Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh14a..01j&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH14A-01
Physics
[2104] Interplanetary Physics / Cosmic Rays, [2114] Interplanetary Physics / Energetic Particles, [2124] Interplanetary Physics / Heliopause And Solar Wind Termination, [2126] Interplanetary Physics / Heliosphere/Interstellar Medium Interactions
Scientific paper
After the Voyagers' crossing of the heliospheric termination shock, there has been great anticipation of the next crossing -- that of the heliopause, which is the boundary between plasma of solar origin and the ambient interstellar plasma. Recent Voyager 1 observations suggest that the spacecraft is approaching the heliopause. Here, I will discuss possible effects of this boundary on energetic particles . The observed galactic cosmic rays (GCR) originate in the galaxy and must cross the heliopause from the outside, whereas the anomalous cosmic rays (ACR) are most probably accelerated near or inside of the heliopause (termination shock, heliosheath or the heliopause itself). One important question involves the effects of the interstellar medium, beyond the heliopause, on the energetic particles. In most models of the solar modulation of GCR, the heliopause is taken to be where the GCR intensity becomes equal to the undisturbed interstellar GCR intensity. This assumption is difficult to justify, and may in fact be significantly incorrect. Because of uncertainties regarding the local interstellar medium, a number of possibilities regarding this question are compatible with present knowledge. Similarly, models of the ACR generally set a free-escape boundary (zero intensity) at the heliopause . Again, as with galactic cosmic rays, a number of other possibilities are consistent with our present knowledge. ACR escape may be impeded. Energetic particles may be accelerated at the heliopause. It has been proposed that acceleration in reconnections compressions become strong near the heliopause and produce the ACR there. Furthermore, it is possible that fluid velocity shear, which also accelerates energetic charged particles, is strong at the heliopause. It has also been proposed that the energetic-particle transport coefficients are considerably modified in the outer heliosphere, either because the warps of the heliospheric current sheet are brought very close together to less than the gyro-radius of the GCR or ACR, or because reconnection events caused by the warps in the current sheet produce characteristic magnetic structures. Finally, instabilities of various kinds at the heliopause have been proposed and these may result in particle acceleration or changes in transport. The various possibilities will be discussed and compared with available observations. New tests will be discussed.
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