Coupling cloud base height and land surface processes in the Amazon Basin.

摘要

Vegetation plays a critical role in regulating cloud formation in the tropics. Cloud formation depends on vegetation-atmosphere transfers of moisture and energy; however, little research has been directed at determining the underlying mechanisms that affect cloud base height. We use the fully-coupled general circulation model HadCM3LC to compute lifting condensation level (LCL; cloud base height) over the Amazon Basin for three climate scenarios: Last Glacial Maximum (LGM; 21 kya), present day (1970--1990) and future (2070--2090). We analyze the relationship between LCL and land surface processes in each scenario. Our results show that elevated LCL during the LGM (compared to present day) is the result of lower tropical sea surface temperatures (SSTs) and moisture transport, rather than changes in vegetation cover. Elevated LCL in the future, however, is caused by increased land surface temperature and decreased evapotranspiration (ET), largely attributed to a reduction in broadleaf tree cover.