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

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.

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

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.

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

2020 ◽  
Vol 20 (1) ◽  
pp. 457-474 ◽  
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.

scholarly journals Monitoring Aerosol–Cloud Interactions at CESAR Observatory in the Netherlands

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.

scholarly journals Constraints on interactions between aerosols and clouds on a global scale from a combination of MODIS-CERES satellite data and climate simulations

2010 ◽  
Vol 10 (20) ◽  
pp. 9851-9861 ◽  
Author(s):  
X. Ma ◽  
K. von Salzen ◽  
J. Cole
Keyword(s):  
Liquid Water ◽  
Negative Relationship ◽  
Cloud Droplet ◽  
Global Scale ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Cloud Droplets ◽  
Cloud Liquid Water ◽  
Albedo Effect ◽  
Cloud Liquid Water Path

Abstract. Satellite-based cloud top effective radius retrieved by the CERES Science Team were combined with simulated aerosol concentrations from CCCma CanAM4 to examine relationships between aerosol and cloud that underlie the first aerosol indirect (cloud albedo) effect. Evidence of a strong negative relationship between sulphate, and organic aerosols, with cloud top effective radius was found for low clouds, indicating both aerosol types are contributing to the first indirect effect on a global scale. Furthermore, effects of aerosol on the cloud droplet effective radius are more pronounced for larger cloud liquid water paths. While CanAM4 broadly reproduces the observed relationship between sulphate aerosols and cloud droplets, it does not reproduce the dependency of cloud top droplet size on organic aerosol concentrations nor the dependency on cloud liquid water path. Simulations with a modified version of the model yield a more realistic dependency of cloud droplets on organic carbon. The robustness of the methods used in the study are investigated by repeating the analysis using aerosol simulated by the GOCART model and cloud top effective radii derived from the MODIS Science Team.

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

2020 ◽  
Author(s):  
Edward Gryspeerdt ◽  
Tom Goren ◽  
Tristan W. P. Smith
Keyword(s):  
Satellite Images ◽  
Strong Impact ◽  
Natural Experiments ◽  
Liquid Water Path ◽  
Clear Sky ◽  
Cloud Properties ◽  
Aerosol Cloud Interactions ◽  
Aerosol Source ◽  
Retrieval Bias ◽  
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 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.

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

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.

scholarly journals The scale problem in quantifying aerosol indirect effects

2011 ◽  
Vol 11 (9) ◽  
pp. 26741-26789 ◽  
Author(s):  
A. McComiskey ◽  
G. Feingold
Keyword(s):  
Indirect Effects ◽  
Radiative Forcing ◽  
Liquid Water Path ◽  
Aerosol Indirect Effects ◽  
Remote Sensors ◽  
Cloud Properties ◽  
Wide Range ◽  
Albedo Effect ◽  
Cloud Liquid Water Path ◽  
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 affects 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 has 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. Based on our understanding of these biases we propose a new approach for an observationally-based, robust method for estimating aerosol indirect effects that can be used for radiative forcing estimates as well as a better characterization of the uncertainties associated with those estimates.

scholarly journals The scale problem in quantifying aerosol indirect effects

2012 ◽  
Vol 12 (2) ◽  
pp. 1031-1049 ◽  
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.

scholarly journals Effects of absorbing aerosols in cloudy skies: a satellite study over the Atlantic Ocean

2011 ◽  
Vol 11 (4) ◽  
pp. 1393-1404 ◽  
Author(s):  
K. Peters ◽  
J. Quaas ◽  
N. Bellouin
Keyword(s):  
Atlantic Ocean ◽  
Radiative Forcing ◽  
Liquid Water Path ◽  
Aerosol Absorption ◽  
Aerosol Effect ◽  
Direct Scattering ◽  
Planetary Albedo ◽  
Cloud Liquid Water Path ◽  
Absorbing Aerosols ◽  
Aerosol Effects

Abstract. We present a method for deriving the radiative effects of absorbing aerosols in cloudy scenes from satellite retrievals only. We use data of 2005–2007 from various passive sensors aboard satellites of the "A-Train" constellation. The study area is restricted to the tropical- and subtropical Atlantic Ocean. To identify the dependence of the local planetary albedo in cloudy scenes on cloud liquid water path and aerosol optical depth (AOD), we perform a multiple linear regression. The OMI UV-Aerosolindex serves as an indicator for absorbing-aerosol presence. In our method, the aerosol influences the local planetary albedo through direct- (scattering and absorption) and indirect (Twomey) aerosol effects. We find an increase of the local planetary albedo (LPA) with increasing AOD of mostly scattering aerosol and a decrease of the LPA with increasing AOD of mostly absorbing aerosol. These results allow us to derive the direct aerosol effect of absorbing aerosols in cloudy scenes, with the effect of cloudy-scene aerosol absorption in the tropical- and subtropical Atlantic contributing (+21.2 ± 11.1)×10−3 Wm−2 to the global top of the atmosphere radiative forcing.

scholarly journals Satellite-based estimate of the variability of warm cloud properties associated with aerosol and meteorological conditions

2018 ◽  
Author(s):  
Yuqin Liu ◽  
Jiahua Zhang ◽  
Putian Zhou ◽  
Tao Lin ◽  
Juan Hong ◽  
...  
Keyword(s):  
Cloud Cover ◽  
Cloud Droplet ◽  
Cloud Fraction ◽  
Meteorological Conditions ◽  
Atmospheric Conditions ◽  
Liquid Water Path ◽  
Aerosol Cloud ◽  
Cloud Properties ◽  
Low Cloud ◽  
Cloud Liquid Water Path

Abstract. Aerosol-cloud interaction is examined using four years of data from the MODIS/Terra (morning orbit) and MODIS/Aqua (afternoon orbit) satellites. Aerosol optical depth (AOD) and cloud properties retrieved from both sensors are used to explore in a statistical sense the morning-to-afternoon variation of cloud properties in conditions with low and high AOD, over both land and ocean. The results show that the morning-to-afternoon variation of cloud properties during the 3 hours between the Terra and Aqua overpasses have similar patterns (increase or decrease) over land under both low and high AOD conditions. The variation in d(Cloud_X), defined as the mean change in cloud property Cloud_X between the morning and afternoon overpasses in high AOD conditions minus that in low AOD conditions, is different over land and ocean. This applies to cloud droplet effective radius (CDR), cloud fraction (CF) and cloud top pressure (CTP), but not to cloud optical thickness (COT) and cloud liquid water path (CWP). The effects of initial cloud fraction and meteorological conditions on the change in CF are also explored, showing that upward motion of air parcels can enhance the cloud cover much more when AOD is high than when it is low. In contrast, the increase of cloud cover with increasing relative humidity is much stronger in a relatively clean atmosphere with low AOD than in a more polluted atmosphere. Meanwhile, stable atmospheric conditions favour the development of a low cloud cover, especially when AOD is high. Overall, the analysis of the diurnal variation of cloud properties provides a better understanding of aerosol-cloud interaction over land and ocean.

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