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Impact of wildfires and new particle formation on the convective clouds over the Amazon rainforest

Presentation Date
Tuesday, December 13, 2022 at 11:50am - Tuesday, December 13, 2022 at 12:00pm
McCormick Place - E271ab



The Amazon rainforest is a unique natural laboratory to understand how wildfires perturb the convective clouds and precipitation by releasing abundant aerosol particles and producing ultrafine aerosol particles (UAP) through new particle formation (NPF). Using the Weather Research and Forecasting (WRF) model with the spectral-bin microphysics (SBM), we conducted model simulations for a locally occurring convective case over the Amazon occurring on 30 September 2014 under different wildfire aerosol scenarios to investigate how wildfire aerosols and NPF influence clouds and precipitation. We show that wildfire aerosols increase the intensity of surface rain and frequencies of moderate to large rain rates as well as delay the initialization of precipitation. Wildfire aerosols reduce warm and mixed-phase clouds but increase deep clouds. The enhancements in deep clouds and precipitation are mainly because of the invigoration effects of ultrafine aerosols from the NPF processes within the wildfire, whereas the delay of precipitation and the reduction of shallow clouds are mainly the effect of large aerosols that can be activated at cloud bases. Correspondingly, radiative cooling is seen during the warm and mixed-phase stages mainly due to the cloud albedo effects by large aerosol particles whereas radiative warming is shown at the deep cloud stage because of enhanced anvil cloud fraction by ultrafine aerosols. We also find that the new particle formation above the PBL does not affect cloud and precipitation much, since they are not activated to form cloud droplets because of their low hygroscopicity and very small size.

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