Physical settings for all simulations are same except for the boundary layer parameterizations: The Mellor–Yamada–Nakanishi–Niino (MYNN) level-3 planetary boundary layer scheme (Nakanishi and Niino 2006) is adopted for the low-resolution simulations, while the Deardorff subgrid turbulence scheme (Deardorff 1980) is adopted for the intermediate- and high-resolution simulations. Initially, 900 parcels were placed along a circuit surrounding the strong vorticity (Fig. This work was supported by JSPS KAKENHI Grants 18H01277 and 17K14391, and FLAGSHIP2020 of Ministry of Education, Culture, Sports, and Technology within the priority study Advancement of Meteorological and Global Environmental Predictions Utilizing Observational “Big Data.” This research used computational resources of the K computer provided by the RIKEN Advanced Institute for Computational Science (currently Center for Computational Science) through the HPCI System Research project (Project ID: hp160229, hp170246, hp180194). 2013) exhibited somewhat similar size and structure to those of the MBV in this study. From 2200 to 2300 JST 31 August 2015, a widespread precipitation area is found around Tsushima Strait (Figs. Thus, formation process of the tornado-like vortices may be somewhat similar to that of nonsupercell tornadoes (Wakimoto and Wilson 1989) except for the presence of the MBV. Black open circles in (b) and (c) indicate the locations of shipwrecks at around 0355 JST. The first term on the right-hand side (rhs) of Eq. Simple theme. Figure 15b shows a normalized inner product of vorticity and velocity vectors (normalized helicity) in the vertical cross section along the line A–A′ in Fig. At 2100 JST 31 August, a region in which TBB is lower than 221 K started to appear in the south of Tsushima Island. At 0300 JST, a couplet of positive and negative Doppler velocity, which characterizes a vortex flow associated with the MBV, is clearly detected in the southern part of the reflectivity pattern 40 dBZ (around 34.2°N, 129.6°E). In addition, the final locations of forward-integrated trajectories are very close to the initial locations of backward trajectories (not shown). Green circles indicate the positions of EC center. Simulated characteristics of the meso-β vortex on 1 Sep 2015. 12b). Tornadoes often occur in association with large-scale atmospheric disturbances such as extratropical cyclones (ECs) (e.g., Newton 1967; Miller 1972; Johns and Doswell 1992) and tropical cyclones (e.g., Novlan and Gray 1974; McCaul 1991; Sueki and Niino 2016) the horizontal scales of which are on the order of 1000 km. 11b) compared to typical QLCSs such as bow echo and derecho, which typically have strong cold pools (e.g., Wakimoto et al. The horizontal shear was strengthened as the convection intensified (Fig. 10b–d). To accurately calculate the source of the near-surface vorticity, a numerical model with intermediate horizontal resolution of 350 m (2000 × 2000 horizontal grid points; hereafter NHMF350m) and 70 vertical levels is nested (Fig. This Week With Every Kind of Bad Weather Imaginable, The tropics, my home, pt 1. It is seen that the inflow having large normalized helicity turns vertically in the updraft region and causes large vertical vorticity. The evolution of the circulation calculated directly is compared with that calculated by integrating the sum of the rhs of Eq. The forward trajectory analysis have shown that the circulation along the circuit enclosing locations of forward-integrated trajectories at 0408 JST is about 82 000 m2 s−2, which is close to 83 000 m2 s−2 along the circuit enclosing initial locations of backward trajectories. The thermodynamic environment for the MBV is close to moist neutral (Fig. Thus, it is suggested that the vertical vorticity at 700-m height is caused by the tilting of horizontal vorticity, which originates from the vertical shear of winds field associated with the EC (not shown). 16d) to the total circulation, we calculate the circulation along each subcircuit (Fig. An MCV is an area of low pressure that develops aloft within a large, organized, and long-duration complex of thunderstorms known as a mesoscale convective complex (MCC). Unlike mesocyclones associated with a supercell storm, however, its vorticity was largest near the surface and decreased monotonically with increasing height. The purpose of this paper is to report on the formation mechanism and detailed structure of the MBV, and features of tornado-like vortices, as revealed by a high-resolution numerical simulation. (b) Horizontal distribution of vertical velocity at 1000-m height (color shading; m s−1), potential temperature at 118-m height (contour lines; K), and horizontal wind vectors (m s−1) at 118-m height at 0130 JST from NHMF2km. A red cross in (a) indicates the location of the shipwrecks, and red crosses in (b) and (c) indicate the location of the Fukuoka radar. The simulated MBV had a strong cyclonic circulation comparable to a mesocyclone in a supercell storm. 2004; Davis and Galarneau 2009; Conzemius et al. Observed characteristics of the meso-β vortex on 1 Sep 2015. Recent developments in computer technology and numerical models enable us to reliably reproduce mesoscale and microscale phenomena in the atmosphere (e.g., Mashiko et al. (a) Normalized inner products of horizontal vorticity vector and horizontal velocity vector (color shading) at 700-m height at 0130 JST from NHMF2km. This, in effect, creates a "warm-core … The NHMS50m successfully reproduces the essential features of the MBV including the spiral-shaped distribution of rainwater mixing ratio associated with the MBV (Fig. To perform the vorticity budget analysis, we first determine the center of the MBV. 11c). That warming causes the air to expand, reducing the pressure relative to the surrounding environment. That condensation of water vapor into rain releases a lot of latent heat, warming the core of the storm. We also have calculated forward trajectories of the air parcels located at the final positions of the backward trajectories. Pleasant weather again for Sunday. 2009; Mashiko 2016a, b). (c) Time sequence of simulated maximum vorticity (blue dashed line; s−1) and velocity (red line; m s−1) at 30-m height. Between 1200 and 1800 JST 31 August 2018, there is no region in which TBB is lower than 241 K around Tsushima Strait. The first simulation aims to examine the formation and development processes of the MBV: a numerical model that covers a large area (Fig. where is density, p is pressure, is friction vector, and the first term on the rhs is the baroclinic term. A mesoscale convective vortex--(MCV)--is a mid-level low-pressure center within an MCS that pulls winds into a circling pattern, or vortex. 2007) is moist neutral or somewhat more unstable. Over the North American continent, a variety of hazardous mesoscale vortices associated with mesoscale convective systems (MCSs) have been observed: mesoscale convective vortices (MCVs; Zhang 1992; Fritsch et al. A high-resolution numerical simulation with horizontal grid interval of 50 m successfully reproduced the spiral-shaped precipitation pattern associated with the MBV and tornado-like strong vortices that had a maximum wind speed exceeding 50 m s−1 and repeatedly developed in the MBV. 7a) at 30-m height at 0440 JST (Fig. The width of the strongest shear zone in the MBV is roughly estimated to be ~100–150 m based on the zonal distributions of meridional wind meridionally averaged between 34.8225° and 34.83°N (the rectangle in Fig. Two kinds of numerical simulations are performed. 3. (1) is the horizontal advection term, the second is the vertical advection term, the third is the stretching term, the fourth is the tilting term, the fifth is the solenoidal term, and the sixth is the friction term. 2. Figure 4 shows time sequence of blackbody temperature (TBB) observed from the Geostationary Meteorological Satellite Himawari-8. Violent winds associated with tornadoes have a serious impact on society, causing significant damage to structures and fatalities.