Impacts of Amazon Fire Aerosols on the Subseasonal Circulations of the Mid-High Latitudes

Abstract

The strong radiative effects of fire aerosols have been well accepted in the climate community. However, there have been few studies on the aerosol effects at a monthly to subseasonal range. We used the National Centers for Environmental Prediction (NCEP) reanalysis datasets and Community Atmosphere Model Version 5 (CAM5) to explore the impacts of Amazon fire aerosols on the subseasonal climate. With the reanalysis datasets, we found that most of the abnormal high emissions tended to happen more frequently/intensely under a dry and warm condition during the La Niña years. And the composite analysis of the abnormal high emissions showed that there is a La Niña-like pattern of sea surface temperature anomalies (SSTA), precipitation, and circulation anomalies. To isolate the aerosol impacts from the SSTA, we removed the linear regressions of the Nino3.4 SST index, and found that significant anomalies in the pressure field still persisted in the midlatitude. Five wavetrains can be found in the mid-high latitudes of both hemispheres induced by Amazon fire aerosols. Through prescribing climatological mean SST and La Niña-like SSTA in CAM5 simulations respectively, we found that only the latter could reproduce the aerosol impact on circulation in the mid-high latitudes, i.e., five-wave anomalies, although with biased locations. This indicates that the Amazon wildfire aerosol impacts are highly coupled with the La Niña-like SSTA. This study emphasizes that Amazon fire aerosols indeed result in significant circulation anomalies in the mid-high latitudes and including fire aerosols may improve model forecasting skills at the monthly to subseasonal timescale.