Earth system models (ESMs) and mesoscale models have come to employ increasingly complex parameterization schemes for the atmospheric boundary layer, requiring surface boundary conditions for numerous higher order turbulence statistics. Of particular interest is the potential temperature variance (PTV), which is used not only as a boundary condition itself but also to close boundary conditions of other statistics. The existing schemes in ESMs largely rely on the assumptions of Monin‐Obukhov similarity theory (MOST) and are not necessarily applicable over complex and heterogeneous surfaces where large scale circulations and roughness sub‐layer effects may cause deviations from MOST. The National Ecological Observation Network is used here to evaluate existing parameterizations for the surface boundary of PTV, note key deficiencies, and explore possible remedies. The results indicate that existing schemes are acceptable over a variety of surface conditions provided the analysis of a priori filters out low frequency variability not associated with turbulent time scales. There was, however, significant inter‐site variability in observed similarity constants and a significant bias when compared to the textbook values of these parameters. Existing models displayed the poorest performance over heterogeneous sites and rough landscapes. Attempts to use canopy structure and surface roughness characteristics to improve the results confirmed a relation between these variables and PTV but failed to significantly improve the predictive power of the models. The results did not find strong evidence indicating that large scale circulations caused substantial deviations from textbook models, although additional analysis is required to assess their full impacts.

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<p>Earth System Models (ESMs) traditionally operate at large horizontal resolutions, on the order of 100km, which can obscure the effects of smaller scale heterogeneity. The literature, as well as work in the Coupling of Land and Atmospheric Subgrid Parameterizations (CLASP) project, indicates that surface heterogeneity, particularly in surface fluxes, has important implications for not only surface processes but atmospheric processes as well. Previous work using large-eddy simulation (LES) shows that spatial variability in surface heating can produce significant secondary circulations that are closely related to the type and scale of heterogeneity and are not currently captured by single column sub-grid atmospheric parameterizations used in ESMs.. This presentation aims to address this persistent weakness by using a multi-column approach, where two single column models, one over a high sensible heat flux portion of a climate gridcell domain and another over a low sensible heat flux portion, are coupled through a modeled secondary circulation. </p><p> </p><p>To accomplish this task, we run the Cloud Layers Unified By Binomials (CLUBB) standalone single column model over a 100 km box centered at the Southern Great Plains site in Oklahoma for a variety of surface and atmospheric conditions both as a single column model, and with two coupled columns. Results are also compared to LESs that use a homogeneous surface flux field and LESs that use realistic, high resolution surface flux fields. Initial results focus on liquid water path (LWP) response to added heterogeneity for 43 day long simulations. We observed qualitatively similar responses in LWP as a result of accounting for heterogeneity induced secondary circulations in both LES and multi-column CLUBB as well as indications of clear trends in response based on the atmospheric conditions. This work indicates that a multi-column setup has significant promise for modeling the impacts of heterogeneity induced secondary circulations for application in ESMs at a fraction of the computational expense of LES. Continuing work expands this analysis to cover a wider variety of surface and atmospheric conditions, determine when multi column CLUBB has significant sensitivities to heterogeneity induced secondary circulations, and explore avenues for further simplification of the model setup.</p>

The atmospheric boundary layer (ABL) plays a fundamental role in the climate system due to its significance in bridging land surface fluxes of heat and water vapor to convection and cloud formation (Garratt, 1992;Huang & Margulis, 2010;Siqueira et al., 2009). The ABL is characterized by the coexistence of mechanically and thermally generated turbulence, which regulates mixing and transport properties and exchanges between the land surface and the lower atmosphere. The variances of turbulent quantities are of particular interest due to their emerging role in state-of-the-science Earth System Models (ESMs) and numerical weather prediction. They have accordingly received attention in the literature, although most of these studies have focused on the velocity variances. Comparatively few examine the potential temperature variance (PTV) and those that do often focus on flat homogeneous terrain (

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