A long-term study of aerosol–cloud interactions and their radiative effect at a mid latitude continental site using ground-based measurements

Abstract. Empirical estimates of the microphysical response of cloud droplet size distribution to aerosol perturbations are commonly used to constrain aerosol–cloud interactions in climate models. Instead of empirical microphysical estimates, here macroscopic variables are analyzed to address the influences of aerosol particles and meteorological descriptors on instantaneous cloud albedo and radiative effect of shallow liquid water clouds. Long-term ground-based measurements from the Atmospheric Radiation Measurement (ARM) Program over the Southern Great Plains are used. A broad statistical analysis was performed on 14-years of coincident measurements of low clouds, aerosol and meteorological properties. Two cases representing conflicting results regarding the relationship between the aerosol and the cloud radiative effect were selected and studied in greater detail. Microphysical estimates are shown to be very uncertain and to depend strongly on the methodology, retrieval technique, and averaging scale. For this continental site, the results indicate that the influence of aerosol on shallow cloud radiative effect and albedo is weak and that macroscopic cloud properties and dynamics play a much larger role in determining the instantaneous cloud radiative effect compared to microphysical effects.

A long-term study of aerosol–cloud interactions and their radiative effect at the Southern Great Plains using ground-based measurements

10.5194/acp-16-11301-2016 ◽

2016 ◽

Vol 16 (17) ◽

pp. 11301-11318 ◽

Cited By ~ 11

Author(s):

Elisa T. Sena ◽

Allison McComiskey ◽

Graham Feingold

Keyword(s):

Great Plains ◽

Liquid Water ◽

Radiative Properties ◽

Radiative Effect ◽

Southern Great Plains ◽

Aerosol Cloud ◽

Long Term Study ◽

Cloud Radiative Effect ◽

Abstract. Empirical estimates of the microphysical response of cloud droplet size distribution to aerosol perturbations are commonly used to constrain aerosol–cloud interactions in climate models. Instead of empirical microphysical estimates, here macroscopic variables are analyzed to address the influence of aerosol particles and meteorological descriptors on instantaneous cloud albedo and the radiative effect of shallow liquid water clouds. Long-term ground-based measurements from the Atmospheric Radiation Measurement (ARM) program over the Southern Great Plains are used. A broad statistical analysis was performed on 14 years of coincident measurements of low clouds, aerosol, and meteorological properties. Two cases representing conflicting results regarding the relationship between the aerosol and the cloud radiative effect were selected and studied in greater detail. Microphysical estimates are shown to be very uncertain and to depend strongly on the methodology, retrieval technique and averaging scale. For this continental site, the results indicate that the influence of the aerosol on the shallow cloud radiative effect and albedo is weak and that macroscopic cloud properties and dynamics play a much larger role in determining the instantaneous cloud radiative effect compared to microphysical effects. On a daily basis, aerosol shows no correlation with cloud radiative properties (correlation = −0.01 ± 0.03), whereas the liquid water path shows a clear signal (correlation = 0.56 ± 0.02).

Apportionment of the present-day forcing by methane using UKESM1: The role of chemistry-aerosol-cloud interactions

10.5194/egusphere-egu21-16375 ◽

2021 ◽

Author(s):

Fiona O'Connor ◽

Omar Jamil ◽

Timothy Andrews ◽

Ben Johnson ◽

Jane Mulcahy ◽

...

Keyword(s):

Indirect Effects ◽

Radiative Forcing ◽

Cloud Droplet ◽

Aerosol Size Distribution ◽

Radiative Effect ◽

Liquid Water Path ◽

Model Estimate ◽

Aerosol Cloud ◽

Cloud Radiative Effect ◽

The pre-industrial (PI; Year 1850) to present-day (PD; Year 2014) increase in methane concentration leads to a global mean effective radiative forcing (ERF) of 0.97 &#177; 0.04 W m-2 in the UK&#8217;s Earth System Model, UKESM1. In comparison with the multi-model estimate of 0.75 &#177; 0.10 W m-2 from the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP), UKESM1 has the highest methane ERF and lies outside the 1-sigma range. This is, in part, due to UKESM1 including interactive chemistry and positive indirect effects, such as methane-driven changes in tropospheric ozone. However, UKESM1 is the only model within AerChemMIP whose contribution to the methane ERF from tropospheric adjustments is positive &#8211; this is largely driven by the strong positive cloud adjustment in UKESM1, in contrast to other models. In this work, we apportion the total methane ERF between direct and indirect effects (including adjustments) and provide a process-based understanding of what is driving the positive cloud adjustment in UKESM1.Using additional UKESM1 paired simulations, we apportion the total methane ERF between its direct methane contribution and indirect contributions from ozone, water vapour, and aerosols. This approach offers the advantage that linearity is not assumed and it distinguishes between cloud effects that are dynamically-driven via changes in temperature and those that are aerosol-mediated. By analysing the chemistry-aerosol budgets and the cloud responses, we find that the PI to PD increase in methane leads to an indirect positive aerosol ERF of up to 0.3 &#177; 0.06 W m-2, with a near-zero contribution from the instantaneous radiative forcing from aerosol-radiation interactions. Methane-driven changes in oxidants alter the relative contributions of the different sulphur dioxide oxidation pathways, causing a change in new particle formation rates and a shift in the aerosol size distribution towards fewer but larger particles. There is a resulting decrease in cloud droplet number concentration, an increase in cloud droplet effective radius, and a decrease in liquid water path in marine stratocumulus regions from aerosol-cloud interactions (mainly through the cloud lifetime effect). There is a subsequent change in the cloud radiative effect, with the positive change in the shortwave dominating over the negative change in the longwave. However, when aerosol-cloud interactions are disabled, the change in the cloud radiative effect is negative and is dominated by the reduction of cirrus clouds in the tropics, thus making UKESM1 more consistent with the other AerChemMIP models.These results can explain some of the diversity in multi-model estimates of methane forcing and highlight the importance of chemistry-aerosol-cloud interactions when quantifying climate forcing by reactive greenhouse gases.

The source of discrepancies in aerosol–cloud–precipitation interactions between GCM and A-Train retrievals

10.5194/acp-16-15413-2016 ◽

2016 ◽

Vol 16 (23) ◽

pp. 15413-15424 ◽

Cited By ~ 39

Author(s):

Takuro Michibata ◽

Kentaroh Suzuki ◽

Yousuke Sato ◽

Toshihiko Takemura

Keyword(s):

General Circulation ◽

Climate Models ◽

Circulation Model ◽

Cloud Droplet ◽

Systematic Difference ◽

Liquid Water Path ◽

Light Rain ◽

Aerosol Cloud ◽

Nonlinear Complexity ◽

Abstract. Aerosol–cloud interactions are one of the most uncertain processes in climate models due to their nonlinear complexity. A key complexity arises from the possibility that clouds can respond to perturbed aerosols in two opposite ways, as characterized by the traditional “cloud lifetime” hypothesis and more recent “buffered system” hypothesis. Their importance in climate simulations remains poorly understood. Here we investigate the response of the liquid water path (LWP) to aerosol perturbations for warm clouds from the perspective of general circulation model (GCM) and A-Train remote sensing, through process-oriented model evaluations. A systematic difference is found in the LWP response between the model results and observations. The model results indicate a near-global uniform increase of LWP with increasing aerosol loading, while the sign of the response of the LWP from the A-Train varies from region to region. The satellite-observed response of the LWP is closely related to meteorological and/or macrophysical factors, in addition to the microphysics. The model does not reproduce this variability of cloud susceptibility (i.e., sensitivity of LWP to perturbed aerosols) because the parameterization of the autoconversion process assumes only suppression of rain formation in response to increased cloud droplet number, and does not consider macrophysical aspects that serve as a mechanism for the negative responses of the LWP via enhancements of evaporation and precipitation. Model biases are also found in the precipitation microphysics, which suggests that the model generates rainwater readily even when little cloud water is present. This essentially causes projections of unrealistically frequent and light rain, with high cloud susceptibilities to aerosol perturbations.

A long-term satellite study of aerosol effects on convective clouds in Nordic background air

10.5194/acp-14-2203-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 2203-2217 ◽

Cited By ~ 10

Author(s):

M. K. Sporre ◽

E. Swietlicki ◽

P. Glantz ◽

M. Kulmala

Keyword(s):

Cloud Droplet ◽

Radar Data ◽

Nordic Countries ◽

Lower Atmosphere ◽

Convective Clouds ◽

Vertical Extent ◽

Long Term Study ◽

Moderate Resolution Imaging Spectroradiometer ◽

Abstract. Aerosol-cloud interactions constitute a major uncertainty in future climate predictions. This study combines 10 years of ground-based aerosol particle measurements from two Nordic background stations (Vavihill and Hyytiälä) with MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data of convective clouds. The merged data are used to examine how aerosols affect cloud droplet sizes and precipitation from convective clouds over the Nordic countries. From the satellite scenes, vertical profiles of cloud droplet effective radius (re) are created by plotting retrieved cloud top re against cloud top temperature for the clouds in a given satellite scene. The profiles have been divided according to aerosol number concentrations but also meteorological reanalysis parameters from the ECMWF (European Centre for Medium-Range Forecasts). Furthermore, weather radar data from the BALTEX (Baltic Sea Experiment) and precipitation data from several ground-based meteorological measurement stations have been investigated to determine whether aerosols affect precipitation intensity and amount. Small re throughout the entire cloud profiles is associated with high aerosol number concentrations at both stations. However, aerosol number concentrations seem to affect neither the cloud optical thickness nor the vertical extent of the clouds in this study. Cloud profiles with no or little precipitation have smaller droplets than those with more precipitation. Moreover, the amount of precipitation that reaches the ground is affected by meteorological conditions such as the vertical extent of the clouds, the atmospheric instability and the relative humidity in the lower atmosphere rather than the aerosol number concentration. However, lower precipitation rates are associated with higher aerosol number concentrations for clouds with similar vertical extent. The combination of these ground-based and remote-sensing datasets provides a unique long-term study of the effects of aerosols on convective clouds over the Nordic countries.

Investigation of aerosol–cloud interactions under different absorptive aerosol regimes using Atmospheric Radiation Measurement (ARM) southern Great Plains (SGP) ground-based measurements

10.5194/acp-20-3483-2020 ◽

2020 ◽

Vol 20 (6) ◽

pp. 3483-3501 ◽

Cited By ~ 1

Author(s):

Xiaojian Zheng ◽

Baike Xi ◽

Xiquan Dong ◽

Timothy Logan ◽

Yuan Wang ◽

...

Keyword(s):

Great Plains ◽

Cloud Droplet ◽

Atmospheric Radiation ◽

Strong Light ◽

Southern Great Plains ◽

Aerosol Cloud ◽

Atmospheric Radiation Measurement ◽

The Mean ◽

Aerosol Cloud Interactions ◽

Absorbing Aerosols

Abstract. The aerosol indirect effect on cloud microphysical and radiative properties is one of the largest uncertainties in climate simulations. In order to investigate the aerosol–cloud interactions, a total of 16 low-level stratus cloud cases under daytime coupled boundary-layer conditions are selected over the southern Great Plains (SGP) region of the United States. The physicochemical properties of aerosols and their impacts on cloud microphysical properties are examined using data collected from the Department of Energy Atmospheric Radiation Measurement (ARM) facility at the SGP site. The aerosol–cloud interaction index (ACIr) is used to quantify the aerosol impacts with respect to cloud-droplet effective radius. The mean value of ACIr calculated from all selected samples is 0.145±0.05 and ranges from 0.09 to 0.24 at a range of cloud liquid water paths (LWPs; LWP=20–300 g m−2). The magnitude of ACIr decreases with an increasing LWP, which suggests a diminished cloud microphysical response to aerosol loading, presumably due to enhanced condensational growth processes and enlarged particle sizes. The impact of aerosols with different light-absorbing abilities on the sensitivity of cloud microphysical responses is also investigated. In the presence of weak light-absorbing aerosols, the low-level clouds feature a higher number concentration of cloud condensation nuclei (NCCN) and smaller effective radii (re), while the opposite is true for strong light-absorbing aerosols. Furthermore, the mean activation ratio of aerosols to CCN (NCCN∕Na) for weakly (strongly) absorbing aerosols is 0.54 (0.45), owing to the aerosol microphysical effects, particularly the different aerosol compositions inferred by their absorptive properties. In terms of the sensitivity of cloud-droplet number concentration (Nd) to NCCN, the fraction of CCN that converted to cloud droplets (Nd∕NCCN) for the weakly (strongly) absorptive regime is 0.69 (0.54). The measured ACIr values in the weakly absorptive regime are relatively higher, indicating that clouds have greater microphysical responses to aerosols, owing to the favorable thermodynamic condition. The reduced ACIr values in the strongly absorptive regime are due to the cloud-layer heating effect induced by strong light-absorbing aerosols. Consequently, we expect larger shortwave radiative cooling effects from clouds in the weakly absorptive regime than those in the strongly absorptive regime.

New approaches to quantifying aerosol influence on the cloud radiative effect

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1514035112 ◽

2016 ◽

Vol 113 (21) ◽

pp. 5812-5819 ◽

Cited By ~ 31

Author(s):

Graham Feingold ◽

Allison McComiskey ◽

Takanobu Yamaguchi ◽

Jill S. Johnson ◽

Kenneth S. Carslaw ◽

...

Keyword(s):

Radiative Forcing ◽

General Circulation ◽

General Circulation Models ◽

Shortwave Radiation ◽

Emergent Properties ◽

Radiative Effect ◽

Aerosol Composition ◽

Aerosol Cloud ◽

Cloud Radiative Effect ◽

The topic of cloud radiative forcing associated with the atmospheric aerosol has been the focus of intense scrutiny for decades. The enormity of the problem is reflected in the need to understand aspects such as aerosol composition, optical properties, cloud condensation, and ice nucleation potential, along with the global distribution of these properties, controlled by emissions, transport, transformation, and sinks. Equally daunting is that clouds themselves are complex, turbulent, microphysical entities and, by their very nature, ephemeral and hard to predict. Atmospheric general circulation models represent aerosol−cloud interactions at ever-increasing levels of detail, but these models lack the resolution to represent clouds and aerosol−cloud interactions adequately. There is a dearth of observational constraints on aerosol−cloud interactions. We develop a conceptual approach to systematically constrain the aerosol−cloud radiative effect in shallow clouds through a combination of routine process modeling and satellite and surface-based shortwave radiation measurements. We heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.

Reducing uncertainties in satellite estimates of aerosol-cloud interactions over the subtropical ocean by integrating vertically resolved aerosol observations

10.5194/acp-2019-892 ◽

2019 ◽

Author(s):

David Painemal ◽

Fu-Lung Chang ◽

Richard Ferrare ◽

Sharon Burton ◽

Zhujun Li ◽

...

Keyword(s):

Climate Models ◽

Global Climate ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Global Climate Models ◽

Orthogonal Polarization ◽

Near Surface ◽

Aerosol Cloud ◽

Error Characterization ◽

Abstract. Satellite quantification of aerosol effects on clouds relies on aerosol optical depth (AOD) as a proxy for aerosol concentration or cloud condensation nuclei (CCN). However, the lack of error characterization of satellite-based results hampers their use for the evaluation and improvement of global climate models. We show that the use of AOD for assessing aerosol-cloud interactions (ACI) is inadequate over vast oceanic areas in the subtropics. Instead, we postulate that a more physical approach that consists of matching vertically resolved aerosol data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite at the cloud-layer height with Aqua Moderate-resolution Imaging Spectroradiometer (MODIS) cloud retrievals reduces uncertainties in satellite-based ACI estimates. Combined aerosol extinction coefficients (σ) below cloud-top (σBC) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and cloud droplet number concentrations (Nd) from Aqua-MODIS yield high correlations across a broad range of σBC values, with σBC quartile correlations > 0.78. In contrast, CALIOP-based AOD yields correlations with MODIS Nd of less than 0.62 for the two lower AOD quartiles. Moreover, σBC explains 41 % of the spatial variance in MODIS Nd, whereas AOD only explains 17 %, primarily caused by the lack of spatial covariability in the eastern Pacific. Compared with σBC, near-surface σ weakly correlates in space with MODIS Nd, accounting for a 16 % variance. It is concluded that the linear regression calculated from ln(Nd)−ln(σBC) (the standard method for quantifying ACI) is more physically meaningful than that derived from the Nd−AOD pair.

Review of the manuscript "Long-term study of cloud radiative effect, cloud fraction and cloud type at two stations in Switzerland using hemispherical sky cameras" by Christine Aebi et al.

10.5194/amt-2017-184-rc3 ◽

2017 ◽

Author(s):

Anonymous

Keyword(s):

Cloud Fraction ◽

Radiative Effect ◽

Cloud Type ◽

Term Study ◽

Long Term Study ◽

Cloud Radiative Effect

Why do GCMs overestimate the aerosol cloud lifetime effect? A comparison of CAM5 and a CRM

10.5194/acp-2016-612 ◽

2016 ◽

Author(s):

Cheng Zhou ◽

Joyce E. Penner

Keyword(s):

Great Plains ◽

Climate Models ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Cloud Droplet ◽

Condensation Process ◽

Cloud Droplets ◽

Aerosol Cloud ◽

Aerosol Loading

Abstract. Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 05/27/2011 at the Southern Great Plains (SGP) measurement site established by Department of Energy's Atmospheric Radiation Measurement (ARM) Program using a single column version of a global climate model (CAM5.3) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.

Long-term Trend Comparison of Planetary Boundary Layer Height in Observations and CMIP6 models over China

Journal of Climate ◽

10.1175/jcli-d-20-1000.1 ◽

2021 ◽

pp. 1-64

Author(s):

Man Yue ◽

Minghuai Wang ◽

Jianping Guo ◽

Haipeng Zhang ◽

Xinyi Dong ◽

...

Keyword(s):

Boundary Layer ◽

Heat Flux ◽

Planetary Boundary Layer ◽

Climate Models ◽

Radiative Effect ◽

Term Trend ◽

Cloud Radiative Effect ◽

Long Term Trend ◽

Long Term Variations

AbstractThe planetary boundary layer (PBL) plays an essential role in climate and air quality simulations. Nevertheless, large uncertainties remain in understanding the drivers for long-term trend of PBL height (PBLH) and its simulation. Here we combinate the radiosonde data and reanalysis datasets to analyze PBLH long-term trends over China, and to further explore the performance of CMIP6 climate models in simulating these trends. Results show that the observed long-term “positive to negative” trend shift of PBLH is related to the variation in the surface upward sensible heat flux (SHFLX), and the SHFLX is further controlled by the synergistic effect of low cloud cover (LCC) and soil moisture (SM) changes. Variabilities in LCC and SM directly influence the energy balance via surface net downward shortwave flux (SWF) and the latent heat flux (LHFLX), respectively. The CMIP6 climate models, however, cannot reproduce the observed PBLH long-term trend shift over China. The CMIP6 results illustrate an overwhelming continuous downward PBLH trend during the 1979–2014 period, which is largely caused by the poor capability in simulating long-term variations of cloud radiative effect. Our results reveal that the long-term cloud radiative effect simulation is critical for CMIP6 models in reproducing the long-term trend of PBLH. This study highlights the importance of processes associated with LCC and SM in modulating PBLH long-term variations and calls attentions to improve these processes in climate models in order to improve the PBLH long-term trend simulations.