Case Study of a Split Front and Associated Precipitation during the Mei-Yu Season

Abstract This study investigated the relationship between a split front and precipitation over western Japan on 10–11 July 2007 based on data from routine observations and a global objective analysis. The split front formed at the leading edge of a dry intrusion overrunning a mei-yu front in a deep layer from the north. Strong upward motion was present ahead of the frontogenesis associated with the split front. In contrast, upward motion over the mei-yu front was suppressed by downward motion behind the split front. An intense rainband developed along the split front south of the mei-yu front. In contrast, precipitation over the mei-yu front gradually disappeared with the southward advance of the split front. Rainfall as heavy as 99 mm h−1 was observed under the rainband associated with the split front. The strong upward motion that induced heavy rains was attributed to the rising branch of the frontal circulation of the split front and the intense low-level convergence facilitated by the dry intrusion behind the split front. These findings indicate that split fronts have a substantial impact on the development and distribution of precipitation during the mei-yu season.