Satellite retrieval of cloud condensation nuclei concentrations by using clouds as CCN chambers

Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (Wb). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and Wb of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by Wb and the satellite-retrieved cloud base drop concentrations (Ndb), which is the same as CCN(S). Validation against ground-based CCN instruments at Oklahoma, at Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25° restricts the satellite coverage to ∼25% of the world area in a single day.

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The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds

Atmospheric Measurement Techniques ◽

10.5194/amt-5-2039-2012 ◽

2012 ◽

Vol 5 (8) ◽

pp. 2039-2055 ◽

Cited By ~ 31

Author(s):

D. Rosenfeld ◽

E. Williams ◽

M. O. Andreae ◽

E. Freud ◽

U. Pöschl ◽

...

Keyword(s):

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Scientific Basis ◽

Cloud Base ◽

Satellite Measurements ◽

Satellite Mission ◽

Cloud Drop ◽

Aerosol Radiative Forcing ◽

Convective Clouds ◽

Synchronous Orbit

Abstract. The cloud-mediated aerosol radiative forcing is widely recognized as the main source of uncertainty in our knowledge of the anthropogenic forcing on climate. The current challenges for improving our understanding are (1) global measurements of cloud condensation nuclei (CCN) in the cloudy boundary layer from space, and (2) disentangling the effects of aerosols from the thermodynamic and meteorological effects on the clouds. Here, we present a new conceptual framework to help us overcome these two challenges, using relatively simple passive satellite measurements in the visible and infared (IR). The idea is to use the clouds themselves as natural CCN chambers by retrieving simultaneously the number of activated aerosols at cloud base, Na, and the cloud base updraft speed. The Na is obtained by analyzing the distribution of cloud drop effective radius in convective elements as a function of distance above cloud base. The cloud base updraft velocities are estimated by double stereoscopic viewing and tracking of the evolution of cloud surface features just above cloud base. In order to resolve the vertical dimension of the clouds, the field of view will be 100 m for the microphysical retrievals, and 50 m for the stereoscopic measurements. The viewing geometry will be eastward and 30 degrees off nadir, with the Sun in the back at 30 degrees off zenith westward, requiring a Sun-synchronous orbit at 14 LST. Measuring simultaneously the thermodynamic environment, the vertical motions of the clouds, their microstructure and the CCN concentration will allow separating the dynamics from the CCN effects. This concept is being applied in the proposed satellite mission named Clouds, Hazards and Aerosols Survey for Earth Researchers (CHASER).

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Incorporation of advanced aerosol activation treatments into CESM/CAM5: model evaluation and impacts on aerosol indirect effects

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-7485-2014 ◽

2014 ◽

Vol 14 (14) ◽

pp. 7485-7497 ◽

Cited By ~ 33

Author(s):

B. Gantt ◽

J. He ◽

X. Zhang ◽

Y. Zhang ◽

A. Nenes

Keyword(s):

Indirect Effects ◽

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Condensation Nuclei ◽

Activation Kinetics ◽

Aerosol Cloud ◽

Model Version ◽

Cloud Properties ◽

Aerosol Cloud Interactions ◽

Aerosol Activation

Abstract. One of the greatest sources of uncertainty in the science of anthropogenic climate change is from aerosol–cloud interactions. The activation of aerosols into cloud droplets is a direct microphysical linkage between aerosols and clouds; parameterizations of this process link aerosol with cloud condensation nuclei (CCN) and the resulting indirect effects. Small differences between parameterizations can have a large impact on the spatiotemporal distributions of activated aerosols and the resulting cloud properties. In this work, we incorporate a series of aerosol activation schemes into the Community Atmosphere Model version 5.1.1 within the Community Earth System Model version 1.0.5 (CESM/CAM5) which include factors such as insoluble aerosol adsorption and giant cloud condensation nuclei (CCN) activation kinetics to understand their individual impacts on global-scale cloud droplet number concentration (CDNC). Compared to the existing activation scheme in CESM/CAM5, this series of activation schemes increase the computation time by ~10% but leads to predicted CDNC in better agreement with satellite-derived/in situ values in many regions with high CDNC but in worse agreement for some regions with low CDNC. Large percentage changes in predicted CDNC occur over desert and oceanic regions, owing to the enhanced activation of dust from insoluble aerosol adsorption and reduced activation of sea spray aerosol after accounting for giant CCN activation kinetics. Comparison of CESM/CAM5 predictions against satellite-derived cloud optical thickness and liquid water path shows that the updated activation schemes generally improve the low biases. Globally, the incorporation of all updated schemes leads to an average increase in column CDNC of 150% and an increase (more negative) in shortwave cloud forcing of 12%. With the improvement of model-predicted CDNCs and better agreement with most satellite-derived cloud properties in many regions, the inclusion of these aerosol activation processes should result in better predictions of radiative forcing from aerosol–cloud interactions.

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The challenge of simulating the sensitivity of the Amazonian clouds microstructure to cloud condensation nuclei number concentrations

10.5194/acp-2019-474 ◽

2019 ◽

Author(s):

Pascal Polonik ◽

Christoph Knote ◽

Tobias Zinner ◽

Florian Ewald ◽

Tobias Kölling ◽

...

Keyword(s):

Cloud Condensation Nuclei ◽

Regional Scale ◽

Cloud Droplet ◽

Number Concentration ◽

Effective Radius ◽

Cloud Base ◽

Condensation Nuclei ◽

Aerosol Cloud ◽

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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Aircraft observations of aerosol, cloud, precipitation, and boundary layer properties in pockets of open cells over the southeast Pacific

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-8071-2014 ◽

2014 ◽

Vol 14 (15) ◽

pp. 8071-8088 ◽

Cited By ~ 23

Author(s):

C. R. Terai ◽

C. S. Bretherton ◽

R. Wood ◽

G. Painter

Keyword(s):

Boundary Layer ◽

Cloud Condensation Nuclei ◽

Surface Wind ◽

Cloud Droplet ◽

Cloud Base ◽

Cold Pool ◽

Accumulation Mode ◽

Aerosol Cloud ◽

Wide Range ◽

Southeast Pacific

Abstract. Five pockets of open cells (POCs) are studied using aircraft flights from the VOCALS Regional Experiment (VOCALS-REx), conducted in October and November 2008 over the southeast Pacific Ocean. Satellite imagery from the geostationary satellite GOES-10 is used to distinguish POC areas, and measurements from the aircraft flights are used to compare aerosol, cloud, precipitation, and boundary layer conditions inside and outside of POCs. Conditions observed across individual POC cases are also compared. POCs are observed in boundary layers with a wide range of inversion heights (1250 to 1600 m) and surface wind speeds (5 to 11 m s−1) and show no remarkable difference from the observed surface and free-tropospheric conditions during the two months of the field campaign. In all cases, compared to the surrounding overcast region the POC boundary layer is more decoupled, supporting both thin stratiform and deeper cumulus clouds. Although cloud-base precipitation rates are higher in the POC than the overcast region in each case, a threshold precipitation rate that differentiates POC precipitation from overcast precipitation does not exist. Mean cloud-base precipitation rates in POCs can range from 1.7 to 5.8 mm d−1 across different POC cases. The occurrence of heavy drizzle (> 0 dBZ) lower in the boundary layer better differentiates POC precipitation from overcast precipitation, likely leading to the more active cold pool formation in POCs. Cloud droplet number concentration is at least a factor of 8 smaller in the POC clouds, and the ratio of drizzle water to cloud water in POC clouds is over an order of magnitude larger than that in overcast clouds, indicating an enhancement of collision–coalescence processes in POC clouds. Despite large variations in the accumulation-mode aerosol concentrations observed in the surrounding overcast region (65 to 324 cm−3), the accumulation-mode aerosol concentrations observed in the subcloud layer of all five POCs exhibit a much narrower range (24 to 40 cm−3), and cloud droplet concentrations within the cumulus updrafts originating in this layer reflect this limited variability. Above the POC subcloud layer exists an ultraclean layer with accumulation-mode aerosol concentrations < 5 cm−3, demonstrating that in-cloud collision–coalescence processes efficiently remove aerosols. The existence of the ultraclean layer also suggests that the major source of accumulation-mode aerosols, and hence of cloud condensation nuclei in POCs, is the ocean surface, while entrainment of free-tropospheric aerosols is weak. The measurements also suggest that at approximately 30 cm−3 a balance of surface source and coalescence scavenging sinks of accumulation-mode aerosols maintain the narrow range of observed subcloud aerosol concentrations.

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The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-5-1317-2012 ◽

2012 ◽

Vol 5 (1) ◽

pp. 1317-1354 ◽

Cited By ~ 1

Author(s):

D. Rosenfeld ◽

E. Williams ◽

M. O. Andreae ◽

E. Freud ◽

U. Pöschl ◽

...

Keyword(s):

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Scientific Basis ◽

Climate Forcing ◽

Cloud Base ◽

Satellite Measurements ◽

Satellite Mission ◽

Cloud Drop ◽

Convective Clouds ◽

Synchronous Orbit

Abstract. The cloud -mediated radiative forcing is widely recognized as the main source of uncertainty in our knowledge of the anthropogenic climate forcing and in our understanding of climate sensitivity. Current outstanding challenges are (1) global measurements of cloud condensation nuclei (CCN) in the cloudy boundary layer from space, and, (2) disentangling the effects of aerosols from the thermodynamic and meteorological effects on the clouds. Here we present a new concept for a way to overcome these two challenges, using relatively simple passive satellite measurements in the visible and IR. The idea is to use the clouds themselves as natural CCN chambers by retrieving simultaneously the number of activated aerosols at cloud base, Na, and the cloud base updraft speed. The Na is obtained by analyzing the distribution of cloud drop effective radius in convective elements as a function distance above cloud base. The cloud base updraft velocities are estimated by double stereoscopic viewing and tracking of the evolution of cloud surface features just above cloud base. In order to resolve the vertical dimension of the clouds, the field of view will be 100 m for the microphysical retrievals, and 50 m for the stereoscopic measurements. The viewing geometry will be 30 degrees off nadir eastward, with the Sun in the back at 30 degrees off zenith westward, which requires a Sun synchronous orbit at 14:00 LST. Having measured simultaneously the thermodynamic environment, the vertical motions of the clouds, their microstructure and the CCN concentration will allow separating the dynamic from the CCN effects. This concept is being applied in the proposed satellite mission named Clouds, Hazards and Aerosols Survey for Earth Researchers (CHASER).

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The challenge of simulating the sensitivity of the Amazonian cloud microstructure to cloud condensation nuclei number concentrations

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-1591-2020 ◽

2020 ◽

Vol 20 (3) ◽

pp. 1591-1605 ◽

Cited By ~ 1

Author(s):

Pascal Polonik ◽

Christoph Knote ◽

Tobias Zinner ◽

Florian Ewald ◽

Tobias Kölling ◽

...

Keyword(s):

Amazon Basin ◽

Climate Model ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Number Concentration ◽

Effective Radius ◽

Cloud Base ◽

Atmospheric Conditions ◽

Condensation Nuclei ◽

Aerosol Cloud

Abstract. The realistic representation of aerosol–cloud 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 region has been one of the motivations for several field campaigns, 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 and optical properties (droplet number concentration and effective radius). We found agreement between the modeled and observed median cloud droplet number concentration (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 0.3 was found, which implies a systematic underestimation of modeled CDNC when compared to measurements. Variability in cloud condensation nuclei (CCN) number concentrations was also underestimated, and cloud droplet effective radii (reff) were overestimated by the model. Modeled effective radius profiles began to saturate around 500 CCN cm−3 at cloud base, indicating an upper limit for the model sensitivity well below CCN concentrations reached during the burning season in the Amazon Basin. Additional CCN emitted from local fires did not cause a notable change in modeled cloud droplet effective radii. Finally, we also evaluate a parameterization of CDNC at cloud base using more readily available cloud microphysical properties, showing that we are able to derive CDNC at cloud base from cloud-side remote-sensing observations.

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Method to retrieve cloud condensation nuclei number concentrations using lidar measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-12-3825-2019 ◽

2019 ◽

Vol 12 (7) ◽

pp. 3825-3839 ◽

Cited By ~ 3

Author(s):

Wangshu Tan ◽

Gang Zhao ◽

Yingli Yu ◽

Chengcai Li ◽

Jian Li ◽

...

Keyword(s):

Cloud Condensation Nuclei ◽

Number Concentration ◽

New Method ◽

Cloud Base ◽

Chemical Compositions ◽

Condensation Nuclei ◽

Aerosol Cloud ◽

Lidar Measurements ◽

Kohler Theory ◽

Aerosol Cloud Interactions

Abstract. Determination of cloud condensation nuclei (CCN) number concentrations at cloud base is important to constrain aerosol–cloud interactions. A new method to retrieve CCN number concentrations using backscatter and extinction profiles from multiwavelength Raman lidars is proposed. The method implements hygroscopic enhancements of backscatter and extinction with relative humidity to derive dry backscatter and extinction and humidogram parameters. Humidogram parameters, Ångström exponents, and lidar extinction-to-backscatter ratios are then linked to the ratio of CCN number concentration to dry backscatter and extinction coefficient (ARξ). This linkage is established based on the datasets simulated by Mie theory and κ-Köhler theory with in-situ-measured particle size distributions and chemical compositions. CCN number concentration can thus be calculated with ARξ and dry backscatter and extinction. An independent theoretical simulated dataset is used to validate this new method and results show that the retrieved CCN number concentrations at supersaturations of 0.07 %, 0.10 %, and 0.20 % are in good agreement with theoretical calculated values. Sensitivity tests indicate that retrieval error in CCN arises mostly from uncertainties in extinction coefficients and RH profiles. The proposed method improves CCN retrieval from lidar measurements and has great potential in deriving scarce long-term CCN data at cloud base, which benefits aerosol–cloud interaction studies.

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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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Analysis of polarimetric satellite measurements suggests stronger cooling due to aerosol-cloud interactions

Nature Communications ◽

10.1038/s41467-019-13372-2 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 9

Author(s):

Otto P. Hasekamp ◽

Edward Gryspeerdt ◽

Johannes Quaas

Keyword(s):

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Cloud Formation ◽

Anthropogenic Aerosol ◽

Intergovernmental Panel ◽

Aerosol Cloud ◽

Cloud Properties ◽

Aerosol Cloud Interactions ◽

Aerosol Emissions

AbstractAnthropogenic aerosol emissions lead to an increase in the amount of cloud condensation nuclei and consequently an increase in cloud droplet number concentration and cloud albedo. The corresponding negative radiative forcing due to aerosol cloud interactions (RF$${}_{{\rm{aci}}}$$aci) is one of the most uncertain radiative forcing terms as reported in the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Here we show that previous observation-based studies underestimate aerosol-cloud interactions because they used measurements of aerosol optical properties that are not directly related to cloud formation and are hampered by measurement uncertainties. We have overcome this problem by the use of new polarimetric satellite retrievals of the relevant aerosol properties (aerosol number, size, shape). The resulting estimate of RF$${}_{{\rm{aci}}}$$aci = −1.14 Wm$${}^{{\rm{-2}}}$$-2 (range between −0.84 and −1.72 Wm$${}^{{\rm{-2}}}$$-2) is more than a factor 2 stronger than the IPCC estimate that includes also other aerosol induced changes in cloud properties.

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Constraining the instantaneous aerosol influence on cloud albedo

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1617765114 ◽

2017 ◽

Vol 114 (19) ◽

pp. 4899-4904 ◽

Cited By ~ 37

Author(s):

Edward Gryspeerdt ◽

Johannes Quaas ◽

Sylvaine Ferrachat ◽

Andrew Gettelman ◽

Steven Ghan ◽

...

Keyword(s):

Radiative Forcing ◽

Climate Models ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Anthropogenic Aerosol ◽

Cloud Albedo ◽

Aerosol Cloud ◽

Cloud Properties ◽

Aerosol Cloud Interactions ◽

Aerosol Properties

Much of the uncertainty in estimates of the anthropogenic forcing of climate change comes from uncertainties in the instantaneous effect of aerosols on cloud albedo, known as the Twomey effect or the radiative forcing from aerosol–cloud interactions (RFaci), a component of the total or effective radiative forcing. Because aerosols serving as cloud condensation nuclei can have a strong influence on the cloud droplet number concentration (Nd), previous studies have used the sensitivity of theNdto aerosol properties as a constraint on the strength of the RFaci. However, recent studies have suggested that relationships between aerosol and cloud properties in the present-day climate may not be suitable for determining the sensitivity of theNdto anthropogenic aerosol perturbations. Using an ensemble of global aerosol–climate models, this study demonstrates how joint histograms betweenNdand aerosol properties can account for many of the issues raised by previous studies. It shows that if the anthropogenic contribution to the aerosol is known, the RFaci can be diagnosed to within 20% of its actual value. The accuracy of different aerosol proxies for diagnosing the RFaci is investigated, confirming that using the aerosol optical depth significantly underestimates the strength of the aerosol–cloud interactions in satellite data.

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