Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh11b1670s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SH11B-1670
Physics
[2162] Interplanetary Physics / Solar Cycle Variations, [2164] Interplanetary Physics / Solar Wind Plasma, [2169] Interplanetary Physics / Solar Wind Sources, [2199] Interplanetary Physics / General Or Miscellaneous
Scientific paper
The yearly averaged solar wind proton flux seen by spacecraft at L1 has decreased from the previous solar sunspot minimum in May 1996, past the recent minimum in December 2008, and through 2009. During the 2001 solar maximum, the average solar wind proton flux was ≈10% lower than in 1996, and by 2009 the proton flux was ≈ 30% lower than in 1996. The decrease in the yearly averaged helium fluxes from 1996 to 2009 was even greater at ≈50%. However, in contrast to the proton flux, which continued to decrease during solar maximum, the helium flux was enhanced at solar maximum by > 30%, before steadily decreasing through the declining phase. From 1998-2009, the trends in both the protons and helium were verified in three separate data sets: ACE/SWEPAM, ACE SWICS, and Wind/SWE. As a result, we are confident that the observed long-term decrease in proton and helium flux is real, and not attributable to any drifting instrument calibration. Additional measurements from ACE SWICS show that oxygen and carbon ion fluxes were, like the helium fluxes, higher at solar maximum, but lower in 2009 than in 1998 by more than 30%. As the solar wind flux has weakened, the magnitude of the helium-proton differential streaming has decreased as well. The average magnitude of the helium-proton differential velocity reached a peak in 2003, during an interval of recurrent coronal hole high-speed streams. From 2003-2009 the average differential speed decreased from 45 km/s to 20 km/s, correlating with an overall decrease in the average solar wind Alfven speed from 60 km/s to 35 km/s.
Kasper Justin Christophe
Lepri Susan T.
Maruca Bennett A.
Ryland P.
Skoug Ruth M.
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