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Article Dans Une Revue Atmospheric Chemistry and Physics Année : 2021

Cloud droplet formation at the base of tropical convective clouds: closure between modeling and measurement results of ACRIDICON–CHUVA

Ramon Campos Braga
  • Fonction : Auteur
Barbara Ervens
Daniel Rosenfeld
  • Fonction : Auteur
Meinrat Andreae
Jan-David Förster
Daniel Fütterer
  • Fonction : Auteur
Lianet Hernández Pardo
  • Fonction : Auteur
Bruna Holanda
  • Fonction : Auteur
Tina Jurkat-Witschas
  • Fonction : Auteur
Ovid Krüger
  • Fonction : Auteur
Oliver Lauer
  • Fonction : Auteur
Luiz Machado
Christopher Pöhlker
Daniel Sauer
Christiane Voigt
Adrian Walser
Manfred Wendisch
Ulrich Pöschl
Mira Pöhlker
  • Fonction : Auteur

Résumé

Abstract. Aerosol–cloud interactions contribute to the large uncertainties in current estimates of climate forcing. We investigated the effect of aerosol particles on cloud droplet formation by model calculations and aircraft measurements over the Amazon and over the western tropical Atlantic during the ACRIDICON–CHUVA campaign in September 2014. On the HALO (High Altitude Long Range Research) research aircraft, cloud droplet number concentrations (Nd) were measured near the base of clean and polluted growing convective cumuli using a cloud combination probe (CCP) and a cloud and aerosol spectrometer (CAS-DPOL). An adiabatic parcel model was used to perform cloud droplet number closure studies for flights in differently polluted air masses. Model input parameters included aerosol size distributions measured with an ultra-high sensitive aerosol spectrometer (UHSAS), in combination with a condensation particle counter (CPC). Updraft velocities (w) were measured with a boom-mounted Rosemount probe. Over the continent, the aerosol size distributions were dominated by accumulation mode particles, and good agreement between measured and modeled Nd values was obtained (deviations ≲ 10 %) assuming an average hygroscopicity of κ∼0.1, which is consistent with Amazonian biomass burning and secondary organic aerosol. Above the ocean, fair agreement was obtained assuming an average hygroscopicity of κ∼0.2 (deviations ≲ 16 %) and further improvement was achieved assuming different hygroscopicities for Aitken and accumulation mode particles (κAit=0.8, κacc=0.2; deviations ≲ 10 %), which may reflect secondary marine sulfate particles. Our results indicate that Aitken mode particles and their hygroscopicity can be important for droplet formation at low pollution levels and high updraft velocities in tropical convective clouds.

Domaines

Chimie

Dates et versions

hal-03483611 , version 1 (16-12-2021)

Identifiants

Citer

Ramon Campos Braga, Barbara Ervens, Daniel Rosenfeld, Meinrat Andreae, Jan-David Förster, et al.. Cloud droplet formation at the base of tropical convective clouds: closure between modeling and measurement results of ACRIDICON–CHUVA. Atmospheric Chemistry and Physics, 2021, 21 (23), pp.17513-17528. ⟨10.5194/acp-21-17513-2021⟩. ⟨hal-03483611⟩
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