2021 Volume 99 Issue 2 Pages 357-377
A stationary line-shaped precipitation system (SLPS), which is one type of mesoscale convective systems, is a typical heavy rain-producing weather system formed during warm seasons in Japan. Although the Kinki district, western Japan, is known as a frequent occurrence region for SLPSs, their formation mechanisms in the region have not been sufficiently elucidated yet because of their complex formation processes. Using observational data and high-resolution numerical experiments, in this study, we investigated a SLPS event that occurred on 1 September 2015. We also conducted numerical sensitivity experiments regarding the orography and initial time.
The observational data showed that the relative humidity at lower levels was high during the SLPS event. The southwesterly was dominant at middle levels over the Kinki district during the formation of the SLPS. The formation of the SLPS was associated with neither a mesoscale low-pressure system nor a synoptic-scale cold front, demonstrating that these were not necessary conditions for the formation of the SLPS.
In the numerical experiments, we found that the SLPS was formed in a low-level convergence zone of the westerly with the warm and moist south-southwesterly from the Kii Channel. New convective cells formed over the north of Awaji Island and are propagated northeastward by the middle-level southwesterly. This cell formation process was repeated and resulted in the formation of the SLPS. The sensitivity experiments for the orography around the occurrence area of the SLPS indicated that the orography was not a significant factor for the formation of the SLPS in this event. The orography can modify the location of the SLPS.
