Global Heliospheric Modulation of Cosmic Rays: Charge-sign dependence

1. Global Heliospheric Modulation of Cosmic Rays: Charge-sign dependence Marius Potgieter Unit for Space Physics North-West University Potchefstroom, South Africa SA Workshop 2010

2. Transport equation for the transport, modulation and acceleration of cosmic rays in the heliosphere Time-dependent, pitch-angle-averaged distribution function Diffusion Convection with solar wind Particle Drifts Adiabatic energy changes Any local source Second order Fermi acceleration Parker (Planet. Space Science, 13, 9,1965)

3. Heliospheric particle drifts & HCS The wavy current sheet (HCS)

4. The basic heliospheric CR modulation processes As for electrons

5. Gradient, curvature and current sheet drift patterns Strauss, 2009

6. Cosmic rays as indicators of heliospheric conditions Modulation of galactic cosmic rays at Earth at NM energies

7. Major features of observed modulated cosmic rays near Earth: Required as validation of numerical models Observed and computed spectra crossings at Earth, for A > 0 and A < 0 solar minima polarity cycles… Computed latitudinal gradients compared to Ulysses-KET observations; for A > 0, solar minimum to maximum… Langner, Potgieter & Webber, JGR, 2003; ASR, 2004

8. Computed radial gradients for galactic protons During solar minimum modulation; A > 0; A < 0 At Earth 50 AU TS = 91 AU Ngobeni & Potgieter, 2008

9. Computed latitudinal/polar gradients for galactic protons Earth During solar minimum modulation; A > 0; A < 0 50 AU 91 AU Ngobeni & Potgieter, 2008

10. First reported evidence of charge-sign dependent modulation

11. Charge-sign dependent modulation over two solar maxima Electron measurements form ISEE/ICE (Clem et al., 1996; Evenson, 1998) and KET (Heber et al, this conference). He measurements from IMP (McDonald, 1998; McDonald et al., 2001).

12. Drifts during a complete solar activity cycle

13. Cosmic Rays from the Galaxy: Power Laws above 10 GeV But, what about energies well below 1 GeV Computed LIS Solar Modulation E-2.70 E -3.04 Lipari, PAMELA Workshop, May 2009

14. The Electron LIS ‘controversy’ Possible LIS’s for galactic electrons below 1 GeV

15. Heliospheric modulation of galactic carbon: Is the heliosheath an effective modulation ‘barrier’ for galactic cosmic rays? Webber et al. (AIP-IGPP-2006)

16. Effects of gradient and curvature drifts in the heliosheath-nose 200 MeV GCR protons Solar minimum conditions Conclusions: GC&CS-drifts may play a significant role in the HS….? Without drifts the TS seems insignificant for GCRs … The HP is more important to GCR modulation than the TS Langner, Potgieter & Webber, JGR, 2003

17. Computations for anti-proton modulation in the heliosphere

18. Modulation of galactic protons and anti-protons at solar minimum

19. Modulation of galactic electrons and positrons at solar minimum Electrons Positrons Langner & Potgieter, Solar wind termination shock and heliosheath effects on charge-sign dependent modulation for protons and anti-protons, JGR, 109, 2004; Potgieter & Langner, Heliospheric modulation of cosmic ray positrons and electrons: Effects of the heliosheath and solar wind termination shock, ApJ, 602, 2004.

20. Modelling results for galactic electrons, positrons, protons & anti-protons at Earth Ratio of Electrons to Positrons At Earth vs. LIS Solar minimum modulation Two consecutive magnetic field polarities Ratio of Protons to Anti-protons At Earth vs. LIS Solar minimum modulation Two consecutive magnetic field polarities Langner & Potgieter, 2003

21. Observed electron spectra & global modeling results At increasing radial distances w.r.t. the Local Interstellar Spectrum Contributions of Jovian & galctic electrons in the inner heliosphere

22. Ferreira & Potgieter, JGR, 2002

23. Update on observed low-energy galactic electrons from V1 & V2 Potgieter, JGR, 1996 Webber, pricomm, 2009

25. New computations for two electron LIS levels, for 10 MeV, at the V1 position

26. Model predictions compared to V1 electron observations with three LIS levels at 10 MeV

28. Solar wind velocity profiles in the heliosphere Thank you ! IAGA 2, Cairo, Egypt, 2009

29. Extra slides

30. Ratio of Electrons to Positrons At Earth Solar minimum modulation Two consecutive magnetic field polarities Ratio of Electrons to Positrons At Earth Solar maximum modulation Two consecutive magnetic field polarities

31. Summary & Conclusions • Electron observation of 6-14 MeV indicate a radial gradient of up to 25%/AU in the heliosheath … • Since 2005 these electrons have increased by a factor of 25. • At 10 MeV, galactic electrons are significantly modulated in the heliosheath. • The heliosheath thus forms an effective modulation ‘barrier’ at these energies. • Comparison of modelling and observations now indicate that the computed LIS for electrons below 100 MeV may be a factor of 5 too high. • Concerning turbulence & diffusion theory: what is the case in the heliosheath at these low energies? • More theoretical work is needed…

32. Details of modulating parameters and diffusion coefficients • Magnetic field magnitude B pro to r,for r > rs (Burlaga et al., 2007), with rs the position of the TS. • For the convection term, V is kept constant up to rs • at r = rs, V decreases by a factor s. • r > rs, Vr varies from r−4 and r−6, depending on the distance beyond the TS (Ferreira, Potgieter & Scherer, 2007). Ferreira, Potgieter & Scherer, 2007.

33. Details of modulating parameters and diffusion coefficients For a description of basic assumptions based on turbulence and diffusion theory, see also Burger, Potgieter & Heber (ApJ, 2000). Deviating from the latter, λ|| for electrons at Earth as calculated by Teufel and Schlickeiser (2002), based on a random sweeping and a damping model for turbulence, respectively. For the spatial dependence λ|| proportional to r1.3, with r radial distance in AU. At the TS, it decreases proportional to the compression ratio, s, and λ|| proportional to1/r up to HP. Kr and Kscale as K||, according to le Roux et al. (1999).

34. Hydrodynamic modeling of major heliospheric structures HP 245 AU TS 155 AU TS 205 AU HP 140 AU TS 93 AU Ferreira, S. E. S., & Scherer, K. 2004, ApJ, 616, 1215 Scherer, K., & Ferreira, S. E. S. 2005, ASTRA, 1, 17