On the influence of surface heterogeneity on the Bowen-ratio:: A theoretical case study

The influence of surface heterogeneity on spatial distribution, temporal development, and on the domain-average of the ratio between sensible and latent heat-flux (Bowen-ratio) is investigated for synthetic landscapes of differing degrees of surface heterogeneity. In so doing, simulations are performed applying a 3-dimensional non-hydrostatic mesoscale model. The synthetic landscapes consist of patches of sandy loam covered by mixed forest and loamy soil covered by grass. The results of the numerical experiments substantiate that land-surface distributions will non-linearly influence the Bowen-ratio if patches of equal type exceed a certain size. Moreover, the heterogeneity of the upwind region may play a role. Similarity coefficients show that the surface type dominating a landscape does not necessarily determine the mean Bowen-ratio representative for this area. Thus, when applying the strategy of dominant surface type, the margin of error in the regional Bowen-ratio depends on the horizontal resolution of the model or on available data.