Observations of a rotating pyroconvective plume

IF 2.9 3区农林科学 Q1 FORESTRY International Journal of Wildland Fire Pub Date : 2024-03-22 DOI:10.1071/wf23045

Neil P. Lareau, Craig B. Clements, Adam Kochanski, Taylor Aydell, Andrew T. Hudak, T. Ryan McCarley, Roger Ottmar

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Abstract

Background

There is an ongoing need for improved understanding of wildfire plume dynamics.

Aims

To improve process-level understanding of wildfire plume dynamics including strong (>10 m s⁻¹) fire-generated winds and pyrocumulus (pyroCu) development.

Methods

Ka-band Doppler radar and two Doppler lidars were used to quantify plume dynamics during a high-intensity prescribed fire and airborne laser scanning (ALS) to quantify the fuel consumption.

Key results

We document the development of a strongly rotating (>10 m s⁻¹) pyroCu-topped plume reaching 10 km. Plume rotation develops during merging of discrete plume elements and is characterised by inflow and rotational winds an order of magnitude stronger than the ambient flow. Deep pyroCu is initiated after a sequence of plume-deepening events that push the plume top above its condensation level. The pyroCu exhibits a strong central updraft (~35 m s⁻¹) flanked by mechanically and evaporative forced downdrafts. The downdrafts do not reach the surface and have no impact on fire behaviour. ALS data show plume development is linked to large fuel consumption (~20 kg m⁻²).

Conclusions

Interactions between discrete plume elements contributed to plume rotation and large fuel consumption led to strong updrafts triggering deep pyroCu.

Implications

These results identify conditions conducive to strong plume rotation and deep pyroCu initiation.

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对旋转热对流羽流的观测

背景需要不断加深对野火羽流动力学的了解。目的提高对野火烟羽动态的过程级了解，包括火灾产生的强风（10 m s-1）和火积云（pyroCu）的发展。方法使用 Ka 波段多普勒雷达和两个多普勒激光雷达来量化高强度规定火灾期间的烟羽动态，并使用机载激光扫描 (ALS) 来量化燃料消耗。主要结果我们记录了一个强旋转（10 m s-1）的火铜顶烟羽的发展过程，其高度达到 10 km。羽流旋转是在离散羽流元素合并过程中形成的，其特征是流入风和旋转风比环境流强一个数量级。一连串的羽流加深事件将羽流顶部推高到其凝结水平之上，深层热核就是在这些事件之后开始的。深层热核呈现出强烈的中央上升气流（~35 m s-1），两侧是机械和蒸发强迫下沉气流。下沉气流没有到达地表，对火灾行为没有影响。ALS 数据显示，烟羽的发展与大量燃料消耗（约 20 kg m-2）有关。结论离散烟羽元素之间的相互作用促成了烟羽旋转，而大量燃料消耗则导致强劲的上升气流引发了深层热核。影响这些结果确定了有利于强羽流旋转和深层火成铜启动的条件。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

International Journal of Wildland Fire 农林科学-林学

CiteScore

5.50

自引率

9.70%

发文量

审稿时长

12-24 weeks

期刊介绍： International Journal of Wildland Fire publishes new and significant articles that advance basic and applied research concerning wildland fire. Published papers aim to assist in the understanding of the basic principles of fire as a process, its ecological impact at the stand level and the landscape level, modelling fire and its effects, as well as presenting information on how to effectively and efficiently manage fire. The journal has an international perspective, since wildland fire plays a major social, economic and ecological role around the globe. The International Journal of Wildland Fire is published on behalf of the International Association of Wildland Fire.