Abstract
ABSTRACTThe spread of a dense gas in the atmosphere is a phenomenon that occurs widely with natural (and anthropogenic) causes and is often associated with high impact and hazardous events. In this study a method of simulating the spread of dense gases in a numerical weather prediction model is presented. This approach has the advantage that dense gases can be simulated in regions of complex terrain using realistic forcings (in terms of both the driving meteorological fields and the representation of surface characteristics). The model formulation is tested against semi‐idealized gravity‐current‐type experiments and similar modelling studies. As an example application, the Lake Nyos disaster of 1986, where a dense CO2 cloud spread through a mountainous region of Cameroon, is simulated. The predicted spread of CO2 agrees (qualitatively) very well with the observations. The method provides a means of determining a potential ‘safe height’ above which simulated concentrations are not hazardous, and thus the height above which refuge should be taken during similar future events. The simulation demonstrates a novel application which can be rapidly applied to other scenarios.
Highlights
The spread of dense gases, or particle–gas mixtures that can be treated as gas mixtures, is a phenomenon that occurs widely in nature: for example, volcanic degassing and volcanic pyroclastic flows (Sparks et al, 1997) and the movement of dust-rich air masses (e.g. West African frontal systems, Burton et al, 2012)
The release of dense gases in such cases, whether natural or anthropogenic, is generally hazardous in relation to human wellbeing and safety: for example the Bhopal disaster of 1984 where an accidental release of methyl isocyanate from the Union Carbide pesticide plant in India caused as many as 20 000 deaths (Varma and Varma, 2005)
The model is tested against laboratory studies and existing numerical weather prediction (NWP) test cases
Summary
The spread of dense gases, or particle–gas mixtures that can be treated as gas mixtures, is a phenomenon that occurs widely in nature: for example, volcanic degassing and volcanic pyroclastic flows (Sparks et al, 1997) and the movement of dust-rich air masses (e.g. West African frontal systems, Burton et al, 2012). Anthropogenic releases of potentially harmful dense gases have motivated the development of numerous models (see for example Duijm et al, 1997). The release of dense gases in such cases, whether natural or anthropogenic, is generally hazardous (or at least of high impact) in relation to human wellbeing and safety: for example the Bhopal disaster of 1984 where an accidental release of methyl isocyanate from the Union Carbide pesticide plant in India caused as many as 20 000 deaths (Varma and Varma, 2005). The ability to simulate a dense gas release is commonly performed by the use of several models, of increasing complexity. More complex computational fluid dynamics models have been developed that can incorporate the effects of topography and demonstrate how this is beneficial (Scargliali et al, 2005). In addition to the sophisticated representation of physical processes such as turbulence, radiative and microphysical effects,
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