Time‐Integral Correlations of Multiple Variables With the Relativistic‐Electron Flux at Geosynchronous Orbit: The Strong Roles of Substorm‐Injected Electrons and the Ion Plasma Sheet

• Published in: Journal of geophysical research. Space physics 2017-12, Vol.122 (12), p.11,961-11,990
• Main Author: Borovsky, Joseph E.
• Format: Article
• Language: English
• Subjects: Correlation; Correlation coefficients; correlations; Electron density; Electron flux; Electron radiation; electron radiation belt; Electrons; Evolution; Evolutionary algorithms; Fluctuations; Genetic algorithms; Geosynchronous orbits; Integrals; Intervals; Magnetosphere; Magnetospheres; Magnetospheric-solar wind relationships; Optimization; Radiation; Relativism; Relativistic effects; Solar wind; solar wind structure; Spacecraft; substorm injections; systems science
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2017JA024476

Time‐integral correlations are examined between the geosynchronous relativistic electron flux index Fe1.2 and 31 variables of the solar wind and magnetosphere. An “evolutionary algorithm” is used to maximize correlations. Time integrations (into the past) of the variables are found to be superior to time‐lagged variables for maximizing correlations with the radiation belt. Physical arguments are given as to why. Dominant correlations are found for the substorm‐injected electron flux at geosynchronous orbit and for the pressure of the ion plasma sheet. Different sets of variables are constructed and correlated with Fe1.2: some sets maximize the correlations, and some sets are based on purely solar wind variables. Examining known physical mechanisms that act on the radiation belt, sets of correlations are constructed (1) using magnetospheric variables that control those physical mechanisms and (2) using the solar wind variables that control those magnetospheric variables. Fe1.2‐increasing intervals are correlated separately from Fe1.2‐decreasing intervals, and the introduction of autoregression into the time‐integral correlations is explored. A great impediment to discerning physical cause and effect from the correlations is the fact that all solar wind variables are intercorrelated and carry much of the same information about the time sequence of the solar wind that drives the time sequence of the magnetosphere. Key Points Time‐integral correlations with radiation‐belt electron fluxes are stronger than time‐lagged correlations Substorm‐injected electrons and the ion‐plasma sheet pressure appear to play strong roles in the evolution of the electron radiation belt Interpretations are made of the optimal integration times obtained from an evolutionary algorithm to maximize correlation coefficients