This paper presents observations of electromagnetic ion cyclotron (EMIC) waves from multiple data sources during the four Geospace Environment Modeling challenge events in 2013 selected by the Geospace Environment Modeling Quantitative Assessment of Radiation Belt Modeling focus group: 17 and 18 March (stormtime enhancement), 31 May to 2 June (stormtime dropout), 19 and 20 September (nonstorm enhancement), and 23–25 September (nonstorm dropout). Observations include EMIC wave data from the Van Allen Probes, Geostationary Operational Environmental Satellite, and Time History of Events and Macroscale Interactions during Substorms spacecraft in the near-equatorial magnetosphere and from several arrays of ground-based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from low-altitude Polar Operational Environmental Satellite spacecraft. Each of these data sets provides only limited spatial coverage, but their combination shows consistent occurrence patterns and reveals some events that would not be identified as significant using near-equatorial spacecraft alone. Relativistic and ultrarelativistic electron flux observations, phase space density data, and pitch angle distributions based on data from the Relativistic Electron-Proton Telescope and Magnetic Electron Ion Spectrometer instruments on the Van Allen Probes during these events show two cases during which EMIC waves are likely to have played an important role in causing major flux dropouts of ultrarelativistic electrons, particularly near L* ~4.0. In three other cases, identifiable smaller and more short-lived dropouts appeared, and in five other cases, these waves evidently had little or no effect.
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We thank the referees for their helpful comments and corrections. We acknowledge the GEM Quantitative Assessment of Radiation Belt Modeling focus group for motivating this study. We thank David Sibeck and Kjellmar Oksavik for helpful comments, and Viacheslav Pilipenko for his assistance in obtaining the induction coil data from Russian observatories. Work at Augsburg University was supported by National Science Foundation grants PLR-1341493, AGS-1264146, and AGS-1651263, and work performed by M. J. E. at NASA/GSFC was supported by the Van Allen Probes mission. W. L. acknowledges support from NSF grant AGS-1723588, AFOSR grant FA9550-15-1-0158, and the Alfred P. Sloan Research Fellowship FG-2018-10936. Work performed by Q. M. was supported by the Van Allen Probes Mission via JHU/APL contracts 967399 and 921647. A. C. K. acknowledges support from NASA grant NNS16AG78G and NSF grant AGS-1552321. M. R. L. acknowledges support from NSF grant PLR-1341677. Research at the British Antarctic Survey was supported by the Natural Environment Research Council (NERC) Highlight Topic Grant NE/P01738X/1 (Rad/Sat) and National Capability funding grant NE/R016038/1. The authors thank I. R. Mann, D. K. Milling, and the rest of the CARISMA team for data. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency. The operation of STEL magnetometers at Magadan and Paratunka is made in collaboration with the Institute of Cosmophysical Researches and Radio Wave Propagation (IKIR), Far-Eastern Branch of the Russian Academy of Sciences. The operation at Athabasca is made in collaboration with the Athabasca University. K. S. is supported by JSPS KAKENHI 15H05815 and 16H06286. E. E. acknowledges support from Russian Foundation for Basic Research grant 18-05-00108. Van Allen Probes research at the University of Colorado, the University of Iowa, the University of Minnesota, the University of New Hampshire, UCLA, and the Aerospace Corporation was supported by NASA prime contract NAS5-01072 to The Johns Hopkins University Applied Physics Laboratory. We gratefully acknowledge use of NASA/GSFC’s Space Physics Data Facility’s OMNIWeb, SSCweb, and CDAWeb data. Van Allen Probes CDF data files are available at http://www.space.umn.edu/rbspefw-data/ and http://rbsp.space.umn.edu/ rbspdata/ (EFW), http://emfisis.physics. uiowa.edu/data/index (EMFISIS), and https://www.rbsp-ect.lanl.gov/science/ DataDirectories.php (REPT and MagEIS).