The Surface-Boundary Layer Connection across Spatial Scales of Thermal Heterogeneity

In heterogenous areas, non-local processes including advection, secondary circulations and entrainment reduce the experimental energy budget closure (Butterworth et al., 2021; Mauder et al., 2020; Stoy et al., 2013). More specifically, in semi-arid regions, irrigation induces heterogeneity characterized by contrasting and extreme Bowen ratios across a range of spatial scales that impacts the partitioning of the available radiative energy at the surface, and therefore, the development of the atmospheric boundary layer, and the bi-directional interactions between the atmosphere and the surface. Here, we systematically investigate how secondary circulations and entrainment impact observed surface energy fluxes at various spatial scales. Our approach is combining observed surface fluxes and boundary-layer dynamics at high spatial and temporal resolution with a coupled land-atmosphere model.

In this analysis, we use data from the Land Surface Interactions with the Atmosphere in the Iberian Semi-Arid Environment (LIAISE) experiment combined with a coupled land-atmosphere model to understand the role of the scales of irrigation-induced, thermal heterogeneity on the surface fluxes and consequently, the development of the diurnal convective boundary layer. The surface heterogeneity is characterized by Bowen ratios that range from ~0.01 in the irrigated areas to ~30 in the non-irrigated areas; however, the observed boundary-layers dynamics in both locations are similar. In this study, we address the questions of how the surface fluxes impact the development of the boundary-layer dynamics and how the boundary layer influences the diurnal cycle of surface fluxes. Our findings enable us to introduce a heterogeneity scaling scheme where length scales range from local scale (~ 100 m) to regional scale (~ 10 km) to investigate the role of scale on surface representation in numerical models, and as such, the results can be used to address the discrepancy between surface observations and their representation in weather and climate models.

We find that at the surface, both the available energy and its partitioning strongly depend on the spatial scale under study. The observed boundary-layer properties can be explained through the composite of surface fluxes at the regional scale. Surface fluxes at the local scales are unable to replicate the observed boundary layer – even when including large-scale contributions. We find that non-local boundary layer processes like advection are important for diurnal variability of the surface energy budget at the local scale. We explore the connection between surface fluxes and the development of the boundary layer and the potential non-local effects on boundary-layer development.

References:

Butterworth, B.J., Desai, A.R., Townsend, P.A., Petty, G.W., Andresen, C.G., Bertram, T.H., Kruger, E.L., Mineau, J.K., Olson, E.R., Paleri, S., Pertzborn, R.A., Pettersen, C., Stoy, P.C., Thom, J.E., Vermeuel, M.P., Wagner, T.J., Wright, D.B., Zheng, T., Metzger, S., Schwartz, M.D., Iglinski, T.J., Mauder, M., Speidel, J., Vogelmann, H., Wanner, L., Augustine, T.J., Brown, W.O.J., Oncley, S.P., Buban, M., Lee, T.R., Cleary, P., Durden, D.J., Florian, C.R., Lantz, K., Riihimaki, L.D., Sedlar, J., Meyers, T.P., Plummer, D.M., Guzman, E.R., Smith, E.N., Sühring, M., Turner, D.D., Wang, Z., White, L.D., Wilczak, J.M., 2021. Connecting Land–Atmosphere Interactions to Surface Heterogeneity in CHEESEHEAD19. Bull. Am. Meteorol. Soc. 102, E421–E445. https://doi.org/10.1175/BAMS-D-19-0346.1

Mauder, M., Foken, T., Cuxart, J., 2020. Surface-Energy-Balance Closure over Land: A Review. Bound.-Layer Meteorol. 177, 395–426. https://doi.org/10.1007/s10546-020-00529-6

Stoy, P.C., Mauder, M., Foken, T., Marcolla, B., Boegh, E., Ibrom, A., Arain, M.A., Arneth, A., Aurela, M., Bernhofer, C., Cescatti, A., Dellwik, E., Duce, P., Gianelle, D., van Gorsel, E., Kiely, G., Knohl, A., Margolis, H., McCaughey, H., Merbold, L., Montagnani, L., Papale, D., Reichstein, M., Saunders, M., Serrano-Ortiz, P., Sottocornola, M., Spano, D., Vaccari, F., Varlagin, A., 2013. A data-driven analysis of energy balance closure across FLUXNET research sites: The role of landscape scale heterogeneity. Agric. For. Meteorol. 171–172, 137–152. https://doi.org/10.1016/j.agrformet.2012.11.004