Since the middle of July 1991, approximately one month after the explosive eruptions of Mt. Pinatubo in the Philippines, Bishop's ring phenomena were occasionally observed over Japan under favorable conditions of clear skies. On the basis of the single-scattering approximation, the chromaticity of Bishop's rings was simulated. It was found that Bishop's rings are observable only when a sufficient amount of aerosols exist that have an unusually narrow mono-modal size distribution and a mode radius between 0.57 &mgr;m and 0.63 &mgr;m, with an effective variance of less than 0.05. ¿ American Geophysical Union 1993