An electromagnetic field produced in high-energy heavy-ion collisions contains much useful information, because the field can be directly related to the motion of the matter in the whole stage of the reaction. One can divide the total electromagnetic field into three parts, i.e., the contributions from the incident nuclei, nonparticipating nucleons, and charged fluid, the latter consisting of strongly interacting hadrons or quarks. Parametrizing the space-time evolution of the charged fluid based on hydrodynamic model, we study the development of the electromagnetic field which accompanies the high-energy heavy-ion collisions. We found that the incident nuclei bring a rather strong electromagnetic field to the interaction region of hadrons or quarks over a few fm after the collision. On the other hand, the observed charged hadrons' spectra are mostly affected ͑Coulomb effect͒ by the field of the charged fluid. We compare the result of our model with experimental data and found that the model reproduces them well. The pion yield ratio Ϫ / ϩ at a RHIC energy, AuϩAu 100ϩ100 GeV/nucleon, is also predicted. ͓S0556-2813͑99͒00609-3͔PACS number͑s͒: 25.75.Ϫq
II. GLAUBER MODEL
A. Participant and penetrating nucleons in A-B collisionsThe participant nucleon number in a nucleus-nucleus collision can be estimated by using the Glauber model ͓13͔. To *Electronic address: osada@fma.if.usp.br † Electronic address: hama@fma.if.usp.br 1 In a previous work by Barz et al. ͓9͔, the role of the incident nuclei and penetrating systems is not clear. PHYSICAL REVIEW C, VOLUME 60, 034904 0556-2813/99/60͑3͒/034904͑13͒/$15.00