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The effects of different aerosol types on cloud albedo are analysed using the
linear relation between total albedo and cloud fraction found on a monthly
mean scale in regions of subtropical marine stratocumulus clouds and the
influence of simulated aerosol variations on this relation. Model experiments
from the Coupled Model Intercomparison Project...
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... Unlike the representative concentration pathways (RCP) of the CMIP5, the 6th phase SSPs incorporated additional attributes such as land, energy use, and economic activities along with the impact of emissions for respective scenarios (Eyring et al., 2016). Aerosol optical depth from CMIP GCMs had been used to understand the relationship of AA with the global water cycle (Boé, 2016;Lin et al., 2018;Monerie et al., 2022;Sanap et al., 2015;Sobel et al., 2019), their influence on clouds (Cherian & Johannes, 2020;Frey et al., 2017;Hua et al., 2020;Luo et al., 2021) and Asian aerosol dipole patterns (Ramachandran et al., 2022;Wang et al., 2021). Spatiotemporal variations of AA in CMIP5 and CMIP6 models in eastern central China report an underestimation of AOD that decreased from 40% (CMIP5) to 8% (CMIP6) in comparison with satellite AOD during 2000(Ali et al., 2022Li et al., 2021). ...
Global and regional trends of the Aerosol Optical Depth (AOD) from Coupled Model Intercomparison Project (CMIP) Phase 6 simulations for the study period 1971-2014 were compared against the satellite retrievals and the inter-model variations were analysed. The AOD from multimodel mean (MMM) of eight general circulation models (GCMs) has been evaluated against the Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectro Radiometer (MISR) AOD for the 2001-2014 period. Angstrom exponents (AE and its first derivative) that represent the size distribution of aerosols are estimated globally from the perturbed initial condition ensemble of MRI-ESM2-0 and MPI-ESM-1-2-HAM models to report the aerosol variations through their size distribution. We found that the global AOD obtained from the MMM8 showed an insignificant decreasing trend, while this trend is significantly positive over the northern tropical region. The MMM8 has overestimated the MODIS AOD over North Africa, India, China, and Australia while this overestimation is confined to North Africa and eastern China when compared against MISR AOD. The absolute percent bias of MMM8 is 28.1% and 24.1% over the globe when compared against MODIS and MISR AOD, respectively. The spatial pattern of AE showed the dominance of fine-and coarse-mode particles during the boreal/austral winter and summer seasons, respectively, that replicate the seasonality of aerosols. The AE derived from MPI-ESM-1-2-HR demonstrated better agreement with AATSR SU's (Advanced Along Track Scanning Radiometer instrument series, with the algorithm developed by Swansea University) AE (550-870 nm). On the other hand, MRI-ESM2-0 consistently underestimated AE across different regions and wavelength ranges, suggesting an over representation of larger aerosol particles in the model's portrayal of aerosol size distribution compared to satellite observations.
... It is well established that cloud albedo and COD in liquid clouds are primarily a function of liquid water path (Frey et al., 2017), therefore any modifications of cloud optical properties attributable to aerosol-induced microphysical perturbations must be evaluated along with possible adjustments of cloud macrophysical properties. We have studied the relationship of cloud geometrical parameters (H base , H top and H thick ), LWC, albedo, and COD retrieved at MHD by the SYRSOC algorithm with N a and CHL, along with the main meteorological parameters controlling the occurrence of stratiform clouds in this area of the world ocean (Table 1). ...
... The correlation coefficients between CDNC and normalized albedo (normalized COD) are equal to 0.50 (0.43). Our data show that the most important microphysical parameter in controlling cloud albedo is LWC, in agreement with previous studies (Frey et al., 2017;Liu et al., 2020). LWC accounts for up to 53% (R = 0.73; slope = 0.85; intercept = 0.06) of the albedo variance ( Figure S18 in Supporting Information S1). ...
The current understanding of the impact of natural cloud condensation nuclei (CCN) variability on cloud properties in marine air is low, thus contributing to climate prediction uncertainty. By analyzing cloud remote sensing observations (2009–2015) at Mace Head (west coast of Ireland), we show the oceanic biota impact on the microphysical properties of stratiform clouds over the Northeast Atlantic Ocean. During spring to summer (seasons of enhanced oceanic biological activity), clouds typically host a higher number of smaller droplets resulting from increased aerosol number concentration in the CCN relevant‐size range. The induced increase in cloud droplet number concentration (+100%) and decrease in their radius (−14%) are comparable in magnitude to that generated by the advection of anthropogenically influenced air masses over the background marine boundary layer. Cloud water content and albedo respond to marine CCN perturbations with positive adjustments, making clouds brighter as the number of droplets increases. Cloud susceptibility to marine aerosols overlaps with a large variability of cloud macrophysical and optical properties primarily affected by the meteorological conditions. The above findings suggest the existence of a potential feedback mechanism between marine biota and the marine cloud‐climate system.
... Furthermore, the semi-direct effects of absorbing aerosols (e.g., black carbon) are also difficult to be quantified by numerical models (Herbert et al., 2020). Given different model experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5), Frey et al. (2017) estimated the impact of anthropogenic sulfate and non-sulfate aerosol forcing on changing the cloud albedo and concluded that absorbing aerosols play a key role in offsetting the cloud brightening to a certain degree. ...
The cloud albedo in the marine subtropical stratocumulus
regions plays a key role in regulating the regional energy budget. Based on
12 years of monthly data from multiple satellite datasets, the long-term,
monthly and seasonal cycle of averaged cloud albedo in five stratocumulus
regions were investigated to intercompare the atmosphere-only simulations
between phases 5 and 6 of the Coupled Model Intercomparison Project (AMIP5
and AMIP6). Statistical results showed that the long-term regressed cloud
albedos were underestimated in most AMIP6 models compared with the
satellite-driven cloud albedos, and the AMIP6 models produced a similar
spread as AMIP5 over all regions. The monthly averaged values and seasonal
cycle of cloud albedo of AMIP6 ensemble mean showed a better correlation
with the satellite-driven observations than that of the AMIP5 ensemble mean.
However, the AMIP6 model still failed to reproduce the values and amplitude
in some regions. By employing the Modern-Era Retrospective Analysis for
Research and Applications Version 2 (MERRA-2) data, this study estimated the relative
contributions of different aerosols and meteorological factors on the
long-term variation of marine stratocumulus cloud albedo under different
cloud liquid water path (LWP) conditions. The multiple regression models can
explain ∼ 65 % of the changes in the cloud albedo. Under
the monthly mean LWP ≤ 65 g m−2, dust and black carbon dominantly
contributed to the changes in the cloud albedo, while dust and sulfur
dioxide aerosol contributed the most under the condition of 65 g m−2 < LWP ≤ 120 g m−2. These results suggest that the
parameterization of cloud–aerosol interactions is crucial for accurately
simulating the cloud albedo in climate models.
... The cloud-liquid water path (LWP) is an important variable for cloud properties that can be affected by the aerosol second indirect effect 24,39 . The increase in the LWP is because an increased amount of smaller droplets may lead to a reduction in the precipitation efficiency, which is related to the aerosol cloud lifetime effect 7 . ...
In this study, we designed a sensitivity test using the half number concentration of sulfate in the nucleation calculation process to study the aerosol-cloud interaction (ACI) of sulfate on clouds, precipitation, and monsoon intensity in the summer over the eastern China monsoon region (ECMR) with the National Center for Atmospheric Research Community Atmosphere Model version 5. Numerical experiments show that the ACI of sulfate led to an approximately 30% and 34% increase in the cloud condensation nuclei and cloud droplet number concentrations, respectively. Cloud droplet effective radius below 850 hPa decreased by approximately 4% in the southern ECMR, while the total liquid water path increased by 11%. The change in the indirect radiative forcing due to sulfate at the top of the atmosphere in the ECMR during summer was − 3.74 W·m⁻². The decreased radiative forcing caused a surface cooling of 0.32 K and atmospheric cooling of approximately 0.3 K, as well as a 0.17 hPa increase in sea level pressure. These changes decreased the thermal difference between the land and sea and the gradient of the sea-land pressure, leading to a weakening in the East Asian summer monsoon (EASM) and a decrease in the total precipitation rate in the southern ECMR. The cloud lifetime effect has a relatively weaker contribution to summer precipitation, which is dominated by convection. The results show that the ACI of sulfate was one possible reason for the weakening of the EASM in the late 1970s.
... Schwarz et al. (2010Schwarz et al. ( , 2013 found that models overestimate BC concentrations over the remote Pacific compared to aircraft observations, whereas the quantity of biomass burning aerosols above clouds has been found to be underestimated in models over the southeast Atlantic and often prescribed as too reflective (Peers et al., 2016). This is in agreement with Frey et al. (2017), who found that aerosols above the cloud layer occur in CMIP5 (Coupled Model Intercomparison Project phase 5) models without reducing the scene albedo. ...
... The focus regions are similar in regard to dynamical regime but differ in their aerosol signature (e.g., Frey et al., 2017). These subtropical marine stratocumulus regions are located in the subsiding branch of the Hadley cell, and the capping inversion limits the vertical cloud extent. ...
The vertical distribution of aerosols plays an important role in determining the effective radiative forcing from aerosol–radiation and aerosol–cloud interactions. Here, a number of processes controlling the vertical distribution of aerosol in five subtropical marine stratocumulus regions in the climate model NorESM1-M are investigated, with a focus on the total aerosol extinction. A comparison with satellite lidar data (CALIOP, Cloud–Aerosol Lidar with Orthogonal Polarization) shows that the model underestimates aerosol extinction throughout the troposphere, especially elevated aerosol layers in the two regions where they are seen in observations. It is found that the shape of the vertical aerosol distribution is largely determined by the aerosol emission and removal processes in the model, primarily through the injection height, emitted particle size, and wet scavenging. In addition, the representation of vertical transport related to shallow convection and entrainment is found to be important, whereas alterations in aerosol optical properties and cloud microphysics parameterizations have smaller effects on the vertical aerosol extinction distribution. However, none of the alterations made are sufficient for reproducing the observed vertical distribution of aerosol extinction, neither in magnitude nor in shape. Interpolating the vertical levels of CALIOP to the corresponding model levels leads to better agreement in the boundary layer and highlights the importance of the vertical resolution.
... It would further influence the regional and global climate (Rosenfeld, 2006;Seinfeld et al., 2016), such as reducing the precipitation or drizzle (Andreae et al., 2004;Heikenfeld et al., 2019) and further delaying the hydrological cycle (Rosenfeld, 2006). Through model experiments with the Coupled Model Intercomparison Project phase 5 (CMIP5), Frey et al. (2017) also found that the addition of anthropogenic aerosols could increase the monthly mean cloud albedo of subtropical marine stratocumulus clouds. ...
The influence of aerosols, both natural and
anthropogenic, remains a major area of uncertainty when predicting the
properties and the behaviours of clouds and their influence on climate. In
an attempt to better understand the microphysical properties of cloud
droplets, the simultaneous variations in aerosol microphysics and their
potential interactions during cloud life cycles in the North China Plain, an
intensive observation took place from 17 June to 30 July 2018 at the
summit of Mt. Tai. Cloud microphysical parameters were monitored
simultaneously with number concentrations of cloud condensation nuclei
(NCCN) at different supersaturations, PM2.5 mass concentrations,
particle size distributions and meteorological parameters. Number
concentrations of cloud droplets (NC), liquid water content (LWC) and
effective radius of cloud droplets (reff) show large variations among 40
cloud events observed during the campaign. The low values of reff and
LWC observed at Mt. Tai are comparable with urban fog. Clouds on clean days
are more susceptible to the change in concentrations of particle number
(NP), while clouds formed on polluted days might be more sensitive to
meteorological parameters, such as updraft velocity and cloud base height.
Through studying the size distributions of aerosol particles and cloud
droplets, we find that particles larger than 150 nm play important roles in
forming cloud droplets with the size of 5–10 µm. In general, LWC
consistently varies with reff. As NC increases, reff changes
from a trimodal distribution to a unimodal distribution and shifts to
smaller size mode. By assuming a constant cloud thickness and ignoring any
lifetime effects, increase in NC and decrease in reff would increase
cloud albedo, which may induce a cooling effect on the local climate system.
Our results contribute valuable information to enhance the understanding of
cloud and aerosol properties, along with their potential interactions on the
North China plain.
... Through Model experiments with the Coupled Model Intercomparison Project phase 5 (CMIP5), Frey et al. (2017) found that the monthly mean cloud albedo of subtropical marine stratocumulus clouds increased with the addition of anthropogenic aerosols. ...
The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to understand better the microphysical properties of cloud droplets, the aerosol-cloud interactions, and the corresponding climate effect during cloud life cycles in the North China Plain, an intensive observation took place from 17 June to 30 July 2018 at the summit of Mt. Tai. Cloud microphysical parameters were monitored simultaneously with number concentrations of cloud condensation nuclei (NCCN) at different supersaturations, PM2.5 mass concentrations, particle size distributions and meteorological parameters. Number concentrations of cloud droplets (NC), liquid water content (LWC) and effective radius of cloud droplets (reff) show large variations among 40 cloud events observed during the campaign. Perturbations of aerosols will significantly increase the NC of cloud droplets and shift cloud droplets toward smaller size ranges. Clouds in clean days are more susceptible to the change in concentrations of particle number (NP). LWC shows positive correlation with reff. As NC increases, reff changes from a trimodal distribution to a unimodal distribution. By assuming a cloud thickness of 100 m, we find that the albedo can increase 36.4 % if the cloud gets to be disturbed by aerosols. This may induce a cooling effect on the local climate system. Our results contribute more information about regional cloud microphysics and will help to reduce the uncertainties in climate models when predicting climate responses to cloud-aerosol interactions.
Aerosol optical depth (AOD) is a key parameter in atmospheric pollution and climate processes. In this paper, we compared the aerosol loading (550 nm) from 2000–2001 to 2017–2018 and total cloud cover using seasonal, latitudinal and solar activity cycle data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and determined the spectral optical range from the region of relatively clear air (Europe) to the region of more considerable biomass burning activity (Africa). To remove the large annual cycle influence, the data were deseasonalized, allowing exploration of inter-annual variability. Deseasonalization obtains the time series AOD monthly average anomaly over the years for each grid cell. We employ the solar flux index over the regions by correlating the absolute percentage mean difference of aerosol and cloud interactions and validate the result by modeling aerosol and cloud data from 2020 to 2021 using a neural network. AOD and solar flux for Africa show correlations of − 0.638 for 2000–2001 and − 0.218 for Europe, and at the same time, AOD with cloud cover for Africa shows correlations of − 0.129 and 0.360 for Europe. The analysis confirmed an inverse weak correlation of aerosols with cloud cover. This would help resolve the knowledge gap by demonstrating that aerosol and cloud interactions are not only dependent on region but also more dependent on the solar activity cycle and seasons. We observed dependence by the latitude of the aerosol load and solar flux index.
Influenced by stratospheric total ozone column (TOC), cloud cover, aerosols, albedo, and other factors, levels of daily erythemal dose (Her) in a specific geographic region show significant variability in time and space. To investigate the degree of randomness and predictability of Her time series from ground-based observations in Novi Sad, Serbia, during the 2003–2012 time period, we used a set of information measures: Kolmogorov complexity, Kolmogorov complexity spectrum, running Kolmogorov complexity, the largest Lyapunov exponent, Lyapunov time, and Kolmogorov time. The result reveals that fluctuations in daily Her are moderately random and exhibit low levels of chaotic behavior. We found a larger number of occurrences of deviation from the mean in the time series during the years with lower values of Her (2007–2009, 2011–2012), which explains the higher complexity. Our analysis indicated that the time series of daily values of Her show a tendency to increase the randomness when the randomness of cloud cover and TOC increases, which affects the short-term predictability. The prediction horizon of daily Her values in Novi Sad given by the Lyapunov time corrected for randomness by Kolmogorov is between 1.5 and 3.5 days.
The cloud albedo at the subtropical marine subtropical stratocumulus regions has a key role in regulating the regional energy budget. Based on 12 years of monthly data from multiple satellite datasets, the long-term, monthly and seasonal cycle averaged cloud albedo at five stratocumulus regions were investigated to inter-compare the atmosphere-only simulations of Phase 5 and 6 of the Coupled Model Inter-comparison Project (AMIP5 and AMIP6). Statistical results showed that the long-term regressed cloud albedos were underestimated in most AMIP6 models compared with the satellite-driven cloud albedos, and the AMIP6 models produced a similar spread of AMIP5 at all regions. The monthly mean and seasonal cycle of cloud albedo of AMIP6 ensemble mean showed better correlation with the satellite-driven observation than that of AMIP5 ensemble mean, however, fail to reproduce the values and amplitude in some regions. By employing the Modern-Era Retrospective Analysis for Research and Applications Version 2 data, this study estimated the relative contributions of different aerosols and meteorological factors on the marine stratocumulus cloud albedo under different cloud liquid water path (LWP) conditions. The multiple regression models can explain ~60 % of the changes in the cloud albedo. Under the monthly mean LWP ≤ 60 g m−2, dust and black carbon dominantly contributed to the changes in the cloud albedo, while sulfate aerosol contributed the most under the condition of 60 g m−2
