Aerosol–cloud interactions: the representation of heterogeneous ice activation in cloud models

Abstract. The homogeneous nucleation of ice in supercooled liquid-water clouds is characterized by time-dependent freezing rates. By contrast, water phase transitions induced heterogeneously by ice-nucleating particles (INPs) are described by time-independent ice-active fractions depending on ice supersaturation (s). Laboratory studies report ice-active particle number fractions (AFs) that are cumulative in s. Cloud models budget INP and ice crystal numbers to conserve total particle number during water phase transitions. Here, we show that ice formation from INPs with time-independent nucleation behavior is overpredicted when models budget particle numbers and at the same time derive ice crystal numbers from s-cumulative AFs. This causes a bias towards heterogeneous ice formation in situations where INPs compete with homogeneous droplet freezing during cloud formation. We resolve this issue by introducing differential AFs, thereby moving us one step closer to more robust simulations of aerosol–cloud interactions.

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Aerosol-cloud interactions: The representation of heterogeneous ice activation in cloud models

10.5194/acp-2021-511 ◽

2021 ◽

Author(s):

Bernd Kärcher ◽

Claudia Marcolli

Keyword(s):

Phase Transitions ◽

Particle Number ◽

Water Phase ◽

Cloud Formation ◽

Ice Formation ◽

Ice Crystal ◽

Nucleation Behavior ◽

Aerosol Cloud ◽

Cloud Models ◽

Aerosol Cloud Interactions

Abstract. The homogeneous nucleation of ice in supercooled liquid water clouds is characterized by time-dependent freezing rates. By contrast, water phase transitions induced heterogeneously by ice nucleating particles (INPs) are described by time-independent ice-active fractions depending on ice supersaturation (s). Laboratory studies report ice-active particle number fractions (AFs) that are cumulative in s. Cloud models budget INP and ice crystal numbers to conserve total particle number during water phase transitions. Here, we show that ice formation from INPs with time-independent nucleation behavior is overpredicted when models budget particle numbers and at the same time derive ice crystal numbers from s-cumulative AFs. This causes a bias towards heterogeneous ice formation in situations where INPs compete with homogeneous droplet freezing during cloud formation. We resolve this issue by introducing differential AFs, moving us one step closer to more robust simulations of aerosol-cloud interactions.

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Aerosol-cloud interactions from combined observations with geostationary and polar-orbiting sensors

10.5194/egusphere-egu2020-2598 ◽

2020 ◽

Author(s):

Matthias Tesche ◽

Torsten Seelig ◽

Fani Alexandri ◽

Peter Bräuer ◽

Goutam Choudhury ◽

...

Keyword(s):

Rain Rate ◽

Cloud Condensation Nuclei ◽

Cloud Formation ◽

Development Phase ◽

Time Resolved ◽

Aerosol Cloud ◽

Cloud Properties ◽

The Pacific ◽

Aerosol Cloud Interactions ◽

Ice Water

Atmospheric aerosol particles are of great importance for cloud formation in the atmosphere because they are needed to act as cloud condensation nuclei (CCN) in liquid-water clouds and as ice nucleating particles (INP) in ice-containing clouds. Changes in aerosol concentration affect the albedo, development, phase, lifetime and rain rate of clouds. These aerosol-cloud interactions (ACI) and the resulting climate effects still cause the largest uncertainty in assessing climate change as they are understood only with medium confidence.The PACIFIC project, which is embedded in the French-German Make Our Planet Great Again (MOPGA) initiative, aims to improve our understanding of ACI by enhancing the representation of those aerosols that are relevant for cloud processes and by quantifying temporal changes in cloud properties throughout the cloud life cycle. PACIFIC uses a three-fold approach for studying ACI based on spaceborne observations by (i) using spaceborne lidar data to obtain unprecedented insight in CCN and INP concentrations at cloud level opposed to using column-integrated parameters, (ii) characterizing the development of clouds by tracking them in time-resolved geostationary observations opposed to resorting to the snap-shot view of polar-orbiting sensors, and (iii) combining the detailed observations from polar-orbiting sensors with the time-resolved observations of geostationary sensors &#8211; for clouds observed by both &#8211; to study the effects of CCN and INP on the albedo, liquid and ice water content, droplet and crystal size, development, phase and rain rate of clouds within different regimes carefully accounting for the meteorological background.This contribution will present the scope of the MOPGA-GRI project PACIFIC and illustrate the first findings.

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Secondary Ice Formation in Idealised Deep Convection—Source of Primary Ice and Impact on Glaciation

Atmosphere ◽

10.3390/atmos11050542 ◽

2020 ◽

Vol 11 (5) ◽

pp. 542

Author(s):

Annette K. Miltenberger ◽

Tim Lüttmer ◽

Christoph Siewert

Keyword(s):

Deep Convection ◽

Three Dimensional ◽

Convective Cloud ◽

Cloud Formation ◽

Ice Formation ◽

Ice Crystal ◽

Lagrangian Analysis ◽

Vertical Coupling ◽

Convective Clouds ◽

Ice Production

Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations of high ice crystal numbers. We use idealised simulations of a deep convective cloud system to investigate the thermodynamic and cloud microphysical evolution of air parcels, in which the model predicts secondary ice formation. The Lagrangian analysis suggests that the “in-situ” formation of rimers either by growth of primary ice or rain freezing does not play a major role in triggering secondary ice formation. Instead, rimers are predominantly imported into air parcels through sedimentation form higher altitudes. While ice nucleating particles (INPs) initiating heterogeneous freezing of cloud droplets at temperatures warmer than −10 °C have no discernible impact of the occurrence of secondary ice formation, in a scenario with rain freezing secondary ice production is initiated slightly earlier in the cloud evolution and at slightly different places, although with no major impact on the abundance or spatial distribution of secondary ice in the cloud as a whole. These results suggest that for interpreting and analysing observational data and model experiments regarding cloud glaciation and ice formation it is vital to consider the complex vertical coupling of cloud microphysical processes in deep convective clouds via three-dimensional transport and sedimentation.

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Parameterizing the competition between homogeneous and heterogeneous freezing in cirrus cloud formation – monodisperse ice nuclei

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-15665-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 15665-15698 ◽

Cited By ~ 3

Author(s):

D. Barahona ◽

A. Nenes

Keyword(s):

Number Concentration ◽

Cloud Formation ◽

Ice Formation ◽

Average Error ◽

Cirrus Cloud ◽

Ice Crystal ◽

Ice Nuclei ◽

Wide Range ◽

Homogeneous Freezing ◽

Nuclei Number

Abstract. We present a parameterization of cirrus cloud formation that computes the ice crystal number and size distribution under the presence of homogeneous and heterogeneous freezing. The parameterization is very simple to apply and is derived from the analytical solution of the cloud parcel equations, assuming that the ice nuclei population is monodisperse and chemically homogeneous. In addition to the ice distribution, an analytical expression is provided for the limiting ice nuclei number concentration that suppresses ice formation from homogeneous freezing. The parameterization is evaluated against a detailed numerical parcel model, and reproduces numerical simulations over a wide range of conditions with an average error of 6±33%.

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Contact freezing: a review

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-7811-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 7811-7869 ◽

Cited By ~ 2

Author(s):

L. A. Ladino ◽

O. Stetzer ◽

U. Lohmann

Keyword(s):

Potential Role ◽

Experimental Information ◽

Cloud Formation ◽

Ice Formation ◽

Ice Crystal ◽

Ice Cloud ◽

Quantitative Calculation ◽

Ice Nuclei ◽

Immersion Freezing ◽

Reported Data

Abstract. This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing indicate that it can initiate ice formation at the highest temperatures. A difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study this heterogeneous freezing mode in the laboratory and in the field are needed. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.

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Understanding aerosol-cloud interactions in the development of orographic cumulus congestus during IPHEx

10.5194/acp-2017-396 ◽

2017 ◽

Cited By ~ 2

Author(s):

Yajuan Duan ◽

Markus D. Petters ◽

Ana P. Barros

Keyword(s):

Cloud Droplet ◽

Cloud Microphysics ◽

Cloud Formation ◽

Physical Parameters ◽

Aerosol Cloud ◽

Thermodynamic Conditions ◽

Cloud Droplet Number Concentration ◽

Microphysical Processes ◽

Aerosol Cloud Interactions ◽

Cumulus Congestus

Abstract. A new cloud parcel model (CPM) including activation, condensation, collision-coalescence, and lateral entrainment processes is presented here to investigate aerosol-cloud interactions (ACI) in cumulus development prior to rainfall onset. The CPM was employed along with ground based radar and surface aerosol measurements to predict the vertical structure of cloud formation at early stages and evaluated against airborne observations of cloud microphysics and thermodynamic conditions during the Integrated Precipitation and Hydrology Experiment (IPHEx) over the Southern Appalachian Mountains. Further, the CPM was applied to explore the space of ACI physical parameters controlling cumulus congestus growth not available from measurements, and to examine how variations in aerosol properties and microphysical processes influence the evolution and thermodynamic state of clouds over complex terrain via sensitivity analysis. Modelling results indicate that aerosol-cloud droplet number concentration (CDNC) closure is achieved optimally to ~ 1.3 % of the observations for condensation coefficient (ac) = 0.01 and within 5 % for 0.01

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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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Parameterizing the competition between homogeneous and heterogeneous freezing in cirrus cloud formation – monodisperse ice nuclei

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-369-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 369-381 ◽

Cited By ~ 54

Author(s):

D. Barahona ◽

A. Nenes

Keyword(s):

Number Concentration ◽

Cloud Formation ◽

Ice Formation ◽

Average Error ◽

Cirrus Cloud ◽

Ice Crystal ◽

Ice Nuclei ◽

Wide Range ◽

Homogeneous Freezing ◽

Nuclei Number

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Understanding aerosol–cloud interactions through modelling the development of orographic cumulus congestus during IPHEx

10.5194/acp-2018-419 ◽

2018 ◽

Author(s):

Yajuan Duan ◽

Markus D. Petters ◽

Ana P. Barros

Keyword(s):

Vertical Structure ◽

Cloud Droplet ◽

Convective Cloud ◽

Cloud Microphysics ◽

Turbulent Dispersion ◽

Cloud Formation ◽

Cloud Base ◽

Physical Parameters ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

Abstract. A new cloud parcel model (CPM) including activation, condensation, collision-coalescence, and lateral entrainment processes is presented here to investigate aerosol-cloud interactions (ACI) in cumulus development prior to rainfall onset. The CPM was applied with surface aerosol measurements to predict the vertical structure of cloud development at early stages, and the model results were compared with airborne observations of cloud microphysics and thermodynamic conditions collected during the Integrated Precipitation and Hydrology Experiment (IPHEx) in the inner region of the Southern Appalachian Mountains (SAM). Sensitivity analysis was conducted to examine the model response to variations in key ACI physical parameters. The condensation coefficient ac plays a governing role in determining the cloud droplet number concentration (CDNC), liquid water content (LWC), and droplet size distribution. Lower values of ac lead to higher cloud droplet number concentrations, broader droplet spectra, and higher maximum supersaturation near cloud base. The simulated vertical structure of CDNC exhibits strong nonlinear sensitivity to entrainment strength and condensation efficiency illustrative of competitive interference between turbulent dispersion and activation processes. Further, simulated CDNC exhibits high sensitivity to variations in initial aerosol concentration at cloud base, but weak sensitivity to aerosol hygroscopicity. These findings provide new insights into determinant factors of convective cloud formation leading to mid-day warm season rainfall in complex terrain.

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Observation of aerosol induced ‘lower tropospheric cooling’ over Indian core monsoon region

Environmental Research Letters ◽

10.1088/1748-9326/ac3b7a ◽

2021 ◽

Author(s):

Manish Jangid ◽

Amit Kumar Mishra ◽

Ilan Koren ◽

Chandan Sarangi ◽

Krishan Kumar ◽

...

Keyword(s):

Monsoon Season ◽

Regional Scale ◽

Lower Troposphere ◽

Radiation Budget ◽

Cloud Formation ◽

Tropospheric Temperature ◽

Monsoon Region ◽

Remote Sensors ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

Abstract Aerosols play a significant role in regional scale pollution that alters the cloud formation process, radiation budget, and climate. Here, using long-term (2003-2019) observations from multi-satellite and ground-based remote sensors, we show robust aerosol-induced instantaneous daytime lower tropospheric cooling during the pre-monsoon season over the Indian core monsoon region (ICMR). Quantitatively, an average cooling of -0.82±0.11 °C to -1.84±0.25 °C is observed in the lower troposphere. The observed cooling is associated with both aerosol-radiation and aerosol-cloud-radiation interactions processes. The elevated dust and polluted-dust layers cause extinction of the incoming solar radiation, thereby decreasing the lower tropospheric temperature. The aerosol-cloud interactions also contribute to enhancement of cloud fraction which further contributes to the lower tropospheric cooling. The observed cooling results in a stable lower tropospheric structure during polluted conditions, which can also feedback to cloud systems. Our findings suggest that aerosol induced lower tropospheric cooling can strongly affect the cloud distribution and circulation dynamics over the ICMR, a region of immense hydroclimatic importance.

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