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The Intensities of Cosmic Ray H and He Nuclei at ~250 MeV/nuc Measured by Voyagers 1 and 2 - Using these Intensities to Determine the Solar Modulation Parameter in the Inner Heliosphere and the Heliosheath Over a 40 Year Time Period

Webber, W. R. and Stone, E. C. and Cummings, A. C. and Heikkila, B. and Lal, N. (2017) The Intensities of Cosmic Ray H and He Nuclei at ~250 MeV/nuc Measured by Voyagers 1 and 2 - Using these Intensities to Determine the Solar Modulation Parameter in the Inner Heliosphere and the Heliosheath Over a 40 Year Time Period. . (Unpublished) https://resolver.caltech.edu/CaltechAUTHORS:20200204-082135453

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Abstract

We have determined the solar modulation potential, Φ, vs. time that is observed at Voyager 1 and 2 from measurements of the H and He nuclei intensities at a common energy of 250 MeVnuc. The H nuclei have a rigidity 0.7 GV, the He nuclei 1.4 GV. These measurements cover a 40 year time period, which includes almost 4 cycles of solar 11 year sunspot variations, throughout the inner heliosphere out to the HTS at distances of 95 AU and 85 AU, respectively at V1 and V2, and then beyond in the heliosheath. Inside the HTS the modulation potential vs. time curves at V1 and V2 show a very similar temporal structure to those observed at the Earth. During a later period of maximum solar modulation from 2000.0 to 2005.0 when V1 and V2 are in the outer heliosphere between 60-94 AU, the main temporal features of the modulation potential curves at all 3 locations match up with appropriate time delays at V1 and V2 if it is assumed that spatially coherent structures are moving outward past V1 and V2, with outward speeds of up to 700 Kms⁻¹. After 2004.0 V1 and V2 are at latitudes of +35° and -30° respectively, placing lower limits on the latitude extent of these structures. Beyond the HTS in the heliosheath the modulation potential slowly decreases at both spacecraft with only a weak evidence of the unusual modulation minimum observed at the Earth in 2009, for example. A sudden decrease of the modulation potential 50 MV for both H and He nuclei occurs at V1 just before the heliopause crossing at about 122 AU. This decrease has not yet been observed at V2, which is now at 113 AU and still observing a modulation potential 60 MV.


Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription
http://arxiv.org/abs/1706.02772arXivDiscussion Paper
ORCID:
AuthorORCID
Stone, E. C.0000-0002-2010-5462
Cummings, A. C.0000-0002-3840-7696
Additional Information:The authors wish to thank JPL for their unfailing support, both moral and financial, for 40 years since the launch of V1 and V2 in August, 1977.
Group:Space Radiation Laboratory
Record Number:CaltechAUTHORS:20200204-082135453
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200204-082135453
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101101
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Feb 2020 17:21
Last Modified:04 Feb 2020 17:21

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