THEMIS observations of electron cyclotron harmonic emissions, ULF waves, and pulsating auroras

We present multiprobe, multi‐instrument observations of the electron cyclotron harmonic (ECH) emissions and ultralow‐frequency (ULF) waves from Time History of Events and Macroscale Interactions during Substorms (THEMIS) and explore their potential linkage to the concurrent ground‐observed pulsating...

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Published inJournal of Geophysical Research: Space Physics Vol. 115; no. A10
Main Authors Liang, Jun, Uritsky, V., Donovan, E., Ni, B., Spanswick, E., Trondsen, T., Bonnell, J., Roux, A., Auster, U., Larson, D.
Format Journal Article
LanguageEnglish
Published Washington, DC Blackwell Publishing Ltd 01.10.2010
American Geophysical Union
Subjects
Atmospheric sciences
Earth sciences
Earth, ocean, space
ECH emission
Exact sciences and technology
Magnetism
Plasma physics
pulsating aurora
Space
ULF wave
Electron flux
wavelength
waves
time scales
Pitch angle
Relativistic electron
Ultralow frequency
Phase analysis
spatial distribution
in situ
Cyclotron harmonic
intensity
Fine structure
Pulsating aurora
instruments
Neutral sheet
Plasma layer
Diffusion
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Summary:We present multiprobe, multi‐instrument observations of the electron cyclotron harmonic (ECH) emissions and ultralow‐frequency (ULF) waves from Time History of Events and Macroscale Interactions during Substorms (THEMIS) and explore their potential linkage to the concurrent ground‐observed pulsating auroras (PsA) on 4 January 2009. The ECH emissions were observed as discrete packets modulated by the ULF flapping motion of the neutral sheet around the probes. Combining different data sets of the ECH observations, we infer that the ECH emission intensities were strongly fluctuating and contained multi‐time scale fine structures. The distribution of PsA patches featured longitudinal “wavelength” in concert with the in situ ULF wave characteristics inferred from a cross‐phase analysis. The overall activeness of the PsA correlated with the in situ‐measured energetic electron fluxes and ECH wave intensities. We suggest that ECH waves played the key role in the pitch angle diffusion of the plasma sheet electrons that led to the PsA, while the ULF waves structured the plasma sheet and imposed a macroscopic effect over the spatial distribution of the PsA.
Bibliography:ArticleID:2009JA015148
ark:/67375/WNG-13BZ19P4-C
Tab-delimited Table 1.Tab-delimited Table 2.Animation 1. The aurora images in 3 s cadence from THEMIS all-sky imager (ASI) observations at Fort Simpson (FSIM) and Fort Smith (FSMI) during 1000-1230 UT, 4 January 2009. The images are presented in altitude-adjusted corrected geomagnetic coordinates. An emission height of 110 km is adopted, determined from a matching between the substorm expansion bulges seen in two ASIs. The ionospheric projections of three THEMIS probes, TH-A (red), TH-D (green) and TH-E (blue), are shown as color asterisks; they gradually entered the FoV of FSMI ASI after ∼1125 UT. In this paper we particularly focus on the PsA activity during 1130-1150 UT, when the THEMIS probes had moved closer to the PsA regions of interest and detected enhanced energetic electron fluxes and strong ECH wave intensity (see ). The auroral fluctuations of one representative patch structure bound by a red box shown in the animation during this interval were sampled and are demonstrated in .
istex:10ED469C57B1854A24EDE8FB508C8062066B5C6F
ISSN:0148-0227
2169-9380
2156-2202
2169-9402
DOI:10.1029/2009JA015148