Characteristics of a long-lived CIR and the corresponding depression in the GCR flux

Abstract:

We observe a long-lived CIR recurring in 27 consecutive Carrington rotations 2057-2083 in the time period from June 2007 - May 2009. We characterize the in situ measurements of this long-lived CIR as well as the corresponding depression in the GCR count observed by SOHO/EPHIN, and analyze them throughout different rotations. We find that the behavior of the flow speed peak roughly shows a rising phase and a declining phase. This is similar to the evolutionary profile of some observed coronal hole areas, but without a clear peak. The GCR count evolutionary profile roughly follows that of the flow speed peak, but moreover we find that the inverted GCR count time-profile matches very well with that of the flow speed throughout different rotations. We perform a statistical analysis and find the GCR count amplitude correlated to the peak in the magnetic field and flow speed, as expected based on previous statistical studies. In order to characterize a generic CIR profile for modelling purposes, we perform the superposed epoch analysis using relative values of the key parameters. Based on the observed properties we propose a simple analytical model starting from the basic Fokker-Planck equation.