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The Unusual Heliospheric Current Sheet at the End of Cycle 23 A Comparison of Cycles 21,22,& 23

The Unusual Heliospheric Current Sheet at the End of Cycle 23 A Comparison of Cycles 21,22,& 23. J. Todd Hoeksema Stanford University. Comparison of Solar Cycles 21 – 22 – 23 –. Consistent observations from WSO since 1976 – the beginning of Cycle 21

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The Unusual Heliospheric Current Sheet at the End of Cycle 23 A Comparison of Cycles 21,22,& 23

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  1. The Unusual Heliospheric Current Sheet at the End of Cycle 23A Comparison of Cycles 21,22,& 23 J. Todd Hoeksema Stanford University SHINE 2007 – Heliospheric Plasma Sheet

  2. Comparison of Solar Cycles21 – 22 – 23 – • Consistent observations from WSO since 1976 – the beginning of Cycle 21 • Typical evolution of model heliospheric current sheet follows pattern through cycle • Minimum HCS resembles dipole – until now SHINE 2007 – Heliospheric Plasma Sheet

  3. Potential Field – Source SurfaceSimple Model of Coronal Field Carrington Rotation 1912 – August 1996 Whole Sun Month – Elephant’s Trunk SHINE 2007 – Heliospheric Plasma Sheet

  4. Early Decline 1991 Rising 1988 Later Decline 1993 Max & Polar Reversal 1989 Pre-Min 1995 Typical Solar Cycle – 22 Minimum 1986 SHINE 2007 – Heliospheric Plasma Sheet

  5. Solar Cycle 211976 - 1986Every 8th Rotation X2CR 1645-1781 SHINE 2007 – Heliospheric Plasma Sheet

  6. Solar Cycle 221986 - 1996Every 8th Rotation X2CR 1780 - 1916 SHINE 2007 – Heliospheric Plasma Sheet

  7. Solar Cycle 231996 - 2007Every 8th Rotation X2CR 1920 - 2056 SHINE 2007 – Heliospheric Plasma Sheet

  8. Comparison of Cycles 21 & 22Every 9th RotationX21977 – 1986CR 1650 – 1776 1987 – 1996CR 1790 – 1916 SHINE 2007 – Heliospheric Plasma Sheet

  9. Comparison of Cycles 22 & 23Every 9th RotationX21987 – 1996CR 1790 – 1916 1997 – 2006CR 1920 - 2046 SHINE 2007 – Heliospheric Plasma Sheet

  10. Comparison of Cycles 21 & 23Every 9th RotationX21977 – 1986CR 1645 – 1776 1997 – 2006CR 1920 – 2046 SHINE 2007 – Heliospheric Plasma Sheet

  11. Comparison of Minima at Start of Cycles 21-22-23-24 1976 – Cycle 21.0 1996 – Cycle 23.0 1986 – Cycle 22.0 2007 – Cycle 23.95(?) SHINE 2007 – Heliospheric Plasma Sheet

  12. 1976 1981 1986 1991 1996 2001 2006 SHINE 2007 – Heliospheric Plasma Sheet

  13. Polar Field Measured at WSOfrom 1976 - 2007 SHINE 2007 – Heliospheric Plasma Sheet

  14. Summary • Each solar cycle follows a similar pattern of evolution • Each cycle shows different features depending on AR emergence • Polar field dominates HCS@solar minimum • Polar field at end of Cycle 23 is very weak • HCS reaches higher latitude and has more structure in 2007 than expected SHINE 2007 – Heliospheric Plasma Sheet

  15. North Polar Field Strength SHINE 2007 – Heliospheric Plasma Sheet

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