Season-dependent magnetotail By and associated field-aligned currents A.Petrukovich1 and R. Lukianova2,1 1Space 2Arctic Research Institute, Moscow, email@example.com and Antarctic Research Institute, St. Petersburg пѓјModel of quasi-stationary By based on GEOTAIL пѓјSeason dependent By component пѓјAssociated field aligned currents Acknowledgements: Geotail, CCMC GSFC , RFBR-FWF grant Magnetosphere in XZ GSM ZGSM XGSM YGSM Season change: Dipole tilt Bx and Bz : dipole and cross-tail currents By: IMF By, 3D tail and FAC By в‰ 0 is important пѓј Asymmetry of ionosperic footpoints in aurora пѓј Decrease of curvature (isotropisation) in the neutral sheet пѓј Рљi = Rcurv/Rci ~ (By/Bz)2 пѓј North-south asymmetry of particle trajectories (precipitation) пѓј Effect on current sheet instabilities B x Jx x x x ZGSM YGSM Statistics Geotail 11 years 1995-2005 |Y| < 15 RE , |Y|<|X|, вЂ“31 < X < вЂ“8 RE , |Z| < 5 RE 12-sec data averaged in 15-min intervals with >75% |Bx|<15 nT ~30 000 points IMF penetration B IMF y = ( 0 . 33 + 0 . 54 (1 - |X | Y )) cos( 0 . 78 30 10 ) B y i neutral sheet deformation adds a false By use a Neutral sheet model Tsyganenko & 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. Flaring & hinging Tail Flaring results in false By, odd in Y coordinate flaring Classic estimate: B y ~ RB x However NS hinging affects flaring ! Bx BxвЂ™ flaring By * = R ( B x - tan ОЁ B z ) The angle Y* is taken from TF04, R is determined from data. Warping Warping creates season-dependent By, odd in Y coordinate О� By warp Neutral sheet profile during winter By warp If magnetic field is coupled with By = B z tan( the NS normal Qwarp is taken from the TF04 model and depends on season О� warp ) NEW even tilt-related Bytilt Regression coeff. between tilt and By-ByIMF, By-ByIMF-Bywarp After subtraction of Bywarp symmetric (even) Bytilt = В±1-2 nT appears Final By model By пЂЅ By M IMF By B tilt y warp пЂ« By IMF пЂЅ ( a 1 пЂ« a 2 (1 пЂЅ ( a 5 пЂ« a 6 (1 - пЂ« By пЂ« By tilt flaring |X | 30 |X | 30 Magnetic field in nT, X, Y in RE, )) cos( a 3 Y )B y пЂ« a 4 i 10 )) Y Y in degrees a1=0.3247В±0:015, a2=0.5827В±0.042, a3=0.850В±0.066, a4=0.0187В±0.032 a5=0.0305В±0.0027, a6=0.0614В±0.0088 Key coefficients are defined with accuracy 5% Results вЂ“ 1: Model 1. 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 (вЂњevenвЂќ component) Cartoon of season-driven By nT nT nT even 1-2 nT nT Results вЂ“ 2: Even tilt effect Earlier hints: Fairfield, JGR 1979 for IMP-6 (winter) By(tail)=0.13 By(ip) вЂ“ 0.3 auroral breakup asymmetry Г�stgaard 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 вЂњday-nightвЂќ skews polar convection as IMF By, Wolf, JGR 1970, Leontiev, G&A,1974, Atkinson & Hutchison, JGR 1978 Season-dependent By is carried by interhemispheric FAC Low-orbiting satellites Г�rsted, CHAMP, Magsat пѓј low-altitude polar orbit slowly drifting in local time пѓј high precision magnetometers пѓј 26 million samples above В±45Лљ CGL, all local times and seasons in both hemispheres Magnetic storm Quiet time magnetic perturbations minus the main field 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 вЂ“ positive at midnight Results вЂ“ 3: interhemispheric FAC пѓ� Comprehensive decomposition of the statistical maps of FAC derived from magnetic measurements by Г�ersted, CHAMP and Magsat satellites shows presence of interhemispheric FAC (IHFAC). пѓ� 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. пѓ� The current density is about 0.1 ОјРђ m-2. пѓ� The value and direction of IHFAC is consistent with the observed magnetotail By, depending on the season. Warping compare Bywarp and observed By-ByIMF for X<-20 and Y < -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 in Y one more new component of By = -0.75 nT ??? Statistical model of field-aligned currents parameterized by season and IMF Northern winter Southern summer IMF clock angle Meridional profiles of the FAC density averaged over 3h MLT sectors.