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1. Quantifying long‐term seasonal and regional impacts of North American fire activity on continental boundary layer aerosols and cloud condensation nuclei

   https://doi.org/10.1029/2020EA001113  

   Logan, Timothy ; Dong, Xiquan ; Xi, Baike ; Zheng, Xiaojian ; Wang, Yuan ; Wu, Peng ; Marlow, Eleanor ; Maddux, James ( December 2020 , Earth and Space Science)

   An intimate knowledge of aerosol transport is essential in reducing the uncertainty of the impacts of aerosols on cloud development. Datasets from the U. S. Department of Energy (DOE) Atmospheric Radiation Measurement platform in the Southern Great Plains region (ARM-SGP) and the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) showed seasonal increases in aerosol loading and total carbon concentration during the spring and summer months (2008-2016) which was attributed to fire activity and smoke transport within North America. The monthly mean MERRA-2 surface carbonaceous aerosol mass concentration and ARM-SGP total carbon products were strongly correlated (R=0.82, p<0.01) along with a moderate correlation with the ARM-SGP cloud condensation nuclei (NCCN) product (0.5, p~0.1). The monthly mean ARM-SGP total carbon and NCCN products were strongly correlated (0.7, p~0.01). An additional product denoting fire number and coverage taken from the National Interagency Fire Center (NIFC) showed a moderate correlation with the MERRA-2 carbonaceous product (0.45, p<0.01) during the 1981-2016 warm season months (March-September). With respect to meteorological conditions, the correlation between the NIFC fire product and MERRA-2 850 hPa isobaric height anomalies was lower (0.26, p~0.13) due to the variability in the frequency, intensity, and number of fires inmore »North America. An observed increase in the isobaric height anomaly during the past decade may lead to frequent synoptic ridging and drier conditions with more fires, thereby potentially impacting cloud/precipitation processes and decreasing air quality.« less
2. The 2018 Camp Fire: Meteorological Analysis Using In Situ Observations and Numerical Simulations

   https://doi.org/10.3390/atmos11010047  

   Brewer, Matthew J. ; Clements, Craig B. ( January 2020 , Atmosphere)

   The November 2018 Camp Fire quickly became the deadliest and most destructive wildfire in California history. In this case study, we investigate the contribution of meteorological conditions and, in particular, a downslope windstorm that occurred during the 2018 Camp Fire. Dry seasonal conditions prior to ignition led to 100-h fuel moisture contents in the region to reach record low levels. Meteorological observations were primarily made from a number of remote automatic weather stations and a mobile scanning Doppler lidar deployed to the fire on 8 November 2018. Additionally, gridded operational forecast models and high-resolution meteorological simulations were synthesized in the analysis to provide context for the meteorological observations and structure of the downslope windstorm. Results show that this event was associated with mid-level anti-cyclonic Rossby wave breaking likely caused by cold air advection aloft. An inverted surface trough over central California created a pressure gradient which likely enhanced the downslope winds. Sustained surface winds between 3–6 m s−1 were observed with gusts of over 25 m s−1 while winds above the surface were associated with an intermittent low-level jet. The meteorological conditions of the event were well forecasted, and the severity of the fire was not surprising given the firemore »danger potential for that day. However, use of surface networks alone do not provide adequate observations for understanding downslope windstorm events and their impact on fire spread. Fire management operations may benefit from the use of operational wind profilers to better understand the evolution of downslope windstorms and other fire weather phenomena that are poorly understood and observed.« less
3. The December 2021 Marshall Fire: Predictability and Gust Forecasts from Operational Models

   https://doi.org/10.3390/atmos13050765  

   Fovell, Robert G. ; Brewer, Matthew J. ; Garmong, Richard J. ( May 2022 , Atmosphere)

   We analyzed meteorological conditions that occurred during the December 2021 Boulder, Colorado, downslope windstorm. This event is of particular interest due to the ignition and spread of the Marshall Fire, which quickly became the most destructive wildfire in Colorado history. Observations indicated a rapid onset of fast winds with gusts as high as 51 m/s that generally remained confined to the east-facing slopes and foothills of the Rockies, similar to previous Boulder windstorms. After about 12 h, the windstorm shifted into a second, less intense phase. Midtropospheric winds above northwestern Colorado weakened prior to the onset of strong surface winds and the event strength started waning as stronger winds moved back into the area. Forecasts from NOAA high-resolution operational models initialized more than a few hours prior to windstorm onset did not simulate the start time, development rate and/or maximum strength of the windstorm correctly, and day-ahead runs even failed to develop strong downslope windstorms at all. Idealized modeling confirmed that predictability was limited by errors on the synoptic scale affecting the midtropospheric wind conditions representing the Boulder windstorm’s inflow environment. Gust forecasts for this event were critically evaluated.
4. Climate Dynamics Preceding Summer Forest Fires in California and the Extreme Case of 2018

   https://doi.org/10.1175/JAMC-D-21-0198.1  

   Jacobson, Tess W. ; Seager, Richard ; Williams, A. Park ; Henderson, Naomi ( August 2022 , Journal of Applied Meteorology and Climatology)

   Abstract Recent record-breaking wildfire seasons in California prompt an investigation into the climate patterns that typically precede anomalous summer burned forest area. Using burned-area data from the U.S. Forest Service’s Monitoring Trends in Burn Severity (MTBS) product and climate data from the fifth major global reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ERA5) over 1984–2018, relationships between the interannual variability of antecedent climate anomalies and July California burned area are spatially and temporally characterized. Lag correlations show that antecedent high vapor pressure deficit (VPD), high temperatures, frequent extreme high temperature days, low precipitation, high subsidence, high geopotential height, low soil moisture, and low snowpack and snowmelt anomalies all correlate significantly with July California burned area as far back as the January before the fire season. Seasonal regression maps indicate that a global midlatitude atmospheric wave train in late winter is associated with anomalous July California burned area. July 2018, a year with especially high burned area, was to some extent consistent with the general patterns revealed by the regressions: low winter precipitation and high spring VPD preceded the extreme burned area. However, geopotential height anomaly patterns were distinct from those in the regressions. Extreme July heat likelymore »contributed to the extent of the fires ignited that month, even though extreme July temperatures do not historically significantly correlate with July burned area. While the 2018 antecedent climate conditions were typical of a high-burned-area year, they were not extreme, demonstrating the likely limits of statistical prediction of extreme fire seasons and the need for individual case studies of extreme years. Significance Statement The purpose of this study is to identify the local and global climate patterns in the preceding seasons that influence how the burned summer forest area in California varies year-to-year. We find that a dry atmosphere, high temperatures, dry soils, less snowpack, low precipitation, subsiding air, and high pressure centered west of California all correlate significantly with large summer burned area as far back as the preceding January. These climate anomalies occur as part of a hemispheric scale pattern with weak connections to the tropical Pacific Ocean. We also describe the climate anomalies preceding the extreme and record-breaking burned-area year of 2018, and how these compared with the more general patterns found. These results give important insight into how well and how early it might be possible to predict the severity of an upcoming summer wildfire season in California.« less
5. Simulating Potential Impacts of Fuel Treatments on Fire Behavior and Evacuation Time of the 2018 Camp Fire in Northern California

   https://doi.org/10.3390/fire5020037  

   Seto, Daisuke ; Jones, Charles ; Trugman, Anna T. ; Varga, Kevin ; Plantinga, Andrew J. ; Carvalho, Leila M. ; Thompson, Callum ; Gellman, Jacob ; Daum, Kristofer ( April 2022 , Fire)

   Fuel break effectiveness in wildland-urban interface (WUI) is not well understood during downslope wind-driven fires even though various fuel treatments are conducted across the western United States. The aim of this paper is to examine the efficacy of WUI fuel breaks under the influence of strong winds and dry fuels, using the 2018 Camp Fire as a case study. The operational fire growth model Prometheus was used to show: (1) downstream impacts of 200 m and 400 m wide WUI fuel breaks on fire behavior and evacuation time gain; (2) how the downstream fire behavior was affected by the width and fuel conditions of the WUI fuel breaks; and (3) the impacts of background wind speeds on the efficacy of WUI fuel breaks. Our results indicate that WUI fuel breaks may slow wildfire spread rates by dispersing the primary advancing fire front into multiple fronts of lower intensity on the downstream edge of the fuel break. However, fuel break width mattered. We found that the lateral fire spread and burned area were reduced downstream of the 400 m wide WUI fuel break more effectively than the 200 m fuel break. Further sensitivity tests showed that wind speed at the timemore »of ignition influenced fire behavior and efficacy of management interventions.« less