Magnetotail reconnection and flux circulation: Jupiter and Saturn compared

1. Magnetotail reconnection and flux circulation: Jupiter and Saturn compared Jupiter Magnetospheres of the Outer Planets, Boston, July 2011 C.M. Jackman, M.F. Vogt, J.A. Slavin, S.W.H. Cowley, S.A. Boardsen Saturn Cowley et al. [2003] Cowley et al. [2004]

2. In situ reconnection signatures

3. In situ reconnection signatures After reconnection, B component deflected northward/southward Stretched magnetotail Dipolarization Plasmoid ejection Slavin et al. [1984] Vogt et al. [2010] Plasmoid formation and ejection compresses adjacent regions of the magnetosphere to create Travelling Compression Regions (TCRs).

4. Plasmoids at Jupiter Vogt et al. [2010] 249 events found [Vogt et al., 2010] Inferred x-line position ~90 RJpost-midnight from inward/outward flows Some events in isolation, but also observe “chain” events

5. Plasmoids and TCRs at Saturn Northward turnings Localized compressions Jackman et al. [in preparation, 2011] 34 plasmoids, 16 TCRs Most during deep tail orbits in 2006 Most events occur in isolation but some in “chains”, associated with same reconnection event.

6. Average reconnection signatures

7. Average reconnection signatures - Jupiter Field remains northward for ~90min Plasmoid duration: ~8 min Vogt et al. [in preparation, 2011]

8. Average reconnection signatures - Saturn Field remains northward for ~ 58 min Plasmoid duration: 8 min No evidence of core field Jackman et al. [in preparation, 2011]

9. Flux transport estimates - Saturn

10. Role of reconnection in flux transport Jackman et al. [in press, 2011]

11. Flux closure at Saturn VPPPSdt Ly PPPS/Ly =  BVPPPSdt southward PPPS: ~58 min northward VPPPS = 800 km/s, dt = 58 min, PPPS/Ly = 0.555 Wb/m For Ly=90 RS, Each event closes ~3 GWb Jackman et al. [in press, 2011] Changes in area enclosed by auroral emission indicate changes in magnetosphere flux content. Southern pole open flux content can range between ~15-50 GWb, with an average flux content of 40 GWb. Thus it would take ~13 “average” reconnection events to cycle all the flux in Saturn’s tail. Milan [2009] Badman et al. [2005]

12. Recurrence rates of reconnection

13. Plasmoid recurrence rates - Saturn Derivation 1: The overall average flux closure rate: RC= (PPPS/Ly) × Dy × (1/TP) TP= (PPPS/Ly) × Dy × (1/RC) ≥ (PPPS/Ly) × Dy × (1/RO) RO is the dayside reconnection rate, ~45 kV [Jackman et al., 2004; McAndrews et al., 2008]. RO ≥ RC Full tail width at ~45 RS is ~90 RS = Dy TP, time between plasmoid events ~ 19 hours TP independent of cross-tail extent of reconnection region, Ly Derivation 2: Average flux closed ~0.555 Wb/s. Gives ~3 GWb (for 90 RS width) 40 GWb average tail flux content ~13 plasmoids to cycle tail flux For Dungey-cycle timescale of ~6-10 days, mean recurrence rate of ~1.3-2.2 plasmoids per day Observational rate: In 2006, Cassini spent ~84 days in region: R>20 RS, |BR| < 1.5 nT, and found 34 plasmoids Observational recurrence rate of 1 plasmoid every ~2.4 days

14. Summary For more information, see: Vogt et al. Reconnection and flows in the Jovian magnetotail as inferred from magnetometer observations, [JGR, 2010] Jackman et al. Cassini observations of plasmoid structure and dynamics: Implications for the role of magnetic reconnection in magnetospheric circulation at Saturn, [in press, JGR, 2011]