A Caltech Library Service

The Ground Level Enhancement Event of September 2017 and Other Large Solar Energetic Particle Events of Cycle 24

Cohen, C. M. S. and Mewaldt, R. A. (2018) The Ground Level Enhancement Event of September 2017 and Other Large Solar Energetic Particle Events of Cycle 24. Space Weather, 16 (10). pp. 1616-1623. ISSN 1542-7390.

[img] PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


The 10 September 2017 solar energetic particle (SEP) event was the largest since June 2015 and one of only two ground‐level enhancement (GLE) events of solar cycle 24. GLE events are subset of large SEP events (~15% of events identified by Space Weather Prediction Center) with particularly hard spectra, making them a substantial space weather hazard to space‐based instrumentation and exposed astronauts. We present analysis of the 10 September 2017 event and compare it to the other cycle 24 GLE events, to those of cycle 23, and also to two extreme SEP events observed by Solar Terrestrial Relations Observatory (STEREO). We find the 10 September 2017 event had a broken power law spectrum typical of GLE events but was softer than average at high energies. However, it was hard at low energies with a relatively high break energy, which led to 100‐MeV proton fluences within a factor of 4.5 of the largest cycle 23 GLE events. The composition was nominal, except for a low Fe/O ratio, which has also been seen in large SEP events this cycle, but is somewhat atypical of the cycle 23 GLE events. The extreme events seen by STEREO exhibited very hard high‐energy spectra, with one event producing ~80‐MeV proton fluences larger than the largest cycle 23 GLE event. However, even including STEREO events, the top 10 largest cycle 24 events are, on average, 2.4 times smaller than the top 10 of cycle 23 based on >10‐MeV proton fluences.

Item Type:Article
Related URLs:
URLURL TypeDescription
Cohen, C. M. S.0000-0002-0978-8127
Mewaldt, R. A.0000-0003-2178-9111
Additional Information:© 2018 American Geophysical Union. Received 6 JUL 2018; Accepted 2 OCT 2018; Accepted article online 10 OCT 2018; Published online 29 OCT 2018. We are very grateful to Ingmar Sandberg for providing updated estimates of the effective energies for GOES‐8, GOES‐11, and GOES‐13, and for discussions on their use. This work was supported by NSF grants 1156004 and 1156138 and NASA grants NNX11075G, 80NSSC18K0223, and NNX15AG09G. The GOES 8‐15 particle data are produced in real time by the NOAA Space Weather Prediction Center (SWPC) and are distributed by the NOAA National Geophysical Data Center (NGDC). The ACE data are available through the ACE Science Center (, and the STEREO data are available through the STEREO SEP Suite data pages ( The SOHO/EPHIN data are available at www2.physik.uni‐ and the SAMPEX/PET data can be accessed at and
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Issue or Number:10
Record Number:CaltechAUTHORS:20181011-131543573
Persistent URL:
Official Citation:Cohen, C. M. S., & Mewaldt, R. A. (2018). The ground‐level enhancement event of September 2017 and other large solar energetic particle events of cycle 24. Space Weather, 16, 1616–1623.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90251
Deposited By: Tony Diaz
Deposited On:11 Oct 2018 20:25
Last Modified:03 Oct 2019 20:23

Repository Staff Only: item control page