The response of atmospheric carbon dioxide to a given amount of surface flux is inversely proportional to the depth of the boundary layer. Overshooting thermals that entrain free tropospheric air down into the boundary layer modify the characteristics and depth of the lower layer through the insertion of energy and mass. This alters the 5 surface energy budget by changing the Bowen ratio and thereby altering the vegetative response and the surface boundary conditions. Although overshooting

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... als are important in the physical world, their effects are unresolved in most regional models. A parameterization to include the effects of boundary layer entrainment was introduced into a coupled ecosystem-atmosphere model (SiB-RAMS). The parameterization is 10 based on a downward heat flux at the top of the boundary layer that is proportional to the heat flux at the surface. Results with the parameterization show that the boundary layer simulated is deeper, warmer, and drier than when the parameterization is turned off. These results alter the vegetative stress factors thereby changing the carbon flux from the surface. The combination of this and the deeper boundary layer change the 15 concentration of carbon dioxide in the boundary layer. 20 the PBL, such as the potential temperature, mixing ratio, wind speed, concentrations of trace gases, etc. are relatively homogeneous. The depth of the PBL (Z i ) is thus important for determining the concentrations of trace gases within the layer and the exchange of the variables energy, water, momentum, and trace gases between the surface and the free atmosphere, making it a significant factor in studies of pollution, 25 heat island effects, the general circulation and many other problems of meteorology 14312 Abstract ACPD Abstract ACPD Abstract ACPD Abstract layer through entrainment. In addition, since the boundary layer is warmer, less surface