A survey of geomagnetic and plasma time lags in the solar-wind-driven magnetosphere of earth

Abstract

Sixteen variables describing the state of the magnetosphere are examined in the years 1991–2007; the sixteen variables include nine geomagnetic indices plus seven measures of electron and ion precipitation into the atmosphere, the rate of substorm occurrence, the pressure and number density of the ion plasma sheet, the flux of substorm-injected electrons, and the radiation-belt electron flux. Eight other variables are used to represent the properties of the solar wind at Earth. To estimate the time lags between magnetospheric and solar-wind variables bivariate (two-variable) linear correlations, multivariate linear correlations, and vector-vector correlations are utilized. Using bivariate correlation the lag time of each magnetospheric variable with respect to each solar-wind variable is varied to obtain the maximum correlation coefficient. Using multivariate linear correlations, the time series of each magnetospheric variable is correlated with a linear combination of the eight time series of the eight solar-wind variables, with eight independent lead times on the eight solar-wind variables optimized to produce the largest multivariate correlation coefficient. The resulting time lag between each magnetospheric variable and each solar-wind variable is then catalogued. Additionally, the solar-wind variables that most-strongly affect each of the 16 magnetospheric variables are noted. A similar process of optimizing lag times on magnetospheric variables is performed during vector-vector correlations between a 9-dimensional magnetospheric state vector and an 8-dimensional solar-wind state vector.