Wind as a Main Driver of Spatial Variability of Surface Energy Balance Over a Shallow 10²‐km² Scale Lake: Lake Kasumigaura, Japan

Abstract

Lakes have often been treated as one‐dimensional entities for energy balance (EB) studies mostly based on point measurements. Therefore, our knowledge of the spatial variability of lake EB is quite limited. We created EB maps of Lake Kasumigaura, a 172‐km2 shallow lake in Japan, with a 90‐m horizontal resolution at a 3‐hr interval over 5 years based on spatially interpolated meteorological variables and water surface temperature, with turbulent fluxes estimated by the bulk equations. The results indicate that turbulent fluxes and total energy flux into water body G were spatially variable while radiative fluxes were more uniform. The spatial variability of turbulent fluxes averaged over a season, a year, and 5 years was mainly caused by wind speed difference; a longer fetch in downwind areas of the lake resulted in strong winds and higher turbulent fluxes. The spatial difference of turbulent fluxes and quasi‐uniform net radiation caused a total energy flux out of the water in the downwind area and a total energy flux into the lake in an upwind area. This spatial difference of G appeared to be compensated by heat transport from the upwind to downwind area through advection due to lake current.

Contrasting hydrological and thermal intensities determine seasonal lake-level variations – a case study at Paiku Co on the southern Tibetan Plateau

“…Firstly, solar radiation and atmospheric longwave radiation at Qomolangma station were used to represent those at Paiku Co. To evaluate the spatial difference, we made a comparison of solar radiation at Paiku Co and Qomolangma station using Himawari-8 satellite data (Tang et al, 2019;Fig. S4 in the Supplement).…”

“…Here, the Aqua MODIS 8 d lake surface temperature product is used to determine the difference between lake bulk temperature and skin temperature. The product is produced with a spatial resolution of about 1 km, and the accuracy is estimated to be 1 K under clear-sky conditions (Wan, 2013). During the pre-monsoon and monsoon seasons when the lake water got warm, the skin temperature derived from MODIS data was about 1.2 • C higher than lake body temperature.…”

Relative impacts of increases of solar radiation and air temperature on the temperature of surface water in a shallow, eutrophic lake

“…where 1 is emissivity [¼1.0; dimensionless; Sugita et al (2020)], and T w is the surface water temperature (K). Sensible and latent heat fluxes were calculated with the following bulk formulae:…”

“…There are heat fluxes other than those through the water surface, such as heat fluxes associated with river/groundwater inflow and the heat flux through the bottom (Chikita et al 2019;Masunaga & Komuro 2019;Sugita et al 2020). The values of these heat fluxes were unknown at the time of this study.…”

“…However, because the water retention time in Lake Kasumigaura is ∼200 days and the level of the water surface of Lake Kasumigaura is controlled artificially, the heat flux associated with river inflow should be small. Sugita et al (2020) have estimated that the net heat flux associated with river inflow/outflow is ∼3 W m À2 . Further detailed monitoring of heat fluxes associated with the heat stored in the sediment and inflows of groundwater and river water are needed to more accurately estimate the heat flux of Lake Kasumigaura.…”