The magnetosphere-ionosphere coupling model of substorms developed by Kan et al. (1988) is improved by including the realistic recombination time scale in the ionosphere and the quiet-time convection prior to the enhancement of the magnetospheric convection. One of the new features of the improved model is the appearance of highly localized structures of the discrete aurora along the poleward boundary of the diffuse aurora in the evening-midnight sector. This feature is consistent with the auroral image data of the Viking satellite. Our results show that a discrete auroral arc suddenly brightens near midnight and starts moving westward when the auroral brightness increases to a certain level, which is similar to the substorm onset scenario. The bright discrete aurora has an initial velocity of around 2 km s-1, but gradually slows down and dims. This feature is identified with the westward traveling surge. Following passage of the surge, several localized auroral arcs remain along the auroral oval, and the most active auroral region shifts from premidnight toward the evening sector.