Electrified fallout from a wildfire plume

TL;DR

This study investigates the electrification of wildfire plumes, revealing low charge densities on ash particles and suggesting additional mechanisms are needed for lightning formation at large distances from wildfires.

Contribution

It provides the first charge measurements of wildfire plumes at large distances, highlighting the role of ash particle charge and the need for other electrification processes.

Findings

Wildfire plumes remain mildly electrified up to 80 km from the fire.

Ash particles carry charge densities of 10^-8 to 10^-7 C/m^2.

Additional electrification mechanisms are likely necessary for pyrogenic lightning.

Abstract

Large wildfires are becoming more frequent at temperate latitudes. Often, fires generate massive convective columns that can carry solid particles (ash) into the stratosphere. Like their meteorological counterparts, pyrocumulonimbus (pyroCb) clouds can generate intense lightning storms. Recently, pyrogenic lightning has garnered renewed interest for its capacity to ignite new fires at large distances from the initial fire (in addition to representing a hazard in and of itself). Furthermore, and in analogy with volcanogenic lightning, pyrogenic lightning may offer novel opportunities to monitor and infer the internal dynamics of wildfires remotely. However, the electrification mechanisms underlying wildfire lightning require further clarification. Here, we report on charge measurements conducted during the 2022 Cedar Creek ``megafire.'' We find that a wildfire plume associated with various pyCb events remains mildly electrified at $\sim$80 km from the fire. Our measurements suggest that individual ash particles carry charge densities on the order of 10\textsuperscript{-8} - 10\textsuperscript{-7} C m\textsuperscript{-2}. Owing to this low level of charging, additional electrification mechanisms (perhaps, those associated with the nucleation of ice) appear to be necessary to produce pyrogenic lightning at large distances from the source.