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Resolute Bay, Nunavut

Resolute Bay, Nunavut. Auroral Radio Emission Sources: Possible Sources of Radar Backscatter?. James LaBelle Department of Physics and Astronomy Dartmouth College SuperDARN workshop Hanover, New Hampshire May 31, 2011. 02/18/1995 Arviat, Nunavut.

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Resolute Bay, Nunavut

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  1. Resolute Bay, Nunavut Auroral Radio Emission Sources: Possible Sources of Radar Backscatter? James LaBelle Department of Physics and Astronomy Dartmouth College SuperDARN workshop Hanover, New Hampshire May 31, 2011

  2. 02/18/1995 Arviat, Nunavut Frequency (kHz) Universal Time AURORAL ROAR EMISSION 3fce Emission (4-4.5 MHz) 2fce Emission (near 3 MHz) AURORAL MF-BURST AURORAL MF-BURST EMISSION

  3. Resonance frequencies vs altitude in the ionosphere

  4. 70-79o invariant, 300 km From: John Hughes’s PhD Thesis (2000)

  5. Z-mode Cyclotron maser resonance mechanism 2 2 v +v || T 50 0 v-perp [x 103 km/s] -50 w – sw (1-v /c ) - k v = 0 2 2 At right: Measured electron distribution function, with Z-mode cyclotron maser resonance condition for two selected frequencies superposed (courtesy S.R. Bounds and C.A. Kletzing, University of Iowa)Condition for spontaneous emission:f @ fuh@ 2fce  Ellipse in v -v space || || ce || T s=1,2,3,… v-parallel [x 103 km/s] -50 0 50 fuh=2.65 fce=1.35 2.65 MHz s=2 s=2 2.66 MHz

  6. Growth Rate (g/wce) Wavenumber (kc/wce) kc/wce ~ 24  l ~ 4 m kc/wce ~ 8  l ~ 12 m Wavelength is correct for superDARN, but: is the backscatter freq offset by ~3 MHz? log10(g/wce) Calculations courtesy of P. Yoon Yoon et al., J. Geophys. Res., 103(A3), 4071, 1998 (wpe/wce)

  7. Resonance frequencies vs altitude in the ionosphere

  8. Churchill, Manitoba [from: Shepherd et al., 1999]

  9. 1. AURORAL ELECTRONS UPPER HYBRID fuh=2fce OR 3fce  DISCRETE EIGENMODES Z-MODE CYCL MASER DUE TO INHOMOGENEITY (mode conversion) 2. MODE CONVERSION  STRUCTURED O-MODE WAVES ESCAPE RADIO

  10. Radar backscatter [from: Yoon, Weatherwax, LaBelle, 2000]

  11. fuh@2fce 272 274 276 278 280 282 284 Time After Launch (seconds) (expanded view) (expanded view) [from: Samara, LaBelle, Kletzing, and Bounds, 2004]

  12. 02/18/1995 Arviat, Nunavut Frequency (kHz) Universal Time Auroral Roar 3fce Emission (4-4.5 MHz) 2fce Emission (near 3 MHz) MF-burst Emission

  13. Auroral Roar Auroral MF Burst Relatively low energy electron beam (~ hundreds of eV) Lowest frequency > L-cutoff at F-peak and > fpe E-peak Highest frequency < fpe F-peak MFB on poleward edge of expanding substorm aurora Requires low energy  consistent with Alfvenic electron beam “wave aurora” at poleward edge

  14. Vbeam Electron plasma Frequency (=3.30 f_ce In this case) Upper Hybrid Frequency (=3.45 f_ce In this case) Langmuir- Z-mode Electron gyrofrequency Wavelength l >/~ fpe/vbeam = 10 m (assuming fpe~2 MHz, Ebeam~1 keV) Dispersion Surfaces (from Andre, 1985)

  15. Auroral roar emissions Narrowband, ~3, 4.5 MHz sources are upper hybrid waves sources believed to be standing waves wavevector perp to B, l ~ 4-12 m source altitude near 300 km  good candidate for superDARN scatter? frequency offset! Auroral MF burst emissions Broadband ~1.5-4.5 MHz sources believed to be Langmuir waves? sources believed to be propagating waves wavevector parallel to B, l~10-20 m source altitude 300-500 km  must look up the field line related to ISR plasma lines or NEIALs?

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