A preliminary investigation of boundary layer effects on daytime CO₂ concentrations at a mountaintop location in the Rocky Mountains

Simulations are performed with a mesoscale model to examine the effects of atmospheric structure and large-scale flows on the diurnal variability. In the simulations initialized without large-scale winds, the CO₂ minimum occurs earlier compared to the observations.

Upslope flows play an important role in the presence of this early (pre-noon) minimum while the timing and magnitude of the minimum depend only weakly on the temperature structure. An increase in large-scale flow has a noticeable impact on the diurnal variability with a more gradual decrease in daytime CO₂ concentration, similar to summer-averaged observations. From the idealized simulations and a case study, it is concluded that multi-scale flows and their interactions have a large influence on the observed diurnal variability.