Flow structure of radiatively driven convection in inertial and rotating frames under steady and periodic radiative forcing

Freshwater achieves its maximum density at a pressure-dependent temperature which is above the freezing point, close to 4 °C at ambient pressure for pure water. If the temperature of a freshwater column is below the temperature of maximum density, radiative heating at the surface can generate convection, as warmer water at the surface becomes denser and sinks. This particular example of radiatively driven convection (RDC) is prevalent during springtime in temperate lakes. Scales for the vertical velocity, temperature fluctuations, and horizontal extent of the convective cells are derived theoretically and validated with the help of large eddy simulations. The Coriolis effects in temperate lakes are not dominant. However, it is shown that rotation has the effect of limiting the horizontal scale of the convective cells unless the Rossby number is large, in which case the size of the cells is solely determined by the length of daytime.