Geoscience Reference
In-Depth Information
The Heliosphere
(outer) (inner)
Termination Shock
Voyager 1
solar wind
Voyager 2
Bow Shock ?
FIGURE 2.4 Diagram of the heliosphere. SOURCE: Courtesy of J. Giacalone, University of Arizona, modified
from NASA image available at, courtesy
of NASA/Goddard/Walt Feimer.
Giacalone also pointed out that, although the four basic processes of particle diffusion,
convection, drifts, and energy changes have been known for 50 years, the transport coefficients needed to
calculate their effects are still poorly known. However, it is now accepted that none of the processes
included in the classic Parker transport equation can be neglected; it is a complex system. This
complexity limits the accuracy of attempts to use the isotope record to derive the record of solar
irradiance. The solar modulation of cosmic rays is caused by both the relatively gradual evolution in the
background solar wind and by the pulses associated with coronal eruptions, through the complex
processes referred to. Much of the variation in irradiance (at least the 11-year variation) originates from
the emission from plasma heated by the dynamics of the near-surface magnetic field with contributions
from both the open and closed field components both during quiescence and during flarings. This
differential behavior makes it difficult to use radioisotopes to generate more than a rough estimate of
variation in TSI and UV flux, such as those shown by workshop presenter Raimund Muscheler.
Giacalone showed the evidence for a low-level 11-year cycle in radioisotopes during the extended
Maunder Minimum of solar activity during the 17th century. Such isotopic evidence currently provides
the best chance of determining how much the solar magnetic field decreased during that period and
therefore how much the Sun dimmed. He discussed how the differences between galactic cosmic rays
and anomalous cosmic rays (ACRs) could be seen during the most recent solar minimum. The GCR
intensity was the highest measured by spacecraft, but ACRs had a lower intensity compared to previous
solar minima. He suggested one possible interpretation was that fewer ACRs were being produced at the
termination shock of the heliosphere. This difference is useful for determining the physics of cosmic ray
transport in the heliosphere.
Search WWH ::

Custom Search