Coronal and interplanetary transport of solar energetic protons and electrons

G. Wibberenz, K. Kecskeméty, H. Kunow, A. Somogyi, B. Iwers, Yu I. Logachev, V. G. Stolpovskii

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Abstract

We present a new method to separate interplanetary and coronal propagation, starting from intensity variations observed by spaceprobes at different heliolongitudes. In general, a decrease in absolute intensities is observed simultaneously with an increase in temporal delays. The coupling of these two effects can be described by Reid's model of coronal diffusion and can in principle be used to determine the two coronal time constants, diffusion time tc and escape time A. In addition, a least-squares fit method is used to determine the parameters of interplanetary transport, assuming a radial dependence as λ(r) = λ0(r/1 AU)b. The method is applied to the two solar events of 27 December, 1977 and 1 January, 1978 which were observed by the spaceprobes Helios 1, Helios 2, and Prognoz 6. Energetic particle data are analysed for 13-27 MeV protons and ∼-0.5 MeV electrons. For the regions in space encountered during these events the mean free path of electrons is smaller than that of protons. Straight interpolation between the two rigidities leads to a rather flat rigidity dependence λ(P) ∼ Pn with n = 0.17-0.25. This contradicts the prediction of a constant mean free path or of the transition to scatter-free propagation below about 100 MV rigidity. In three of the four cases the mean free path of 13-27 MeV protons is of the order 0.17 AU, the mean free path of electrons of the order 0.06 AU. For protons we find b ∼- 0.7 for the exponent of the radial variation. The concept of two different coronal propagation regimes is confirmed. It is remarkable that in both regimes electrons are transported more efficiently than protons. This holds for the temporal delay as well as for the amplitude decrease. This is in contrast with the long existing concept of 'rigidity independent transport' and puts severe limits to any model of coronal transport. For the December event all three spaceprobes are in the fast propagation regime up to an angular distance of 62°. For protons we find a finite delay even in the fast propagation region, corresponding to a coronal delay rate of about 0.8 hr rad-1 up to 60° angular distance. In contrast, relativistic electrons may reach this distance within a few minutes. The fast transport of electrons and the different behaviour of electrons and protons is in contradiction to the expanding bottle concept. An explanation of coronal transport by shock acceleration directly on open field lines could in principle work in case of protons in the fast propagation region, but would fail in case of the electrons. The fast and efficient transport of electrons is most likely due to a region of field lines extending over a wide range of longitudes directly from the active region into interplanetary space. The much slower transport of both particle types at large azimuthal distances can neither be explained by direct access to open field lines not by the direct shock acceleration concept. A possible explanation is the loop reconnection model in a modified version, allowing for a faster lateral transport of electrons.

Original languageEnglish
Pages (from-to)353-392
Number of pages40
JournalSolar Physics
Volume124
Issue number2
DOIs
Publication statusPublished - Sep 1 1989

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Wibberenz, G., Kecskeméty, K., Kunow, H., Somogyi, A., Iwers, B., Logachev, Y. I., & Stolpovskii, V. G. (1989). Coronal and interplanetary transport of solar energetic protons and electrons. Solar Physics, 124(2), 353-392. https://doi.org/10.1007/BF00156275