CLIMATE VARIABILITY AND LAND-SURFACE PROCESSES

The coupled ocean-atmosphere-land climate system is characterized by substantial amounts of variability on a wide range of spatial and temporal scales. This natural variability of climate increases the difficulty of detecting climate change attributable to increasing greenhouse gas concentrations. A key issue in climate research is obtaining a better description of this variability and the physical mechanisms responsible for it. One of the important physical processes contributing to this variability is the interaction between the land surface and the atmosphere. Through its effect on the surface energy flux components, the land surface can exert a pronounced effect on the variability of the atmosphere. The potential importance of such interactions for climate variability is examined through the use of numerical modeling studies. The physical mechanisms governing the time scales of soil moisture variability in the model are outlined, and observational evidence is presented supporting this analysis. In addition, it is shown that interactions between soil wetness and the atmosphere can both increase the total variability of the atmosphere and lengthen the time scales of near-surface atmospheric fluctuations.