This paper examines AKR spectra using the long-term observation from the Polar satellite to prove the comprehensive features of field-aligned auroral acceleration and to give observational constraints to the theoretical mechanisms for acceleration at substorm. The remote observations of substorm phenomena through auroral radio waves from the high altitude polar magnetosphere disclosed some fundamental characteristics of the vertical auroral acceleration region and provided new information on the formation process for field-aligned electric field at substorm onset. Furthermore, we reveal new aspect of the relationship between the plasma state in the plasma sheet and the formation of aurora acceleration.