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Preprints
https://doi.org/10.5194/acp-2020-1089
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-1089
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  22 Oct 2020

22 Oct 2020

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This preprint is currently under review for the journal ACP.

Impact of absorbing and non-absorbing aerosols on radiation and low-level clouds over the Southeast Atlantic from co-located satellite observations

Alejandro Baró Pérez1,2, Abhay Devasthale3, Frida Bender1,2, and Annica M. L. Ekman1,2 Alejandro Baró Pérez et al.
  • 1Department of Meteorology, Stockholm University, Stockholm, Sweden
  • 2Bolin Centre for Climate Research, Stockholm, Sweden
  • 3Atmospheric Remote Sensing, Research and development, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

Abstract. We use data derived from instruments onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat satellites as well as meteorological parameters from reanalysis to explore situations when moist aerosol layers overlie stratocumulus clouds over the Southeast Atlantic during the biomass burning season (June to October). One main goal is to separate and quantify the impacts of aerosol loading, aerosol type, and humidity on the radiative fluxes, including cloud top cooling. To achieve our objectives we split the data into different levels of aerosol and moisture loadings. By using the aerosol classification available from the CALIPSO products, we also separate and compare situations with pristine air, with smoke, and with other (mixed) types of aerosols. We find a substantial number of cases with mixed aerosols above clouds that occur under similar meteorological conditions as the smoke cases. In contrast, the meteorology is substantially different for the pristine situations, making a direct comparison with the aerosol cases ambiguous. The moisture content is enhanced within the aerosol layers, but we do not find a monotonous increase of the relative humidity with increasing aerosol optical depth. Shortwave (SW) heating rates within the moist aerosol plumes increase with increasing aerosol loading and are higher in the smoke cases compared to the mixed cases. However, there is no clear correlation between moisture changes and SW absorption. Cloud top cooling rates tend to decrease with increasing moisture within the overlying aerosol layers, but the influence is relatively weak and confounded by the strong variability of the cooling rates caused by other meteorological factors (most notably cloud top temperature). No clear influence of aerosol type or loading on cloud top cooling rates is detected. We also do not find any correlation between aerosol loading and the thermodynamic structure of the atmosphere nor the cloud top height, i.e. no indication of a semi-direct aerosol effect. This result is consistent with previous studies that examined clearly separated aerosol and cloud layers (in our case at least 0.4 km).

Alejandro Baró Pérez et al.

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Alejandro Baró Pérez et al.

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Latest update: 24 Nov 2020
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Short summary
We study the impacts of biomass burning plumes on radiation and clouds over the Southeast Atlantic using data derived from satellite observations and data-constrained models simulations. A substantial fraction of the aerosols within the plumes is not classified as smoke by the satellite. The atmosphere warms more with increasing smoke aerosol loading, but we find no effect on the clouds. The cloud top radiative cooling decreases weakly with increasing moisture within the overlying aerosol layer.
We study the impacts of biomass burning plumes on radiation and clouds over the Southeast...
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