On the parameterization of activation spectra from cloud condensation nuclei microphysical properties

Abstract. The realistic representation of cloud-aerosol interactions is of primary importance for accurate climate model projections. The investigation of these interactions in strongly contrasting clean and polluted atmospheric conditions in the Amazon area has been one of the motivations for several field observations, including the airborne Aerosol, Cloud, Precipitation, and Radiation Interactions and DynamIcs of CONvective cloud systems – Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON-CHUVA) campaign based in Manaus, Brazil in September 2014. In this work we combine in situ and remotely sensed aerosol, cloud, and atmospheric radiation data collected during ACRIDICON-CHUVA with regional, online-coupled chemistry-transport simulations to evaluate the model’s ability to represent the indirect effects of biomass burning aerosol on cloud microphysical properties (droplet number concentration and effective radius). We found agreement between modeled and observed median cloud droplet number concentrations (CDNC) for low values of CDNC, i.e., low levels of pollution. In general, a linear relationship between modeled and observed CDNC with a slope of two was found, which means a systematic underestimation of modeled CDNC as compared to measurements. Variability in cloud condensation nuclei (CCN) number concentrations and cloud droplet effective radii (reff) was also underestimated by the model. Modeled effective radius profiles began to saturate around 500 CCN per cm3 at cloud base, indicating an upper limit for the model sensitivity well below CCN concentrations reached during the burning season in the Amazon Basin. Regional background aerosol concentrations were sufficiently high such that the additional CCN emitted from local fires did not cause a notable change in modelled cloud microphysical properties. In addition, we evaluate a parameterization of CDNC at cloud base using more readily available cloud microphysical properties, aimed at in situ observations and satellite retrievals. Our study casts doubt on the validity of regional scale modeling studies of the cloud albedo effect in convective situations for polluted situations where the number concentration of CCN is greater than 500 cm−3.

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Comparing calculated microphysical properties of tropical convective clouds at cloud base with measurements during the ACRIDICON-CHUVA campaign

10.5194/acp-2016-872 ◽

2016 ◽

Author(s):

Ramon Campos Braga ◽

Daniel Rosenfeld ◽

Ralf Weigel ◽

Tina Jurkat ◽

Meinrat O. Andreae ◽

...

Keyword(s):

Cloud Condensation Nuclei ◽

Convective Cloud ◽

Cloud Formation ◽

Cloud Base ◽

Condensation Nuclei ◽

Cloud Drop ◽

Convective Clouds ◽

Microphysical Properties ◽

Vertical Evolution ◽

Good Agreement

Abstract. Reliable aircraft measurements of cloud microphysical properties are essential for understanding liquid convective cloud formation. In September 2014, the properties of convective clouds were measured with a Cloud Combination Probe (CCP), a Cloud and Aerosol Spectrometer (CAS-DPOL), and a cloud condensation nuclei (CCN) counter on board the HALO (High Altitude and Long Range Research Aircraft) aircraft during the ACRIDICON-CHUVA campaign over the Amazon region. An intercomparison of the cloud drop size distributions (DSDs) and the cloud water content derived from the different instruments generally shows good agreement within the instrumental uncertainties. The objective of this study is to validate several parameterizations for liquid cloud formation in tropical convection. To this end the directly measured cloud drop concentrations (Nd) near cloud base were compared with inferred values based on the measured cloud base updraft velocity (Wb) and cloud condensation nuclei (CCN) vs. supersaturation (S) spectra. The measurements of Nd at cloud base were also compared with drop concentrations (Na) derived on the basis of an adiabatic assumption and obtained from the vertical evolution of cloud drop effective radius (re) above cloud base. The results demonstrate agreement of the measured and theoretically expected values of Nd based on CCN, S, Wb at cloud base, and the height profile of re. The measurements of NCCN(S) and Wb did reproduce the observed Nd. Furthermore, the vertical evolution of re with height reproduced the observation-based nearly adiabatic cloud base drop concentrations, Na. Achieving such good agreement is possible only with accurate measurements of DSDs. This agreement supports the validity of the applied parameterizations for continental convective cloud evolution, which now can be used more confidently in simulations and satellite retrievals.

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Cloud condensation nuclei as a modulator of ice processes in Arctic mixed-phase clouds

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-8003-2011 ◽

2011 ◽

Vol 11 (15) ◽

pp. 8003-8015 ◽

Cited By ~ 55

Author(s):

S. Lance ◽

M. D. Shupe ◽

G. Feingold ◽

C. A. Brock ◽

J. Cozic ◽

...

Keyword(s):

Droplet Size ◽

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Droplet Size Distribution ◽

Mixed Phase ◽

Condensation Nuclei ◽

Microphysical Properties ◽

Ice Particles ◽

Northern Alaska ◽

Mixed Phase Clouds

Abstract. We propose that cloud condensation nuclei (CCN) concentrations are important for modulating ice formation of Arctic mixed-phase clouds, through modification of the droplet size distribution. Aircraft observations from the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study in northern Alaska in April 2008 allow for identification and characterization of both aerosol and trace gas pollutants, which are then compared with cloud microphysical properties. Consistent with previous studies, we find that the concentration of precipitating ice particles (>400 μm) is correlated with the concentration of large droplets (>30 μm). We are further able to link the observed microphysical conditions to aerosol pollution, originating mainly from long range transport of biomass burning emissions. The case studies demonstrate that polluted mixed-phase clouds have narrower droplet size distributions and contain 1–2 orders of magnitude fewer precipitating ice particles than clean clouds at the same temperature. This suggests an aerosol indirect effect leading to greater cloud lifetime, greater cloud emissivity, and reduced precipitation. This result is opposite to the glaciation indirect effect, whereby polluted clouds are expected to precipitate more readily due to an increase in the concentration of particles acting as ice nuclei.

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Vertical distribution of cloud condensation nuclei concentrations and their effect on microphysical properties of clouds over the sea near the southwest islands of Japan

Journal of Geophysical Research Atmospheres ◽

10.1029/2004jd004758 ◽

2005 ◽

Vol 110 (D10) ◽

Cited By ~ 19

Author(s):

M. Adhikari

Keyword(s):

Vertical Distribution ◽

Cloud Condensation Nuclei ◽

Condensation Nuclei ◽

Microphysical Properties

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Cloud condensation nuclei as a modulator of ice processes in Arctic mixed-phase clouds

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-6737-2011 ◽

2011 ◽

Vol 11 (2) ◽

pp. 6737-6770 ◽

Cited By ~ 2

Author(s):

S. Lance ◽

M. D. Shupe ◽

G. Feingold ◽

C. A. Brock ◽

J. Cozic ◽

...

Keyword(s):

Droplet Size ◽

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Droplet Size Distribution ◽

Mixed Phase ◽

Condensation Nuclei ◽

Microphysical Properties ◽

Ice Particles ◽

Northern Alaska ◽

Mixed Phase Clouds

Abstract. We propose that cloud condensation nuclei (CCN) concentrations are important for modulating ice formation of Arctic mixed-phase clouds, through modification of the droplet size distribution. Aircraft observations from the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study in northern Alaska in April 2008 allow for identification and characterization of both aerosol and trace gas pollutants, which are then compared with cloud microphysical properties. Consistent with previous studies, we find that the concentration of precipitating ice particles (>400 μm) is correlated with the concentration of large droplets (>30 μm). We are further able to link the observed microphysical conditions to aerosol pollution, originating mainly from long range transport of biomass burning emissions. The case studies demonstrate that polluted mixed-phase clouds have narrower droplet size distributions and contain 1–2 orders of magnitude fewer precipitating ice particles than clean clouds at the same temperature. This suggests an aerosol indirect effect leading to greater cloud lifetime, greater cloud emissivity, and reduced precipitation. This result is opposite to the glaciation indirect effect, whereby polluted clouds are expected to precipitate more readily due to an increase in the concentration of particles acting as IN.

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