A143-0001
A case study of microphysics impacts on pyrocumulus development in fire simulations

Monday, 14 December 2020
Poster
Stephanie Redfern, University of Colorado at Boulder, Boulder, CO, United States and Julie K Lundquist, University of Colorado Boulder, Atmospheric and Oceanic Sciences, Boulder, CO, United States; National Renewable Energy Laboratory Golden, Golden, CO, United States
Abstract:
In 2014, a large wildfire was started by lightning in Northern California. The Bald Fire, as it was later named, grew over the next two days to consume over 14,000 hectares of land. During the afternoon of the second day of burning, a pyrocumulus cloud (pyroCu) developed, which later matured into a pyrocumulonimbus (pyroCb). This cloud growth corresponded with deep smoke lofting; the plume rose above 12 km at its peak. Observations of the fire and cloud formation were taken via lidar, radar, and radiosonde and published in a 2016 study (Lareau and Clements, 2016).

In this study, we simulate the Bald Fire using WRF-ARW Version 4.0.1 and WRF-Fire. The simulation employs 3 nested domains, with resolutions of 3km, 1km, and 100m. A fire is lit in the finest-resolution domain, and downscaling of 4:1 is applied to model the fire spread. Because smoke in WRF-Fire is, by default, considered a passive tracer, we compare the results from simulations with different microphysics schemes: Thompson (Thompson et al., 2008), Thompson with Water-Friendly Aerosols (Thompson and Eidhammer, 2014), and a modified Thompson with Water-Friendly Aerosols, in which an estimated number of smoke particles released from the fire are added to the number of environmental aerosols already present in the domain. The presentation will highlight the role of smoke particulate matter acting as cloud condensation nuclei (CCNs) in pyroCb formation.

References

Lareau, N. P., & Clements, C. B. (2016). Environmental controls on pyrocumulus and pyrocumulonimbus initiation and development. Atmospheric Chemistry and Physics, 16(6), 4005.

Thompson, G., Field, P. R., Rasmussen, R. M., & Hall, W. D. (2008). Explicit forecasts of winter precipitation using an improved bulk microphysics scheme. Part II: Implementation of a new snow parameterization. Monthly Weather Review, 136(12), 5095-5115.

Thompson, G., & Eidhammer, T. (2014). A study of aerosol impacts on clouds and precipitation development in a large winter cyclone. Journal of the atmospheric sciences, 71(10), 3636-3658.

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