JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-OS Ocean Sciences & Ocean Environment

[A-OS20] Coastal physical processes associated with mixing, eddies, and internal waves

convener:Taira Nagai(Graduate School of Science, The University of Tokyo), Eisuke Tsutsumi(Atmosphere and Ocean Research Institute, The University of Tokyo), Eiji Masunaga(Ibaraki University)

[AOS20-07] Effects of the wind forcing on a shallow lake associated with the lake size and stratification

*Daiki Asaoka1, Eiji Masunaga1, shunsuke komuro2, Tatsumi Kitamura2 (1.Ibaraki University, 2.Ibaraki Kasumigaura Environmental Science Center)

Keywords:Wind forcing, Stratification, Mixing

This study shows effects of the wind forcing on a shallow lake associated with the lake size and stratification. Mixing in lakes and reservoirs are frequently evaluated by using nondimensional parameters, for example the Wedderbrun number (We). We can be estimated for a steady state wind condition or computed by using time averaged wind data, however, winds largely vary within several hours or less. Time scales associated with mixing in a shallow lake were investigated using a two dimensional (x-z) numerical simulator, SUNTANS. Several conditions of the horizontal scale of the modeled lake, stratification and wind speed were used in simulations with We ranging 0.1–10. This study employees two time scales: (1) time scale required for a steady state temperature distribution estimated from the tilt of the thermocline, Ts, and (2) time scale required for complete vertical mixing, Tmix.Tmix is computed from change in the potential energy. Numerical results showed that Ts linearly decreases with decreasing in the stratification or increasing in the horizontal distance under a same We condition. Tmix also increased when the stratification decreased or the horizontal distance increased under a same We condition. A quarter of the internal seiche period (Ti) was calculated using a stratification and a horizontal distance. Numerical results showed a linear relationship between Ti and Ts. Moreover, a quarter of Ti was fundamentally shorter than Tmix under a same stratification and horizontal distance. This implies that the lower limit of the mixing time scale is determined by a quarter of Ti.