The Modulation of Static Heterogeneity by Precipitation

The term static heterogeneity, in contrast to dynamic heterogeneity, is used to refer to surface heterogeneity that varies on a time scale much longer than one diurnal cycle. In this study, interactions between static and dynamic heterogeneities, the latter being initiated by the localized infiltration of precipitation into the soil, are explored. To that aim two weeks of large-eddy simulations are performed. The static heterogeneity is prescribed using a leaf area index in a checkerboard pattern, whereas the effect of dynamic heterogeneity is isolated by turning on and off the infiltration of precipitation into the soil.

The presence of static heterogeneity leads to the formation of thermally induced circulations that force the development of precipitation on the warmer patch. The subsequent infiltration of precipitation into the soil enhances the soil moisture of the initially warmer patch and leads to an enhancement of the latent heat flux at the expense of the sensible heat flux. This homogenizes the surface flux difference induced by the background static heterogeneity. However, even after two weeks of simulation, the effects of the static heterogeneity are still visible, and the infiltration of precipitation does not manage to introduce new length scales in the system. Moisture and surface energy budget calculations confirm that in the vast majority of possible surface and atmospheric conditions, dynamic heterogeneity cannot compensate for the effect of static heterogeneity. These results are verified against observations.