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20 September 2005Double Star -Cluster Noordwijk Sept 20051 WBD Studies of AKR: Coordinated Observations of Aurora and the SAKR – Ion Hole Connection R.

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Presentation on theme: "20 September 2005Double Star -Cluster Noordwijk Sept 20051 WBD Studies of AKR: Coordinated Observations of Aurora and the SAKR – Ion Hole Connection R."— Presentation transcript:

1 20 September 2005Double Star -Cluster Noordwijk Sept 20051 WBD Studies of AKR: Coordinated Observations of Aurora and the SAKR – Ion Hole Connection R. L. Mutel University of Iowa

2 20 September 2005Double Star -Cluster Noordwijk Sept 20052 Outline Summary of AKR Properties AKR-Auroral Studies –VLBI technique, uncertainties –AKR – Auroral zone source location studies –Example: 8 June 2004 Striated AKR SAKR – Ion ‘holes’ –Summary of SAKR properties –Comparison with Ion Solitary Structures –Do Ion solitary structures trigger SAKR?

3 20 September 2005Double Star -Cluster Noordwijk Sept 20053 Characteristics of Terrestrial Auroral Kilometric Radiation Detected 25% - 50% of time Seasonal dependence: more frequent in winter Strongly associated w. geomagnetic activity, aurora Frequency 50 KHz – 1 MHz Satellite detection only (ionosphere blocks terrestrial reception) Generation mechanism: e - cyclotron maser Requires e- distribution function: Freq-time spectra show complex structure Broadband drifting bursts last ~hrs Fine structure – narrowband, drifting timescale ~ seconds SAKR (Striated AKR) Negative freq. drift => V~100-200 km/s Assoc w. solitary structures? (focus of this talk)

4 20 September 2005Double Star -Cluster Noordwijk Sept 20054 AKR Source region: FAST Observations of AKR Source Region (Ergun et al. Ap. J. 538, 456) Note e - depletion in auroral cavity

5 20 September 2005Double Star -Cluster Noordwijk Sept 20055 FAST Observations of AKR Source Region (Ergun et al. Ap. J. 538, 456) Shell instability

6 20 September 2005Double Star -Cluster Noordwijk Sept 20056 Closed cycle system connecting AKR with auroral region From Strangeway et al. 2000 Free energy source for AKR consists of accelerated primary electrons (downward) and mirrored electrons (upward) with substantial V ┴ Mirroring (& turbulence) scatters beamed (V || ) electrons in velocity space

7 20 September 2005Double Star -Cluster Noordwijk Sept 20057 Sample AKR dynamical spectra showing effect of angular beaming (see Christopher et al. poster Thursday) SC1-SC4 angular sep’n ~14º SC1-SC4 angular sep’n ~30º

8 20 September 2005Double Star -Cluster Noordwijk Sept 20058 VLBI Source Location Algorithm: Differential delay measurement

9 20 September 2005Double Star -Cluster Noordwijk Sept 20059 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

10 20 September 2005Double Star -Cluster Noordwijk Sept 200510 Fly-through of AKR positions

11 20 September 2005Double Star -Cluster Noordwijk Sept 200511 VLBI position uncertainty calculation Delay uncertainties in plane  and parallel to line of sight: Typical uncertainty in plane: Typical uncertainty in  plane:

12 20 September 2005Double Star -Cluster Noordwijk Sept 200512 Movies of temporal behavior of Aurora, AKR

13 20 September 2005Double Star -Cluster Noordwijk Sept 200513 AKR Source Electron acceleration region Auroral bright spot Case 1: Electron Acceleration Region Above AKR Source Region Nominal Predictions: High Correlation Between AKR Source and Auroral Bright Features on Same Magnetic Field line Assumes electron precipitation continues to auroral region [suitable f(v)] But upward mirrored elecgtrons can still contribute

14 20 September 2005Double Star -Cluster Noordwijk Sept 200514 AKR Source Electron acceleration region Auroral bright spot Case 2: Electron Acceleration Region Below AKR Source Region Nominal Predictions: Low Correlation Between AKR Source and Auroral Bright Features on Same Magnetic Field line If AKR emission, sources not on same field line Possibility that upward scattered electrons could trigger AKR

15 20 September 2005Double Star -Cluster Noordwijk Sept 200515 IMAGE Auroral Images 8 June 2004 11:30 – 11:49 UT

16 20 September 2005Double Star -Cluster Noordwijk Sept 200516 AKR Source Locations 8 June 2004 (11:13 – 11:51 UT)

17 20 September 2005Double Star -Cluster Noordwijk Sept 200517 Both movies

18 Striated AKR (SAKR)

19 20 September 2005Double Star -Cluster Noordwijk Sept 200519

20 20 September 2005Double Star -Cluster Noordwijk Sept 200520

21 20 September 2005Double Star -Cluster Noordwijk Sept 200521

22 20 September 2005Double Star -Cluster Noordwijk Sept 200522 Small Angular Sizes imply much lower ERS luminosities (10-100 W) vs. ~10 4 W previously assumed)

23 20 September 2005Double Star -Cluster Noordwijk Sept 200523

24 20 September 2005Double Star -Cluster Noordwijk Sept 200524

25 20 September 2005Double Star -Cluster Noordwijk Sept 200525 Summary of SAKR Properties and Implied properties of trigger Observed SAKR Property Implied Trigger Property Negative slopeUpward traveling Slope -3 → -12 km/sSpeed 75 – 300 km/s Narrowband (20 - 40 Hz) Spatial scale < 1 km (along B field) Much more common at low frequency (100 KHz vs. 500 KHz Trigger more common at higher altitude (R > 2.5Re) High intensity (comparable with normal AKR E field must disturb electron f(v) significantly (for max. growth)

26 20 September 2005Double Star -Cluster Noordwijk Sept 200526 Ion and Electron Solitary Structures (Bounds et al. 1999 JGR)

27 20 September 2005Double Star -Cluster Noordwijk Sept 200527 Ion solitary structures move up B field at V ~75 - 300 km/s (Bounds et al. 1999)

28 20 September 2005Double Star -Cluster Noordwijk Sept 200528 Dipolar and Tripolar structures seen by Cluster 4.5 -6.5 R e (Pickett et al. 2004)

29 20 September 2005Double Star -Cluster Noordwijk Sept 200529 Velocity of tri-polar structure from Cluster SC lags V~ 925 km/s

30 20 September 2005Double Star -Cluster Noordwijk Sept 200530 Ion hole and tri-polar solitary structures: Consistent with narrow bandwidths

31 20 September 2005Double Star -Cluster Noordwijk Sept 200531 Bandwidths in excellent agreement

32 20 September 2005Double Star -Cluster Noordwijk Sept 200532 Ion holes: trigger for striated AKR bursts?

33 20 September 2005Double Star -Cluster Noordwijk Sept 200533 Electron-Cyclotron Maser (ECM) Resonance condition

34 20 September 2005Double Star -Cluster Noordwijk Sept 200534 Electron energy dist function (‘horseshoe’) in magnetospheric acceleration region (Polar in situ obs)

35 20 September 2005Double Star -Cluster Noordwijk Sept 200535 Observed SAKR Property Implied Trigger Property Ion Solitary Structures Negative slopeUpward travelingYes Slope -3 → -12 km/sSpeed 75 – 300 km/sYes (e.g. Bounds, 1999) Narrowband (20 - 40 Hz) Spatial scale < 1 km (along B field) Yes (many refs) Much more common at low frequency (100 KHz vs. 500 KHz Trigger more common at higher altitude (R > 2.5Re) Unknown (but FAST measures in situ) High intensity (comparable with normal AKR E field must disturb electron f(v) significantly (for max. growth) dE/dx ~ 0.5 V/m, V tot ~ 0.1 kV. Requires detailed PIC code to verify SAKR: A Tracer of Ion Solitary Structures?

36 20 September 2005Double Star -Cluster Noordwijk Sept 200536 Summary Preliminary joint AKR (Cluster WBD VLBI) imaging with aurora (IMAGE) shows some correlation (but not high) –Is electron current return inefficient? –Ongoing joint observations started June 05 should clarify connection Striated AKR may be triggered by ion ‘holes’ (solitary structures) –Most observed parameters consistent with ion holes –Detailed PIC calculation, analytic integration of growth rate needed for verify

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