The Solar Energetic Particle Event of 14 December 2006

Abstract

ations in the particle intensity that occurred during the first few hours. These fluctuations were observed inside a magnetic cloud that originated in a solar event on 13 December and show both similarities and variations at the different spacecraft. Interestingly, the most striking difference is between observations at the two closely-separated STEREO spacecraft. In particular, large fluctuations in the proton intensity were seen by the High Energy Telescope (HET) on STEREO A, and to a lesser extent at Wind and ACE, but not by the STEREO B HET. We conclude that the differences in intensity-time profiles were caused by anisotropies in the particle distribution and the different viewing directions of the individual particle telescopes. The intensity/anisotropy variations suggest that flux tubes with different particle propagation conditions existed within this magnetic cloud despite the absence of local magnetic field signatures associated with these regions. The intensity fluctuations are similar to those occasionally seen in impulsive particle events. There were also spacecraftto-spacecraft differences during the onset of the particle event. An initial rapid onset of energetic (> 40 MeV) protons was observed by the STEREO A and B spacecraft outside the magnetic cloud, but not by spacecraft such as SOHO that were already inside the magnetic cloud at this time. The latter spacecraft observed a slower, lower intensity increase. Evidently, energetic proton propagation from the solar event to the vicinity of Earth was inhibited within the magnetic cloud compared to outside.

Particle Acceleration in Two Converging Shocks∗

“…The distances of all these spacecraft from the Sun −Earth line were within 50R e along the Y GSE and Z GSE directions (Liu et al 2008). According to the WIND magnetic cloud list (https://wind.nasa.gov/mfi/mag_cloud_CA1.html), the 2006 December 13 shock event originated from the western hemisphere of the Sun with an interplanetary "magnetic cloud" axis orientation with a latitude of q =  27 and a longitude of f =  85 in GSE coordinates (von Rosenvinge et al 2009). From the perspective of the WIND, SOHO, ACE, and STEREO spacecraft, the observed CME-driven shock is a quasi-parallel diffusive shock, so their observations provided an example of a quasi-parallel shock interacting with the Earth's bow shock.…”

Interplanetary Propagation of Solar Energetic Particle Heavy Ions Observed at 1 Au and the Role of Energy Scaling

“…Although it would take observations from many spacecraft to fully understand the structures responsible for this behavior, we ascribe them to anisotropies and/or changing magnetic connection to the acceleration region. These cause the ACE instruments to sample different portions of the pitch angle distribution, or regions of the accelerating region that have different though closely related intensities (for discussions of these effects in SEP events observed with multiple spacecraft, see von Rosenvinge et al 2009;Chollet et al 2010b). Intensity changes of this type have been observed in both electrons and ions and although they are sometimes correlated with changes in the local IMF, often that is not the case (Anderson & Dougherty 1986;Mazur et al 2000;Chollet & Giacalone 2008).…”

A current sheet traced from the Sun to interplanetary space

“…1 show the magnitude of the magnetic field and the three components B x , B y , and B z , in Geocentric Solar Magnetospheric, or GSM, coordinates. Combined Panels (a), (b) and (c), the CMErelated MC (gray interval "4") are said to have begun at about 22:40 UT on December 14 and connected to the Sun as indicated by BDEs (see also Liu et al 2008;Rosenvinge et al 2009). The magnetic structures between the shock sheath and the MC that also connected to the Sun as indicated by the BDEs were interpreted as signatures of nested magnetic loops overlying the MC flux rope by Gosling et al (1987).…”