Wildfire and Weather Radar: A Review

Abstract

Research in the pursuit of better understanding of fire behavior and fire‐atmosphere interaction has frequently encountered a dearth of observational data, especially from events that cause most impact. Here we show that meteorological radar has been demonstrated as an effective tool for profiling the microphysics, thermodynamics, and fire behavior feedback of wildfire plumes, including for cases with deep and moist convection occurring in the fire plume. A synthesis of knowledge on the use of radar for the analysis of wildfire is presented, and the new term pyrometeor is introduced to describe the range of scatterers observed by radar, the reflectivity signature of which is determined by interacting processes of wildfire behavior and atmospheric convection. The reflectivity theories of pyrometeors are compared, and it is shown that there are gaps in knowledge on the size distributions of pyrometeors as well as the complex dielectrics. Observational case studies are compared across plume microphysics, plume thermodynamics and deep pyroconvection, and operational usage of radar to monitor wildfire. The dominant hypothesis of reflectivity is scattering from ash particles, though theories for scattering such as from larger debris exist, although evidence is limited for any hypothesis. Vortices have also been identified using Doppler velocity radar data, but there is limited understanding of their cause and influence on fire‐atmosphere interactions. Recommendations are provided for methods and data sets to advance the application of radar for observing and understanding wildfires, including for plume microphysics and atmosphere‐fire interactions.

Of Fire and Smoke Plumes, Polarimetric Radar Characteristics

“…Radar observations of pyroconvection combined with lightning mapping array indicates that lightning occurred whenever the smoke plume grew to 10 km [9] of mean sea level. These scientists capitalized on the polarimetric data (CSU CHILL, Colorado State University and Chicago Illinois radar) to identify the smoke part of plumes by noting low reflectivities (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25), increased Z DR (1-5 dB), and small correlation coefficient between returns at orthogonal polarizations, ρ hv of about 0.6.…”

“…A comprehensive review of wildfire observations with radars is in [12]. The authors introduce the term pyrometeor for the ash particles causing the returns and advocate "radar research to establish the cross section and dielectric factor K m for scatterers of pyrogenic origin".…”

Identifying Plume Mode via WSR-88D Observations of Wildland Fire Convective Plumes and Proposed Tactical Decision Support Applications

“…The intense convective plume mode is characterized Murdoch et al NWA Journal of Operational Meteorology 8 October 2019 by a buoyancy-driven and vertically oriented updraft associated with inflow and outflow winds that spread the fire erratically (Banta et al 1992). The basic premise behind a convective plume, as observed on the Weather Surveillance Radar-1988 Doppler (WSR-88D, Crum andAlberty, 1993) is that heat flux increases combustion, and as resultant buoyant forces accelerate upward, pyrometeors (McCarthy et al 2019) are lofted higher in the plume (Jones and Christopher 2010). This provides an indirect estimate of the general intensity of a fire by the magnitude of returned reflectivity.…”

“…This provides an indirect estimate of the general intensity of a fire by the magnitude of returned reflectivity. McCarthy (2019) emphasizes that to understand a radar's depiction of a plume it is important to know the properties and distribution of pyrogenic scatterers. The particle size distribution of the pyroconvective plumes has a wide spectrum ranging from ash (2 μm to 1 mm in diameter) to large vegetation (on the order of centimeters in diameter to even larger) (McCarthy et al 2019).…”

Evolution of an extreme Pyrocumulonimbus-driven wildfire event in Tasmania, Australia

“…The most significant events have produced plumes that have reached the upper troposphere/lower stratosphere (UTLS) region. Insights into pyroCb development have relied on weather radar (Melnikov et al, 2008;McCarthy et al, 2019;Peace et al, 2017;McRae, 2010;Johnson et al, 2014;Fromm et al, 2012) that provides high temporal resolution imagery of the pyroconvection, although importantly they do not accurately detect the exact extent of entrained gaseous and fine particulate emissions because they are 'tuned' to identify larger particles such as rain and ice crystals, and can therefore fortuitously detect ash and embers.…”