Investigation of temporal stability of fieldaligned currents in

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 Cluster Workshop 2010 -05 -20

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

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

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

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

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

Raw correlations 2002 -2009 7938 correlations, 1323 oval crossings Cross correlation coefficient day night lag (s) Cluster Workshop 2010 -05 -20

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

Correlations, full oval, 2002 -2009 Cross correlation coefficient Fit equation: C = 0. 37 C 0 = 0. 53 t = 546 s lag (s) Cluster Workshop 2010 -05 -20

Correlations, full oval, 2002 -2009 Kp dependence Cross correlation coefficient 0 < Kp ≤ 1 1 < Kp ≤ 3 3 < Kp ≤ 9 lag (s) Cluster Workshop 2010 -05 -20

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

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

Correlations 2002 -2007, n=95 154 Window size = 3° ILAT cross correlation coefficient 1. 0 0. 5 0. 0 lag (s) Cluster Workshop 2010 -05 -20

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

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

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

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

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

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 lifetime of around 9 min, consistent with Le et al. (10 min). • Meso-scale current life-time dependence on MLT and scale size: • Morning/day Evening 1° 10 s 30 -100 s 3° 30 -100 s 100 -300 s Low-latitude currents somewhat more temporally stable than high-latitude currents. 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 Cluster Workshop 2010 -05 -20