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Electromagnetic and Electrostatic Ion Cyclotron Waves in Auroral Kilometric Radiation

Explore the fine structure of Auroral Kilometric Radiation (AKR) and the evidence supporting electromagnetic and electrostatic ion cyclotron waves. This seminar presented in October 2004 by R.L. Mutel and D. Menietti from the University of Iowa delves into dynamic AKR bursts, AKR source regions, and innovative Wideband Data Plasma Wave Instrument (WBD). Learn about AKR burst positions, VLBI source location algorithms, and refractive effects affecting AKR burst determinations. Discover the intricacies of AKR burst locations and uncertainties through detailed analyses and visualizations.

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Electromagnetic and Electrostatic Ion Cyclotron Waves in Auroral Kilometric Radiation

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  1. Fine Structure in Auroral Kilometric Radiation: Evidence for Electromagnetic and Electrostatic Ion Cyclotron Waves R. L. Mutel (& D. Menietti) University of Iowa Astrophysics Seminar October 2004

  2. Earth as a radio source UI Space/Astro Seminar October 2004

  3. AKR is generated 6000-12000 km above the visible aurora AKR is generated at f = ωce by electron cyclotron maser UI Space/Astro Seminar October 2004

  4. Dynamic Spectra of Common AKR Bursts Geotail Cluster UI Space/Astro Seminar October 2004

  5. May 15 AKR Event: Variation with Magnetic Latitude m = -53° m = -38° m = -32° UI Space/Astro Seminar October 2004

  6. Example of WBD Dynamic Spectra (250-262 KHz, 30 sec), S/C separation ~300 km Auroral Kilometric Radiation (AKR) Bursts Spacecraft 1 3 4 UI Space/Astro Seminar October 2004

  7. FAST Observations of AKR Source Region (Ergun et al. Ap. J. 538, 456) Note e- depletion in auroral cavity UI Space/Astro Seminar October 2004

  8. FAST Observations of AKR Source Region (Ergun et al. Ap. J. 538, 456) Shell instability UI Space/Astro Seminar October 2004

  9. University of Iowa Wideband Data Plasma Wave Instrument (WBD) • Identical WBD instruments are mounted on all four spacecraft. Single dipole antenna used. • Real-time downlink of 220 kb/s to the NASA Deep Space Network (DSN). (One DSN antenna per S/C!) • DSN provides real-time time stamps (accuracy 10 s). • AKR studies use 125, 250, and 500 KHz bands, 10 KHZ bandwidth, 37 s sampling time. • High frequency/time resolution capability of WBD is the primary characteristic that makes WBD unique from the other Cluster wave experiments, which operate at much lower data rates. UI Space/Astro Seminar October 2004

  10. VLBI Source Location Algorithm: Differential delay measurement UI Space/Astro Seminar October 2004

  11. Sample Dynamic Spectrum, Waveform and Cross-correlation Waveforms from each Cluster WBD receiver for AKR burst shown at left Peak is fit with Gaussian, delay uncertainty  ~ 0.3 ms UI Space/Astro Seminar October 2004

  12. AKR Burst Position search algorithm • A uniform 3-d grid of points is constructed centered on the Earth with spacing 0.1 Re and dimension 8 Re on each side (512,000 pts). • The propagation time to each satellite is computed from each grid point. • Differential delays are then computed for each baseline and compared with the observed delays, as measured by cross-correlating the waveforms from each pair of spacecraft UI Space/Astro Seminar October 2004

  13. VLBI position uncertainty calculation Delay uncertainties in plane  and parallel to line of sight: Typical uncertainty in  plane: Typical uncertainty in plane: UI Space/Astro Seminar October 2004

  14. Uncertainty ~ 500 km -1000 km Uncertainty mapped to Earth (CGM coordinates) Uncertainty ~ 200 km -400 km UI Space/Astro Seminar October 2004

  15. Refractive effects effect on AKR burst location determination unimportant for S/C magnetic latitudes > 40°(plasmasphere model Gallagher et al.2000) UI Space/Astro Seminar October 2004

  16. Refractive Ray tracing corrections UI Space/Astro Seminar October 2004

  17. AKR Bursts: Locus of Allowed Locations • Locus of allowed locations for AKR burst on 10 July 2002 at 08:47:02 and illustrated at right. • The top panels show the unconstrained solution of all allowed points (left is oblique view; right view is from spacecraft). • The lower panel shows the constrained solution assuming the AKR emission arises from a radius distance from Earth consistent with the observed frequency being identified with the electron gyrofrequency. A model auroral oval is shown for reference. UI Space/Astro Seminar October 2004

  18. AKR Burst Locations: The movie UI Space/Astro Seminar October 2004

  19. Summary of 4 Spacecraft VLBI Epochs (Fully Analyzed) UI Space/Astro Seminar October 2004

  20. November 9 Locations: Varying Perspectives (Animation) UI Space/Astro Seminar October 2004

  21. Nov 9 :The Movie Mapped onto CGM coordinates UI Space/Astro Seminar October 2004

  22. Observed distribution of AKR bursts UI Space/Astro Seminar October 2004

  23. AKR Burst locations vs. UI Space/Astro Seminar October 2004

  24. Example of position uncertainty including depth-of-field(9 Oct 02) Blue: fgyro – 10% Red: fgyro + 10% UI Space/Astro Seminar October 2004

  25. Example of AKR Burst location with Uncertainties projected into 100km Altitude, CGM coordinates(29 Dec 02) UI Space/Astro Seminar October 2004

  26. Evening Peak ~22h MLT April -May Polar Average Images of Northern Auroral by month (Liou et al. 1997) Day peak at ~15h MLT June -July UI Space/Astro Seminar October 2004

  27. Summary of 4 Spacecraft VLBI Epochs (Fully Analyzed) UI Space/Astro Seminar October 2004

  28. Histogram of AKR Burst Locations CGM coordinates, 5 epochs Southern hemisphere only UI Space/Astro Seminar October 2004

  29. November 9 Locations: Varying Perspectives (Animation) UI Space/Astro Seminar October 2004

  30. Nov 9 :The Movie Mapped onto CGM coordinates UI Space/Astro Seminar October 2004

  31. Observed distribution of AKR bursts UI Space/Astro Seminar October 2004

  32. AKR Burst locations vs. UI Space/Astro Seminar October 2004

  33. Example of position uncertainty including depth-of-field(9 Oct 02) Blue: fgyro – 10% Red: fgyro + 10% UI Space/Astro Seminar October 2004

  34. Example of AKR Burst location with Uncertainties projected into 100km Altitude, CGM coordinates(29 Dec 02) UI Space/Astro Seminar October 2004

  35. Evening Peak ~22h MLT April -May Polar Average Images of Northern Auroral by month (Liou et al. 1997) Day peak at ~15h MLT June -July UI Space/Astro Seminar October 2004

  36. UI Space/Astro Seminar October 2004

  37. AKR burst mean location drift: example119 Aug 2002,Southern hemisphere UI Space/Astro Seminar October 2004

  38. AKR burst mean location drift: example222 Jan 2003, N hemisphere UI Space/Astro Seminar October 2004

  39. First simultaneous AKR/VLBI location map with UV image (IMAGE). June 8 , 2004 AKR burst is associated with discrete auroral arc UI Space/Astro Seminar October 2004

  40. “Rain” AKR bursts “normal” AKR burst ‘Rain’ AKR bursts: Narrow, rapidly drifting structures UI Space/Astro Seminar October 2004

  41. Slope -8.7 KHz/sec AKR Dynamic Spectrum 125 KHz17 July 2002 11:42:30 – 11:43:00 UI Space/Astro Seminar October 2004

  42. Slope = -3.1 KHz/sec AKR Dynamic Spectrum 125 KHz17 July 2002 11:42:30 – 11:43:00 UI Space/Astro Seminar October 2004

  43. Slope -6.3 KHz/sec Modulated periodic structures Rain AKR bursts at 125 KHz31Aug 2002 16:14:30-16:15:00 UT UI Space/Astro Seminar October 2004

  44. Slope -12.5 KHz/sec Rain AKR bursts at 500 KHz31Aug 2002 19:26:00- 19:26:30 UT UI Space/Astro Seminar October 2004

  45. 500 KHz 250 KHz 125 KHz Derived Speed compared withAlfven, and Electron, Ion Acoustic speeds versus Radial distance (assumes 0.1-10 keV particles) Alfven speed Electron acoustic speed Ion acoustic speed UI Space/Astro Seminar October 2004

  46. Derived Exciter speed along B field 125 KHz 500 KHz UI Space/Astro Seminar October 2004

  47. Exitor speed derived from frequency drift 1. Assume EM at electron gyro-frequency, dipolar magnetic field 2. Use (negative) frequency drift to derive (upward) wave speed 3. Recast in terms of fobs 4.Amplitude modulation conversion to spatial wavelength UI Space/Astro Seminar October 2004

  48. Striated AKR from 0-120 KHz(Menietti et al. 2000) Slope ~ 1 KHz/sec @100 KHz Slope ~ 0.5 KHz/sec @40 KHz UI Space/Astro Seminar October 2004

  49. UI Space/Astro Seminar October 2004

  50. Modulation of Striated AKR: Is it due to Faraday rotation? • Requires: • Linearly polarized emission (but AKR is circularly polarized) • Δ≈ 3 turns/KHz @ 125 KHz (λ=2.4 km) => • RM = 10-3 rad-m-2 • This may be plausible: B ~ 0.1 gauss, ne ~ 10 cm-3, L ~ 100 km UI Space/Astro Seminar October 2004

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