A magnetic field model of the magnetotail current sheet based on cellular automation (CA) is presented. The present isotropic model is a continuously driven, two-dimensional running CA. The model has a physical interpretation in terms of magnetohydrodynamic (MHD) equations, and features self-organized critical (SOC) behavior with power-law scalings both in durations and sizes of instabilities (avalanches). The model has nonlinear energy dissipation, and shows avalanches with and without an external trigger. Thus the model reproduces some of the statistical features recently observed in the magnetotail. ¿ 1999 American Geophysical Union