Normal text - click to edit 1 August 2011 Auroral asymmetries in the conjugate hemispheres (and where KuaFu B can do better……) Nikolai Østgaard University of Bergen, Norway Coauthors: B. Krøvel Humberset, K.M. Laundal, A.Aasnes, S. Haaland H. U. Frey, J. B. Sigwarth, J. Weygand

Normal text - click to edit 2 August 2011 Outline: 1.Asymmetric auroral intensities 2.Substorm onset location asymmetries 3.What happen to asymmetry during substorm expansion phase 4.Theta Aurora in only one hemisphere 5.Cusp Aurora in both hemispheres

Normal text - click to edit 3 August 2011 Movie: UT 1. Very asymmetric aurora – closed field lines WIC/FUV - IMAGE VIS Earth Camera - Polar

Normal text - click to edit 4 August Asymmetric auroral intensities - Asymmetric intensities - Poleward expansion Conditions: -Seasons: -North-summer -South- winter -Bx dominated IMF -By ~0

Normal text - click to edit 5 August 2011 Interpretation Laundal and Østgaard, Nature, 2009 X x A combination of - the more efficient solar wind dynamo - inter-hemispheric currents: - Persistent spot in south (dynamo + interhemispheric currents) - Transient spot in the north (interhemispheric currents) and the significant increase in reconnection (poleward expansion) can explain its transient character.

Normal text - click to edit 6 August Asymmetric substorm onset location Westward bulge: SH ~1.1 MLT duskward of NH Duskward – B Y negative !

Normal text - click to edit 7 August 2011 Statistical distribution – Polar and IMAGE 6600 substorms by IMAGE and Polar 4671 Northern hemisphere 1930 Southern hemisphere Time shifts ACE and Wind: -10 Re +/- 5 min average -20 Re +/- 5 min average -10 Re - 40 min average 294/ / / / / /293

Normal text - click to edit 8 August 2011 Statistical distribution

Normal text - click to edit 9 August 2011 Average onset location – clock angle Clock angle controls average onset location in each hemispheres Onset locations are still distributed in a large range of MLTs Interhemispheric asymmetry might be more robust result Indirect indication that tail reconnection is significant for Northward IMF -10 Re +/- 5 min average -20 Re +/- 5 min average -10 Re - 40 min average

Normal text - click to edit 10 August 2011 Average onset location – By, IMF to -10 Re Reveals saturation towards dusk for - positive By in north - negative By in south Asymmetric penetration of IMF By in the deep tail (Khurana et al., 1996) extends to closed field lines z y Østgaard et al, GRL, L08104, 2011.

Normal text - click to edit 11 August What happen to asymmetries during expansion phase Oct 22, 2001: 5 hours of conjugate images 2 substorms IMAGE VIS Earth

Normal text - click to edit 12 August 2011 Method 1.Used available DMSP data to ensure pointing accuracy 2.Visual Inspection method 3.Mapped onto rectangular magnetic grid -0.1 MLT - 1° Maglat resolution 4.1D correlation (cross correlation) 5.2D correlation (chi square)

Normal text - click to edit 13 August 2011 Substorm assymmetry Onset is asymmetric During expansion phase the asymmetry disappears – regardless of clock angle or By. Grey diamonds: all images < 1 min overlap Black diamonds: - time overlap (< 21 sec) - corr.coeff > 0.4 (1D) - chi square < 0.4 (2D)

Normal text - click to edit 14 August 2011 i) Asymmetry is created in the mid-tail ii) I inverted-V structures are formed which decouple magnetosphere from the ionosphere,– iii) and magnetic stress is released (Haerendel, 2007 rectifying the asymmetric field lines Rectifying the field lines during expansion phase b) Twist on field lines create net electric field pointing from north to south c) Faradays loop on closed field lines ∆ Østgaard et al, GRL, L03101,2011

Normal text - click to edit 15 August 2011 Non-conjugate theta (transpolar arcs) consistent with IMF Bx but more observations to see if this holds statistically Østgaard et al., Geophys. Res. Lett., 2003 Also the cusp aurora in both hemispheres IMF By: longitudinal shift Tilt angle: latitudinal shift Østgaard et al., Geophys. Res. Lett., Theta 4. Cusp aurora

Normal text - click to edit 16 August 2011 Summary: 1. Asymmetric auroral intensities Indication of interhemispheric currents 2. Substorm onset asymmetries Usually asymmetric locations at substorm onset Strong statistical correlation with clock angle and By 3. Substorm expansion phase Field lines are rectified during expansion phase 4. Theta Aurora Maybe a IMF-Bx control of theta aurora? 5. Cusp Aurora IMF control of longitudinal shifts and maybe a tilt angle of the latitudinal shift? KuaFu can address these questions and many more ….

Normal text - click to edit 17 August 2011 Thank you!

Normal text - click to edit 18 August 2011 Tilt angle effects More intense nightside FACs were found by Ohtani et al., 2005 in the winter hemisphere Needs more data to confirm! Onset in south is downward of north onset for positive tilt, i.e., south=winter

Normal text - click to edit 19 August 2011 Summary and challenges: Cusp and reconnection – temporal behavior 1.We have shown the asymmetry of cusp location 2.Challenge: To determine the relative reconnection rate 1.Optical measurements: Relative intensity of the cusp spot 2.Even better: Reconnection rate with radars (Pinnock et al., 1999) and optical data. More than one radar, get the relative reconnection rate. Critical: OC boundary position, tilt and speed. 3. Relative size of the polar caps, optics and radars to get the opening and closing of magnetic flux in the two hemispheres Transpolar arcs and theta aurora 1.We have shown that theta can be non-conjugate, but to determine what controls it; more observations are needed: ground based optics, GUVI and SSUSI, low altitude satellites. Subtsorm onset location 1.The IMF clock angle control is well documented. The global asymmetry suggests that the tilt effect and difference in FAC may be insignificant. Dynamic features of the expansion phase of substorms 1.The potential mismatch??

Normal text - click to edit 20 August 2011 The penetration of the IMF field Has been directly observed in the outer magnetosphere by Sibeck et al, 1985 and the inner magnetosphere Wing et al., 1995 How IMF affect the magnetospheric configuration noon midnight dawn Wing et al, 1995

Normal text - click to edit 21 August 2011 Reconnection rate - Method – Vasyliunas [1984] (>300 km) Faraday’s law Assumptions

Normal text - click to edit 22 August 2011 Is it real? 1) Relative variations in counts North-WIC: red South-VIS: black 2) Electron Energies and different cameras: Dawn-spot: 10 kR (WIC) ~5 kR (VIS) High electron energies will give higher intensity in WIC than in VIS, If 25 keV mean energy -> 40 mW/m2 and should give about 10 kR in VIS, but we see only 5 kR. Energy cannot explain the dusk differences. 3) N2/O2 ratio increases due to heating WIC would be slightly brighter – this effect is very small; intensity differences would be underestimated at dusk and exagerated at dawn.

Normal text - click to edit 23 August 2011 Challenge: Dayside reconnection rate with radars and imaging Pinnock et al., 1999 Two critical points: 1) get the OC boundary and its speed correct Imaging is needed 2) More than one radar: Differences in E_rec strength are interpreted as moving away from the throat region (i.e. anti- parallel site) North South IMF Bz<0 Variable By Vasyliunas [1984]