scholarly journals A Satellite-Based Parameter to Monitor the Aerosol Impact on Convective Clouds

2007 ◽  
Vol 46 (5) ◽  
pp. 660-666 ◽  
Author(s):  
Itamar M. Lensky ◽  
Ron Drori
Keyword(s):  
Forest Fires ◽  
Land Surface ◽  
Cloud Condensation Nuclei ◽  
Urban Air Pollution ◽  
Sensible Heat Flux ◽  
Urban Pollution ◽  
Convective Cloud ◽  
Cloud Base ◽  
Suppression Effect ◽  
Convective Clouds

Abstract A method to monitor the aerosol impact on convective clouds using satellite data is presented. The impacts of forest fires and highly polluting megacities on cloud precipitation formation processes are quantified by the vertical extent above cloud base to which convective cloud tops have to develop for onset of precipitation in terms of temperature difference D15. Large D15 is a manifestation of the precipitation suppression effect of small cloud condensation nuclei aerosols that elevate the altitude where effective precipitation processes are initiated. A warmer land surface with a greater sensible heat flux that increases the updraft velocity at cloud base may also contribute to the same effect. Therefore, D15 is greater for clouds that develop over more polluted and/or warmer surfaces that result from smoke and urban pollution and/or urban heat island, respectively. The precipitation suppression effects of both smoke from forest fires and urban effects can be vividly seen in a case study over Southeast Asia. Typical values of D15 are 1°–6°C for tropical maritime clouds, 8°–15°C for tropical clouds over land, 16°–26°C for urban air pollution, and 18°–39°C for clouds ingesting smoke from forest fires.

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 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.

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

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.

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 Strong sensitivity of aerosol concentrations to convective wet scavenging parameterizations in a global model

2012 ◽  
Vol 12 (1) ◽  
pp. 1687-1732 ◽  
Author(s):  
B. Croft ◽  
J. R. Pierce ◽  
R. V. Martin ◽  
C. Hoose ◽  
U. Lohmann
Keyword(s):  
Cloud Droplet ◽  
Convective Cloud ◽  
Cloud Base ◽  
Ice Crystal ◽  
Cloud Droplets ◽  
Convective Clouds ◽  
The Standard Model ◽  
Wet Scavenging ◽  
Limiting Case ◽  
Precipitation Formation

Abstract. This study examines the influences of assumptions in convective wet scavenging parameterizations on global climate model simulations of aerosol concentrations and wet deposition. To facilitate this study, an explicit representation of the uptake of aerosol mass and number into convective cloud droplets and ice crystals by the processes of activation, collisions, freezing and evaporation is introduced into the ECHAM5-HAM model. This development replaces the prescribed aerosol cloud-droplet-borne/ice-crystal-borne fractions of the standard model. Relative to the standard model, the more consistent treatment between convective aerosol-cloud microphysical processes yields a reduction of aerosol wet removal in mixed liquid and ice phase convective clouds by at least a factor of two, and the global, annual mean aerosol burdens are increased by at least 20%. Two limiting cases regarding the wet scavenging of entrained aerosols are considered. In the first case, aerosols entering convective clouds at their bases are the only aerosols that are scavenged into cloud droplets, and are susceptible to removal by convective precipitation formation. In the second case, aerosols that are entrained into the cloud above the cloud base layer can activate, can collide with existing cloud droplets and ice crystals, and can subsequently be removed by precipitation formation. The limiting case that allows aerosols entrained above cloud base to become cloud-droplet-borne and ice-crystal-borne reduces the annual and global mean aerosol burdens by 30% relative to the other limiting case, and yields the closest agreement with global aerosol optical depth retrievals, and black carbon vertical profiles from aircraft campaigns (changes of about one order of magntiude in the upper troposphere). Predicted convective cloud droplet number concentrations are doubled in the tropical middle troposphere when aerosols entrained above cloud base are allowed to activate. These results show that aerosol concentrations and wet deposition predicted in a global model are strongly sensitive to the assumptions made regarding the wet scavenging of aerosols in convective clouds.

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

2016 ◽  
Vol 113 (21) ◽  
pp. 5828-5834 ◽  
Author(s):  
Daniel Rosenfeld ◽  
Youtong Zheng ◽  
Eyal Hashimshoni ◽  
Mira L. Pöhlker ◽  
Anne Jefferson ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Cloud Condensation Nuclei ◽  
Global Scale ◽  
Cloud Base ◽  
Condensation Nuclei ◽  
Anthropogenic Aerosol ◽  
Convective Clouds ◽  
Aerosol Cloud ◽  
High Uncertainty

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.

scholarly journals 3-D model simulations of dynamical and microphysical interactions in pyro-convective clouds under idealized conditions

2013 ◽  
Vol 13 (7) ◽  
pp. 19527-19557 ◽  
Author(s):  
P. Reutter ◽  
J. Trentmann ◽  
A. Seifert ◽  
P. Neis ◽  
H. Su ◽  
...  
Keyword(s):  
Forest Fires ◽  
Aerosol Particles ◽  
Three Dimensional ◽  
Convective Cloud ◽  
Atmospheric Model ◽  
Cloud Microphysics ◽  
Aerosol Concentration ◽  
Activation Process ◽  
Cloud Droplets ◽  
Convective Clouds

Abstract. Pyro-convective clouds, i.e. convective clouds forming over wildland fires due to high sensible heat, play an important role for the transport of aerosol particles and trace gases into the upper troposphere and lower stratosphere. Additionally, due to the emission of a large number of aerosol particles from forest fires, the microphysical structure of a pyro-convective cloud is clearly different from that of ordinary convective clouds. A crucial step in the microphysical evolution of a (pyro-) convective cloud is the activation of aerosol particles to form cloud droplets. The activation process affects the initial number and size of cloud droplets and can thus influence the evolution of the convective cloud and the formation of precipitation. Building upon a realistic parameterization of CCN activation, the model ATHAM is used to investigate the dynamical and microphysical processes of idealized three-dimensional pyro-convective clouds in mid-latitudes. A state-of-the-art two-moment microphysical scheme has been implemented in order to study the influence of the aerosol concentration on the cloud development. The results show that the aerosol concentration influences the formation of precipitation. For low aerosol concentrations (NCN=1000 cm−3), rain droplets are rapidly formed by autoconversion of cloud droplets. This also triggers the formation of large graupel and hail particles resulting in an early and strong onset of precipitation. With increasing aerosol concentration (NCN=20 000 cm−3 and NCN=60 000 cm−3) the formation of rain droplets is delayed due to more but smaller cloud droplets. Therefore, the formation of ice crystals and snowflakes becomes more important for the eventual formation of graupel and hail. However, this causes a delay of the onset of precipitation and its intensity for increasing aerosol concentration. This work shows the first detailed investigation of the interaction between cloud microphysics and dynamics of a pyro-convective cloud using the combination of a high resolution atmospheric model and a detailed microphysical scheme.

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

2016 ◽  
Author(s):  
J. W. Taylor ◽  
T. W. Choularton ◽  
A. M. Blyth ◽  
M. J. Flynn ◽  
P. I. Williams ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Convective Cloud ◽  
Cloud Formation ◽  
Convective Precipitation ◽  
Cloud Base ◽  
Sea Spray ◽  
Cloud Drop ◽  
Order Of Magnitude ◽  
The Uk ◽  
Marine Air

Abstract. 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 mass loadings were typically 2–3 μg m−3, the majority of which was sulphuric acid over the sea, or ammonium sulphate 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 100–500 cm−3. The concentration of CCN at 0.1 % SST was well correlated with non-sea-salt sulphate, meaning marine sulphate formation was likely the main source of CCN. Marine organic aerosol (OA) had a similar mass spectrum to sea spray, 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 sulphate, and black carbon. The CCN concentrations here were around six times higher than in the clean cases, and the cloud drop number concentrations were 3–4 times higher. Sources of ice nuclei (IN) were assessed by comparing different parameterisations of the nucleation of ice, using measured aerosol concentrations as input. The parameterisations based on total aerosol produced IN 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, meaning either a source of IN was present that was not characterised by our measurements, and/or one or more of the compositionspecific parameterisations greatly underestimated IN in this environment.

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