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

This study compares the heliospheric plasma sheet characteristics from Solar Cycles 21, 22, and 23. Consistent observations reveal evolving patterns with unique features in each cycle. The North Polar Field Strength shows interesting variations.

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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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