Observing the timescales of aerosol-cloud interactions in snapshot satellite images

Abstract. The response of cloud processes to an aerosol perturbation is one of the largest uncertainties in the anthropogenic forcing of the climate. It occurs at a variety of timescales, from the near-instantaneous Twomey effect, to the longer timescales required for cloud adjustments. Understanding the temporal evolution of cloud properties following an aerosol perturbation is necessary to interpret the results of so-called "natural experiments" from a known aerosol source, such as a ship or industrial site. This work uses reanalysis windfields and ship emission information matched to observations of shiptracks to measure the timescales of cloud responses to aerosol in instantaneous (or "snapshot") images taken by polar-orbiting satellites. As found in previous studies, the local meteorological environment is shown to have a strong impact on the occurrence and properties of shiptracks, but there is a strong time dependence in their properties. The largest droplet number concentration (Nd) responses are found within three hours of emission, while cloud adjustments continue to evolve over periods of ten hours or more. Cloud fraction is increased within the early life of shiptracks, with the formation of shiptracks in otherwise clear skies indicating that around 5–10 % of clear-sky cases in this region may be aerosol-limited. The liquid water path (LWP) enhancement and the Nd-LWP sensitivity are also time dependent and strong functions of the background cloud and meteorological state. The near-instant response of the LWP within shiptracks may be evidence of a retrieval bias in previous estimates of the LWP response to aerosol derived from natural experiments. These results highlight the importance of temporal development and the background cloud field for quantifying the aerosol impact on clouds, even in situations where the aerosol perturbation is clear.

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Observing the timescales of aerosol–cloud interactions in snapshot satellite images

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-6093-2021 ◽

2021 ◽

Vol 21 (8) ◽

pp. 6093-6109

Author(s):

Edward Gryspeerdt ◽

Tom Goren ◽

Tristan W. P. Smith

Keyword(s):

Strong Impact ◽

Natural Experiments ◽

Wind Fields ◽

Liquid Water Path ◽

Clear Sky ◽

Cloud Properties ◽

Ship Tracks ◽

Aerosol Cloud Interactions ◽

Aerosol Source ◽

Ship Emission

Abstract. The response of cloud processes to an aerosol perturbation is one of the largest uncertainties in the anthropogenic forcing of the climate. It occurs at a variety of timescales, from the near-instantaneous Twomey effect to the longer timescales required for cloud adjustments. Understanding the temporal evolution of cloud properties following an aerosol perturbation is necessary to interpret the results of so-called “natural experiments” from a known aerosol source such as a ship or industrial site. This work uses reanalysis wind fields and ship emission information matched to observations of ship tracks to measure the timescales of cloud responses to aerosol in instantaneous (or“snapshot”) images taken by polar-orbiting satellites. As in previous studies, the local meteorological environment is shown to have a strong impact on the occurrence and properties of ship tracks, but there is a strong time dependence in their properties. The largest droplet number concentration (Nd) responses are found within 3 h of emission, while cloud adjustments continue to evolve over periods of 10 h or more. Cloud fraction is increased within the early life of ship tracks, with the formation of ship tracks in otherwise clear skies indicating that around 5 %–10 % of clear-sky cases in this region may be aerosol-limited. The liquid water path (LWP) enhancement and the Nd–LWP sensitivity are also time dependent and strong functions of the background cloud and meteorological state. The near-instant response of the LWP within ship tracks may be evidence of a bias in estimates of the LWP response to aerosol derived from natural experiments. These results highlight the importance of temporal development and the background cloud field for quantifying the aerosol impact on clouds, even in situations where the aerosol perturbation is clear.

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Radiative Effect of Clouds at Ny-Ålesund, Svalbard, as Inferred from Ground-Based Remote Sensing Observations

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-19-0080.1 ◽

2020 ◽

Vol 59 (1) ◽

pp. 3-22 ◽

Cited By ~ 6

Author(s):

Kerstin Ebell ◽

Tatiana Nomokonova ◽

Marion Maturilli ◽

Christoph Ritter

Keyword(s):

Remote Sensing ◽

The Arctic ◽

Radiative Effect ◽

Liquid Water Path ◽

Ice Clouds ◽

Surface Warming ◽

Clear Sky ◽

Cloud Properties ◽

Cloud Radiative Effect ◽

The Difference

AbstractFor the first time, the cloud radiative effect (CRE) has been characterized for the Arctic site Ny-Ålesund, Svalbard, Norway, including more than 2 years of data (June 2016–September 2018). The cloud radiative effect, that is, the difference between the all-sky and equivalent clear-sky net radiative fluxes, has been derived based on a combination of ground-based remote sensing observations of cloud properties and the application of broadband radiative transfer simulations. The simulated fluxes have been evaluated in terms of a radiative closure study. Good agreement with observed surface net shortwave (SW) and longwave (LW) fluxes has been found, with small biases for clear-sky (SW: 3.8 W m−2; LW: −4.9 W m−2) and all-sky (SW: −5.4 W m−2; LW: −0.2 W m−2) situations. For monthly averages, uncertainties in the CRE are estimated to be small (~2 W m−2). At Ny-Ålesund, the monthly net surface CRE is positive from September to April/May and negative in summer. The annual surface warming effect by clouds is 11.1 W m−2. The longwave surface CRE of liquid-containing cloud is mainly driven by liquid water path (LWP) with an asymptote value of 75 W m−2 for large LWP values. The shortwave surface CRE can largely be explained by LWP, solar zenith angle, and surface albedo. Liquid-containing clouds (LWP > 5 g m−2) clearly contribute most to the shortwave surface CRE (70%–98%) and, from late spring to autumn, also to the longwave surface CRE (up to 95%). Only in winter are ice clouds (IWP > 0 g m−2; LWP < 5 g m−2) equally important or even dominating the signal in the longwave surface CRE.

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Satellite observations of aerosols and clouds over southern China from 2006 to 2015: analysis of changes and possible interaction mechanisms

10.5194/acp-2018-982 ◽

2018 ◽

Author(s):

Nikos Benas ◽

Jan Fokke Meirink ◽

Karl-Göran Karlsson ◽

Martin Stengel ◽

Piet Stammes

Keyword(s):

Southern China ◽

Liquid Water Path ◽

Cloud Droplets ◽

Emission Data ◽

Cloud Properties ◽

Main Driver ◽

Satellite Sensors ◽

Cloud Liquid Water Path ◽

Aerosol Cloud Interactions ◽

Absorbing Aerosols

Abstract. Aerosol and cloud properties over southern China during the 10-year period 2006–2015 are analysed based on observations from passive and active satellite sensors and emission data. The results show a decrease in aerosol optical depth over the study area by about 20 % on average, accompanied by an increase in liquid cloud cover and cloud liquid water path (LWP) by 5 % and 13 %, respectively. Analysis of aerosol types and emissions suggests that the main driver for their reduction is a decrease in biomass burning aerosols. These changes occurred mainly in late autumn and early winter months and coincided with changes in cloud properties. For the latter, possible explanatory mechanisms were examined, including changes in circulation patterns and aerosol-cloud interactions. Further analysis of changes in aerosol vertical profiles demonstrates a consistency of the observed aerosol and cloud changes with the aerosol semi-direct effect, which depends on their relative heights. Based on this mechanism, fewer absorbing aerosols in the cloud layer would lead to an overall decrease in evaporation of cloud droplets, thus increasing cloud LWP and cover.

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The scale problem in quantifying aerosol indirect effects

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-1031-2012 ◽

2012 ◽

Vol 12 (2) ◽

pp. 1031-1049 ◽

Cited By ~ 98

Author(s):

A. McComiskey ◽

G. Feingold

Keyword(s):

Radiative Forcing ◽

Process Model ◽

Full Range ◽

Liquid Water Path ◽

Aerosol Cloud ◽

Cloud Properties ◽

Wide Range ◽

Albedo Effect ◽

Aerosol Cloud Interactions ◽

The Impact

Abstract. A wide range of estimates exists for the radiative forcing of the aerosol effect on cloud albedo. We argue that a component of this uncertainty derives from the use of a wide range of observational scales and platforms. Aerosol influences cloud properties at the microphysical scale, or the "process scale", but observations are most often made of bulk properties over a wide range of resolutions, or "analysis scales". We show that differences between process and analysis scales incur biases in quantification of the albedo effect through the impact that data aggregation and computational approach have on statistical properties of the aerosol or cloud variable, and their covariance. Measures made within this range of scales are erroneously treated as equivalent, leading to a large uncertainty in associated radiative forcing estimates. Issues associated with the coarsening of observational resolution particular to quantifying the albedo effect are discussed. Specifically, the omission of the constraint on cloud liquid water path and the separation in space of cloud and aerosol properties from passive, space-based remote sensors dampen the measured strength of the albedo effect. We argue that, because of this lack of constraints, many of these values are in fact more representative of the full range of aerosol-cloud interactions and their associated feedbacks. Based on our understanding of these biases we propose a new observationally-based and process-model-constrained, method for estimating aerosol-cloud interactions that can be used for radiative forcing estimates as well as a better characterization of the uncertainties associated with those estimates.

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Satellite observations of aerosols and clouds over South China from 2006 to 2015: analysis of changes and possible interactions

10.5194/acp-2018-554 ◽

2018 ◽

Author(s):

Nikos Benas ◽

Jan Fokke Meirink ◽

Karl-Göran Karlsson ◽

Martin Stengel ◽

Piet Stammes

Keyword(s):

South China ◽

Liquid Water Path ◽

Cloud Droplets ◽

Emission Data ◽

Cloud Properties ◽

Main Driver ◽

Satellite Sensors ◽

Cloud Liquid Water Path ◽

Aerosol Cloud Interactions ◽

Absorbing Aerosols

Abstract. Aerosol and cloud properties over South China during the 10-year period 2006–2015 are analysed based on observations from passive and active satellite sensors and emission data. The results show a decrease in aerosol optical depth over the study area by about 20 % on average, accompanied by an increase in liquid cloud cover and cloud liquid water path (LWP) by 5 % and 13 %, respectively. Analysis of aerosol types and emissions suggests that the main driver for their reduction is a decrease in biomass burning aerosols. These changes occurred mainly in late autumn and early winter months and coincided with changes in cloud properties. For the latter, possible explanatory mechanisms were examined, including changes in circulation patterns and aerosol-cloud interactions. Further analysis of changes in aerosol vertical profiles demonstrates a consistency of the observed aerosol and cloud changes with the aerosol semi-direct effect, which depends on their relative heights. Based on this mechanism, less absorbing aerosols in the cloud layer would lead to an overall decrease in evaporation of cloud droplets, thus increasing cloud LWP and cover.

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Impact of ship emission controls recorded by cloud properties

10.5194/egusphere-egu2020-2324 ◽

2020 ◽

Author(s):

Edward Gryspeerdt ◽

Tristan Smith ◽

Eoin O'Keefe ◽

Matthew Christensen ◽

Fraser Goldsworth

Keyword(s):

Meteorological Factors ◽

Sulphate Aerosol ◽

Cloud Properties ◽

Emission Controls ◽

Meteorological Variation ◽

Aerosol Cloud Interactions ◽

The Impact ◽

Ship Emission ◽

The Ideal

<p>The impact of aerosols on cloud properties is one of the largest uncertainties in the anthropogenic forcing of the climate system. As large, isolated sources of aerosol, ships provide the ideal opportunity to investigate aerosol-cloud interactions. However, their use for quantifying the aerosol impact on clouds has been limited by a lack on information on the aerosol perturbation generated by the ship.</p><p>In this work, satellite cloud observations are combined with ship emissions estimated from transponder data. Using over 17,000 shiptracks during the implementation of emission controls, the central role of sulphate aerosol in controlling shiptrack properties is demonstrated. Meteorological factors are shown to have a significant impact on shiptrack formation, particularly cloud-top relative humidity. Accounting for this meteorological variation, this work also demonstrates the potential for satellite retrievals of ship sulphate emissions, providing a pathway to the use of cloud observations for monitoring air pollution.</p>

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Effect of volcanic emissions on clouds during the 2008 and 2018 Kilauea degassing events

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-7749-2021 ◽

2021 ◽

Vol 21 (10) ◽

pp. 7749-7771

Author(s):

Katherine H. Breen ◽

Donifan Barahona ◽

Tianle Yuan ◽

Huisheng Bian ◽

Scott C. James

Keyword(s):

Anthropogenic Activities ◽

Volcanic Eruptions ◽

Atmospheric Modeling ◽

Natural Experiments ◽

Volcanic Emissions ◽

Aerosol Cloud ◽

Aerosol Loading ◽

Cloud Properties ◽

Satellite Retrievals ◽

Aerosol Cloud Interactions

Abstract. Volcanic eruptions in otherwise clean environments are “natural experiments” wherein the effects of aerosol emissions on clouds and climate can be partitioned from meteorological variability and anthropogenic activities. In this work, we combined satellite retrievals, reanalysis products, and atmospheric modeling to analyze the mechanisms of aerosol–cloud interactions during two degassing events at the Kilauea volcano in 2008 and 2018. The eruptive nature of the 2008 and 2018 degassing events was distinct from long-term volcanic activity for Kilauea. Although previous studies assessed the modulation of cloud properties from the 2008 event, this is the first time such an analysis has been reported for the 2018 event and that multiple degassing events have been analyzed and compared at this location. Both events resulted in significant changes in cloud effective radius and cloud droplet number concentration that were decoupled from local meteorology and in line with an enhanced cloud albedo. However, it is likely that the effects of volcanic emissions on liquid water path and cloud fraction were largely offset by meteorological variability. Comparison of cloud anomalies between the two events suggested a threshold response of aerosol–cloud interactions to overcome meteorological effects, largely controlled by aerosol loading. In both events, the ingestion of aerosols within convective parcels enhanced the detrainment of condensate in the upper troposphere, resulting in deeper clouds than observed under pristine conditions. Accounting for ice nucleation on ash particles led to enhanced ice crystal concentrations at cirrus levels and a slight decrease in ice water content, improving the correlation of the model results with the satellite retrievals. Overall, aerosol loading, plume characteristics, and meteorology contributed to changes in cloud properties during the Kilauea degassing events.

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Satellite observations of aerosols and clouds over southern China from 2006 to 2015: analysis of changes and possible interaction mechanisms

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-457-2020 ◽

2020 ◽

Vol 20 (1) ◽

pp. 457-474 ◽

Cited By ~ 1

Author(s):

Nikos Benas ◽

Jan Fokke Meirink ◽

Karl-Göran Karlsson ◽

Martin Stengel ◽

Piet Stammes

Keyword(s):

Southern China ◽

Carbonaceous Aerosol ◽

Present Observation ◽

Liquid Water Path ◽

Cloud Droplets ◽

Emission Data ◽

Cloud Properties ◽

Cloud Liquid Water Path ◽

Aerosol Cloud Interactions ◽

Absorbing Aerosols

Abstract. Aerosol and cloud properties over southern China during the 10-year period 2006–2015 are analysed based on observations from passive and active satellite sensors and emission data. The results show a strong decrease in aerosol optical depth (AOD) over the study area, accompanied by an increase in liquid cloud cover and cloud liquid water path (LWP). The most significant changes occurred mainly in late autumn and early winter: AOD decreased by about 35 %, coinciding with an increase in liquid cloud fraction by 40 % and a near doubling of LWP in November and December. Analysis of emissions suggests that decreases in carbonaceous aerosol emissions from biomass burning activities were responsible for part of the AOD decrease, while inventories of other, anthropogenic emissions mainly showed increases. Analysis of precipitation changes suggests that an increase in precipitation also contributed to the overall aerosol reduction. Possible explanatory mechanisms for these changes were examined, including changes in circulation patterns and aerosol–cloud interactions (ACIs). Further analysis of changes in aerosol vertical profiles demonstrates a consistency of the observed aerosol and cloud changes with the aerosol semi-direct effect, which depends on relative heights of the aerosol and cloud layers: fewer absorbing aerosols in the cloud layer would lead to an overall decrease in the evaporation of cloud droplets, thus increasing cloud LWP and cover. While this mechanism cannot be proven based on the present observation-based analysis, these are indeed the signs of the reported changes.

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Aerosol midlatitude cyclone indirect effects in observations and high-resolution simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-5821-2018 ◽

2018 ◽

Vol 18 (8) ◽

pp. 5821-5846 ◽

Cited By ~ 10

Author(s):

Daniel T. McCoy ◽

Paul R. Field ◽

Anja Schmidt ◽

Daniel P. Grosvenor ◽

Frida A.-M. Bender ◽

...

Keyword(s):

High Resolution ◽

Rain Rate ◽

Cloud Droplet ◽

Moisture Flux ◽

Conveyor Belt ◽

Liquid Water Path ◽

Aerosol Cloud ◽

Cloud Properties ◽

The Difference ◽

Aerosol Cloud Interactions

Abstract. Aerosol–cloud interactions are a major source of uncertainty in inferring the climate sensitivity from the observational record of temperature. The adjustment of clouds to aerosol is a poorly constrained aspect of these aerosol–cloud interactions. Here, we examine the response of midlatitude cyclone cloud properties to a change in cloud droplet number concentration (CDNC). Idealized experiments in high-resolution, convection-permitting global aquaplanet simulations with constant CDNC are compared to 13 years of remote-sensing observations. Observations and idealized aquaplanet simulations agree that increased warm conveyor belt (WCB) moisture flux into cyclones is consistent with higher cyclone liquid water path (CLWP). When CDNC is increased a larger LWP is needed to give the same rain rate. The LWP adjusts to allow the rain rate to be equal to the moisture flux into the cyclone along the WCB. This results in an increased CLWP for higher CDNC at a fixed WCB moisture flux in both observations and simulations. If observed cyclones in the top and bottom tercile of CDNC are contrasted it is found that they have not only higher CLWP but also cloud cover and albedo. The difference in cyclone albedo between the cyclones in the top and bottom third of CDNC is observed by CERES to be between 0.018 and 0.032, which is consistent with a 4.6–8.3 Wm−2 in-cyclone enhancement in upwelling shortwave when scaled by annual-mean insolation. Based on a regression model to observed cyclone properties, roughly 60 % of the observed variability in CLWP can be explained by CDNC and WCB moisture flux.

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Monitoring Aerosol–Cloud Interactions at CESAR Observatory in the Netherlands

10.5194/amt-2016-262 ◽

2016 ◽

Author(s):

K. Sarna ◽

H. W. J. Russchenberg

Keyword(s):

Remote Sensing ◽

The Netherlands ◽

Climate Models ◽

Backscatter Coefficient ◽

Liquid Water Path ◽

Cloud Droplets ◽

Aerosol Cloud ◽

Cloud Properties ◽

Daily Data ◽

Aerosol Cloud Interactions

Abstract. The representation of aerosol–cloud interactions (ACI) processes in the climate models, although long studied, still remains the source of high uncertainty. Very often there is a mismatch between the scale of observations used for ACI quantification and the ACI process itself. This can be changed by using the observations from ground-based remote sensing instruments. In this paper we presented a direct application of the Aerosol–Cloud Interactions monitoring technique (ACI monitoring). ACI monitoring is based on the standardized Cloudnet data stream, which provides measurements from ground-based remote sensing instruments working in synergy. For the dataset collected at the CESAR Observatory in the Netherlands we calculate ACI metrics. We use specifically attenuated backscatter coefficient (ATB) for the characterisation of the aerosol properties and cloud droplets effective radius (re) and number concentration (Nd) for the characterisation of the cloud properties. We calculate two metrics: ACIr = ln(re)/ln(ATB) and ACIN = ln(Nd)/ln(ATB). The calculated values of ACIr were ranging from 0.016 to 0.17, which corresponds to the values reported in previous studies. We also evaluated impact of the updraft and liquid water path (LWP) on ACI metrics. The values of ACIr were highest for the LWP between 50 and 100 g/m2 . For the higher LWP other processes, such as collision and coalescence, seem to be dominant and obscure the ACI processes. We also saw that the values of ACIr are higher when only data points located in the updraft area are considered. The method presented in this study enables monitoring aerosol–cloud interactions daily and further aggregating daily data into bigger datasets.

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