Intra and Inter Seasonal Variability of Land-Atmosphere Coupling over North America

Abstract:

Land-atmosphere coupling was long thought not to be strong enough to have a profound effect on climatic conditions during colder months. Hence, while the impact of land-atmosphere coupling on summer is well documented, its effect on spring, winter and fall is less well established. In particular, soil moisture could be influenced by the considerable amount of snow/ice melt that occur during spring, which makes it an ideal season to investigate further. Here, we use the 5^th Generation Canadian Regional Climate Model (CRCM5) to run coupled simulations, where the land and the atmosphere are allowed to interact freely, and uncoupled simulations, where the soil moisture content is prescribed, to evaluate the strength of land-atmosphere coupling and its impact on present and future spring climate over North America. Analysis of the coupled and uncoupled simulations reveal that soil moisture/temperature coupling in spring is indeed strong over the Great Plains but weaker over the same areas compared to summer under present climatic conditions. It is also strong over the Canadian Prairies in May, which is a transition month between spring and summer. Strong land-atmosphere coupling during transition periods could therefore be analogous to transition zones between dry and wet climates that were the land-atmosphere hotspots identified in the GLACE experiment. This study thus provides insight on the seasonal evolution of land-atmosphere coupling strength and its impact on extremes over North America.