Breakout Session F: Anomalous and Galactic Cosmic Rays

1. Breakout Session F:Anomalous and Galactic Cosmic Rays Rick Leske and Maher Dayeh 5 presentations…and lots of discussion

2. Observations during the last prolonged solar minimumDuring late 2009, GCR intensities at 1 AU were at record high levels for the Space Age, while ACR intensities were similar to those reached 2 solar minima ago (in A<0 conditions), and well below those seen in the previous (A>0) minimum. However, compared with the last A<0 cycle at a given tilt angle, both GCR and ACR intensities are much HIGHER.

3. Discussion Topics • How do these observations confirm or challenge our understanding of energetic particle transport and modulation in the heliosphere? • What constraints do they place on the origin of anomalous cosmic rays? • How can multi-spacecraft observations throughout the heliosphere help to address these questions?

4. A New Look at the Heliosphere and Solar Modulation (Frank McDonald) • The ongoing period of very low solar activity has a multi-faceted effect on the modulation process: • The decrease in the heliospheric magnetic field appears to be strongly related to the increase of 265 MeV/n He (7.4%/year) and H (15.5%/year), which is temporal and not spatial in nature. • Changes in the heliospheric current sheet tilt angle plays a major role for ACR O and for Neutron Monitors. • The lower solar wind velocity and pressure affect the dimensions of the heliosphere and thus the particle diffusion coefficients. • Over the last 1000 years there have been previous epochs of low solar activity that have resulted in significant increases in the GCR intensity. As measured by archival data from 10Be in polar ice cores and 10C in tree rings. The current solar minimum is unusual but not unique.

5. He & e-s change slopes at the same time, suggesting the same path in the heliosphere, possibly subjected to similar modulation effects.

6. GCRs in the prolonged solar minimum between cycles 23 and 24 (Nathan Schwadron) • Provided a historic look into GCR levels and reported on radiation hazards during the current solar minimum: • Evidence of much lower floors in heliospheric magnetic field over last 600 years • Significant hazard to long-term human exploration • Modeled the modulation potential and deduced that reductions in modulation potential are caused by enhanced diffusion, allowing greater access and therefore higher fluxes of GCRs in the inner heliosphere. • Galactic Weather? • 10Be records in Antarctic ice show two prominent peaks 35,000 (also present in marine sediment records) and 60,000 years ago. This is supported by the observed correlation between geomagnetic field strength and 10Be levels in marine sediment records, but contradicts the large variations observed at high latitudes where geomagnetic effects are small. • Many of the long-term changes in the cosmic ray fluxes incident on Earth may be due to external effects; either due to changes in the shielding of the inner heliosheath or due to changes in the incident fluxes of GCRs from outside the heliosphere. Possibility of LISM and/or TS changes over 10,000 year timescales (35,000 and 60,000 years ago).

7. Quantifying the GCR Hazard

8. Record-Breaking Cosmic-Ray intensities in 2009 and 2010 (Dick Mewaldt) • Discussed the effects of Solar/Interplanetary parameters on cosmic ray intensities: • The interplanetary magnetic is at its lowest level of the space age (Smith & Balough 2008). Solar wind turbulence has also decreased. • - The magnetic field strength determines the gyroradius of cosmic rays and the • turbulence level affects their scattering rate. • - Cosmic-ray intensity is anti-correlated with the IMF strength (Burlaga & Ness 1998, Cane et al. 2003). • Solar Wind Velocity. • - Affects the loss rate of cosmic rays due to convection. • Decreased solar-wind dynamic pressure • - The termination shock and heliopause are moving in => easier GCR access to 1 AU • - Voyager observations point out this is not major effect at 1 AU. • 4. Tilt of the heliospheric current sheet • - Drifts play a major role in cosmic ray transport (Levy 1975, 1976; Jokipii & Levy 1977). During A < 0 positively-charged ions drift in along the current sheet. As a result, their 1-AU intensity is sensitive to the HCS tilt. • 5. CMEs and other Solar Transients • - Both the CME rate and mass reached minimum levels in 2007-2008.

10. Drift Patterns for qA>0 General comments … (Alan Cummings) Drifts carry positive particles from high latitudes to low latitudes during A>0 portion of solar cycle. Expect positive latitudinal gradient in A>0. Arrows reversed in A<0. Expect negative latitudinal gradient in A<0, which is the current situation. Adapted from Jokipii & Thomas, 1981 Observationally, Radial (and latitudinal) gradients showed strong dependences on current sheet tilt angle in last A<0 period (1986-1989) and more moderate dependence in A>0 – in outer heliosphere

11. ACRs source intensity changes near helioequator for A<0 and A>0.  This is why it’s OK to have GCRs be at their all-time high intensity at 1 AU but not ACRs – ACRs more sensitive to tilt than GCRs because of different source distributions. Jokipii and co-workers

12. Constraints on the Acceleration of Charged Particles in the Heliosphere (Randy Jokipii) • Observed ACR charge states limit the acceleration time of ACRs to less than a few years (e.g., Adams 1991; Jokipii 1992; Mewaldt et al 1996). • Spatial constraints: Larger systems can accelerate particles to higher energies. • Stochastic versus deterministic acceleration • - Stochastic acceleration • -- Example: 2nd-order Fermi • -- Involves a random walk or diffusion in energies. • Too slow to produce the energetic ACRs • - Deterministic acceleration • -- Examples: Diffusive shock acceleration; compression acceleration. • -- Usually is uni-directional in energy – involves a directed electric field. • The termination shock, essentially a quasi perpendicular one, readily gives us ACRs

13. Thank you