Modelling low-level boundary layer structure in complex terrain: verification of TAPM meteorological predictions in the Canberra region

Abstract

The performance of the meteorological component of The Air Pollution Model (TAPM) in the Canberra region is assessed using temperature and wind profiles from a Radio Acoustic Sounding System (RASS) and high frequency Doppler sodar. The region has relatively complex terrain and the period of the study included a significant fraction of time where winds were light and the boundary layer was strongly stable. Overall, TAPM’s performance was similar to that found in other verification studies which have compared TAPM vertical wind profiles against observations. However, when a bulk Richardson number was used to classify the boundary layer into three classes (unstable, neutral and weakly stable, and strongly stable), it was found that model performance was poorer for the strongly stable class. The observed nocturnal cooling was greater than that predicted by TAPM and the model did not generate the complex vertical wind profiles which occur under strongly stably-stratified conditions at the site. Problems with TAPM simulations under light wind stable conditions have been observed in regions with simple terrain before, but this study indicates that they are exacerbated by the more complex terrain, and associated terrain-driven flows.