Investigation of short-term effective radiative forcing of fire aerosols over North America using nudged hindcast ensembles
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 th...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/31/2018/acp-18-31-2018.pdf |
| Summary: | 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 −3.0 W m<sup>−2</sup>. Over the central US, the SCRE
is positive in the north but negative in the south, and the regional mean SCRE
is small (−0.56 W m<sup>−2</sup>). 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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| ISSN: | 1680-7316 1680-7324 |