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Season-dependent magnetotail B y and associated field-aligned currents

Season-dependent magnetotail B y and associated field-aligned currents Petrukovich 1 and R. Lukianova 2,1 1 Space Research Institute, Moscow, apetruko@iki.rssi.ru 2 Arctic and Antarctic Research Institute, St. Petersburg Model of quasi-stationary B y based on GEOTAIL

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Season-dependent magnetotail B y and associated field-aligned currents

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  1. Season-dependent magnetotail By and associated field-aligned currents • Petrukovich1 and R. Lukianova2,1 • 1Space Research Institute, Moscow, apetruko@iki.rssi.ru • 2Arctic and Antarctic Research Institute, St. Petersburg • Model of quasi-stationary By based on GEOTAIL • Season dependent By component • Associated field aligned currents Acknowledgements: Geotail, CCMC GSFC , RFBR-FWF grant

  2. Magnetosphere in XZ GSM YGSM Season change: Dipole tilt ZGSM XGSM Bx and Bz: dipole and cross-tail currents By: IMFBy, 3D tail and FAC

  3. x x x x x x x x x x • By ≠ 0 is important • Asymmetry of ionosperic footpoints in aurora • Decrease of curvature (isotropisation) in the neutral sheet • Кi = Rcurv/Rci ~ (By/Bz)2 • North-south asymmetry of particle trajectories (precipitation) • Effect on current sheet instabilities B J ZGSM YGSM

  4. StatisticsGeotail 11 years1995-2005|Y|< 15 RE , |Y|<|X|, –31 < X< –8 RE , |Z|< 5RE 12-sec data averaged in15-min intervals with >75% |Bx|<15 nT ~30 000 points

  5. IMF penetration

  6. neutral sheet deformation adds a false By use a Neutral sheet modelTsyganenko & Fairfield JGR 2004 - TF04 Z ~ X, Y, Y, IMF Byi Bzi hinge warp twist Note: it is assumed, that magnetic field follows (on average) the neutral sheet normal.

  7. Flaring & hinging Tail Flaring results in falseBy,odd inY coordinate Classic estimate: However NS hinging affects flaring ! Bx Bx’ The angle Y*is taken from TF04, R is determined from data.

  8. By By Warping Warping creates season-dependentBy, odd inYcoordinate Neutral sheet profile during winter If magnetic field is coupled with the NS normal Qwarp is taken from the TF04 model and depends on season

  9. NEW even tilt-related Bytilt Regression coeff. betweentilt and By-ByIMF, By-ByIMF-Bywarp After subtraction of Bywarp symmetric (even) Bytilt = ±1-2 nT appears

  10. Final By model Magnetic fieldin nT, X, Y in RE, Y in degrees a1=0.3247±0:015, a2=0.5827±0.042,a3=0.850±0.066,a4=0.0187±0.032 a5=0.0305±0.0027,a6=0.0614±0.0088 Key coefficients are defined with accuracy 5%

  11. Results – 1: Model • Comprehensive By model includes IMF and dipole tilt driving • as well as 3D effects (NS deformation) • 2 . New By component, depending on season: By>0 in summer • and By<0 in winter with max ~1-2 nT (“even” component) Cartoon of season-driven By nT nT even 1-2 nT nT nT

  12. Results – 2: Even tilt effect Earlier hints: Fairfield, JGR 1979 for IMP-6 (winter) By(tail)=0.13 By(ip) – 0.3 auroral breakup asymmetry Østgaard et al, GRL 2005 Liou and Newell, GRL 2010 Reinforcement of IMF in polar cap convection for combinations summer/Byi+ and winter/Byi- (Ruohoniemi & Greenwald JGR 2005) Conductivity gradient “day-night” skews polar convection as IMF By, Wolf, JGR 1970, Leontiev, G&A,1974, Atkinson & Hutchison, JGR 1978

  13. Season-dependent By is carried by interhemispheric FAC Low-orbiting satellites Ørsted, CHAMP, Magsat • low-altitude polar orbitslowly drifting in local time • highprecision magnetometers • 26 million samples above ±45˚ CGL, all local times and seasons in bothhemispheres Magnetic storm Quiet time magnetic perturbations minus the main field

  14. Decomposition of seasonal effect For IMF By=0, Bz=-5 nT North South Revealing seasonal interhemispheric FAC summer map - winter map Expected interhemispheric FAC trace – positive at midnight

  15. Results – 3: interhemispheric FAC • Comprehensive decomposition of the statistical maps of FAC derived from magnetic measurements by Øersted, CHAMP and Magsat satellites shows presence of interhemispheric FAC (IHFAC). • The IHFACs are downward (upward) in the summer (winter) hemisphere being located mainly in the near-noon and premidnight-midnight MLT sectors in the vicinity of the polar cap boundary. • The current density is about 0.1 μА m-2. • The value and direction of IHFAC is consistent with the observed magnetotail By, depending on the season.

  16. Warping compare Bywarpand observedBy-ByIMF forX<-20 andY < -20o warp model zone -0.75 nT, A season-dependent shift warp model is correct for |Y| <10, Bywarp < 1-2 nT and has odd profile inY one more new component of By = -0.75 nT???

  17. IMF clock angle Statistical model of field-aligned currents parameterized by season and IMF Northern winter Southern summer

  18. Meridional profiles of the FAC density averaged over 3h MLT sectors.

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