Maintenance condition of back‐building squall‐line in a numerical simulation of a heavy rainfall event in July 2010 in Western Japan

Back‐building squall‐lines (BBSs) cause local heavy rainfalls and lead to natural disasters. Therefore, better understanding BBSs would have a significant impact on disaster prevention and mitigation. Although a conceptual maintenance condition of BBSs is proposed by previous studies, the concept stands on a case study. We clarified that a mesoscale moist area in water vapor front localizes the continuous forming of new cells in the BBS and reinforced the concept with another case. A numerical simulation of the heavy rainfall during July 11–12, 2010, in western Japan was used to confirmation of the conceptual maintenance condition of the BBS. We found that the new cells of BBS are continually formed at the confluence zone of the synoptic‐scale cold front and the mesoscale area with large water vapor amount at low‐level. It supports the conceptual maintenance condition, and the mesoscale moist area in water vapor front is a distinct characteristic in this case. The position where new cells are formed has been anchored by the mesoscale moist area for 2 hr.