Physics
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1043g&link_type=abstract
Journal of Geophysical Research (Space Physics), Volume 107, Issue A4, pp. SMP 3-1, CiteID 1043, DOI 10.1029/2001JA000155
Physics
10
Magnetospheric Physics: Ring Current, Magnetospheric Physics: Storms And Substorms, Magnetospheric Physics: Magnetosphere-Inner
Scientific paper
Close to the peak of a magnetic storm, the ratio of the O+ to the H+ contribution to the ring current energy, U(O+)/U(H+), depends on both solar EUV flux and storm size. This ratio provides a lower limit on the importance of the ionospheric plasma source compared to the solar wind source since only the ionosphere supplies O+ while both the solar wind and the ionosphere supply H+. We have used measurements from the CHEM ion spectrometer on the Active Magnetospheric Particle Tracer Explorers (AMPTE) CCE spacecraft to assess U(O+)/U(H+) near storm maximum. CHEM measured equatorial ion composition over the energy per charge range 1.5-300 keV/e for more than 4 years, from solar minimum through much of the rising phase of Solar Cycle 22. Thus our data set is large, including 67 magnetic storms with minimum Dst values less than -50 nT. To estimate the O+ and H+ contributions to the ring current energy, we have multiplied local measurements of each ion's energy density along the CCE trajectory by the appropriate dipole L shell volume and summed over L values from two to seven. We have used a bilinear regression to assess the dependence of U(O+)/U(H+) on solar EUV flux, parameterized by F10.7, and storm size, parameterized by minimum Dst value Dstmin. We have found that both F10.7 and Dstmin are important (and nearly independent) predictors of U(O+)/U(H+). Only four storms of 67 had U(O+)/U(H+) > 1. Two of the four were fairly small, with |Dstmin| < 100 nT but with high F10.7 values. This shows that O+ can sometimes contribute the majority of the ring current energy during small storms when the solar EUV flux is high (i.e., near solar maximum) as well as during very large storms throughout the solar cycle.
Greenspan Marian E.
Hamilton Douglas C.
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