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Astrophysics Seminar October 2004

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. Earth as a radio source. AKR is generated 6000-12000 km above the visible aurora.

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Astrophysics Seminar October 2004

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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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