Global Estimates of Changes in Shortwave Low‐Cloud Albedo and Fluxes Due to Variations in Cloud Droplet Number Concentration Derived From CERES‐MODIS Satellite Sensors

Painemal, David

doi:10.1029/2018gl078880

Cited by 22 publications

(32 citation statements)

References 31 publications

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“…Even though the Twomey or cloud-albedo effect might be considered as the most studied, discussions are still on-going to better understand the correlation between cloud condensation nuclei (CCN), supersaturation (S), vertical wind velocity (w), cloud droplet number concentration (N d ), and the impact on cloud albedo depending on the environmental conditions (Hudson and Noble (2014a); Werner et al (2014); Cecchini et al (2017); Sarangi et al (2018)). With the support of fifteen years of satellite measurements, calculation of albedo susceptibilities helps to better understand the cloud radiative response due to 10 aerosol-cloud interactions, and supports the conclusion that polluted clouds less efficiently change their albedo compared to more pristine clouds for the same change in N d (Painemal, 2018). Cloud droplet number concentrations have been the center of interest for satellite retrieval calculations based on cloud optical depth, cloud droplet effective radius, and cloud top temperature.…”

Section: Introductionmentioning

confidence: 83%

Aerosol–Cloud Closure Study on Cloud Optical Properties using Remotely Piloted Aircraft Measurements during a BACCHUS Field Campaign in Cyprus

Calmer¹,

Roberts²,

Sanchez³

et al. 2019

Preprint

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In the framework of the EU-FP7 BACCHUS project, an intensive field campaign was performed in Cyprus (2015/03).Remotely Piloted Aircraft System (RPAS), ground-based instruments, and remote-sensing observations were operating in parallel to provide an integrated characterization of aerosol-cloud interactions. Remotely Piloted Aircraft (RPA) were equipped with a 5-hole probe, pyranometers, pressure, temperature and humidity sensors, and measured updraft velocity at cloud base and cloud optical properties of a stratocumulus layer. Ground-based measurements of dry aerosol size distributions and cloud 5 condensation nuclei spectra, and RPA observations of vertical wind velocity and meteorological state parameters are used here to initialize an Aerosol-Cloud Parcel Model (ACPM) and compare the in situ observations of cloud optical properties measured by the RPA to those simulated in the ACPM. Two different cases are studied with the ACPM, including an adiabatic case and an entrainment case, in which the in-cloud temperature profile from RPA is taken into account. Adiabatic ACPM simulation yields cloud droplet number concentrations at cloud base (ca. 400 cm -3 ) that are similar to those derived from a Hoppel minimum 10 analysis. Cloud optical properties have been inferred using the transmitted fraction of shortwave radiation profile measured by downwelling and upwelling pyranometers mounted on a RPA, and the observed transmitted fraction of solar radiation is then compared to simulations from the ACPM. ACPM simulations and RPA observations show better agreement when associated with entrainment compared to that of an adiabatic case. The mean difference between observed and adiabatic profiles of transmitted fraction of solar radiation is 0.12, while this difference is only 0.03 between observed and entrainment profiles. 15A sensitivity calculation is then conducted to quantify the relative impacts of two-fold changes in aerosol concentration, and updraft velocity to highlight the importance of accounting for the impact of entrainment in deriving cloud optical properties, as well as the ability of RPAs to leverage ground-based observations for studying aerosol-cloud interactions.Atmos. Chem. Phys. Discuss., https://doi.

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Section: Introductionmentioning

confidence: 83%

Aerosol–Cloud Closure Study on Cloud Optical Properties using Remotely Piloted Aircraft Measurements during a BACCHUS Field Campaign in Cyprus

Calmer¹,

Roberts²,

Sanchez³

et al. 2019

Preprint

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“…Daily cloud drop number concentrations ( N d ) were estimated (Grosvenor et al., 2018) using Aqua MODerate resolution Imaging Spectroradiometer (MODIS)‐based cloud effective radius, cloud optical depth, and temperature from Level 3 data (1 ° × 1 ° grid resolution) using an adiabatic framework documented in Painemal (2018). We used the Single Scanning Footprint daily product of the Cloud and the Earth's Radiant Energy System Edition 4 (CERES‐MODIS; https://ceres.larc.nasa.gov/data/) (Minnis et al., 2011, 2020) obtained between 2013 and 2017 for the region encompassed by 31–34°N and 63–66°W surrounding Bermuda; although these data represent a different time period than other data used, the annual cycle is expected to be unaffected, which is our primary focus.…”

Section: Methodsmentioning

confidence: 99%

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

et al. 2021

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Aerosol characteristics and aerosol–cloud interactions remain uncertain in remote marine regions. We use over a decade of data (2000–2012) from the NASA AErosol RObotic NETwork, aerosol and wet deposition samples, satellite remote sensors, and models to examine aerosol and cloud droplet number characteristics at a representative open ocean site (Bermuda) over the Western North Atlantic Ocean (WNAO). Annual mean values were as follows: aerosol optical depth (AOD) = 0.12, Ångström Exponent (440/870 nm) = 0.95, fine mode fraction = 0.51, asymmetry factor = 0.72 (440 nm) and 0.68 (1020 nm), and Aqua‐MODIS cloud droplet number concentrations = 51.3 cm−3. The winter season (December–February) was characterized by high sea salt optical thickness and the highest aerosol extinction in the lowest 2 km. Extensive precipitation over the WNAO in winter helps contribute to the low FMFs in winter (∼0.40–0.50) even though air trajectories often originate over North America. Spring and summer had more pronounced influence from sulfate, dust, organic carbon, and black carbon. Volume size distributions were bimodal with a dominant coarse mode (effective radii: 1.85–2.09 µm) and less pronounced fine mode (0.14–0.16 µm), with variability in the coarse mode likely due to different characteristic sizes for transported dust (smaller) versus regional sea salt (larger). Extreme pollution events highlight the sensitivity of this site to long‐range transport of urban emissions, dust, and smoke. Differing annual cycles are identified between AOD and cloud droplet number concentrations, motivating a deeper look into aerosol–cloud interactions at this site.

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“…CERES-MODIS r e and τ are estimated, respectively, from MODIS 0.64 and 3.79 µm bands, with the latter being less sensitive to three-dimensional radiative effects and biases due to subpixel inhomogeneity than the more widely used 2.1 µm r e (Zhang and Platnick, 2011;. The cloud microphysical variable used in this study is the cloud droplet number concentration N d , which is estimated using the adiabatic formulation (Painemal and Zuidema, 2011;Grosvenor et al, 2018) as…”

Section: Datasetmentioning

confidence: 99%

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

et al. 2020

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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 (ACIs) 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 Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua 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 MODIS Aqua 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 0.54–0.62 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 ACIs) is more physically meaningful than that derived from the Nd–AOD pair.

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Global Estimates of Changes in Shortwave Low‐Cloud Albedo and Fluxes Due to Variations in Cloud Droplet Number Concentration Derived From CERES‐MODIS Satellite Sensors

Cited by 22 publications

References 31 publications

Aerosol–Cloud Closure Study on Cloud Optical Properties using Remotely Piloted Aircraft Measurements during a BACCHUS Field Campaign in Cyprus

Aerosol–Cloud Closure Study on Cloud Optical Properties using Remotely Piloted Aircraft Measurements during a BACCHUS Field Campaign in Cyprus

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

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

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