GC23I-1210
Thermal Coupling Between Air and Ground Temperatures in the CMIP5 Historical and Future Simulations
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Almudena García-García1, Francisco José Cuesta-Valero1, Jason E Smerdon2 and Hugo Beltrami3,4, (1)St. Francis Xavier University, Climate & Atmospheric Sciences Institute and Department of Earth Sciences, Antigonish, Canada, (2)LDEO of Columbia University, Palisades, NY, United States, (3)Université du Québec à Montréal, Centre ESCER pour l'étude et la simulation du climate à l'échelle régionale, Montréal, QC, Canada, (4)St. Francis Xavier University, Climate & Atmospheric Sciences Institute and Department of Earth Sciences, Ottawa, ON, Canada
Abstract:
The thermal coupling between air and ground temperatures is investigated herein for General Circulation Models (GCMs) that participated in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). For each simulation, we evaluate the regional relationship between air and ground temperatures to study surface energy fluxes and the attenuation of the annual temperature signal across the air-ground interface and into the shallow subsurface for North America. Our results show that the transport of energy across the air-ground interface and into the shallow subsurface is different across GCMs and is dependent on the land surface models that each employs. The variability of the difference between air and ground temperatures is high among simulations and is not dependent on the depth of the bottom boundary of the subsurface soil model. The difference between air and ground temperatures differs significantly from observations. Additionally, while the variability among GCMs can be explained by the physics of the land surface models, the regional variability of the air-ground coupling is associated with the model treatment of soil properties as well as snow and vegetation processes within GCMs. The difference between air and ground temperatures at high latitudes within the majority of the CMIP5 models is directly proportional to the amount of snow on the ground, due to the insulating effect of snow cover. On the other hand, the difference between air and ground temperatures at low latitudes within some of the CMIP5 models is inversely proportional to the vegetation cover (leaf area index), due to changes in latent and sensible heat fluxes. The large variability among GCMs and the marked dependency of the results on the choice of the land-surface model illustrates the need for improving the simulation of air-ground coupling in land-surface models towards a robust simulation of near-surface processes, such as permafrost and soil carbon stability within GCMs.
