Thermodynamics of Pyrocumulus: A Conceptual Study
Thermodynamics of Pyrocumulus: A Conceptual Study
复制标题
火积云热力学：概念研究
DOI：
10.1175/mwr-d-17-0377.1
复制
发表时间：
2018
影响因子：
3.2
通讯作者：
J. Kepert
中科院分区：
文献类型：
--
作者：
K. Tory;W. Thurston;J. Kepert
在有利的大气条件下，火灾可以产生类似于传统雷暴的深对流柱形式的焦碳云团(PyroCb)，这可能伴随着强烈的流入、危险的下击和雷击，这些可能会导致火灾行为的危险变化。人们对PyroCb的形成条件没有很好的了解，也很难预测。本文对火焰羽流的热力学进行了理论研究，以更好地了解各种因素对羽流凝结的影响。烟羽气体在火源被认为是未稀释的，在烟羽顶部接近100%稀释(中性浮力)。羽流凝结高度的变化被考虑到这一全范围的稀释和一组给定的因素，包括环境温度和湿度、火灾温度和火-水-热比。计算冷凝高度，并在热力学图上绘制饱和点(SP)曲线。通过SP曲线的位置和斜率，可以深入了解羽流凝结是如何受到环境热力学和火焰热湿比的影响的。图中添加了来自大涡模型模拟的羽流温度轨迹，为了解羽流凝结高度和凝结时的羽流浮力提供了更多的洞察力。将SP曲线添加到标准热力学图上的混合层抬升凝结水平，可以用来确定发展深层、潮湿、自由对流所需的最小羽流凝结高度和浮力，这将有助于对pyroCb的预测。
In favorable atmospheric conditions, fires can produce pyrocumulonimbus cloud (pyroCb) in the form of deep convective columns resembling conventional thunderstorms, which may be accompanied by strong inflow, dangerous downbursts, and lightning strikes that can produce dangerous changes in fire behavior. PyroCb formation conditions are not well understood and are difficult to forecast. This paper presents a theoretical study of the thermodynamics of fire plumes to better understand the influence of a range of factors on plume condensation. Plume gases are considered to be undiluted at the fire source and approach 100% dilution at the plume top (neutral buoyancy). Plume condensation height changes are considered for this full range of dilution and for a given set of factors that include environmental temperature and humidity, fire temperature, and fire-moisture-to-heat ratios. The condensation heights are calculated and plotted as saturation point (SP) curves on thermodynamic diagrams. The position and slope of the SP curves provide insight into how plume condensation is affected by the environment thermodynamics and ratios of fire heat to moisture production. Plume temperature traces from large-eddy model simulations added to the diagrams provide additional insight into plume condensation heights and plume buoyancy at condensation. SP curves added to a mixed layer lifting condensation level on standard thermodynamic diagrams can be used to identify the minimum plume condensation height and buoyancy required for deep, moist, free convection to develop, which will aid pyroCb prediction.