Multiscale Features of Line-Shaped Precipitation System Generation in Central Japan during Late Baiu Season

Abstract

Multiscale structures near the line-shaped precipitation systems observed around Osaka Bay on July 2 and 5 2006, were analyzed using observational data and a numerical model. In both cases, a cold front extending from a meso-a-scale cyclone in the Sea of Japan moved eastward over central Japan, and just before its passage a mesob-scale low (named ''Tokushima small low'') was formed over the eastern part of Shikoku Island in the warm sector of the meso-a-scale cyclone. On the eastern side of Tokushima small low, the southwesterly below 900-hPa level was intensified (@15 m s À1 ) in the warm sector, and it converged with westerly on the western (cold) side of the cold front. Clockwise rotating vertical shear was produced between this southwesterly and the Baiu jet (20-30 m s À1 ) around 700-hPa level. The stability over Osaka Bay decreased in warm-moist air transported by the southwesterly (equivalent potential temperature > 345 K at 950-hPa level and < 335 K at 600-hPa level). In addition, meso-g-scale lee waves were generated by the westerly on the western side of the cold front flowing over the mountains (Awaji Island and Rokko Mountains) surrounding Osaka Bay, and they triggered the development of the line-shaped precipitation system around Osaka Bay. A Tokushima small low was generated in four cases from among 15 cases of meso-a-scale cold fronts that passed in

Formation Mechanism of a Stationary Line-Shaped Precipitation System in the Kinki District, Japan —Case Study on 1 September 2015 Event—

“…The Kinki district was influenced by the southwesterly on the west side of the North Pacific high-pressure system and the westerly on the south side of the extratropical cyclone. This surface pressure pattern was similar to those in the SLPS events studied previously (Seko et al 2006;Higashi et al 2010;MRI 2010). However, the cold front associated with the extratropical cyclone was located to the further west of the Kinki district during the formation of the SLPS.…”

“…Second, other previous studies have suggested that large-scale forcing, such as a cold front, was an essential factor for generating a convergence zone (Kato and Goda 2001;Kato 2006;Seko et al 2006;Higashi et al 2010;MRI 2010;Kato 2020). However, no large-scale forcings were found in the observation data and numerical experiments in this study.…”

“…unstable over the Kinki district. Consequently, the formation of convective cells was suppressed in EXP_00.Previous studies have shown that the formation of SLPSs in the Kinki district was caused by orography effects such as Mount Rokko or Awaji Island(Higashi et al 2010;Ishihara and Takara 2018). To investigate the role of the orography surrounding Osaka Bay, we conducted several sensitivity experiments for the orography.Figure 14shows the differences in…”

“…1, except Shikoku Island), western Japan, is a region where SLPSs are frequently observed. Higashi et al (2010) studied the SLPS formation mechanisms in the Kinki district during the post-Baiu season in August and September. They proposed that several mesoscale factors facilitated the formation of SLPSs.…”

Quantitative Analysis of Water Vapor Transport during Mei-Yu Front Rainstorm Period over the Tibetan Plateau and Yangtze-Huai River Basin

“…ere have been many studies of precipitation in Mei-yu fronts. Great progress has been made in many aspects, including the classification of Mei-yu fronts [4,5], cloud structure [6][7][8], terrain effects [9,10] and mesoscale systems [11][12][13]. In addition, abundant water vapor is necessary to form the heavy rainfall in Mei-yu fronts [14].…”