Taking advantage of the huge computational power a massive parallel supercomputer (K-supercomputer), this study conducts large eddy simulations entire tropical cyclones by employing numerical weather prediction model, and explores near-surface coherent structures. The maximum wind changes little from that simulated based on coarse-resolution runs. Three kinds structures appeared inside boundary layer. first is Type-A roll, which caused an inflection-point instability radial flow prevails...

A tornado hit Nobeoka city on the southeast coast of Kyushu Island, Japan 22 September 2019 when Typhoon Tapah was located about 500 km to southwest Island and moving northeastward. Triply-nested numerical simulations are performed reproduce typhoon, a parent storm, associated tornadoes. The simulation with coarsest resolution reasonably reproduces outer rainbands at several east its center, where environment around rainband is found be favorable for mini-supercells. finest train...

Formation of dust devils in diurnally-evolving convective mixed layers is studied by means a large eddy simulation. It found that weaker general wind and stronger surface heat flux for which cellular convection rather than roll prevails are favorable the formation devils. The simulation results show when weak, maximum vertical vorticity layer monotonically increasing function w*, where w* velocity scale layer. Therefore, occur most frequently early afternoon grows to significant height.The...

Abstract Dust devils are small-scale vertical vortices often observed over deserts or bare land during the daytime under fair weather conditions. Previous numerical studies have demonstrated that dust devil–like can be simulated in idealized convective mixed layers absence of background winds environmental shear. Their formation mechanism, however, has not been completely clarified. In this paper, authors attempt to clarify vorticity source a vortex by means large-eddy simulation, which...

Abstract A mesoscale atmospheric numerical model is used to simulate two cases of Kármán vortex shedding in the lee Jeju Island, South Korea, winter 2013. Observed cloud patterns associated with are successfully reproduced. When monsoon flows out from Eurasian continent, a convective mixed layer develops through supply heat and moisture relatively warm Yellow Sea encounters Island dynamical conditions favorable for formation vortices realized. Vortices that form behind island induce updrafts...

Abstract A heavy rainfall event caused by mesoscale convective systems (MCSs) resulted in flooding over areas of Davao City Mindanao Island, Philippines, on 03 May 2017. The occurred during the summer season (April–May) under weak large-scale conditions. This study investigated initiation and development MCSs performing high-resolution numerical simulations with finest grid spacing 200 m, using Weather Research Forecasting (WRF) model. It was found that merging two meso- $$\beta$$ <mml:math...

This study evaluated the performance of a regional weather prediction model. The horizontal resolution is increased to sub-kilometer scale in series experiments over areas Japan through summer or winter seasons 2015-2016. improves less when increasing from 2 km 1 500 m than it does 5 km, especially topography and ice microphysics are relevant. Although velocity magnitude updrafts, cloud size, convection boundary layer indeed change with resolution, these differences turn out have little...

Abstract An accident occurred when an aircraft landed at Narita International Airport, Japan, on 20 June 2012. The encountered rapid changes of winds together with strong turbulence, although the weather was fair. In present study, a two‐domain nested regional prediction models are used. results in outer domain show that southwesterly associated synoptic extratropical cyclone were locally accelerated to southwest airport resulting vertical shear. simulation inner reproduces horizontal...

Observations show that optical depth over desert increase during daytime when a convective mixed layer develops under light general wind condition. This implies dust suspension by horizontal winds associated with motions occur even in the absence of winds. In present paper, large eddy simulation is performed to study how much suspended without wind. The results particle concentration can reach on order 10 μg m-3, which reasonable agreement observations. Tiny particles have small terminal...

An intense rainband associated with Typhoon 1326 (Wipha) induced a fatal debris flow on Izu Oshima, Japan, October 15-16, 2013. This formed along local front between the southeasterly humid warm air around typhoon and northeasterly cold from Kanto Plain. In this paper, Japan Meteorological Agency Nonhydrostatic Model was optimized for “K computer”, ultra-high-resolution (500-250 m grid spacing) numerical simulations of large domain were conducted.

Abstract Diurnal variations of an atmospheric boundary layer from 0900 LST on day 33 to 0600 34 the Wangara experiment are studied using a large-eddy simulation (LES) model that includes longwave radiation and baroclinicity. The present study directs its particular attention phenomena in residual (RL). As surface heat flux decreases, inertial oscillation is initiated accompanied by low-level jet (LLJ) at height approximately 200 m. maximum wind speed LLJ exceeds 12 m s−1 0300 34. After 2100...

Abstract Record-breaking precipitation due to a back-building convective system occurred in Kyushu Island, Japan, on 5 July 2017. In this paper, quasi-stationary is reproduced using regional weather prediction model initialized with single representative sounding which the land–sea distribution around observed crudely simplified. The simulated and heavy are reasonably similar observations. Horizontal resolution finer than 1 km found be necessary for reproducing system. area of tends shift...

A previous Doppler-lidar observation near a sea-breeze front revealed that small-scale vertical vortices, similar to dust devils, have preferred direction of rotation, which suggests their rotation was affected by meso-scale vorticity associated with the front. In contrast, planetary is believed negligible effect on devils. This paper investigates effects ambient devils means large eddy simulation, yielded following findings: when as small earth's only tiny asymmetry found in occurrences...

A five-year research project of high performance regional numerical weather prediction is underway as one the five fields Strategic Programs for Innovative Research (SPIRE). The ultimate goal to demonstrate feasibility precise severe phenomena using K-computer. Three sub-themes are shown with achievements at present and developments in near future.

Ultra-high-resolution numerical weather prediction (NWP) experiments over a large domain have been conducted to investigate the impacts of different factors an NWP model in simulating Hiroshima heavy rain event August 2014. This is continuation study Part 1 which similar were carried out for Izu Oshima October 2013. We demonstrated benefit using high-resolution (500-m grid spacing or less) with torrential events.

Dust devils are small-scale atmospheric vortices that often observed on deserts. Using a video of dust devil occurred in close distance, this study attempts to apply Particle Image Velocimetry (PIV) obtain flows the for first time. Images taken by two cameras enable us connect pixel size into actual length scale. The estimated maximum tangential wind and updraft 16 m s-1 6 s-1, respectively. These speeds comparable these strong ones reported previous observational studies.

Abstract A large eddy simulation (LES) is used to estimate a reliable horizontal turbulent diffusion coefficient, $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq \ge =\geqslant \geq \def \Pr {\mathit {Pr}}\def \Fr {Fr}}\def \Rey {Re}}K_{{h}}$ , in convective mixed layer (CML). The introduction of passive scalar field with fixed gradient at given time enables $K_{{h}}$ estimation as function height, based on the simulated flux. Here found be order...

Abstract A clear air turbulence (CAT) occurred on 30 December 2020 over Tokyo, Japan. The CAT was largely generated by breaking Kelvin‐Helmholtz (KH) instability waves in the free atmosphere. regional numerical weather prediction model simulated event with fine resolution (35 m). Onboard‐recorded flight data and a simulation were utilized to validate meteorological simulation. locations of reproduced strong agree well regions where flights encountered that day. In finest resolution, KH their...