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

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

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

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

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

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

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

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

9. UI Space/Astro Seminar October 2004 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.

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

11. UI Space/Astro Seminar October 2004 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

12. UI Space/Astro Seminar October 2004 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 AKR Burst Position search algorithm

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

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

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

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

17. UI Space/Astro Seminar October 2004 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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

36. UI Space/Astro Seminar October 2004

37. AKR burst mean location drift: example1 19 Aug 2002, Southern hemisphere

38. UI Space/Astro Seminar October 2004 AKR burst mean location drift: example2 22 Jan 2003, N hemisphere

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

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

41. UI Space/Astro Seminar October 2004 AKR Dynamic Spectrum 125 KHz 17 July 2002 11:42:30 – 11:43:00 Slope -8.7 KHz/sec

42. UI Space/Astro Seminar October 2004 AKR Dynamic Spectrum 125 KHz 17 July 2002 11:42:30 – 11:43:00 Slope = -3.1 KHz/sec

43. UI Space/Astro Seminar October 2004 Rain AKR bursts at 125 KHz 31Aug 2002 16:14:30-16:15:00 UT Modulated periodic structures Slope -6.3 KHz/sec

44. UI Space/Astro Seminar October 2004 Rain AKR bursts at 500 KHz 31Aug 2002 19:26:00- 19:26:30 UT Slope -12.5 KHz/sec

45. UI Space/Astro Seminar October 2004 Derived Speed compared with Alfven, and Electron, Ion Acoustic speeds versus Radial distance (assumes 0.1-10 keV particles) Ion acoustic speed Electron acoustic speed Alfven speed 500 KHz250 KHz125 KHz

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

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

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

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, n e ~ 10 cm -3, L ~ 100 km

51. UI Space/Astro Seminar October 2004

52. Sampled at 1024 channels

53. UI Space/Astro Seminar October 2004 Sampled at 2048 channels

54. UI Space/Astro Seminar October 2004 Wavelet dynamic spectrum of Striated bursts, 2 spacecraft correlation

55. UI Space/Astro Seminar October 2004 Electromagnetic Ion-Cyclotron Wave Group Speed vs. Frequency where Note: Plot assumes Dipolar B field N e (r) ~ r -3.2 (Persoon model)

56. UI Space/Astro Seminar October 2004 Banded Modulation of AKR: Evidence for Electrostatic Ion Cyclotron (EIC) Waves?

57. UI Space/Astro Seminar October 2004 Close-up of AKR banded modulation Separation = 120 ± 5 Hz

58. UI Space/Astro Seminar October 2004

60. What excites rain AKR? Model assumptions Observed emission is same as ‘normal’ AKR: electron cyclotron maser near electron cyclotron frequency Earth’s magnetic field is strictly dipolar (OK for r < 2.5 Re) A disturbance traveling parallel to B stimulates EM emission Observed slope indicates phase speed of wave along B field Observed banded modulation may indicates characteristic wavelength of exciter (after conversion to spatial separation)