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Cluster Workshop 2010-05-20

Cluster Workshop 2010-05-20

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Cluster Workshop 2010-05-20

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  1. Cluster Workshop 2010-05-20 Space and Plasma PhysicsSchool of Electrical EngineeringRoyal Institute of TechnologyStockholmSweden Investigation of temporal stability of field-aligned currents in the auroral ovalTomas Karlsson, Johanna Myde

  2. Cluster Workshop 2010-05-20 Introduction Boudouridis and Spence, 2007 DMSP particle data Le, Wang, Slavin, and Strangeway, 2007 Space Technology 5, magnetic field data tLS = 10 mintMS = 1 min

  3. Cluster Workshop 2010-05-20 Magnetic field data from auroral oval passage East j DB ILAT(S/C 1)=80 ILAT(S/C 1)=65 DBEAST (nT) 3200 s t (s)

  4. Cluster Workshop 2010-05-20 Cross correlation lag S/C 1 ILAT=65 80 S/C 2 ILAT=65 80 t cross-covariance lag auto-covariances (for L=0)

  5. Cluster Workshop 2010-05-20 Magnetic field data from auroral oval passage ILAT(S/C 1)=80 ILAT(S/C 1)=65 DBEAST (nT) t (s)

  6. Cluster Workshop 2010-05-20 Cross correlation 14 12 13 Cross correlation coefficient 23 24 34 lag (s)

  7. Cluster Workshop 2010-05-20 Raw correlations 2002-20097938 correlations, 1323 oval crossings day night Cross correlation coefficient lag (s)

  8. Cluster Workshop 2010-05-20 Correlations, full oval, 2002-2009 Cross correlation coefficient lag (s)

  9. Cluster Workshop 2010-05-20 Correlations, full oval, 2002-2009 Fit equation: Cross correlation coefficient C = 0.37C0 = 0.53t = 546 s lag (s)

  10. Cluster Workshop 2010-05-20 Correlations, full oval, 2002-2009 Kp dependence 0 < Kp ≤ 11 < Kp ≤ 33 < Kp ≤ 9 Cross correlation coefficient lag (s)

  11. Cluster Workshop 2010-05-20 Correlations, full oval, 2002-2009 MLT dependence EveningNight MorningDay (18-20)(22-00)(01-03)(11-13) Cross correlation coefficient lag (s)

  12. S/C 1 ILAT=65 80 S/C 2 ILAT=65 80 S/C 2 ILAT=65 80 Cluster Workshop 2010-05-20 Sliding Cross Correlations pre-lag t winsize S/C 1 ILAT=65 80

  13. 1.0 cross correlation coefficient 0.5 0.0 Cluster Workshop 2010-05-20 Correlations 2002-2007, n=95 154 Window size = 3° ILAT lag (s)

  14. Cluster Workshop 2010-05-20 Correlations, 2002-2007 Window size = 1° Window size = 3° ilat cross correlation coefficienrt lag (s)

  15. Cluster Workshop 2010-05-20 Correlations, 2002-2007 Window size = 3° MLT lag (s)

  16. Cluster Workshop 2010-05-20 Correlations, 2002-2007 Window size = 1° Window size = 3° MLT cross correlation coefficienrt lag (s)

  17. Cluster Workshop 2010-05-20 Correlations, 2002-2007 Window size = 3° lag < 10 s 10 s < lag < 30 s cross correlation coefficienrt ilat 30 s < lag < 100 s 100 s < lag < 300 s MLT

  18. Cluster Workshop 2010-05-20 Correlations, 2002-2007 Window size = 1° lag < 10 s 10 s < lag < 30 s cross correlation coefficienrt ilat 30 s < lag < 100 s 100 s < lag < 300 s MLT

  19. Cluster Workshop 2010-05-20 Conclusions • Cross correlation method is a useful method for studying the temporal variations in the auroral oval, • FAC on the scale of the oval size have a characteristic life-time of around 9 min, consistent with Le et al. (10 min). • Meso-scale current life-time dependence on MLT and scale size: • Low-latitude currents somewhat more temporally stable than high-latitude currents.

  20. Cluster Workshop 2010-05-20 Future work • Modify normalization in in cross correlation function • Study scale-size dependence with proper cross-spectral analysis (coherence function) • Study temporal characteristics of electric fields • Study energetic importance by calculating Poynting flux

  21. Cluster Workshop 2010-05-20 Coherence function

  22. 1.0 cross correlation coefficient 0.5 0.0 Cluster Workshop 2010-05-20 Correlations 2002-2007, n=109 542 Window size = 1° ILAT lag (s)

  23. Cluster Workshop 2010-05-20 Correlations, 2002-2007 Window size = 1° MLT lag (s)

  24. Cluster Workshop 2010-05-20 This and that Smooth window in dB calculation: 400 s = 200 km