In the course of reminiscing about the first studies of the newly discovered galactic proton and helium nuclei and their modulation in the 1950's, we recognized that this field has actually come full circle with the Voyager studies of these same nuclei out to beyond 120 AU in 2012. In the 1950's the first models of the heliospheric modulation postulated a "ring current" or something equivalent, which produced a modulation potential of up to 1 to 3 GV as a source of solar modulation. This potential difference was needed to explain the relative modulation of protons and helium nuclei. Later this modulation was explained as a force field potential by Gleeson and Axford in a Parker description of cosmic ray transport. Recent Voyager measurements of the proton, helium and carbon spectra in the outer heliosphere beyond the heliospheric termination shock (HTS) up to the beginning of 2012 are in accordance with this same earlier picture describing the modulation as due to a modulation potential. However, there is no longer a solar wind in the outermost heliosphere so Parker's original description is no longer complete. So our reminiscences have led us back to a modern picture of solar modulation in the heliosphere that is very similar to that existing in the 50's and 60's, searching for a cause for the modulation. Since Voyager 1 now appears to be at a location where this modulation potential is approaching zero, a whole new field of study of the unmodulated spectra of the charged species of galactic cosmic rays at lower energies down to perhaps as low as 10-20 MeV also is being opened up, similar in development to the original studies of these individual nuclei in the 1950's that were the result of newly developed high altitude balloons and also new experimental techniques that separated the individual charges.
Skip Nav Destination
Research Article| February 07 2013
Reminiscences - Interrupted: A solar modulation theory once lost, now found?
AIP Conf. Proc. 1516, 89–96 (2013)
William R. Webber; Reminiscences - Interrupted: A solar modulation theory once lost, now found?. AIP Conf. Proc. 7 February 2013; 1516 (1): 89–96. https://doi.org/10.1063/1.4792546
Download citation file: