scholarly journals Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

2006 ◽  
Vol 6 (1) ◽  
pp. 519-548
Author(s):  
G. J. Roelofs ◽  
P. Stier ◽  
J. Feichter ◽  
E. Vignati ◽  
J. Wilson
Keyword(s):  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Base ◽  
Cloud Drop ◽  
Direct Role ◽  
Accumulation Mode ◽  
Cloud Processing ◽  
Sulfate Production ◽  
Particle Activation ◽  
Aerosol Activation

Abstract. A parameterization for cloud processing is presented that calculates activation of aerosol particles to cloud drops, cloud drop size, and pH-dependent aqueous phase sulfur chemistry. The parameterization is implemented in the global aerosol-climate model ECHAM5-HAM. The cloud processing parameterization uses updraft speed, temperature, and aerosol size and chemical parameters simulated by ECHAM5-HAM to estimate the maximum supersaturation at the cloud base, and subsequently the cloud drop number concentration (CDNC) due to activation. In-cloud sulfate production occurs through oxidation of dissolved SO2 by ozone and hydrogen peroxide. The model simulates realistic distributions for annually averaged CDNC although it is underestimated especially in remote marine regions. On average, CDNC is dominated by particles from the accumulation mode, with smaller contributions from the Aitken and coarse modes. The simulations indicate that in-cloud sulfate production is a potentially important source of accumulation mode sized cloud condensation nuclei, due to chemical growth of activated Aitken particles and to enhanced coalescence of processed particles. The strength of this source depends on the distribution of produced sulfate over the activated modes. This distribution is affected by uncertainties in many parameters that play a direct role in particle activation, such as the updraft velocity, the aerosol chemical composition and the organic solubility, and the simulated CDNC is found to be relatively sensitive to these uncertainties.

scholarly journals Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

2006 ◽  
Vol 6 (9) ◽  
pp. 2389-2399 ◽  
Author(s):  
G. J. Roelofs ◽  
P. Stier ◽  
J. Feichter ◽  
E. Vignati ◽  
J. Wilson
Keyword(s):  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Base ◽  
Cloud Drop ◽  
Cloud Droplets ◽  
Direct Role ◽  
Accumulation Mode ◽  
Cloud Processing ◽  
Sulfate Production ◽  
Particle Activation

Abstract. A parameterization for cloud processing is presented that calculates activation of aerosol particles to cloud drops, cloud drop size, and pH-dependent aqueous phase sulfur chemistry. The parameterization is implemented in the global aerosol-climate model ECHAM5-HAM. The cloud processing parameterization uses updraft speed, temperature, and aerosol size and chemical parameters simulated by ECHAM5-HAM to estimate the maximum supersaturation at the cloud base, and subsequently the cloud drop number concentration (CDNC) due to activation. In-cloud sulfate production occurs through oxidation of dissolved SO2 by ozone and hydrogen peroxide. The model simulates realistic distributions for annually averaged CDNC although it is underestimated especially in remote marine regions. On average, CDNC is dominated by cloud droplets growing on particles from the accumulation mode, with smaller contributions from the Aitken and coarse modes. The simulations indicate that in-cloud sulfate production is a potentially important source of accumulation mode sized cloud condensation nuclei, due to chemical growth of activated Aitken particles and to enhanced coalescence of processed particles. The strength of this source depends on the distribution of produced sulfate over the activated modes. This distribution is affected by uncertainties in many parameters that play a direct role in particle activation, such as the updraft velocity, the aerosol chemical composition and the organic solubility, and the simulated CDNC is found to be relatively sensitive to these uncertainties.

scholarly journals Automated Mapping of Convective Clouds (AMCC) Thermodynamical, Microphysical, and CCN Properties from SNPP/VIIRS Satellite Data

2019 ◽  
Vol 58 (4) ◽  
pp. 887-902 ◽  
Author(s):  
Zhiguo Yue ◽  
Daniel Rosenfeld ◽  
Guihua Liu ◽  
Jin Dai ◽  
Xing Yu ◽  
...  
Keyword(s):  
Climate Models ◽  
Weather Forecasting ◽  
Meteorological Data ◽  
Cloud Condensation Nuclei ◽  
Convective Cloud ◽  
Cloud Base ◽  
Base Temperature ◽  
Cloud Drop ◽  
Automated Mapping ◽  
Convective Clouds

AbstractThe advent of the Visible Infrared Imager Radiometer Suite (VIIRS) on board the Suomi NPP (SNPP) satellite made it possible to retrieve a new class of convective cloud properties and the aerosols that they ingest. An automated mapping system of retrieval of some properties of convective cloud fields over large areas at the scale of satellite coverage was developed and is presented here. The system is named Automated Mapping of Convective Clouds (AMCC). The input is level-1 VIIRS data and meteorological gridded data. AMCC identifies the cloudy pixels of convective elements; retrieves for each pixel its temperature T and cloud drop effective radius re; calculates cloud-base temperature Tb based on the warmest cloudy pixels; calculates cloud-base height Hb and pressure Pb based on Tb and meteorological data; calculates cloud-base updraft Wb based on Hb; calculates cloud-base adiabatic cloud drop concentrations Nd,a based on the T–re relationship, Tb, and Pb; calculates cloud-base maximum vapor supersaturation S based on Nd,a and Wb; and defines Nd,a/1.3 as the cloud condensation nuclei (CCN) concentration NCCN at that S. The results are gridded 36 km × 36 km data points at nadir, which are sufficiently large to capture the properties of a field of convective clouds and also sufficiently small to capture aerosol and dynamic perturbations at this scale, such as urban and land-use features. The results of AMCC are instrumental in observing spatial covariability in clouds and CCN properties and for obtaining insights from such observations for natural and man-made causes. AMCC-generated maps are also useful for applications from numerical weather forecasting to climate models.

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

2012 ◽  
Vol 5 (8) ◽  
pp. 2039-2055 ◽  
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).

scholarly journals Aerosol measurements during COPE: composition, size, and sources of CCN and INPs at the interface between marine and terrestrial influences

2016 ◽  
Vol 16 (18) ◽  
pp. 11687-11709 ◽  
Author(s):  
Jonathan W. Taylor ◽  
Thomas W. Choularton ◽  
Alan M. Blyth ◽  
Michael J. Flynn ◽  
Paul I. Williams ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Convective Cloud ◽  
Cloud Formation ◽  
Convective Precipitation ◽  
Cloud Base ◽  
Sea Spray ◽  
Cloud Drop ◽  
Aerosol Mass ◽  
Order Of Magnitude ◽  
The Uk

Abstract. Heavy rainfall from convective clouds can lead to devastating flash flooding, and observations of aerosols and clouds are required to improve cloud parameterisations used in precipitation forecasts. We present measurements of boundary layer aerosol concentration, size, and composition from a series of research flights performed over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) of summer 2013. We place emphasis on periods of southwesterly winds, which locally are most conducive to convective cloud formation, when marine air from the Atlantic reached the peninsula. Accumulation-mode aerosol mass loadings were typically 2–3 µg m−3 (corrected to standard cubic metres at 1013.25 hPa and 273.15 K), the majority of which was sulfuric acid over the sea, or ammonium sulfate inland, as terrestrial ammonia sources neutralised the aerosol. The cloud condensation nuclei (CCN) concentrations in these conditions were  ∼  150–280 cm−3 at 0.1 % and 400–500 cm−3 at 0.9 % supersaturation (SST), which are in good agreement with previous Atlantic measurements, and the cloud drop concentrations at cloud base ranged from 100 to 500 cm−3. The concentration of CCN at 0.1 % SST was well correlated with non-sea-salt sulfate, meaning marine sulfate formation was likely the main source of CCN. Marine organic aerosol (OA) had a similar mass spectrum to previous measurements of sea spray OA and was poorly correlated with CCN. In one case study that was significantly different to the rest, polluted anthropogenic emissions from the southern and central UK advected to the peninsula, with significant enhancements of OA, ammonium nitrate and sulfate, and black carbon. The CCN concentrations here were around 6 times higher than in the clean cases, and the cloud drop number concentrations were 3–4 times higher. Sources of ice-nucleating particles (INPs) were assessed by comparing different parameterisations used to predict INP concentrations, using measured aerosol concentrations as input. The parameterisations based on total aerosol produced INP concentrations that agreed within an order of magnitude with measured first ice concentrations at cloud temperatures as low as −12 °C. Composition-specific parameterisations for mineral dust, fluorescent particles, and sea spray OA were 3–4 orders of magnitude lower than the measured first ice concentrations, meaning a source of INPs was present that was not characterised by our measurements and/or one or more of the composition-specific parameterisations greatly underestimated INPs in this environment.

scholarly journals A simple relationship between cloud drop number concentration and precursor aerosol concentration for the regions of earth's large marine stratocumulus decks

2011 ◽  
Vol 11 (10) ◽  
pp. 28663-28687 ◽  
Author(s):  
D. A. Hegg ◽  
D. S. Covert ◽  
H. H. Jonsson ◽  
R. K. Woods
Keyword(s):  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
Mode Number ◽  
Simple Relationship ◽  
Cloud Drop ◽  
Marine Stratocumulus ◽  
Accumulation Mode ◽  
The Pacific ◽  
Drop Number ◽  
Climate Studies

Abstract. Aircraft-based measurements of cloud condensation nuclei (CCN), accumulation mode and Aitken mode number concentrations, cloud drop number concentration (CDNC), and selected ancillary measurements are presented for the three large, semi-permanent marine stratocumulus decks of the earth (in the Pacific offshore of California and Chile and in the Atlantic offshore of Namibia). Based on these data, a simple linear relationship between CDNC and the accumulation mode number concentration (AMNC) is derived via regression. The R2 value for this regression is 0.90, higher than those found for CDNC-CCN linear regressions. Explanations of the relatively favorable CDNC-AMNC relationship and its utility for climate studies are discussed.

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

2014 ◽  
Vol 14 (15) ◽  
pp. 8071-8088 ◽  
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.

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

2012 ◽  
Vol 5 (1) ◽  
pp. 1317-1354 ◽  
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).

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

2020 ◽  
Vol 20 (3) ◽  
pp. 1591-1605 ◽  
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.

scholarly journals Aerosol–Cloud Interactions in a Mesoscale Model. Part II: Sensitivity to Aqueous-Phase Chemistry

2008 ◽  
Vol 65 (2) ◽  
pp. 309-330 ◽  
Author(s):  
Irena T. Ivanova ◽  
Henry G. Leighton
Keyword(s):  
Aqueous Phase ◽  
Mesoscale Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Microphysics ◽  
Size Spectrum ◽  
Chemical Processing ◽  
Strong Constraint ◽  
Cloud Processing ◽  
Sulfate Production ◽  
The Impact

Abstract The feedbacks between aerosols, cloud microphysics, and cloud chemistry are investigated in a mesoscale model. A simple bulk aqueous-phase sulfur chemistry scheme was fully coupled to the existing aerosol and microphysics schemes. The representation of aerosol and microphysics follows the explicit bulk double-moment approach. A case of summertime stratocumulus cloud system is simulated at high resolution (3-km grid spacing), and the evolution of an observed continental aerosol spectrum that changes during the course of the simulation as a result of cloud processing is examined. The results demonstrate that the bulk approach to the aerosol and droplet spectra correctly represents the feedbacks in the coupled system. The simulations capture the characteristic bimodal aerosol size spectrum resulting from cloud processing, with the first mode consisting of particles that did not participate as cloud condensation nuclei and the second mode, in the region of 0.08–0.12-μm radii, comprising the particles that were affected by processing. New information is revealed about the impact of the two main processing pathways and about the spatial distribution of the processed aerosol. One cycle of physical processing produced a relatively modest impact of 3%–5% on the processed particle mean radius of the order that was comparable to the impact of chemical processing, while continuous physical recycling produced a much larger impact as high as 30%–50%. A strong constraint on the chemical processing was found to be the initial chemistry input and the assumption of bulk chemical composition. Simple tests with a more slowly depleting primary oxidant (H2O2) and including the droplet chemical heterogeneity effect favor stronger sulfate production, by, respectively, the H2O2 and O3 oxidation reaction, and both show a larger impact on the processed particle mean radius of similar magnitude, 10%–20%. Spatially, the impact of processing is found initially in the downdraft regions below cloud and at later times at substantial distances downwind. It is shown that cloud processing can either enhance or suppress the number of activated drops in subsequent cycles.

scholarly journals Comparing parameterized versus measured microphysical properties of tropical convective cloud bases during the ACRIDICON–CHUVA campaign

2017 ◽  
Vol 17 (12) ◽  
pp. 7365-7386 ◽  
Author(s):  
Ramon Campos Braga ◽  
Daniel Rosenfeld ◽  
Ralf Weigel ◽  
Tina Jurkat ◽  
Meinrat O. Andreae ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Convective Cloud ◽  
Cloud Base ◽  
Aircraft Measurements ◽  
Cloud Drop ◽  
Convective Clouds ◽  
Microphysical Properties ◽  
Cloud Water Content ◽  
Satellite Retrievals ◽  
Vertical Evolution

Abstract. The objective of this study is to validate parameterizations that were recently developed for satellite retrievals of cloud condensation nuclei supersaturation spectra, NCCN(S), at cloud base alongside more traditional parameterizations connecting NCCN(S) with cloud base updrafts and drop concentrations. This was based on the HALO aircraft measurements during the ACRIDICON–CHUVA campaign over the Amazon region, which took place 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 CCN counter onboard the HALO aircraft. An intercomparison of the cloud drop size distributions (DSDs) and the cloud water content (CWC) derived from the different instruments generally shows good agreement within the instrumental uncertainties. 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 NCCN(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 measurements of NCCN(S) and Wb reproduced the observed Nd within the measurements uncertainties when the old (1959) Twomey's parameterization was used. The agreement between the measured and calculated Nd was only within a factor of 2 with attempts to use cloud base S, as obtained from the measured Wb, Nd, and NCCN(S). This underscores the yet unresolved challenge of aircraft measurements of S in clouds. Importantly, the vertical evolution of re with height reproduced the observation-based nearly adiabatic cloud base drop concentrations, Na. The combination of these results provides aircraft observational support for the various components of the satellite-retrieved methodology that was recently developed to retrieve NCCN(S) under the base of convective clouds. This parameterization can now be applied with the proper qualifications to cloud simulations and satellite retrievals.

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