SM41H-2575
Comparing Local-Time and Storm-Phase Distributions of EMIC Waves Observed by Van Allen Probes A, GOES-13, and Halley, Antarctica
Thursday, 17 December 2015
Poster Hall (Moscone South)
Mackenzie Ohnsted1, Mark J. Engebretson1, Jennifer L Posch1, Marc Lessard2, Howard J Singer3, Craig Kletzing4, Charles William Smith2 and Richard B. Horne5, (1)Augsburg College, Minneapolis, MN, United States, (2)University of New Hampshire Main Campus, Durham, NH, United States, (3)NOAA Boulder, Boulder, CO, United States, (4)University of Iowa, Iowa City, IA, United States, (5)British Antarctic Survey, Cambridge, United Kingdom
Abstract:
Electromagnetic ion cyclotron (EMIC) waves are expected to be highly efficient in depleting the ring current and in removing outer radiation belt electrons. However, the distribution of these waves in subauroral regions has not been well characterized. In this study we present 0-5 Hz magnetic field data from the Van Allen Probes A (RBSP A) spacecraft (in elliptical equatorial orbit with apogee at 5.8 R
E), 0-1 Hz data from GOES-13 (in geosynchronous orbit), and 0-5 Hz data from Halley, Antarctica (L ~4.6), during the first full local-time precession of the Van Allen Probes from October 2012 through July 2014. The considerably different hourly local time vs. L distributions observed point to distinct locations and geomagnetic activity-dependent patterns of EMIC wave activity. GOES-13 wave occurrences exhibited a broad peak in the noon-to-dusk sector. He
+ band events peaked near dusk, while H
+ band waves peaked near noon, with a secondary peak centered near dawn. More EMIC waves occurred during storm main phase in the He
+ band (5%) than in the H
+ band (1%), and 80% and 89% of the He
+ and H
+ band waves, respectively, occurred under late storm recovery or quiet conditions. During all storm phases the local time occurrence patterns of < 0.4 Hz and 0.4–1.0 Hz events at Halley resembled those of He
+ and H
+ band waves, respectively, at GOES-13. The relatively few wave events at Halley with f > 1.0 Hz occurred at all local times, but with a modest, broad peak near dawn. Roughly 90% of both the 1570 Halley events < 1.0 Hz and the 142 Halley events > 1.0 Hz occurred during late storm recovery and quiet conditions. Events during compressions at GOES-13 (10%), Halley (6%), and RBSP A (6%) peaked near local noon, but with a secondary peak near midnight. Waves observed by RBSP A were distributed rather evenly in local time in all L shell ranges between 3 and 6, and the percentage occurring during late storm recovery or quiet conditions was only 65%. We interpret the difference in event occurrence during these latter storm phases between GOES-13 and RBSP A to be a function of the L dependence of the injection boundary and plasmapause on magnetic activity, and their frequency-dependent occurrence at Halley to be evidence of horizontal ducting.
