Abstract
Based on energetic particle observations made at \({\approx}\,1\) AU, we present a catalogue of 46 wide-longitude (\({>}\,45^{\circ}\)) solar energetic particle (SEP) events detected at multiple locations during 2009 – 2016. The particle kinetic energies of interest were chosen as \({>}\,55\) MeV for protons and 0.18 – 0.31 MeV for electrons. We make use of proton data from the Solar and Heliospheric Observatory/Energetic and Relativistic Nuclei and Electron Experiment (SOHO/ERNE) and the Solar Terrestrial Relations Observatory/High Energy Telescopes (STEREO/HET), together with electron data from the Advanced Composition Explorer/Electron, Proton, and Alpha Monitor (ACE/EPAM) and the STEREO/Solar Electron and Proton Telescopes (SEPT). We consider soft X-ray data from the Geostationary Operational Environmental Satellites (GOES) and coronal mass ejection (CME) observations made with the SOHO/Large Angle and Spectrometric Coronagraph (LASCO) and STEREO/Coronagraphs 1 and 2 (COR1, COR2) to establish the probable associations between SEP events and the related solar phenomena. Event onset times and peak intensities are determined; velocity dispersion analysis (VDA) and time-shifting analysis (TSA) are performed for protons; TSA is performed for electrons. In our event sample, there is a tendency for the highest peak intensities to occur when the observer is magnetically connected to solar regions west of the flare. Our estimates for the mean event width, derived as the standard deviation of a Gaussian curve modelling the SEP intensities (protons \({\approx}\,44^{\circ}\), electrons \({\approx}\,50^{\circ}\)), largely agree with previous results for lower-energy SEPs. SEP release times with respect to event flares, as well as the event rise times, show no simple dependence on the observer’s connection angle, suggesting that the source region extent and dominant particle acceleration and transport mechanisms are important in defining these characteristics of an event. There is no marked difference between the speed distributions of the CMEs related to wide events and the CMEs related to all near-Earth SEP events of similar energy range from the same time period.
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Notes
This limit was intentionally somewhat flexible, so as to allow some small events, better detectable in data averaged over several minutes, to be taken into account.
Here and everywhere else in this work, 1 pfu = 1 particle \(\mbox{cm}^{-2}\,\mbox{s}^{-1}\,\mbox{sr}^{-1}\).
A detailed description of STEREO/SEPT electron energy channels is included in the document “STEREO/SEPT level 2 science data format specification and caveats”, available at http://www2.physik.uni-kiel.de/stereo/data/sept/level2/ .
These data can be accessed at http://cdaweb.gsfc.nasa.gov ; on the main page, select “Wind” and “Radio and Plasma Waves (space)”, then “Wind Radio/Plasma Wave, (WAVES) Hi-Res Parameters”.
Although SOHO/ERNE did record a minor 55 – 80 MeV proton intensity enhancement on 26 December 2013, it was not substantial enough to be classified as a proton event according to our criteria. We note that in lower proton energies, however, the near-Earth SEP activity on that date could have qualified as an event.
This somewhat simpler method was preferred over the one used in proton intensity intercalibration between SOHO/ERNE and STEREO/HET due to the electron observations having much better particle count statistics and the fact that the ACE/EPAM and STEREO/SEPT electron energy channels of interest match each other better than the SOHO/ERNE and STEREO/HET proton energy channels.
References
Bougeret, J.-L., Kaiser, M.L., Kellogg, P.J., Manning, R., Goetz, K., Monson, S.J., Monge, N., Friel, L., Meetre, C.A., Perche, C., Sitruk, L., Hoang, S.: 1995, Waves: The radio and plasma wave investigation on the wind spacecraft. Space Sci. Rev. 71, 231. DOI . ADS .
Bougeret, J.L., Goetz, K., Kaiser, M.L., Bale, S.D., Kellogg, P.J., Maksimovic, M., Monge, N., Monson, S.J., Astier, P.L., Davy, S., Dekkali, M., Hinze, J.J., Manning, R.E., Aguilar-Rodriguez, E., Bonnin, X., Briand, C., Cairns, I.H., Cattell, C.A., Cecconi, B., Eastwood, J., Ergun, R.E., Fainberg, J., Hoang, S., Huttunen, K.E.J., Krucker, S., Lecacheux, A., MacDowall, R.J., Macher, W., Mangeney, A., Meetre, C.A., Moussas, X., Nguyen, Q.N., Oswald, T.H., Pulupa, M., Reiner, M.J., Robinson, P.A., Rucker, H., Salem, C., Santolik, O., Silvis, J.M., Ullrich, R., Zarka, P., Zouganelis, I.: 2008, S/WAVES: The radio and plasma wave investigation on the STEREO mission. Space Sci. Rev. 136, 487. DOI . ADS .
Brueckner, G.E., Howard, R.A., Koomen, M.J., Korendyke, C.M., Michels, D.J., Moses, J.D., Socker, D.G., Dere, K.P., Lamy, P.L., Llebaria, A., Bout, M.V., Schwenn, R., Simnett, G.M., Bedford, D.K., Eyles, C.J.: 1995, The Large Angle Spectroscopic Coronagraph (LASCO). Solar Phys. 162, 357. DOI . ADS .
Cane, H.V., Erickson, W.C., Prestage, N.P.: 2002, Solar flares, type III radio bursts, coronal mass ejections, and energetic particles. J. Geophys. Res. Space Phys. 107(A10), SSH 14, 1315. DOI .
Cane, H.V., Richardson, I.G., St. Cyr, O.C.: 1998, The interplanetary events of January–May, 1997 as inferred from energetic particle data, and their relationship with solar events. Geophys. Res. Lett. 25(14), 2517. DOI .
Dresing, N., Gómez-Herrero, R., Heber, B., Klassen, A., Malandraki, O., Dröge, W., Kartavykh, Y.: 2014, Statistical survey of widely spread out solar electron events observed with STEREO and ACE with special attention to anisotropies. Astron. Astrophys. 567, A27. DOI . ADS .
Dresing, N., Gómez-Herrero, R., Heber, B., Klassen, A., Temmer, M., Veronig, A.: 2018, Long-lasting injection of solar energetic electrons into the heliosphere. Astron. Astrophys. In press.
Gold, R.E., Krimigis, S.M., Hawkins, S.E. III, Haggerty, D.K., Lohr, D.A., Fiore, E., Armstrong, T.P., Holland, G., Lanzerotti, L.J.: 1998, Electron, Proton, and Alpha Monitor on the Advanced Composition Explorer Spacecraft. Space Sci. Rev. 86, 541. DOI . ADS .
Gopalswamy, N., Yashiro, S., Michalek, G., Stenborg, G., Vourlidas, A., Freeland, S., Howard, R.: 2009, The SOHO/LASCO CME catalog. Earth Moon Planets 104, 295. DOI . ADS .
Gopalswamy, N., Akiyama, S., Yashiro, S., Xie, H., Makela, P., Michalek, G.: 2015a, The mild space weather in solar cycle 24. ArXiv e-prints. ADS .
Gopalswamy, N., Xie, H., Akiyama, S., Mäkelä, P., Yashiro, S., Michalek, G.: 2015b, The peculiar behavior of halo coronal mass ejections in solar cycle 24. Astrophys. J. 804, L23. DOI . ADS .
Howard, R.A., Moses, J.D., Socker, D.G.: 2000, Sun–Earth connection coronal and heliospheric investigation (SECCHI). In: Fineschi, S., Korendyke, C.M., Siegmund, O.H., Woodgate, B.E. (eds.) Instrumentation for UV/EUV Astronomy and Solar Missions, Proc. SPIE 4139, 259. DOI . ADS .
Huttunen-Heikinmaa, K., Valtonen, E., Laitinen, T.: 2005, Proton and helium release times in SEP events observed with SOHO/ERNE. Astron. Astrophys. 442, 673. DOI . ADS .
Kallenrode, M.-B., Wibberenz, G., Kunow, H., Müller-Mellin, R., Stolpovskii, V., Kontor, N.: 1993, Multi-spacecraft observations of particle events and interplanetary shocks during November/December 1982. Solar Phys. 147, 377. DOI . ADS .
Klassen, A., Dresing, N., Gómez-Herrero, R., Heber, B., Müller-Mellin, R.: 2016, Unexpected spatial intensity distributions and onset timing of solar electron events observed by closely spaced STEREO spacecraft. Astron. Astrophys. 593, A31. DOI . ADS .
Kwon, R.-Y., Zhang, J., Olmedo, O.: 2014, New insights into the physical nature of coronal mass ejections and associated shock waves within the framework of the three-dimensional structure. Astrophys. J. 794(2), 148. http://stacks.iop.org/0004-637X/794/i=2/a=148 .
Laitinen, T., Dalla, S.: 2017, Energetic particle transport across the mean magnetic field: Before diffusion. Astrophys. J. 834, 127. DOI . ADS .
Laitinen, T., Dalla, S., Marriott, D.: 2017, Early propagation of energetic particles across the mean field in turbulent plasmas. Mon. Not. Roy. Astron. Soc. 470, 3149. DOI . ADS .
Laitinen, T., Kopp, A., Effenberger, F., Dalla, S., Marsh, M.S.: 2016, Solar energetic particle access to distant longitudes through turbulent field-line meandering. Astron. Astrophys. 591, A18. DOI . ADS .
Lario, D., Kallenrode, M.-B., Decker, R.B., Roelof, E.C., Krimigis, S.M., Aran, A., Sanahuja, B.: 2006, Radial and longitudinal dependence of solar 4 – 13 MeV and 27 – 37 MeV proton peak intensities and fluences: Helios and IMP 8 observations. Astrophys. J. 653, 1531. DOI . ADS .
Lario, D., Aran, A., Gómez-Herrero, R., Dresing, N., Heber, B., Ho, G.C., Decker, R.B., Roelof, E.C.: 2013, Longitudinal and radial dependence of solar energetic particle peak intensities: STEREO, ACE, SOHO, GOES, and MESSENGER observations. Astrophys. J. 767, 41. DOI . ADS .
Lario, D., Kwon, R.-Y., Vourlidas, A., Raouafi, N.E., Haggerty, D.K., Ho, G.C., Anderson, B.J., Papaioannou, A., Gómez-Herrero, R., Dresing, N., Riley, P.: 2016, Longitudinal properties of a widespread solar energetic particle event on 2014 February 25: Evolution of the associated CME shock. Astrophys. J. 819, 72. DOI . ADS .
Luhmann, J.G., Mays, M.L., Odstrcil, D., Li, Y., Bain, H., Lee, C.O., Galvin, A.B., Mewaldt, R.A., Cohen, C.M.S., Leske, R.A., Larson, D., Futaana, Y.: 2017, Modeling solar energetic particle events using ENLIL heliosphere simulations. Space Weather 15(7), 934. DOI .
McComas, D.J., Bame, S.J., Barker, P., Feldman, W.C., Phillips, J.L., Riley, P., Griffee, J.W.: 1998, Solar Wind Electron Proton Alpha Monitor (SWEPAM) for the advanced composition explorer. Space Sci. Rev. 86, 563. DOI . ADS .
McGuire, R.E., Lal, N., Van Hollebeke, M.A.I.: 1983, A multi-spacecraft study of the coronal and interplanetary transport of solar cosmic rays. I, II. In: International Cosmic Ray Conference, 10, 353. ADS .
McKibben, R.B.: 1972, Observations of solar proton events made from very widely separated spacecraft. In: Bulletin of the American Astronomical Society, Bulletin of the American Astronomical Society 4, 387. ADS .
Mewaldt, R.A., Cohen, C.M.S., Cook, W.R., Cummings, A.C., Davis, A.J., Geier, S., Kecman, B., Klemic, J., Labrador, A.W., Leske, R.A., Miyasaka, H., Nguyen, V., Ogliore, R.C., Stone, E.C., Radocinski, R.G., Wiedenbeck, M.E., Hawk, J., Shuman, S., von Rosenvinge, T.T., Wortman, K.: 2008, The Low-Energy Telescope (LET) and SEP central electronics for the STEREO mission. Space Sci. Rev. 136, 285. DOI . ADS .
Mewaldt, R.A., Cohen, C.M.S., Mason, G.M., von Rosenvinge, T.T., Li, G., Smith, C.W., Vourlidas, A.: 2015, Investigating the causes of solar-cycle variations in solar energetic particle fluences and composition. In: Proceedings of the 34th International Cosmic Ray Conference, The Hague, The Netherlands. https://pos.sissa.it/archive/conferences/236/030/ICRC2015_030.pdf .
Müller-Mellin, R., Böttcher, S., Falenski, J., Rode, E., Duvet, L., Sanderson, T., Butler, B., Johlander, B., Smit, H.: 2008, The Solar Electron and Proton Telescope for the STEREO mission. Space Sci. Rev. 136, 363. DOI . ADS .
Neupert, W.M.: 1968, Comparison of solar X-ray line emission with microwave emission during flares. Astrophys. J. 153, L59. DOI . ADS .
Ogilvie, K.W., Chornay, D.J., Fritzenreiter, R.J., Hunsaker, F., Keller, J., Lobell, J., Miller, G., Scudder, J.D., Sittler, E.C. Jr., Torbert, R.B., Bodet, D., Needell, G., Lazarus, A.J., Steinberg, J.T., Tappan, J.H., Mavretic, A., Gergin, E.: 1995, SWE, a comprehensive plasma instrument for the WIND spacecraft. Space Sci. Rev. 71, 55. DOI . ADS .
Paassilta, M., Raukunen, O., Vainio, R., Valtonen, E., Papaioannou, A., Siipola, R., Riihonen, E., Dierckxsens, M., Crosby, N., Malandraki, O., Heber, B., Klein, K.-L.: 2017, Catalogue of 55-80 MeV solar proton events extending through solar cycles 23 and 24. J. Space Weather Space Clim. 7(27), A14. DOI . ADS .
Papaioannou, A., Malandraki, O.E., Dresing, N., Heber, B., Klein, K.-L., Vainio, R., Rodríguez-Gasén, R., Klassen, A., Nindos, A., Heynderickx, D., Mewaldt, R.A., Gómez-Herrero, R., Vilmer, N., Kouloumvakos, A., Tziotziou, K., Tsiropoula, G.: 2014, SEPServer catalogues of solar energetic particle events at 1 AU based on STEREO recordings: 2007 – 2012. Astron. Astrophys. 569, A96. DOI . ADS .
Papaioannou, A., Sandberg, I., Anastasiadis, A., Kouloumvakos, A., Georgoulis, M.K., Tziotziou, K., Tsiropoula, G., Jiggens, P., Hilgers, A.: 2016, Solar flares, coronal mass ejections and solar energetic particle event characteristics. J. Space Weather Space Clim. 6, A42. DOI .
Reames, D.V.: 1999, Particle acceleration at the Sun and in the heliosphere. Space Sci. Rev. 90(3), 413. DOI .
Reames, D.V.: 2013, The two sources of solar energetic particles. Space Sci. Rev. 175, 53. DOI . ADS .
Reames, D.V., Barbier, L.M., Ng, C.K.: 1996, The spatial distribution of particles accelerated by coronal mass ejection – driven shocks. Astrophys. J. 466, 473. DOI . ADS .
Richardson, I.G., von Rosenvinge, T.T., Cane, H.V., Christian, E.R., Cohen, C.M.S., Labrador, A.W., Leske, R.A., Mewaldt, R.A., Wiedenbeck, M.E., Stone, E.C.: 2014, \({>}\,25\) MeV proton events observed by the high energy telescopes on the STEREO A and B spacecraft and/or at Earth during the first ∼ seven years of the STEREO mission. Solar Phys. 289, 3059. DOI . ADS .
Torsti, J., Valtonen, E., Lumme, M., Peltonen, P., Eronen, T., Louhola, M., Riihonen, E., Schultz, G., Teittinen, M., Ahola, K., Holmlund, C., Kelhä, V., Leppälä, K., Ruuska, P., Strömmer, E.: 1995, Energetic particle experiment ERNE. Solar Phys. 162, 505. DOI . ADS .
Vainio, R., Valtonen, E., Heber, B., Malandraki, O.E., Papaioannou, A., Klein, K.-L., Afanasiev, A., Agueda, N., Aurass, H., Battarbee, M., Braune, S., Dröge, W., Ganse, U., Hamadache, C., Heynderickx, D., Huttunen-Heikinmaa, K., Kiener, J., Kilian, P., Kopp, A., Kouloumvakos, A., Maisala, S., Mishev, A., Miteva, R., Nindos, A., Oittinen, T., Raukunen, O., Riihonen, E., Rodríguez-Gasén, R., Saloniemi, O., Sanahuja, B., Scherer, R., Spanier, F., Tatischeff, V., Tziotziou, K., Usoskin, I.G., Vilmer, N.: 2013, The first SEPServer event catalogue \({\sim}\,68\)-MeV solar proton events observed at 1 AU in 1996 – 2010. J. Space Weather Space Clim. 3(27), A12. DOI . ADS .
Vainio, R., Raukunen, O., Tylka, A.J., Dietrich, W.F., Afanasiev, A.: 2017, Why is solar cycle 24 an inefficient producer of high-energy particle events? Astron. Astrophys. 604, A47. DOI . ADS .
Veronig, A., Vršnak, B., Dennis, B.R., Temmer, M., Hanslmeier, A., Magdalenić, J.: 2002, Investigation of the Neupert effect in solar flares. I. Statistical properties and the evaporation model. Astron. Astrophys. 392, 699. DOI . ADS .
von Rosenvinge, T.T., Reames, D.V., Baker, R., Hawk, J., Nolan, J.T., Ryan, L., Shuman, S., Wortman, K.A., Mewaldt, R.A., Cummings, A.C., Cook, W.R., Labrador, A.W., Leske, R.A., Wiedenbeck, M.E.: 2008, The High Energy Telescope for STEREO. Space Sci. Rev. 136, 391. DOI . ADS .
Vourlidas, A., Balmaceda, L.A., Stenborg, G., Dal Lago, A.: 2017, Multi-viewpoint coronal mass ejection catalog based on STEREO COR2 observations. Astrophys. J. 838, 141. DOI . ADS .
Wiedenbeck, M.E., Mason, G.M., Cohen, C.M.S., Nitta, N.V., Gómez-Herrero, R., Haggerty, D.K.: 2013, Observations of solar energetic particles from 3He-rich events over a wide range of heliographic longitude. Astrophys. J. 762, 54. DOI . ADS .
Acknowledgements
The research described in this paper was supported by ESA contract 4000120480/17/NL/LF/hh. M. Paassilta and R. Vainio acknowledge the funding from Academy of Finland (decisions 267186 and 297395). N. Dresing and B. Heber acknowledge the funding from Deutscher Akademischer Austauschdienst (DAAD 57247608) and the STEREO/SEPT, Chandra/EPHIN and SOHO/EPHIN project which is supported under grant 50OC1702 by the Federal Ministry of Economics and Technology on the basis of a decision by the German Bundestag. We would like to acknowledge and express our gratitude to the organizations and teams responsible for maintaining the data sources used in this article (SEPServer, CDAW SOHO LASCO CME Catalog, SolarSoft Latest Events Archive, NOAA/Solar-Terrestrial Physics at the National Centers for Environmental Information, Coordinated Data Analysis Web, and the ACE Science Center). CDAW SOHO LASCO CME Catalog: this CME catalog is generated and maintained at the CDAW Data Center by NASA and The Catholic University of America in cooperation with the Naval Research Laboratory. SOHO is a project of international cooperation between ESA and NASA. The Radio Monitoring website: this survey is generated and maintained at the Observatoire de Paris by the LESIA UMR CNRS 8109 in cooperation with the Artemis team, Universities of Athens and Ioanina and the Naval Research Laboratory. The STEREO/SECCHI/COR2 CME catalog (the Dual-Viewpoint CME Catalog from the SECCHI/COR Telescopes): this catalogue is generated and maintained at JHU/APL, in collaboration with the NRL and GSFC, and is supported by NASA.
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Appendix: Notes on Particle Data
Appendix: Notes on Particle Data
1.1 A.1 Proton Intensity Intercalibration
Although a detailed attempt to intercalibrate the measured proton intensities accurately between different instruments, so as to account for differences in instrument efficiency, was felt to be outside the scope of this article, an intensity comparison and a simple tentative intercalibration was performed to evaluate the need for correction factors. To ensure that the spacecraft observations were made of nearly identical SEP populations, the decay phase of the high-energy proton event of 14 December 2006 was chosen for this purpose. The time range of interest was taken to span from the noon of 15 December to 20:00 UT on 16 December, eliminating the rise phase and ending approximately when the STEREO-A/HET measured 40 – 100 MeV proton intensity fell below \({\approx}\,2.0\times10^{-3}~\mbox{pfu}\,\mbox{MeV}^{-1}\). To compensate for the imperfect match between the energy bins of HET and ERNE, the intensities recorded by the former were separately examined in two energy ranges, 40 – 100 MeV and 60 – 100 MeV. The background intensities were visually estimated as \({\approx}\,5.0\times10^{-4}~\mbox{pfu} \,\mbox{MeV}^{-1}\) for ERNE, \({\approx}\,1.0\times10^{-4}~\mbox{pfu}\,\mbox{MeV}^{-1}\) for the HET 40 – 60 MeV channels, \({\approx}\,4.0\times10^{-4}~\mbox{pfu}\,\mbox{MeV}^{-1}\) for the HET 60 – 100 MeV channels, and \({\approx}\, 3.0\times10^{-4}~\mbox{pfu}\,\mbox{MeV}^{-1}\) for the combined HET 40 – 100 MeV channels of both STEREO-A and -B; these were subtracted from the measured intensities before the intercalibration analysis. The time resolution was one hour for all data sets. In the following, (the intensities of) the energy channels mentioned above are referred to as \(I_{\mathrm{ERNE}}\), \(I_{\mathrm{HET} 40\,\text{--}\,100~\text{MeV}}\), \(I_{\mathrm{HET} 40\,\text{--}\,60~\text{MeV}}\), and \(I_{\mathrm{HET} 60\,\text{--}\,100~\text{MeV}}\); the respective quiet-time background intensities have been subtracted.
The average and the standard deviation of the intensity ratio HET-A/HET-B during the period of interest are 1.09 and 0.09 for the 40 – 60 MeV channels, 0.92 and 0.11 for the 60 – 100 MeV channel, and 1.02 and 0.08 for the 40 – 100 MeV channel; these intensities, with the background intensities given above subtracted, are shown in Figure 21. The results suggest that the proton intensities measured in this energy range by both HETs usually differ by not more than some 20%, possibly less still in the 40 – 100 MeV combined channel, which enjoys better count statistics than its constituent channels during times of elevated particle flux. For this reason, an intercalibration between HET-A and HET-B was not considered necessary. In the following, the HET-A proton intensities are taken as representative of both HET-A and HET-B as regards any comparison with ERNE.
For the purpose of the intercalibration, a linear combination of \(I_{\mathrm{HET} 40\,\text{--}\,60~\text{MeV}}\) and \(I_{\mathrm{HET} 60\,\text{--}\,100~\text{MeV}}\) was defined as follows:
where \(a\) is a parameter within the range \([0,1]\). Choosing \(a\) so that \(I_{\mathrm{HET},\mathrm{lin}}\) coincides as closely as possible with \(I_{\mathrm{ERNE}}\) and then comparing the uncorrected maximum intensities in \(I_{\mathrm{HET} 40\,\text{--}\,100~\text{MeV}}\) with \(I_{\mathrm{HET},\mathrm{lin}}\) gives a coarse estimate of the measured intensity difference between ERNE and HET and, therefore, of the intercalibration factor. Minimizing the sum of the squares of the quantity \(\log_{10}(I_{\mathrm{ERNE}}) - \log_{10}(I_{\mathrm{HET},\mathrm{lin}})\) over the time range of interest suggests that \(I_{\mathrm{HET},\mathrm{lin}}\) and \(I_{\mathrm{ERNE}}\) coincide best when \(a \approx 0.78\). However, it must be emphasized that this result is strictly applicable only to periods of moderate, decreasing proton intensities. The intensities \(I_{ \mathrm{HET},\mathrm{lin}}\) and \(I_{\mathrm{ERNE}}\), with \(a = 0.78\), are shown in Figure 22 for the comparison period.
To study the effects of this correction briefly, the peak intensities of the events considered in this work were determined using both \(I_{\mathrm{HET},\mathrm{lin}}\) and \(I_{\mathrm{HET} 40\,\text{--}\,100~\text{MeV}}\), with \(a\) set to 0.78. The maximum intensity values derived from \(I_{\mathrm{HET},\mathrm{lin}}\) are between 1.3 and 2.2 times greater than those derived from \(I_{\mathrm{HET} 40\,\text{--}\,100~\text{MeV}}\), which implies that the intercalibration factor for the ERNE and HET high-energy proton channels of interest would also lie approximately in this range.
A visual inspection of ERNE and HET data recorded in December 2006 confirms that \(I_{\mathrm{ERNE}}\) and \(I_{\mathrm{HET} 40\,\text{--}\,100~\text{MeV}}\) typically agree to within a factor of \({\approx}\,2\) during periods of clearly enhanced proton flux and good data coverage. The only notable exceptions to this are the short, very high intensity spike in HET data on 12 December 2006 and a period of about 24 hours during the decay phase of the 13 December 2006 event. ERNE did not detect anything corresponding to the first feature, but in contrast appears to have resolved some structure not readily visible in the 1-hour-averaged HET data in the latter case. Such discrepancies are likely to be due to local structures in the proton flux.
Considering the fact that when widely separated, SOHO and the STEREOs encounter different particle populations, a precise proton intensity intercalibration between ERNE and the HETs would be, in general, not possible. For this reason, it was not pursued here any further and the measured proton intensity values are reported and analysed as such for each observing spacecraft, without applying any correction. In the light of the results presented above, it nevertheless does not seem unreasonable to expect that the measured intensities are likely accurate and comparable to each other within a factor of \({\approx}\,2\) in most cases.
1.2 A.2 Electron Data Intercalibration
Approximate intercalibration factors were determined for STEREO/SEPT and ACE/EPAM omnidirectional electron intensities. The decay phases of two small electron events in late May of 2007 – during which STEREO-A and -B were separated from the Earth by \({\approx}\,6^{\circ}\) and \({\approx}\,3^{\circ}\), respectively – were chosen for comparison and the data points selected from the approximate time of intensity maximum onward until the 0.165 – 0.335 MeV electron intensity recorded by SEPT-A fell below \(10~\mbox{pfu}\,\mbox{MeV}^{-1}\). Since electron intensities are usually more isotropic during the event decay than the onset and peak phases (see e.g. Dresing et al., 2014), only the decay phases were investigated to minimise the effect of differing instrument responses due to particle flux anisotropies. SEPT intensities were separately examined in two energy ranges, 0.165 – 0.335 MeV and 0.195 – 0.335 MeV, to compensate for the imperfect match between the energy bins of SEPT and EPAM. After visually estimated quiet-time background intensities were subtracted (\(2.0~\mbox{pfu}\,\mbox{MeV}^{-1}\) for SEPT-A and -B in both energy ranges, \(8.0~\mbox{pfu}\,\mbox{MeV}^{-1}\) for EPAM LEFS60, \(20.0~\mbox{pfu}\,\mbox{MeV}^{-1}\) for EPAM DE30), the data were smoothed with 15-minute sliding average.Footnote 6
SEPT-A and SEPT-B were considered first. Since the average difference of their intensities was less than 2% in both energy ranges during the period of interest, no intercalibration between them was regarded as necessary. However, the averages and standard deviations of the SEPT-A/EPAM (LEFS60) and the SEPT-A/EPAM (DE30) intensity ratios were next determined, respectively, as \(0.96 \pm 0.10\) and \(0.74 \pm 0.12\) for the SEPT 0.165 – 0.335 MeV energy range and as \(0.72 \pm 0.10\) and \(0.56 \pm 0.10\) for the SEPT 0.195 – 0.335 MeV energy range. Based on these results, the intercalibration factor was selected as 0.84 for EPAM LEFS60 and 0.65 for EPAM DE30, these being the mean values of the averages given above for each EPAM data type. It must be noted that, as in the case of protons, explained in Section 2.1, these factors are fully applicable only when moderate and decreasing electron fluxes are being observed.
Figures 23, 24, and 25 demonstrate the intensity intercalibration process for electron data. Figure 23 shows the data with background intensity subtracted for SEPT-A and SEPT-B in the energy ranges 0.165 – 0.335 MeV (upper panel) and 0.195 – 0.335 MeV (lower panel); Figure 24 shows a comparison between SEPT-A 0.165 – 0.335 MeV intensity with EPAM LEFS60 and DE30 intensity (upper panel) and SEPT-A 0.195 – 0.335 MeV intensity with the same EPAM data (lower panel), all with background intensity subtracted; and finally, Figure 25 displays the same data as Figure 24 but with the intercalibration factors applied to both EPAM data types.
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Paassilta, M., Papaioannou, A., Dresing, N. et al. Catalogue of \({>}\,55\) MeV Wide-longitude Solar Proton Events Observed by SOHO, ACE, and the STEREOs at \({\approx}\,1\) AU During 2009 – 2016. Sol Phys 293, 70 (2018). https://doi.org/10.1007/s11207-018-1284-7
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DOI: https://doi.org/10.1007/s11207-018-1284-7