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Nordic Cluster Meeting 2011

Investigation of temporal stability of field-aligned currents in the auroral oval Tomas Karlsson, Johanna Myde. Space and Plasma Physics School of Electrical Engineering Royal Institute of Technology Stockholm Sweden. Nordic Cluster Meeting 2011. Introduction. Boudouridis and Spence, 2007

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Nordic Cluster Meeting 2011

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  1. Investigation of temporal stability of field-aligned currents in the auroral ovalTomas Karlsson, Johanna Myde Space and Plasma PhysicsSchool of Electrical EngineeringRoyal Institute of TechnologyStockholmSweden Nordic Cluster Meeting 2011

  2. Introduction Boudouridis and Spence, 2007 DMSP particle data Le, Wang, Slavin, and Strangeway, 2007 Space Technology 5, magnetic field data Nordic Cluster Meeting 2011

  3. j z x y Current sheet approximation and Ampére’s law But and eller Ampére’s law (no time dependence): Nordic Cluster Meeting 2011

  4. Magnetic field data from auroral oval passage ILAT(S/C 1)=80 ILAT(S/C 1)=65 DBEAST (nT) t (s) Nordic Cluster Meeting 2011

  5. AGU Chapman Conference 2011 Cross correlation lag S/C 1 ILAT=65 80 S/C 2 ILAT=65 80 t cross-covariance lag auto-covariances (for L=0)

  6. Magnetic field data from auroral oval passage ILAT(S/C 1)=80 ILAT(S/C 1)=65 DBEAST (nT) t (s) Nordic Cluster Meeting 2011

  7. Cross correlation 14 12 13 Cross correlation coefficient 23 24 34 lag (s) Nordic Cluster Meeting 2011

  8. Raw correlations 2002-20097938 correlations, 1323 oval crossings day night Cross correlation coefficient lag (s) Nordic Cluster Meeting 2011

  9. Correlations, full oval, 2002-2009 Cross correlation coefficient lag (s) Nordic Cluster Meeting 2011

  10. Correlations, full oval, 2002-2009 Fit equation: Cross correlation coefficient C = 0.37C0 = 0.53t = 546 s lag (s) Nordic Cluster Meeting 2011

  11. Correlations, full oval, 2002-2009 Kp dependence 0 < Kp ≤ 11 < Kp ≤ 33 < Kp ≤ 9 Cross correlation coefficient lag (s) Nordic Cluster Meeting 2011

  12. Correlations, full oval, 2002-2009 MLT dependence EveningNight MorningDay (18-20)(22-00)(01-03)(11-13) Cross correlation coefficient lag (s) Nordic Cluster Meeting 2011

  13. S/C 1 ILAT=65 80 S/C 2 ILAT=65 80 S/C 2 ILAT=65 80 Sliding Cross Correlations pre-lag t winsize S/C 1 ILAT=65 80 Nordic Cluster Meeting 2011

  14. 1.0 cross correlation coefficient 0.5 0.0 Correlations 2002-2007, n=95 154 Window size = 3° ILAT lag (s) Nordic Cluster Meeting 2011

  15. Correlations, 2002-2007 Window size = 1° Window size = 3° ilat cross correlation coefficienrt lag (s) Nordic Cluster Meeting 2011

  16. Correlations, 2002-2007 Window size = 3° MLT lag (s) Nordic Cluster Meeting 2011

  17. Correlations, 2002-2007 Window size = 1° Window size = 3° MLT cross correlation coefficienrt lag (s) Nordic Cluster Meeting 2011

  18. 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 Nordic Cluster Meeting 2011

  19. 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 Nordic Cluster Meeting 2011

  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. Nordic Cluster Meeting 2011

  21. 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 Nordic Cluster Meeting 2011

  22. Physics questions S S E E B J Changes in FAC  Alfvén wave FAC  zero frequency Alfvén wave Is the auroral acceleration electric field explainable by AW physics, or is other physics needed? Temporal behaviour of E and B may give clues. Large-scale SW-M-I coupling time scales. Energetic importance of processes with different temporal and spatial scales. Differences in temporal scales of upward and downward currents Implications for MI coupling modes, e.g. ionospheric plasma evacuation. Is temporal variation of currents due to motion of current systems or change of shape and magnitude? (Relation to Maria’s results.) Nordic Cluster Meeting 2011

  23. Cluster Workshop 2010-05-20 Coherence function

  24. 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)

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

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

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