Junshi Ito

Junshi Ito
Tohoku University | Tohokudai · Department of Geophysics

PhD

About

30
Publications
3,565
Reads
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312
Citations
Additional affiliations
April 2015 - September 2015
April 2010 - March 2015
The University of Tokyo
Position
  • Research Associate
April 2010 - March 2015
Kogakuin University
Position
  • Lecturer
Description
  • C-language programming

Publications

Publications (30)
Article
Within wall turbulence, there is a sublayer where the mean wall-normal flux of the streamwise momentum is constant and related to the logarithmic wall-normal profile of the mean streamwise velocity. This relation, i.e., the law of the wall, has been used to estimate the mean stress at the wall surface. However, the momentum flux exhibits large temp...
Article
Within turbulent boundary layers, the relationship between instantaneous surface momentum fluxes and streamwise velocities is more complicated than that between their ensemble averages described by the law of the wall. Although these fluxes need to be considered in large eddy simulations, the conventional approaches are not feasible. As an alternat...
Article
Ultra-high resolution numerical weather prediction (NWP) experiments over a large domain have been carried out to investigate impacts of some different factors of an NWP model in simulating the Hiroshima heavy rain event in August 2014. This is a continuation of the study in Part 1 in which similar experiments were carried out, however for the Izu...
Article
Record-breaking precipitation due to a back-building convective system occurred in Kyushu Island, Japan, on 5 July 2017. In this paper, a quasi-stationary back-building convective system is reproduced using a regional weather prediction model initialized with a single representative sounding in which the land–sea distribution around the observed co...
Article
Full-text available
Recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters, comparable to the dominant turbulence length scales in the atmospheric boundary layer. As a result, models are starting to partially resolve the coherent overturning structu...
Article
Full-text available
Plain Language Summary Synoptic/mesoscale fronts and downbursts (strong downdrafts from a thunderstorm and diverging winds after they hit the ground) are known to be serious threats to airplanes during takeoff and landing. However, it is less known that there is another type of danger under fair weather conditions. An aircraft landing at Narita Int...
Article
A renowned local wind in Japan, “Hijikawa-Arashi,” is a thermally driven nocturnal gap wind accompanied by fog. The wind is visually identified by the fog along the valley of the Hijikawa River between the Ozu basin and the Seto Inland Sea during the early morning in autumn and winter. A fine-resolution numerical model is employed to reproduce the...
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This study examines the performance of radiation processes (shortwave and longwave radiations) using numerical weather prediction models (NWPs). NWP were calculated using four different horizontal resolutions (5, 2 and 1 km, and 500 m). Validation results on solar irradiance simulations with a horizontal resolution of 500 m indicated positive biase...
Article
An intense rainband associated with Typhoon 1326 (Wipha) induced a fatal debris flow on Izu Oshima, Japan, on October 15 – 16, 2013. This rainband formed along a local front between the southeasterly humid warm air around the typhoon and the northeasterly cold air from the Kanto Plain. In this paper, the Japan Meteorological Agency Nonhydrostatic M...
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This study evaluated the performance of a regional weather prediction model. The horizontal resolution is increased to the sub-kilometer scale in a series of experiments over areas of Japan through the summer or winter seasons of 2015-2016. The performance improves less when increasing the horizontal resolution from 2 km to 1 km or 500 m than it do...
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Taking advantage of the huge computational power of a massive parallel supercomputer (K-supercomputer), this study conducts large eddy simulations of entire tropical cyclones by employing a numerical weather prediction model, and explores near-surface coherent structures. The maximum of the near-surface wind changes little from that simulated based...
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Strong winds associated with dust devils can induce locally large heat fluxes from the surface, and resulting enhanced buoyancy may further intensify the dust devils. This positive wind—surface-heat-flux feedback is studied using a large-eddy simulation of a convective boundary layer. A comparison of the results with and without the feedback proces...
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In this review, we address the use of numerical computations called Large-Eddy Simulations (LES) to study dust devils, and the more general class of atmospheric phenomena they belong to (convective vortices). We describe the main elements of the LES methodology. We review the properties, statistics, and variability of dust devils and convective vor...
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The essential dynamical characteristic of convective vortices, including dust devils, is a highly localized vorticity tube that extends into the vertical. This chapter is concerned with both the generation of vorticity and the subsequent focusing of that vorticity into a tight vortex, and with the environmental conditions that are conducive to the...
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A mesoscale atmospheric numerical model is used to simulate two cases of Karman vortex shedding in the lee of Jeju Island, South Korea, in the winter of 2013. Observed cloud patterns associated with the Karman vortex shedding are successfully reproduced. When the winter monsoon flows out from the Eurasian continent, a convective mixed layer develop...
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The terra incognita (TI) or grey zone arises in conventional planetary boundary-layer parametrizations when the grid resolution of a numerical model is comparable to the size of the energy-containing turbulent eddies $$\sim $$∼1 km or less. Here, we investigate a simple, plausible extension of the Mellor–Yamada (MY) level-3 scheme for TI-scale grid...
Article
We modify the velocity applied to the bulk relation for surface heat flux using turbulent kinetic energy, such that the effect of horizontal flow induced by unresolved free convection is incorporated. Numerical experiments with a large-eddy simulation (LES) and a single-column model (SCM) are examined for an ideal convective boundary layer. The sur...
Article
The effects of discretization on the equations, and their solutions, describing Rayleigh-Bénard convection are studied through linear stability analysis and numerical integration of the discretized equations. Linear stability analyses of the discretized equations were conducted in the usual manner except that the assumed solution contained discreti...
Article
Diurnal variations of an atmospheric boundary layer from 0900 LST on day 33 to 0600 LST on day 34 of 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 to phenomena in a residual layer (RL). As the surface heat flux decre...
Article
Full-text available
A large eddy simulation (LES) is used to estimate a reliable horizontal turbulent diffusion coefficient, K-h, in a convective mixed layer (CML). The introduction of a passive scalar field with a fixed horizontal gradient at a given time enables Kh estimation as a function of height, based on the simulated turbulent horizontal scalar flux. Here Kh i...
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Dust devils are small-scale atmospheric vortices that are often observed on deserts. Using a video of a dust devil that occurred in a close distance, this study attempts to apply Particle Image Velocimetry (PIV) to obtain flows in the dust devil for the first time. Images taken by two cameras enable us to connect a pixel size into actual length sca...
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A five-year research project of high performance regional numerical weather prediction is underway as one of the five research fields of the Strategic Programs for Innovative Research (SPIRE). The ultimate goal of the project is to demonstrate feasibility of precise prediction of severe weather phenomena using the K-computer. Three sub-themes of th...
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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 vertical vortices can be simulated in idealized convective mixed layers in the absence of background winds or environmental shear. Their formation...
Article
A previous Doppler-lidar observation near a sea-breeze front revealed that small-scale vertical vortices, similar to dust devils, have a preferred direction of rotation, which suggests that their rotation was affected by meso-scale vertical vorticity associated with the front. In contrast, planetary vorticity is believed to have a negligible effect...
Article
Observations show that optical depth over desert increase during daytime when a convective mixed layer develops under a light general wind condition. This implies that dust suspension by horizontal winds associated with convective motions occur even in the absence of general winds. In the present paper, a large eddy simulation is performed to study...
Article
Full-text available
Formation of dust devils in diurnally-evolving convective mixed layers is studied by means of a large eddy simulation. It is found that a weaker general wind and a stronger surface heat flux for which cellular convection rather than roll convection prevails are favorable for the formation of dust devils. The simulation results show that when the ge...

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