Dependence of Energetic Storm Particle Heavy Ion Peak Intensities and Spectra on Source CME Longitude and Speed

We examine variations in energetic storm particle (ESP) heavy ion peak intensities and energy spectra at CME-driven interplanetary shocks. We focus on their dependence with heliolongitude relative to the source region of their associated CMEs, and with CME speed, for events observed in Solar Cycle 24 at the STEREO-A, STEREO-B, and/or ACE spacecraft. We find that observations of ESP events at 1 au are organized by longitude relative to their CME solar source. The ESP event longitude distribution also showed organization with CME speed. The near-Sun CME speeds (V ( i )) for these events ranged from similar to 560 to 2650 km s(-1) while the average CME transit speeds to 1 au were significantly slower. The angular width of the events had a clear threshold at V ( i ) of similar to 1300 km s(-1), above which events showed significantly larger angular extension compared to events with speeds below. High-speed events also showed larger heavy ion peak intensities near the nose of the shock compared to the flanks while their spectral index was smaller near the nose and larger near the flanks. This organization for events with V ( i ) < 1300 km s(-1) was not as clear. These ESP events were observed over a narrower range of longitudes though the heavy ion peak intensities still appeared largest near the nose of the shock. Their heavy ion spectra showed no clear organization with longitude. These observations highlight the impact of spacecraft position relative to the CME source longitude and V ( i ) on the properties of ESP events at 1 au.

Automated summary

We examined the variations in heavy ion peak intensities and energy spectra of energetic storm particles (ESP) at CME-driven interplanetary shocks. The observations showed dependence on heliolongitude relative to the source region of their associated CMEs and CME speed. We found that the organization of ESP events at 1 au is influenced by the longitude of their CME solar source and the speed of the CME. The observations also revealed that high-speed events have larger angular extension and heavier ion peak intensities near the nose of the shock. The study emphasizes the significance of spacecraft position relative to CME source longitude and CME speed in understanding the properties of ESP events at 1 au.