NUMERICAL SIMULATION OF THERMAL INDUCED GYRES IN LAKE BIWA

摘要

Three gyres formation process, observed by ADCP in Lake Biwa, has beenrnsimulated using Distorted Numerical Model (DNM) and compared with Large EddyrnSimulation (LES) with Dynamic Mixed Model (DMM). In DNM, all calculation arernformulated in Distorted Virtual Grid(DVG), whose vertical grids are expanded fromrnnormal grid spacing according to the Distortion Ratio DR and vertical gravity force isrnreduced by the proportion to DR. Quasi-Isotropic turbulent model, which is commonlyrnused for Sub Grid Scale(SGS) model of LES, is employed to this DVG. Driving forcernof gyre formation was assumed as differential heating due to heat volume differencernbetween lake and shoreline. This condition was employed in the simulation settingrninitial temperature distribution of lake obtained from field observation. Significant gyrernformation pattern was calculated both by DNM which looks more realistic thanrnnormal-grid-spacing LES. DNM makes significant change in Buoyancy(Brunt-rnVaisala)Frequency, as well as Density Froude Number, however maintains Rossby,rnEkman, as well as Burger number. This model is useful when the effect of buoyancydrivenrninternal wave is insignificant or when one intensionally eliminate this effect.