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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 1 | Copyright
Atmos. Chem. Phys., 18, 31-47, 2018
https://doi.org/10.5194/acp-18-31-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Jan 2018

Research article | 03 Jan 2018

Investigation of short-term effective radiative forcing of fire aerosols over North America using nudged hindcast ensembles

Yawen Liu1,2, Kai Zhang2, Yun Qian2, Yuhang Wang3, Yufei Zou3, Yongjia Song3, Hui Wan2, Xiaohong Liu4, and Xiu-Qun Yang1 Yawen Liu et al.
  • 1School of Atmospheric Sciences, Nanjing University, Nanjing, China
  • 2Pacific Northwest National Laboratory, Richland, Washington, USA
  • 3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 4Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming, USA

Abstract. Aerosols from fire emissions can potentially have large impact on clouds and radiation. However, fire aerosol sources are often intermittent, and their effect on weather and climate is difficult to quantify. Here we investigated the short-term effective radiative forcing of fire aerosols using the global aerosol–climate model Community Atmosphere Model version 5 (CAM5). Different from previous studies, we used nudged hindcast ensembles to quantify the forcing uncertainty due to the chaotic response to small perturbations in the atmosphere state. Daily mean emissions from three fire inventories were used to consider the uncertainty in emission strength and injection heights. The simulated aerosol optical depth (AOD) and mass concentrations were evaluated against in situ measurements and reanalysis data. Overall, the results show the model has reasonably good predicting skills. Short (10-day) nudged ensemble simulations were then performed with and without fire emissions to estimate the effective radiative forcing. Results show fire aerosols have large effects on both liquid and ice clouds over the two selected regions in April 2009. Ensemble mean results show strong negative shortwave cloud radiative effect (SCRE) over almost the entirety of southern Mexico, with a 10-day regional mean value of −3.0Wm−2. Over the central US, the SCRE is positive in the north but negative in the south, and the regional mean SCRE is small (−0.56Wm−2). For the 10-day average, we found a large ensemble spread of regional mean shortwave cloud radiative effect over southern Mexico (15.6% of the corresponding ensemble mean) and the central US (64.3%), despite the regional mean AOD time series being almost indistinguishable during the 10-day period. Moreover, the ensemble spread is much larger when using daily averages instead of 10-day averages. This demonstrates the importance of using a large ensemble of simulations to estimate the short-term aerosol effective radiative forcing.

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Fire aerosols have large impact on weather and climate through their effect on clouds and radiation, but it is difficult to quantify. Here we investigated the short-term effective radiative forcing of fire aerosols using the nudged hindcast ensemble simulations from global aerosol-climate model. Results show large effects of fire aerosols on both liquid and ice cloud and large ensemble spread of regional mean shortwave cloud radiative forcing over southern Mexico and the central US.
Fire aerosols have large impact on weather and climate through their effect on clouds and...
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