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Cosmic-ray Generation, Propagation and Atmospheric Effects

Cosmic-ray Generation, Propagation and Atmospheric Effects. Keran O’Brien Department of Physics and Astronomy Northern Arizona University. To Be Discussed. Cosmic-ray generation Cosmic-ray propagation Solar Cycles Rigidity Loss in the heliosphere Atmospheric ionization

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Cosmic-ray Generation, Propagation and Atmospheric Effects

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  1. Cosmic-ray Generation, Propagation and Atmospheric Effects Keran O’Brien Department of Physics and Astronomy Northern Arizona University

  2. To Be Discussed • Cosmic-ray generation • Cosmic-ray propagation • Solar Cycles • Rigidity Loss in the heliosphere • Atmospheric ionization • Possible effects on Climate • Be-10 production

  3. Natural Units • Speed of Light: • Energy: • Mass: • Rigidity:

  4. Plane Shock Front O B A F G K M L N S

  5. Calculating the Local Interstellar Spectrum

  6. The Local Interstellar Spectrum

  7. Heliosphere and Heliosheath

  8. The Solar Wind The sun’s corona is at approximately two million degrees and is continuously boiling off, forming the heliosphere, a bubble in the interplanetary medium. Increasing sunspot numbers result in increasing turbulence in the interplanetary medium that fills the heliosphere.

  9. Heliosphere and Heliosheath

  10. Sunspots and Cosmic-ray Rigidity Loss Cosmic rays must do work to pass from the interstellar medium through the interplanetary medium. Turbulence decreases the diffusion coefficient increasing the cosmic-ray rigidity loss and decreasing the cosmic-ray intensity.

  11. Sunspots and Rigidity Loss Here U is the rigidity loss in volts, V is the solar wind velocity, about 400 km/s, r is the distance to the solar wind termination (about 90 times the earth-sun distance, 90 AU), and κ is the diffusion coefficient. As κ decreases, U increases.

  12. Solar Cycles • 11-year sunspot cycle • 22-year Hale cycle • Gleissberg cycle

  13. Eleven-year Solar Cycle

  14. Cosmic-ray Peaks

  15. Ionization: The Proposed Mechanism

  16. The Little Ice Age

  17. Cooling During (Part of) the Dalton Minimum

  18. Then and Now A paper by Palle, Butler and I, based on declining cosmic-ray ionization from 1990 until 2000 and its effect on cloud cover, estimated that, over that period, cosmic-ray forcing raised global temperature by 0.2°C.

  19. Decline in Cosmic-ray Intensity: 1900 to 2000

  20. High Clouds, Low Clouds 2, 4.5 and 10.5 km altitudes: 2 km altitude cloud-cover cell is closely correlated with cosmic-ray intensity

  21. End of the Grand Solar Maximum in 2000

  22. Solar Cycle 24

  23. Another Cosmic-ray Process: Data on Ancient Climate Change The collision of a cosmic-ray hadron (neutron, proton, meson) having an energy greater than 100 MeV with an atmospheric nucleus will produce nuclear fragments. One fragment may have an atomic number of 4, and an atomic mass of 10, or Beryllium-10. The Be-10 yield per collision is about 1.4%. The half-life is 15 million years and is used to date ice cores from Greenland and the Antarctic to give information about past climates. The total atmospheric Be-10 inventory is about 4 MCi (0.2 EBq).

  24. What has Been Discussed • Cosmic-ray generation • Cosmic-ray propagation • Solar Cycles • Rigidity Loss in the heliosphere • Atmospheric ionization • Possible effects on Climate • Be-10 production and inventory keran.o’brien@nau.edu

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