A wildland fire experiment was conducted on a 40-ha tall grass prairie in Texas to study fire-atmosphere interactions. The experiment coincided with a Red Flag Warning, signifying specific weather conditions associated with an elevated risk of wildfire ignition and rapid spread. This provided a rare opportunity to observe wildland fire behavior and its impact on atmospheric flows under conditions deliberately avoided in similar experiments. This study analyzed the high frequency meteorological data collected during the experiment using three-dimensional sonic anemometers mounted on a 43-m tower (at 5.8, 10 and 20 m) and on three 10-m towers (at 5.3 m) within the burn block. The tower placements were carefully chosen to capture the impact of both head and flank fires on the mean and turbulent flows. The hypothesis is that fire-induced perturbations in the lower atmosphere, quantified through parameters like turbulent kinetic energy (TKE) and vertical fluxes, would be substantially stronger than those observed in similar wildland fires under less fire-prone atmospheric conditions. While this hypothesis was validated for heat flux and TKE, it did not hold for momentum fluxes or friction velocity. Additionally, the observations failed to confirm the hypothesis that head fires would produce more intense perturbations than flank fires. Given the homogeneity of fuel, terrain and meteorological elements across the burn unit, this underscores the challenge of disentangling the effects of fire type from other natural factors in a real-world setting. Nevertheless, the finding holds promise for improving turbulence parameterizations in fire-behavior and smoke dispersion models.

中文翻译：

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与快速蔓延的草火相关的表面层湍流

在德克萨斯州一片 40 公顷高的草地上进行了荒地火灾实验，以研究火灾与大气的相互作用。该实验恰逢红旗警告，表示特定的天气条件与野火点燃和迅速蔓延的风险增加有关。这提供了一个难得的机会，可以在类似实验中刻意避免的条件下观察荒地火灾行为及其对大气流动的影响。本研究使用安装在燃烧区内的 43 米塔（5.8、10 和 20 m）和三个 10 米塔（5.3 m）上的三维声波风速计分析了实验期间收集的高频气象数据。塔的位置经过精心选择，以捕捉头部和侧面火力对平均流和湍流的影响。假设认为，通过湍流动能（TKE）和垂直通量等参数量化的低层大气中由火灾引起的扰动将比在不易发生火灾的大气条件下在类似的野地火灾中观察到的扰动强得多。虽然这一假设在热通量和 TKE 方面得到了验证，但它不适用于动量通量或摩擦速度。此外，观察结果未能证实头部火力会比侧翼火力产生更强烈扰动的假设。考虑到整个燃烧单元的燃料、地形和气象要素的同质性，这凸显了在现实世界环境中将火灾类型的影响与其他自然因素分开的挑战。尽管如此，这一发现有望改善火灾行为和烟雾扩散模型中的湍流参数化。