Stationary Line-Shaped Precipitation Systems in Summer Season over the Kinki District, Japan

Kyeong-seok MIN

In Japan, a stationary line-shaped precipitation system (SLPS) which is one meso-scale convective systems (MCSs) is a typical heavy rain producing weather system in summer. The previous studies have shown that SLPSs are caused by the convergence of the westerly and the southerly in the Kinki District. The formation mechanism of SLPSs in the Kinki District is not sufficiently clarified yet because of complex processes in several different scales. In the present study, we studied characteristics of SLPSs from 2011 to 2015 in summer season over the Kinki District. Three events of SLPSs in summer, are studied in detail using observation data. High-resolution simulation experiments of the SLPS event observed on September 1, 2015 was also conducted. Sensitivity experiments for the orography were also made. Finally, the data assimilation experiment conducted to improve the forecast of the SLPS. SLPSs observed in the Kinki District often extend from the northeast to the southwest and move northeastward. In one of the three events, the humidity in the lower levels was large while the stability of the upper levels was large. The wind direction of the lower levels agreed with the SLPSs direction when the length of SLPS is large. On the other hand, the length of SLPS is short. Unlike previous studies, we found that the SLPS formed without extratropical cyclone and cold front. An eastward directed SLPS occurred with the passing of a cold front. This indicates that the surface pressure systems are not always a necessary condition for the formation of SLPSs in the Kinki District. According to numerical experiments, we found that the SLPS formed by the convergence of the westerly south-southwesterly with a moist and warm air in the southern Kinki District on September 1, 2015. New cells formed and moved following the southwesterly in the middle layer. The sensitivity experiments of orography showed that Rokko Mountain and Awaji Island are not essential in the event. On the other hand, Shikoku Island affects the location, distribution, and precipitation rate of SLPS in the present. Finally, sensitivity experiments of data assimilation, we found that the initial condition is important for the simulation of SLPS.