A Modeling and Observational Framework for Diagnosing Local Land–Atmosphere Coupling on Diurnal Time Scales

Abstract

Land-atmosphere interactions play a critical role in determining the diurnal evolution of both planetary boundary layer (PBL) and land surface temperature and moisture states. The degree of coupling between the land surface and PBL in numerical weather prediction and climate models remains largely unexplored and undiagnosed due to the complex interactions and feedbacks present across a range of scales. Further, uncoupled systems or experiments (e.g., the Project for Intercomparison of Land Parameterization Schemes, PILPS) may lead to inaccurate water and energy cycle process understanding by neglecting feedback processes such as PBL-top entrainment. In this study, a framework for diagnosing local land-atmosphere coupling is presented using a coupled mesoscale model with a suite of PBL and land surface model (LSM) options along with observations during field experiments in the U. S. Southern Great Plains. Specifically, the Weather Research and Forecasting (WRF) model has been coupled to the Land Information System (LIS), which provides a flexible and high-resolution representation and initialization of land surface physics and states. Within this framework, the coupling established by each pairing of the available PBL schemes in WRF with the LSMs in LIS is evaluated in terms of the diurnal temperature and humidity evolution in the mixed layer.The co-evolution of these variables and the convective PBL is sensitive to and, in fact, integrative of the dominant processes that govern the PBL budget, which are synthesized through the use of mixing diagrams. Results show how the sensitivity of land-atmosphere interactions to the specific choice of PBL scheme and LSM varies across surface moisture regimes and can be quantified and evaluated against observations. As such, this methodology provides a potential pathway to study factors controlling local land-atmosphere coupling (LoCo) using the LIS-WRF system, which will serve as a testbed for future experiments to evaluate coupling diagnostics within the community.3

Effects of explicit convection on global land‐atmosphere coupling in the superparameterized CAM

“…By incorporating CRMs, SPCAM explicitly resolves convection and improves the precipitation simulation in many aspects, which alters soil moisture variability. To better understand the effects of explicitly resolved convection on the surface flux response to soil moisture variability, more constrained experiments and land-atmosphere coupling studies at subdaily scales and at process levels (e.g., the mixing diagram approach in Santanello et al [2009]) would be useful.…”

“…As the results show, the sensitivity terms (surface fluxes response to soil moisture or rainfall response to surface fluxes) in the coupling indices play dominant roles in many cases. To better understand these effects of superparameterization at a process level, we report in a separate manuscript the results of applying a local land-atmosphere coupling (LoCo) framework [Santanello et al, 2009[Santanello et al, , 2011a in observationally constrained SPCAM and CAM experiments.…”

Diagnosing the Nature of Land–Atmosphere Coupling: A Case Study of Dry/Wet Extremes in the U.S. Southern Great Plains

“…This comprehensive analysis extends from the work of Santanello et al (2009 hereafter referred to as S09 and S11) by performing an evaluation using observations along with composite and regional (including reanalysis product) analyses. The case studies chosen for these experiments are composed of extreme dry and wet conditions in terms of soil moisture and precipitation relative to normal, and are therefore ideally suited to capture a wide range of variability in L-A interactions and coupling.…”

“…This was performed in a global climate model context using a large number of ensemble simulations, and therefore parsing out the reasons for differences in coupling strength amongst models (and inherent land surface and PBL physics) remains a difficult task. A companion effort has since been launched that focuses on local L-A coupling (LoCo; Santanello et al 2009 in coupled models by diagnosing land-PBL interactions at the process level using a regional, high-resolution testbed. The methodology developed in LoCo can be applied to any model or observations, and it is particularly well suited to isolate the impacts of land surface perturbations on the PBL (and vice-versa) that are crucial for sustaining flood and drought conditions.…”

Impact of Land Model Calibration on Coupled Land–Atmosphere Prediction

“…where EF is the evaporative fraction, defined as feedback of the atmosphere (through the PBL) on surface fluxes (EF atm ) (Santanello et al 2007;249 van Heerwaarden et al 2009 of LoCo research and the related diagnostic framework can be found in Santanello et al (2009Santanello et al ( , 263 2011aSantanello et al ( , 2011bSantanello et al ( , 2012; hereafter referred to as S09, S11a, S11b, S12 OPT/UE) algorithms to be applied to the LSMs to exploit further the information content from 296 observations. The algorithms (e.g.…”