Modeling Impacts of Subsurface Thermal Anomalies on Atmospheric Energy Fluxes in Berlin, Germany Using PALM-4U

We developed different set-ups with cyclic lateral boundary conditions (LBC) and external dynamic forcing from the mesoscale model WRF. For each setup, we subtract a heat scenario in which the soil temperature in the deepest layer (2.91 m below ground) is increased by 5 K from a reference scenario. Under cyclic LBC we detect marginal air potential temperature differences averaged over the domain but significant differences in variance and distribution.

Those differences have a high diurnal variation and are height dependent. In contrast, using WRF as forcing, there are pronounced differences in surface sensible heat flux (maximum positive and maximum negative: 13.1~W/m² at 21:00 local time, -7.0~W/m² at 14:00), ground heat flux (4.1~W/m² at 20:00, -3.6~W/m² at 14:00), and 2~m air potential temperature (0.64~K at 17:00, -0.87~K at 14:00). Hence, additional subsurface heat does not lead to uniform warming, but rather to an energy redistribution, ultimately resulting in an overall increase in total energy.

With increasing height, differences due to altered soil temperatures become negligible.