The empirical approach in global modeling the proton distributions of the inner magnetosphere (Orsini et al., 2004) is here applied for a detailed analysis of the 21--25 April 2001 storm. This method, based on comparison of the Milillo et al. (2001) model with local proton spectra, results as a simple and powerful tool for inner magnetospheric studies. In this work we use the Los Alamos National Laboratory proton spectra in order to obtain the time-evolving model parameters at different magnetic local times (MLT). We compare the model parameters with the geomagnetic indexes as well as with the solar wind data. The final outcome of this study is the analysis of the evolution of the magnetospheric populations during storms. This analysis shows that specific local characteristics of the proton fluxes, as the width of proton spectra, can be interpreted as global plasma distributions tracers. Furthermore, their temporal evolution is recurrent during any storm development, depending on solar wind characteristics. In particular, this study suggests the existence of a MLT-dependent time delay between the solar wind disturbance arrival and the broadening of the energy spectra of proton fluxes in the inner magnetosphere. Finally, the model shows how the particles convected or injected from the nightside during storm main phase quickly decay or diffuse gaining energy so that the diffused particles play a major role during the recovery phase.