How Much Do Different Land Models Matter for Climate Simulation? Part II: A Decomposed View of the Land-Atmosphere Coupling Strength

The Global Land-Atmosphere Coupling Experiment (GLACE) built a framework to estimate the strength of the land-atmosphere interaction across many weather and climate models. Within this framework, GLACE-type experiments are performed with a single atmospheric model coupled to three different land models. The precipitation time series is decomposed into three frequency bands to investigate the large-scale connection between external forcing, precipitation variability and predictability, and land-atmosphere coupling strength. It is found that coupling to different land models or prescribing subsurface soil moisture does not change the global pattern of precipitation predictability and variability too much. However, the regional impact of soil moisture can be highlighted by calculating the land-atmosphere coupling strength, which shows very different patterns for the three models. The estimated precipitation predictability and land-atmosphere coupling strength is mainly associated with the low-frequency component of precipitation (periods beyond 3 weeks). Based on these findings, the land-atmosphere coupling strength is conceptually decomposed into the impact of low-frequency external forcing and the impact of soil moisture. Because most models participating in GLACE have overestimated the low-frequency component of precipitation, a calibration to the GLACE-estimated land-atmosphere coupling strength is performed. The calibrated coupling strength is generally weaker, but the global pattern does not change much. This study provides an important clarification of land-atmosphere coupling strength and increases the understanding of the land-atmosphere interaction.