Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm13a1792r&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM13A-1792
Physics
[2720] Magnetospheric Physics / Energetic Particles: Trapped, [2722] Magnetospheric Physics / Forecasting, [2774] Magnetospheric Physics / Radiation Belts, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions
Scientific paper
Thirty years ago Paulikas and Blake, [1979] showed a remarkable correlation between geosynchronous relativistic electron fluxes and the speed of the solar wind (Vsw). This seminal result has been a foundation of radiation belt studies, space weather forecasting, and our current picture of how the solar wind couples energy into the inner magnetosphere. We have repeated their analysis with the considerably longer-running data sets (1989 through 2009) from the LANL geosynchronous energetic particle instruments. While our results do not contradict those of Paulikas and Blake, the more complete data set points to several surprising differences in interpretation. While we do find a strong relationship between relativistic electron flux and Vsw we show that the relationship is distinctly non-linear. In fact the scatter plot shows a rather distinct triangle-shaped plot. The distribution has a distinct velocity-dependent lower limit on fluxes rather than a velocity-dependent upper limit that one might expect. There is also a sharp upper limit on electron fluxes that is roughly independent of Vsw. High electron fluxes can be observed for any value of Vsw with no indication of a Vsw threshold. We also find a distinct solar cycle dependence with the triangle-shaped distribution most evident in two declining phase years but weak or no correlation in the conditions found during two solar maximum years. We examine and test a number of possible explanations for the shape of the distribution. We examine the role of time dependence and time lag. We also look at the same relationship but at much lower energies than considered previously. We find that the relationship between Vsw and flux at 62 keV show roughly the same features as the triangle distribution seen at MeV energies suggesting that Vsw likely controls the source population, the source of free energy for acceleration, or both. We conclude that the relationship between radiation belt electron fluxes and solar wind velocity is substantially more complex than suggested by previous statistical studies. We find that there are important ways in which the ‘conventional wisdom’ stating that high velocity wind drives high MeV electron fluxes is, in general, either misleading or overly simplistic.
Blake J.
Cayton Thomas E.
Friedel Reiner H.
Henderson Gideon M.
Morley S.
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