take place during magnetic storms. Fig. 3 shows the relativistic and sub-relativistic electron dynamics in the outer radiation belt during Dec. 2006 observed by the ‘‘UniversitetskiyTatiana” microsatellite. Due to the parameters of the orbit, the instruments on board ‘‘Universitetskiy-Tatiana” microsatellite could detect trapped radiation in the region of the South Atlantic Anomaly. In this work variations of the trapped electrons in the following energy ranges 300– 600 keV, 700–900 keV and >3.5 MeV were considered. Radiation belt variations during two time periods were analyzed: Dec. 5, near the weak magnetic disturbance near noon on Dec. 6 (Dst = 34 nT) caused by the first CME (see Table 1) and Dec. 12–16, during and after the magnetic storm with Dst = 144 nT which had the main phase at midnight from Dec. 14–15. It should be noted, that the >3.5 MeV electron channel is contaminated by protons when crossing the polar caps as it detects protons with energies of some tens MeV. However, in the outer ERB, where the protons of such energies are absent, measurements of this electron channel can be considered. The presented data indicate that the radiation belt dynamics during the Dec. 2006 storms was rather similar to dynamics observed during earlier strong storms (e.g. Panasyuk et al., 2004; Yermolaev et al., 2005; Kuznetsov et al., 2005, 2007a; Myagkova et al., 2005, 2007) namely: (a) the intensity of the flux of relativistic electrons decreased during the magnetic storm main phase, even for weak geomagnetic disturbances like Dec. 6; (b) during the recovery phase the intensity of the electron fluxes from the Earth’s outer radiation belt sharply increased, the electron belt significantly widened, and the belt maximum shifted to smaller L. Strong long-time variations of the relativistic and subrelativistic electrons in the outer ERB after the Dec. 15 geomagnetic storm at low (950 km) altitudes were measured by ‘‘Universitetskiy-Tatiana”. Prior to Dec. 15 a weak belt of electrons with boundaries L = 4–5 L was detected. Since Dec. 16 and up to the end of the month a strong belt of relativistic electrons was detected from L = 3 to L = 5.5–6 with maximum near L = 4. The most impressive variations of the 300–600 keV and 700–900 keV electron belts were observed on Dec. 15, when their intensity increased a half of magnitude and its maximum shifted from L = 5 to
L = 3.2–3.5. In according data presented on http://cdaweb.gsfc.nasa.gov/istp_public/, the strong variations of IMF parameters: B (from 5 to 17 nT), Bz (from 16 to 18 nT), solar wind (from 480 to 920 km/s) speed and plasma density (from 2 to 14 n/cc) took place from noon Dec. 14 to midnight between Dec. 14 and 15. In Myagkova et al. (2005) it was proposed that in some similar cases the observed relativistic electron flux variations can be explained by particle acceleration due to the radial diffusion and their scattering in the loss cone due to interactions with the whistler mode of electromagnetic waves. It is possible, that electron flux increases can be caused by diffusion on the cyclotron emission of the enhanced flux of some tens of keV protons (electrons can be in a parasitic resonance with the protons of much smaller energy). Some experiments permit to suggest that the relativistic electrons are scattered into the loss cone by electromagnetic ion cyclotron (EMIC) waves. In the anisotropic zone the ring current (RC) protons are unstable and can generate EMIC waves (Søraas et al., 2004). It is the agreement with the theory that suggested that ion cyclotron waves generated by the unstable proton population can precipitate relativistic electrons in the >1 MeV range (Thorne and Kennel, 1971). Important results of outer ERB studies were published by Reeves et al. (2003). They found that over a half of magnetic storms led to an increase of REB flux increase, however, for the other cases both decreases and absence of significant variations was still observed. Li et al. (1997) have shown that the solar wind speed is the leading controlling parameter on the variations of daily averaged energetic electron fluxes at geosynchronous orbit over a wide energy range: 50 keV to 6.0 MeV. Electrons with energy >1 MeV respond more to the solar wind speed but all the electrons in this energy range are well correlated with solar wind speed. Two possible interpretations for the enhancements of higher energy (>1 MeV) can be used: inward radial diffusion or in situ heating by ULF and VLF waves. However, the relative importance of these two mechanisms is still unknown. These electrons are sometimes named ‘‘killer electrons” as they are very dangerous to electronic devices, in particular the microcircuits that are used in spacecraft. Relativistic electrons of the outer ERB produce volumetric ionization in microcircuits of spacecrafts and breakdown their normal operation. Therefore, the measurement of relativistic electron dynamics is both of practical and scientific interest (e.g. Reeves et al., 2003; Kuznetsov et al., 2005; Myagkova et al., 2005, and references therein). We suggest that the high enhancements of relativistic electrons in the outer ERB observed by ‘‘Universitetskiy-Tatiana” microsatellite are useful for space weather studies. 5. Summary In this paper observational results obtained by the ‘‘Universitetskiy-Tatiana” spacecraft have been presented. The main results are:
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Fig. 3. Comparison of radiation belt particle flux profiles as a function of L-shell for electrons with energies of 300–600 keV, 700–900 keV and >3.5 MeV during Dec. 5–10, 2006 (left-side panel) and Dec. 12–16, 2006 (right-side panel).
1. ‘‘Universitetskiy-Tatiana” microsatellite observations during Dec. 2006 demonstrate that near-Earth space environment monitoring at low-altitude orbits is important during both solar maximum and minimum. 2. Monitoring of SEP penetration boundaries in the Earth’s magnetosphere is also useful during magnetic storms, since SEPs can penetrate deep into the Earth’s magnetosphere during the main phase of moderate
and even weak magnetic storms. In particular due to measurements of the SEP penetration boundaries one has the opportunity to estimate the radiation damage for space missions. 3. It is shown that the joint influence of the magnetic storm and the SEPs on the near-Earth environment is more significant due to SEP penetration into the Earth’s magnetosphere.
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4. The presented experimental results demonstrate the successful application of small educational spacecrafts ‘‘Universitetskiy-Tatiana” to be used for space weather studies.
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