Based on hourly averaged data, the ring current decay parameter and the injection function associated with interplanetary medium parameters are analysed. The distinction among the decay parameter values during a magnetic storm has been carefully drawn, the dependence ofτ on the injection function during the main phase and on the DR variation during the recovery phase being emphasized. The modeling of the DR variation for weak and/or moderate storms as well as intensive storms carried out demonstrates a good agreement between the model time profiles and observed data of magnetic storm activity.