Comparison of the coronal mass ejection shock acceleration of three widespread SEP events during solar cycle 24

Abstract

We studied three solar energetic particle (SEP) events observed on 14 August 2010, 3 November 2011, and 5 March 2013 by Solar Terrestrial Relations Observatory (STEREO) A, B, and near‐Earth (L1) spacecraft with a longitudinal distribution of particles >90°. Using a forward modeling method combined with extreme ultraviolet and white‐light images, we determined the angular extent of the shock, the time and location (cobpoint) of the shock intersection with the magnetic field line connecting to each spacecraft, and compute the shock speed at the cobpoint of each spacecraft. We then examine whether the observations of SEPs at each spacecraft were accelerated and injected by the spatially extended shocks or whether another mechanism such as cross‐field transport is required for an alternative explanation. Our analyses results indicate that the SEPs observed at the three spacecraft on 3 November, STEREO B (STB) and L1 on 14 August, and the 5 March SEP event at STEREO A (STA) can be explained by the direct shock acceleration. This is consistent with the observed significant anisotropies, short time delays between particle release times and magnetic connection times, and sharp rises in the SEP time profiles. Cross‐field diffusion is the likely cause for the 14 August SEP event observed by STA and the 5 March SEPs observed by STB and L1 spacecraft, as particle observations featured weak electron aniotropies and slow rising intensity profiles. Otherwise, the wide longitudinal spread of these SEP increases would require an existence of a circumsolar shock, which may not be a correct assumption in the corona and heliosphere.

Source of Energetic Protons in the 2014 September 1 Sustained Gamma-ray Emission Event

“…In order to get the three-dimensional speed of the CME and shock, we used STEREO and SOHO observations to fit a 10 flux rope to the CME and a spheroid to the leading shock dome using the GCS model for the flux rope (Thernisien 2011) and the spheroidal model for the shock (Olmedo et al, 2013). The flux rope-shock model has been applied successfully to track the leading edges of CME events (Hess and Zhang, 2014;Mäkelä et al, 2015;Xie et al, 2017). Figure 5 shows the shock and flux rope fits to STEREO and SOHO coronagraph images at 11:10 UT and 11:12 UT, respectively.…”

Statistical Study on Multispacecraft Widespread Solar Energetic Particle Events During Solar Cycle 24

“…where I( ) is the intensity at a given pitch-angle direction and is the pitch angle cosine (see details in Xie et al, 2017). In Figure 4a, we can see a good correlation between DT and |CA| with a correlation coefficient of 0.70.…”

“…We use graduated cylindrical shell (GCS) FR model (Thernisien et al, 2009;Thernisien, 2011) plus oblate spheroid shock model combined with EUV and WL data from STA, STB, SOHO, and SDO to determine 3-D structures of CME shocks (Kwon et al, 2014;Xie et al, 2017). The GCS model is used to describe the FR-like CME structure which is constrained by CME components such as three-part structure or bright frontal loops in the WL images; the oblate spheroid is used to describe the shock front, which is constrained by EUV wave and wave-like disturbances in the WL images.…”

“…The GCS model is used to describe the FR-like CME structure which is constrained by CME components such as three-part structure or bright frontal loops in the WL images; the oblate spheroid is used to describe the shock front, which is constrained by EUV wave and wave-like disturbances in the WL images. The oblate spheroid shock model also has six free parameters: the heights of the spheroid nose and center h and h 0 , the length of the two semiprincipal axes (a, b), and longitude and latitude of the spheroid center (see details in Xie et al, 2017). The GCS model has three parameters defining the FR geometry (heliocentric height [h FR ], aspect ratio [ ], and half-width [ ], where FR edge-on width EO = 2 , = asin( ) and FR face-on width FO = 2( + )) and three parameters defining the FR orientation (longitude, latitude, and tilt angle of the FR; Thernisien et al, 2009).…”

“…The GCS model has three parameters defining the FR geometry (heliocentric height [h FR ], aspect ratio [ ], and half-width [ ], where FR edge-on width EO = 2 , = asin( ) and FR face-on width FO = 2( + )) and three parameters defining the FR orientation (longitude, latitude, and tilt angle of the FR; Thernisien et al, 2009). The oblate spheroid shock model also has six free parameters: the heights of the spheroid nose and center h and h 0 , the length of the two semiprincipal axes (a, b), and longitude and latitude of the spheroid center (see details in Xie et al, 2017). Table 1, Columns 11-13, list fit results: true shock speed v = dh∕dt, aspect radio , and half-width .…”