Application of a one-dimensional scheme to model diurnal water temperature fluctuations near the surface of a stratified lake

When simulating the atmosphere across various scales, accurately resolving the diurnal warming of sea and lake surfaces is a critical requirement. For example, regional atmospheric models must correctly simulate air-water temperature gradients to successfully capture mesoscale circulations such as sea and lake breezes. Often the SST (or Lake Surface Temperature LST) applied to the atmospheric simulator is modelled using a “slab model” of a certain thickness and thermal mass. However slab models often predict diurnal variation of SST poorly. In this talk I will discuss preliminary results from “DiuSST”, recently proposed by R. Börner et al (2025; https://doi.org/10.5194/gmd-18-1333-2025) to provide boundary conditions for diurnally varying SST to atmospheric simulators. Börner et al ’s testing and validation of DiuSST was based on an ocean cruise that measured skin surface temperature with an infrared radiometer, and water temperature at 3m depth. By contrast I cross-check DiuSST results against near-surface temperature profiles in a stratified lake, Lake Biwa, that were recorded at nearshore and offshore locations during the early summer of 2021.