A Global Intercomparison of Modeled and Observed Land-Atmosphere Coupling

Land-atmosphere coupling strength or the degree to which land surface anomalies influence boundary layer development and in extreme cases, rainfall is arguably the single most fundamental criterion for evaluating hydrological model performance. The Global Land Atmosphere Coupling Experiment (GLACE) showed that strength of coupling and its representation can affect a model's ability to simulate climate predictability at the seasonal time scale. And yet, the lack of sufficient observations of coupling at appropriate temporal and spatial scales has made achieving true coupling in models an elusive goal. This study uses Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) soil moisture (SM), multisensor remote sensing (RS) evaporative fraction (EF), and Atmospheric Infrared Sounder (AIRS) lifting condensation level (LCL) to evaluate the realism of coupling in the Global Land Data Assimilation System (GLDAS) suite of land surface models (LSMs), Princeton Global Forcing Variable Infiltration Capacity model (PGF-VIC), seven global reanalyses, and the North American Regional Reanalysis (NARR) over a 5-yr period (2003-07). First, RS and modeled estimates of SM, EF, and LCL are intercompared. Then, emphasis is placed on quantifying RS and modeled differences in convective-season daily correlations between SM LCL, SM EF, and EF LCL for global, regional, and conditional samples. RS is found to yield a substantially weaker state of coupling than model products. However, the rank order of basins by coupling strength calculated from RS and models do roughly agree. Using a mixture of satellite and modeled variables, a map of hybrid coupling strength was produced, which supports the findings of GLACE that transitional zones tend to have the strongest coupling.