Untangling the Solar Wind and Magnetospheric Drivers of the Radiation Belt Electrons

摘要

Many solar wind parameters correlate with one another, which complicates the causaleffect studies of solar wind driving of the magnetosphere. Conditional mutual information (CMI) is used to untangle and isolate the effect of individual solar wind and magnetospheric drivers of the radiation belt electrons. The solar wind density (n_(sw)) negatively correlates with electron phase space density (PSD; average energy ~1.6 MeV) with time lag (τ) = 15 hr. The effect of nsw has been attributed to magnetopause shadowing or other loss mechanisms, but when the effect of solar wind velocity (Vsw) is removed, τ shifts to 7–11 hr, which is a more accurate time scale for this process. The peak correlation between V_(sw) and PSD shifts from τ = 30–50 to 44–56 hr, when the effect of nsw is removed. This suggests that the time scale for electron acceleration to 1–2 MeV is about 44–56 hr following V_(sw) enhancements. The effect of nsw is significant only at L~* = 4.5–6 (L~* > 6 is highly variable), whereas the effect of V_(sw) is significant only at L~* = 3.5–6.5. The peak response of PSD to V_(sw) is the shortest and most significant at L~* = 4.5–5.5. As time progresses, the peak response broadens and shifts to higher τ at higher and lower L~*, consistent with local acceleration at L~* = 4.5–5.5 followed by outward and inward diffusion. The outward radial diffusion time scale at L~* = 5–6 is ~40 hr per RE.