STRADIVARI Project II: Atmospheric Boundary Layer (ABL) Dynamics

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The equations modeling the ABL are extensively covered under various aspects (Stull, 1988; Yin and Porporato, 2022, Honnert at al., 2020; Canché-Cab et al., 2024) and implemented in various software. However, the interaction between soil moisture, land surface fluxes, and convection initiation, leading to rainfall, remains challenging (Dirmeyer et al., 2006; Koster et al., 2004; Santanello et al., 2007). This stems from the complexity of the Soil-Plant-Atmosphere Continuum interactions across multiple spatial and temporal scales. The ABL, influenced by mechanical and thermal turbulence, links surface processes with synoptic phenomena, while plant physiology regulates sensible and latent heat fluxes. These fluxes affect the energy needed for convection and ABL growth, as well as the transfer of water vapor from the root zone to the atmosphere and determine the Lifting Condensation Level (LCL) (Siqueira et al., 2009; Cuxart et al., 2020), and its intersection with the ABL, critical for rainfall initiation. The height of this crossing, visible as cloud base, highlights the soil-plant system's control over hydrological self-regulation, which implies that drier soils may increase sensible heat flux, enhancing convection and raising ABL depths, thus elevating the likelihood of ABL-LCL crossing and rainfall, an example of negative feedback. Conversely, reduced latent heat flux can lower ABL water vapor concentration, raising the LCL above the ABL, leading to sustained dry conditions, exemplifying positive feedback.

Stradivari's Hellier

Beyond the conceptual framework, a critical implementation challenge emerges from the fundamental mismatch between hydrological and atmospheric process scales and their characteristic timescales. Figure below illustrates the multi-scale coupling mechanisms central to STRADIVARI, adapted from Miralles et al. (2025). 

Vegetation controls surface energy, water, and carbon fluxes at local scales through processes governed by soil moisture dynamics and groundwater table fluctuations. These surface controls propagate to the atmosphere via turbulent fluxes, driving convective and mechanical instability that alters the diurnal evolution of the atmospheric boundary layer (ABL). The ABL growth dynamics regulate moisture and heat entrainment processes, determining the lifting condensation level (LCL) and subsequent convective cloud formation—the critical link between local surface processes and regional precipitation patterns. While contemporary atmospheric models can resolve these multi-scale interactions, their representation of surface phenomena remains heavily parameterized, obscuring the mechanistic coupling that STRADIVARI seeks to capture. 

Critical Gap: Current Land Surface Models rely predominantly on bulk aerodynamic formulations and Monin-Obukhov Similarity Theory parameterizations that treat the ABL as a prescribed boundary condition rather than solving governing transport equations (Santanello et al., 2018). PLUMBER-2 analysis shows systematic LSM failures in water-limited regions where soil-plant coupling becomes critical, while TRENDY simulations reveal persistent discrepancies in vegetation-atmosphere CO2 exchange (Friedlingstein et al., 2023). These failures stem from models using parameters as "garbage collectors" (sensu Beven, 2006) rather than physically meaningful quantities corresponding to independently measurable soil, plant, and atmospheric properties. The most widespread conceptual framework in treating these issues reduces the SPAC complexity to an electrical circuit analogy (Monson & Baldocchi, 2015; Bonan, 2019), conflating aerodynamic transport, physiological regulation, and soil physics into parameterized "resistances" that obscure actual mechanisms at play. While full resolution of precipitation recycling mechanisms remains beyond current capabilities, the hydrological modeling community lacks tools to explore even minimal surface-atmosphere processes complexity.

STRADIVARI innovation: Rather than claiming to resolve precipitation recycling, STRADIVARI deconstructs the resistance framework by resolving atmospheric turbulence through governing equations rather than parameterizations. This allows temperature, wind velocity, and humidity profiles to emerge naturally from ABL physics, creating boundary conditions at leaf and soil surfaces that couple directly with plant hydraulic solutions while isolating plant conductance as a purely physiological phenomenon rather than a catch-all for system-level behaviors we fail to resolve mechanistically. The approach bridges the gap between hydrological and micrometeorological communities, providing tools for collaborative investigation of coupled processes at scales where both communities can contribute observational constraints and process understanding. STRADIVARI addresses this challenge by starting the implementation of hierarchical ABL modeling framework with four levels of increasing complexity: The framework implements a hierarchical ABL approach: (1) Wood (2000) statistical-dynamical corrections for basic terrain effects, (2) spectral methods for turbulent scalar transport following Katul et al. (2011) and Poggi et al. (2004), (3) multi-scale atmospheric boundary layer modeling incorporating canopy-atmosphere interactions (Finnigan et al., 2009; Brunet & Irvine, 2000), and (4) machine learning-enhanced parameterizations for complex terrain effects (Cheng et al., 2021; Rasp et al., 2018). Validation against Alpine meteorological stations determines minimum complexity required for meaningful surface-atmosphere coupling.

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References - Atmospheric Boundary Layer

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• Siqueira, Mario, Gabriel Katul, and Amilcare Porporato. 2009. "Soil Moisture Feedbacks on Convection Triggers." Journal of Hydrometeorology 10(1): 96-112.
• Stull, R. B. 1988. An Introduction to Boundary Layer Meteorology. Kluwer Academic Publishers.
• Wood, Eric F., et al. 2011. "Hyperresolution Global Land Surface Modeling: Meeting a Grand Challenge for Monitoring Earth's Terrestrial Water." Water Resources Research 47(5).
• Yin, Jin, and Amilcare Porporato. 2022. Ecohydrology: Dynamics of Life and Water in the Critical Zone. Cambridge University Press.

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