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STAMMS Conference Meeting, Orleans, France May 2003

Spatial and Temporal Properties of AKR Burst Emission Derived From WBD VLBI Studies. R. L. Mutel, D. A. Gurnett, I. Christopher, M. Schlax University of Iowa. STAMMS Conference Meeting, Orleans, France May 2003. University of Iowa Wideband Data Plasma Wave Instrument (WBD).

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STAMMS Conference Meeting, Orleans, France May 2003

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  1. Spatial and Temporal Properties of AKR Burst Emission Derived From WBD VLBI Studies R. L. Mutel, D. A. Gurnett, I. Christopher, M. Schlax University of Iowa STAMMS Conference Meeting, Orleans, France May 2003

  2. 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. STAMMS Meeting, Orleans, May 2003

  3. Example of WBD Dynamic Spectra (250-262 KHz, 30 sec), S/C separation ~300 km Auroral Kilometric Radiation (AKR) Bursts Spacecraft 1 3 4 STAMMS Meeting, Orleans, May 2003

  4. Example of shadowing by plasmasphere at low magnetic latitude (15 May 2001) m = -53° m = -38° m = -32° STAMMS Meeting, Orleans, May 2003

  5. Dynamic Spectra of Common AKR Bursts AKR bursts have 100-400 KHz bandwdth (courtesy R. Anderson, GEOTAIL) Cluster spectra (10 KHz bandwidth) STAMMS Meeting, Orleans, May 2003

  6. VLBI Source Location Algorithm: Differential delay measurement STAMMS Meeting, Orleans, May 2003

  7. 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 STAMMS Meeting, Orleans, May 2003

  8. 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 STAMMS Meeting, Orleans, May 2003

  9. VLBI position uncertainty calculation Delay uncertainties in plane  and parallel to line of sight: Typical uncertainty in  plane: Typical uncertainty in plane: STAMMS Meeting, Orleans, May 2003

  10. Uncertainty ~ 500 km -1000 km Uncertainty mapped to Earth (CGM coordinates) Uncertainty ~ 200 km -400 km STAMMS Meeting, Orleans, May 2003

  11. Refractive effects effect on AKR burst location determination unimportant for S/C magnetic latitudes > 40°(plasmasphere model Gallagher et al.2000) STAMMS Meeting, Orleans, May 2003

  12. Refractive Ray tracing corrections STAMMS Meeting, Orleans, May 2003

  13. 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. STAMMS Meeting, Orleans, May 2003

  14. AKR Burst Locations: The movie STAMMS Meeting, Orleans, May 2003

  15. Summary of 4 Spacecraft VLBI Epochs (Fully Analyzed) STAMMS Meeting, Orleans, May 2003

  16. Histogram of AKR Burst Locations CGM coordinates, 5 epochs Southern hemisphere only STAMMS Meeting, Orleans, May 2003

  17. November 9 Locations: Varying Perspectives (Animation) STAMMS Meeting, Orleans, May 2003

  18. Nov 9 :The Movie Mapped onto CGM coordinates STAMMS Meeting, Orleans, May 2003

  19. Observed distribution of AKR bursts STAMMS Meeting, Orleans, May 2003

  20. AKR Burst locations vs. STAMMS Meeting, Orleans, May 2003

  21. Example of position uncertainty including depth-of-field(9 Oct 02) Blue: fgyro – 10% Red: fgyro + 10% STAMMS Meeting, Orleans, May 2003

  22. Example of AKR Burst location with Uncertainties projected into 100km Altitude, CGM coordinates(29 Dec 02) STAMMS Meeting, Orleans, May 2003

  23. 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 STAMMS Meeting, Orleans, May 2003

  24. STAMMS Meeting, Orleans, May 2003

  25. AKR burst mean location drift: example119 Aug 2002,Southern hemisphere STAMMS Meeting, Orleans, May 2003

  26. AKR burst mean location drift: example222 Jan 2003, N hemisphere STAMMS Meeting, Orleans, May 2003

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