Author(s): Yosuke Yamashiki; Saburo Matsui; Michio Kumagai; Joe Asada
Linked Author(s):
Keywords: Distorted Numerical Model (DNM); LES; DMM; Gyre; Lake Biw
Abstract: Three gyres formation process, observed by ADCP in Lake Biwa, has been simulated using Distorted Numerical Model (DNM) and compared with Large Eddy Simulation (LES) with Dynamic Mixed Model (DMM). In DNM, all calculation are formulated in Distorted Virtual Grid (DVG), whose vertical grids are expanded from normal grid spacing according to the Distortion Ratio DR and vertical gravity force is reduced by the proportion to DR. Quasi-Isotropic turbulent model, which is commonly used for Sub Grid Scale (SGS) model of LES, is employed to this DVG. Driving force of gyre formation was assumed as differential heating due to heat volume difference between lake and shoreline. This condition was employed in the simulation setting initial temperature distribution of lake obtained from field observation. Significant gyre formation pattern was calculated both by DNM which looks more realistic than normal-grid-spacing LES. DNM makes significant change in Buoyancy (BruntVaisala) Frequency, as well as Density Froude Number, however maintains Rossby, Ekman, as well as Burger number. This model is useful when the effect of buoyancydriven internal wave is insignificant or when one intensionally eliminate this effect.
Year: 1999