PNNL

The Science

Wildfires emit tremendous amounts of gases, aerosols, and sensible heat, which impact environmental temperature and severe convective storms. However, weather forecasting and climate models lack the capability to account for the impact of sensible heat on meteorology and associated severe storms. In addition, a quantitative understanding is needed for how the heat and aerosol effects of wildfires influence severe storm characteristics such as intensity, hail, and lightning. Researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory led a study to model heat’s impact and apply this to understand how wildfires contribute to storm severity. They found the heat released from fires plays a predominant role in triggering a strong storm, while aerosols also play a significant role in enhancing storm intensity, hail, and lightning after the storm is initiated.

The Impact

The model developed in this study enables scientists to study wildfire impacts on environmental thermodynamics and forecast pyrocumulonimbus storm severity. Quantifying the respective heat and contribution of aerosols from wildfires that invigorate pyro-convection and produce hail and lightning provides significant scientific guidance to identify hazardous weather threats and overall impact of wildfires on weather and climate.

Summary

In addition to forming atmospheric particles (aerosols) with global impact on clouds, precipitation, and radiation, wildfire activity can significantly influence environmental thermodynamics. Researchers developed a model that accounts for the impact of heat flux from wildfires and is computationally efficient. Using the new model to explore a pyrocumulonimbus event associated with the Texas Mallard Fire on May 11-12, 2018, researchers used comparisons and observations to investigate the effects of both heat flux and aerosol emissions from the wildfire and predict radar reflectivity, precipitation, hailstone size, and lightning. The analysis showed that heat flux and aerosol emissions from the wildfire increased low-level temperatures and mid-level thermal buoyancy significantly, causing stronger upward motion that lifted more supercooled water to higher levels. The increase in available supercooled water for hail growth and invigorated updrafts led to larger hail size and enhanced lightning. Overall, the effect of heat flux on storm intensity was more significant than that of aerosol emissions. However, after the storm was initiated, aerosols were shown to greatly enhance storm intensity and the production of hailstones and lightning.

PNNL Contact

Jiwen Fan, Pacific Northwest National Laboratory, jiwen.fan@pnnl.gov

Funding

This study is supported by the U.S. Department of Energy Office of Science Early Career Award Program. PNNL is operated for the U.S. Department of Energy (DOE) by Battelle Memorial Institute under contract DE‐AC05‐76RL01830. Zhanqing Li acknowledges the support of NASA grant (NNX16AN61G).