A new pattern of coupling strength in North America using a linear inverse modeling framework of the land-atmosphere system

The efficiency of water and energy exchange between the land and atmosphere defines the land-atmosphere coupling strength, which is a vital component for understanding and predicting land-atmosphere feedbacks, climate change, ecosystems, and life. This study presents a new approach to investigate land-atmosphere coupling strength. Our approach uses a linear inverse modeling (LIM) framework that defines coupling strength as the covariance between soil moisture (land) and the Palmer Drought Severity Index (atmosphere). Our method uses LIM to decouple the land-atmosphere system with two numerical experiments. In these experiments, we use canopy transpiration from vegetation to couple or decouple the land-atmosphere system. The analysis was done over North America, focusing on the summer season. We use a millennial simulation the Community Earth System Model (CESM) to test the LIM approach. The CESM simulation is used because we can test the statistical significance of patterns of coupling strength in a millennial record. The outcome of this study reveals a new pattern of the coupling strength over North America that differs from recent studies. The pattern of the coupling strength is strongest over the Great Plains, with secondary influence over the Southwest related to climate variability of the North American monsoon. For the summer season (June-July), the pattern seems to match with the climate extreme (pluvial and drought) of the Great Plains and the Southwest. If this coupling pattern is validated with further studies, for example, complementing this model-based analysis with a LIM of observational data, a better understanding of the coupling strength could be used to explore and assess climate change impacts and predictability.