Eighth Symposium on Fire and Forest Meteorology


Including the environmental wind effects on smoke plume rise of vegetation fires in 1D cloud models

Saulo R. Freitas, Centro de Previsao de Tempo e Estudos Climaticos / INPE, Cachoeira Paulista, SP, Brazil; and K. Longo, J. Trentmann, and D. Latham

Biomass burning emits hot gases and particles which are quickly transported upward with the positive buoyancy of the fire. It is well recognized the importance of a correct vertical injection layer of biomass burning emissions in 3d atmospheric chemistry-transport models. However, including the sub-grid scale smoke plume rise of vegetation fires in this kind of models is still a challenge. Freitas et al. (2006, 2007) introduced a methodology to include this sub-grid transport mechanism by embedding a 1D cloud resolving model, with appropriate lower boundary conditions, in each column of a 3D host model. Typically, the final vertical height that the smoke plumes reaches is controlled by the thermodynamic stability of the atmospheric environment and the surface heat flux released from the fire. However, in presence of strong horizontal wind, it might enhance the lateral entrainment and induces an additional drag, particularly for small fires, impacting the injection height. In this paper, the authors improve the methodology by including the effect of the environmental wind on transport and dilution of the smoke plume at the cloud scale. This process is quantitatively represented by introducing an additional entrainment term to represent the organized inflow of the cooler and drier ambient air into the plume and its drag by the momentum transfer. An extended set of equations including the horizontal motion of the plume and the additional increase of the plume radius size is now solved to explicitly simulate the time evolution of the plume rise. One-dimensional (1D) model results are presented for two hypothetical deforestation fires in the Amazon basin with sizes of 10 and 50 ha and under calm and windy environments. The results are then confronted with corresponding simulations generated by the complex non-hydrostatic 3D Active Tracer High resolution Atmospheric Model (ATHAM). We show that the 1D model can generate feasible comparisons with the fully 3D simulations.

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Session 11A, Smoke from Wildland Fires II
Thursday, 15 October 2009, 1:30 PM-2:45 PM, Lake McDonald/ Swift Current/ Hanging Gardens

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