1 sounding rocket measurements of decameter structures in the cusp k. oksavik 1, j. moen 1,2, d. a....
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Sounding rocket measurements of decameter structures in the cusp
K. Oksavik1, J. Moen1,2 , D. A. Lorentzen1, F. Sigernes1, T. Abe3, Y. Saito3, and
M. Lester4
1) UNIS, Longyearbyen, Norway2) Department of Physics, Univ. Oslo, Oslo, Norway3) ISAS, Japan Aerospace Exploration Agency, Japan 4) Department of Physics & Astronomy, Univ. Leicester, UK
SD2011
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ICI-2 Sounding Rocket
• Launched at 10:35:10 UT on 05 December 2008
• Rocket instrumentation:– Four-Needle Langmuir
Probe (4-NLP):• Absolute Ne
– Electric Field Wave Experiment (EFW):
• E-field (AC and DC)
– Low Energy Particle spectrometer (LEP-ESA):
• Electrons 0.01-10 keV
• Ground optics, EISCAT and SuperDARN Photo: Martin Langteigen
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The ICI-2 trajectory
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Comparing rocket and EISCAT measurements during flight
ICI-2 reveals fine structure in the electron density
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ICI-2 flew through the F-region
• Several minutes were spent in the F-region• An auroral form was intersected on the up-leg,
and the cusp aurora was intersected on the down-leg
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ICI-2 flew through an area of HF backscatter in the cusp
On its down-leg ICI-2 intersected the poleward boundary of HF backscatter and cusp aurora
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Decameter scale irregularities were observed
10-20% electron density gradients over a distance of a few tens of meters
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Encountering HF backscatter
• Highly structured Ne• Inverted-V signatures• Fluctuating electron flux• Gradients in Ne at all
spatial scales (10 m, 100 m, and 1000 m)
• Gradient Drift instability is stable on the poleward side of the blob, and unstable on the equatorward side [Ossakow and Chaturvedi, 1979]
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Analysis of the entire flight:Kelvin-Helmholtz Instability (KHI)
• Highest growth rate around 200-230 s• 1-5 min. growth time of 4-6 km irregularities
LVKH 2.0
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Analysis of the entire flight:Gradient Drift Instability (GDI)
• Many occurrences of decameter scale gradients• Growth times often between 10 s and 1 min.• Gradient Drift Instability is dominant!
xN
NV
0
0GD
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Conclusions• ICI-2 made the first direct observation of HF backscatter
targets (decameter scale plasma density irregularities)• Km-scale irregularities were most likely modulated by
auroral particle precipitation onto which plasma instabilities can operate [Kelley et al., 1998]
• The plasma gradient on the poleward cusp boundary was stable to GDI growth, while the equatorward boundary was unstable
• GDI alone, working on km scale gradients, can explain the generation of HF backscatter targets, but other instability processes may also contribute
• The growth rate of the KHI mechanism was too slow to explain any of the observed plasma irregularities