Solar wind-driven electron radiation belt response functions at 100-min time scales

We present a simple yet numerically robust technique, using autoregressive linear filters, to remove unwanted “colored noise” from solar wind and radiation belt electron data at sub-daily resolution. The remaining signal is then studied using finite impulse response linear prediction filters to represent the driven portion of the linear dynamics that describe the coupling between solar wind speed and electron flux. Sub-daily resolution response profiles covering magnetic L-shells between 1.1 and 8.0 RE are presented which are consistent with daily resolution response functions. Namely, while there is strong global coherence governing electron flux dynamics, there are at least two distinct responses. The first response is an immediate dropout of electrons between L = 4 and L = 7 that is at least a partly adiabatic effect associated with enhancements in the ring current. This is followed by a 1–2 day delayed enhancement across the same L-shells that is likely a result of increased radial diffusion. The second response is an immediate enhancement seen between L = 3 and L = 4 with a typical duration of less than one day. Plausible explanations for this second response are briefly discussed, but neither empirical nor theoretical evidence can establish conclusively a definite physical cause. Finally, the response profiles show significant solar cycle and seasonal dependencies, indicating that better model output might be achieved with: (1) additional simultaneous solar wind inputs; (2) more sophisticated dynamical model structures capable of incorporating non-linear feedback; and/or (3) time-adaptive linear filters that can track non-stationary dynamics in time.