Tuesday, 18 November 2003: 11:15 AM
Combining the Haines Index and turbulent kinetic energy for fire-weather predictions
Daily 24-48 hour fire-weather predictions for different regions of the U.S. are now readily available from the regional Fire Consortia for Advanced Modeling of Meteorology and Smoke (FCAMMS) that were established as part of the U.S. National Fire Plan. These predictions are based on daily MM5 model simulations of atmospheric conditions and fire-weather indices over specific modeling domains. One of the many fire-weather indices routinely provided in the FCAMMS fire-weather predictions is the well-known Haines Index (HI). The HI is an operational atmospheric “mesoscale-type” index that includes only stability and moisture conditions in the lower to middle troposphere to characterize the atmospheric risk of extreme fire behavior. However, there are other atmospheric variables that also influence the risk of extreme fire behavior, especially those that characterize conditions in the atmospheric boundary layer where small-scale fire-atmosphere interactions are so important. Atmospheric turbulence, as measured by turbulent kinetic energy (TKE), is one of those variables, and TKE can be classified as a “boundary-layer-type” index. The generation and dissipation of TKE in the atmosphere are dependent on wind shear and buoyancy conditions, which are two factors that affect the local environment surrounding wildland fires. Although predictions of TKE in the boundary layer using level-2.5-closure from the Mellor-Yamada turbulence hierarchy are available from the daily FCAMMS MM5 model simulations, they have not been used in the past for characterizing atmospheric risk of extreme fire behavior.
This study is a first step in examining the utility of combining the Haines Index, a “mesoscale-type” fire-weather index, with TKE, a “boundary-layer-type” turbulence index, for assessing the potential atmospheric risk of extreme fire behavior. Output from the FCAMMS - Eastern Area Modeling Consortium (EAMC) MM5 simulations of fire-weather conditions over two 4-km grid-spacing domains in the north central and northeastern U.S. are being used to identify regional patterns of HI and TKE on a daily basis. A comparison of the patterns of the two indices allows for an assessment of whether large HI values typically occur with large near-surface TKE values, a potentially dangerous fire-weather condition.