Inspect the Time Lag in Galactic Cosmic-Ray Solar Modulation

Abstract It is well known that there is a time lag between the solar activity and the galactic cosmic-ray flux. How to accurately describe this delay is the key problem in making precise predictions of cosmic-ray flux. In this work, a response function in convolution is first used to describe the relative contribution of the solar wind blowout at earlier times to the current flux (the origin of time lag), and its explicit profile is obtained by our 3D time-dependent numerical model. It is found that our response function is superior to other functions in accounting for the time lag effect, and its rigidity and physical process dependence are studied thoroughly. At last, this description is partly demonstrated by a simplified derivation based on the underling physical processes.