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Sounding rocket measurements of decameter structures in the cusp

SD2011. Sounding rocket measurements of decameter structures in the cusp. K. Oksavik 1 , J. Moen 1,2 , D. A. Lorentzen 1 , F. Sigernes 1 , T. Abe 3 , Y. Saito 3 , and M. Lester 4 1) UNIS, Longyearbyen, Norway 2) Department of Physics, Univ. Oslo, Oslo, Norway

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Sounding rocket measurements of decameter structures in the cusp

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  1. SD2011 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, Norway 2) Department of Physics, Univ. Oslo, Oslo, Norway 3) ISAS, Japan Aerospace Exploration Agency, Japan 4) Department of Physics & Astronomy, Univ. Leicester, UK

  2. Photo: Martin Langteigen 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

  3. The ICI-2 trajectory

  4. Comparing rocket and EISCAT measurements during flight ICI-2 reveals fine structure in the electron density

  5. 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 ICI-2 flew through the F-region

  6. 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

  7. Decameter scale irregularities were observed 10-20% electron density gradients over a distance of a few tens of meters

  8. 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]

  9. 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

  10. 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!

  11. 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

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