TY - JOUR
T1 - Fine scale structures of pulsating auroras in the early recovery phase of substorm using ground-based EMCCD camera
AU - Nishiyama, Takanori
AU - Sakanoi, Takeshi
AU - Miyoshi, Yoshizumi
AU - Kataoka, Ryuho
AU - Hampton, Donald
AU - Katoh, Yuto
AU - Asamura, Kazushi
AU - Okano, Shoichi
PY - 2012
Y1 - 2012
N2 - [1] We have carried out ground-based observations, optimized to temporal and spatial characteristics of pulsating auroras (PAs) in the micro/meso scale, using an electron multiplying charge coupled device (EMCCD) camera with a wide field of view corresponding to 100 × 100 km at an altitude of 110 km and a high sampling rate up to 100 frames per second. We focus on transient PAs propagating southward around 1100 UT, in the early recovery phase of the substorm, on 4th March 2011. Three independent patches (PA1-3) each with different periods between 4 and 7 s were observed, which means that the periodicity was not explained by the electron bounce motion and strongly depended on local plasma conditions in the magnetosphere or in the ionosphere. One more insight is that only PA1 had also a sharp peak of modulations around 1.5 Hz, with a narrow frequency width of 0.30 Hz, and the strong modulations existed as a small spot in the center of PA1. We have also conducted cross spectrum analysis and have obtained coherence and phase distributions for auroral variations between 0.1 and 3.0 Hz. The results indicated that low frequency variations from 0.2 to 0.5 Hz inside PA1-3 propagated as a collective motion in well-defined directions. The estimated horizontal propagation velocities ranged from 50 to 120 km/s at the auroral altitude. The velocities are almost consistent with the Alfven speed at the magnetic equator, which suggests that compressional waves have an effect on PA via modulations of the ambient plasma environment.
AB - [1] We have carried out ground-based observations, optimized to temporal and spatial characteristics of pulsating auroras (PAs) in the micro/meso scale, using an electron multiplying charge coupled device (EMCCD) camera with a wide field of view corresponding to 100 × 100 km at an altitude of 110 km and a high sampling rate up to 100 frames per second. We focus on transient PAs propagating southward around 1100 UT, in the early recovery phase of the substorm, on 4th March 2011. Three independent patches (PA1-3) each with different periods between 4 and 7 s were observed, which means that the periodicity was not explained by the electron bounce motion and strongly depended on local plasma conditions in the magnetosphere or in the ionosphere. One more insight is that only PA1 had also a sharp peak of modulations around 1.5 Hz, with a narrow frequency width of 0.30 Hz, and the strong modulations existed as a small spot in the center of PA1. We have also conducted cross spectrum analysis and have obtained coherence and phase distributions for auroral variations between 0.1 and 3.0 Hz. The results indicated that low frequency variations from 0.2 to 0.5 Hz inside PA1-3 propagated as a collective motion in well-defined directions. The estimated horizontal propagation velocities ranged from 50 to 120 km/s at the auroral altitude. The velocities are almost consistent with the Alfven speed at the magnetic equator, which suggests that compressional waves have an effect on PA via modulations of the ambient plasma environment.
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U2 - 10.1029/2012JA017921
DO - 10.1029/2012JA017921
M3 - Article
AN - SCOPUS:84868381877
SN - 2169-9380
VL - 117
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 10
M1 - A10229
ER -