The Emerging Features of Bipolar Magnetic Regions during Solar Minima

Abstract

Solar magnetic synoptic charts obtained by NSO/Kitt Peak and SOHO/MDI are analyzed for studying the appearance of bipolar magnetic regions (BMRs) during solar minima. As a result, we find the emergence of long-lived BMRs has three typical features. (1) BMRs' emerging rates of the new cycles increase about 3 times faster than those of the old cycles decrease. (2) Two consecutive solar cycles have an overlapping period of near 10 Carrington rotations. During this very short overlapping time interval, BMRs of two cycles tend to concentrate in the same longitudes. (3) About 53% BMRs distribute with a longitudinal distance of 1/8 solar rotation. Such phenomenon suggests a longitudinal mode of m=8 existing during solar minima.