Correlated Pc4-5 ULF waves, whistler-mode chorus and pulsating aurora observed by the Van Allen Probes and ground-based systems

Friday, 18 December 2015
Poster Hall (Moscone South)
Allison N Jaynes1, Marc Lessard2, Kazue Takahashi3, Ashar Ali4, David Malaspina5, Robert Michell6, Emma Spanswick7, Daniel N. Baker4, J Bernard Blake8, Christopher M Cully7, Eric Donovan7, Craig Kletzing9, Geoffrey D Reeves10, Marilia Samara11, Harlan E. Spence12 and John R Wygant13, (1)University of Colorado at Boulder, LASP, Boulder, CO, United States, (2)University of New Hampshire Main Campus, Durham, NH, United States, (3)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (4)University of Colorado at Boulder, Boulder, CO, United States, (5)University of Colorado, Boulder, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (6)University of Maryland College Park, College Park, MD, United States, (7)University of Calgary, Calgary, AB, Canada, (8)Aerospace Corporation Santa Monica, Santa Monica, CA, United States, (9)University of Iowa, Iowa City, IA, United States, (10)Los Alamos National Laboratory, Los Alamos, NM, United States, (11)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (12)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (13)University of Minnesota Twin Cities, Minneapolis, MN, United States
Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch-angle scattering of 10's keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and 10's keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4-5 compressional pulsations and modulation of whistler-mode chorus using THEMIS.

In the current study, we present simultaneous in-situ observations of structured chorus waves and an apparent field line resonance (in the Pc4-5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4-5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth's atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. Such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades, and may be a result of nonlinear chorus wave interactions in the equatorial region. This work illustrates the significant understanding of magnetospheric processes that can be gained through use of conjunctive ground- and space-based observations.