Erratum to: Solar Phys (2016) 291:1225–1239 DOI 10.1007/s11207-016-0877-2

An error has been found in the paper by Mishev and Usoskin (2016) that is related to the presentation of Figure 6, which depicts the computed neutron monitor (NM) asymptotic directions during GLE 70 on 13 December 2006 and the apparent direction of the interplanetary magnetic field (IMF) at 03:00 UT as derived from the ACE satellite measurements. We note that the latter (the apparent position of the IMF direction) is incorrectly shown in the figure, with no consideration of the propagation time between the L1-point, where the ACE spacecraft is located, and the Earth’s location. Moreover, the instant value of IMF was taken, without averaging for the period of gyration of energetic particles.

The correct IMF position has been recalculated, allowing for the propagation time and with a proper 20 min averaging. The correct IMF position near Earth at 03:00 UT on 13 December 2006 is \({\approx}\,30^{\circ}\mbox{S}\) and \({\approx}\,110^{\circ}\mbox{E}\), which is different from that shown in Figure 6 (about \(30^{\circ}\) by latitude and \(20^{\circ}\) by longitude) and is in good agreement with Figure 2 in Bütikofer et al. (2009). The corrected Figure 6 is shown as Figure 1 here.

Figure 1
figure 1

Calculated NM asymptotic directions during GLE 70 on 13 December 2006. The cross represents the direction of interplanetary magnetic field (IMF) derived from the ACE satellite measurements considering the time needed to propagate between the L1 point and the location of Earth and averaged for the period of gyration of energetic particles. The small circle represents the derived apparent source position. The lines of equal pitch angles relative to the derived anisotropy axis are plotted for 30∘, 60∘, 120∘, and 150∘. The asymptotic directions of polar NMs are plotted with solid lines, while mid-latitude NMs are plotted with dashed lines.

Full size image

We have checked that this error does not affect the main results of the article (reconstruction of the energy spectra and pitch-angle distribution) since the erroneous IMF position was used only as the first guess for the iterative fitting procedure, and the final result of the fit remains unaltered. Accordingly, the derived rigidity spectra and anisotropy characteristics shown in Figure 7 and summarized in Table 2 are correct.