Shallow layer simulation of heavy gas released on a slope in a calm ambient Part II. Instantaneous releases

This paper assesses the value of shallow layer modelling for instantaneous releases of heavy gas over a slope using the established computer model TWODEE [R.K.S. Hankin, Heavy gas dispersion over complex terrain, Ph.D. thesis, Cambridge University, 1997; J. Hazard. Mater. 66 (1999) 211; J. Hazard. Mater. 66 (1999) 227; J. Hazard. Mater. 66 (1999) 239] and the experimental results of Schatzmann et al. [M. Schatzmann, K. Marotzke, J. Donat, Research on continuous and instantaneous heavy gas clouds, Contribution of sub-project EV 4T-0021-D to the final report of the joint CEC project, Technical report, Meteorological Institute, University of Hamburg, February 1991]. This is the second of a two-part paper; part I considered continuous releases using the same model, using the same entrainment parameters. Schatzmann et al. carried out instantaneous releases of heavy gas over three slopes; each experiment was repeated five times under nominally identical conditions. The goodness-of-fit measures (GFMs) of Hanna et al. [Atmos. Environ. 27A (15) (1993) 2265] are generalized to account for the multiple releases carried out by Schatzmann et al. Using these statistical GFMs, predicted peak concentrations are generally correct to within a factor of two; and cloud arrival times are generally late