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

Abstract. 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 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 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. A 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.

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Aerosol–cloud closure study on cloud optical properties using remotely piloted aircraft measurements during a BACCHUS field campaign in Cyprus

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-13989-2019 ◽

2019 ◽

Vol 19 (22) ◽

pp. 13989-14007 ◽

Cited By ~ 1

Author(s):

Radiance Calmer ◽

Gregory C. Roberts ◽

Kevin J. Sanchez ◽

Jean Sciare ◽

Karine Sellegri ◽

...

Keyword(s):

Optical Properties ◽

Solar Radiation ◽

Cloud Base ◽

Field Campaign ◽

Aerosol Cloud ◽

Holistic Understanding ◽

Remotely Piloted Aircraft ◽

Aerosol Cloud Interactions ◽

The Impact ◽

Adiabatic Case

Abstract. In the framework of the EU-FP7 BACCHUS (impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) project, an intensive field campaign was performed in Cyprus (March 2015). 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 five-hole probe, pyranometers, pressure, temperature and humidity sensors, and measured vertical wind at cloud base and cloud optical properties of a stratocumulus layer. Ground-based measurements of dry aerosol size distributions and cloud condensation nuclei spectra, and RPA observations of updraft 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 (approximately 400 cm−3) that are similar to those derived from a Hoppel minimum 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 shows 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. A sensitivity calculation is then conducted to quantify the relative impacts of 2-fold changes in aerosol concentration, and updraft 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.

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Dust Impacts on the 2012 Hurricane Nadine Track during the NASA HS3 Field Campaign

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-17-0237.1 ◽

2018 ◽

Vol 75 (7) ◽

pp. 2473-2489 ◽

Cited By ~ 5

Author(s):

E. P. Nowottnick ◽

P. R. Colarco ◽

S. A. Braun ◽

D. O. Barahona ◽

A. da Silva ◽

...

Keyword(s):

Optical Properties ◽

General Circulation ◽

Circulation Model ◽

Temperature Perturbation ◽

Field Campaign ◽

Aerosol Cloud ◽

Steering Flow ◽

Close Proximity ◽

Aerosol Cloud Interactions ◽

Total Life

Abstract During the 2012 deployment of the NASA Hurricane and Severe Storm Sentinel (HS3) field campaign, several flights were dedicated to investigating Hurricane Nadine. Hurricane Nadine developed in close proximity to the dust-laden Saharan air layer and is the fourth-longest-lived Atlantic hurricane on record, experiencing two strengthening and weakening periods during its 22-day total life cycle as a tropical cyclone. In this study, the NASA GEOS-5 atmospheric general circulation model and data assimilation system was used to simulate the impacts of dust during the first intensification and weakening phases of Hurricane Nadine using a series of GEOS-5 forecasts initialized during Nadine’s intensification phase (12 September 2012). The forecasts explore a hierarchy of aerosol interactions within the model: no aerosol interaction, aerosol–radiation interactions, and aerosol–radiation and aerosol–cloud interactions simultaneously, as well as variations in assumed dust optical properties. When only aerosol–radiation interactions are included, Nadine’s track exhibits sensitivity to dust shortwave absorption, as a more absorbing dust introduces a shortwave temperature perturbation that impacts Nadine’s structure and steering flow, leading to a northward track divergence after 5 days of simulation time. When aerosol–cloud interactions are added, the track exhibits little sensitivity to dust optical properties. This result is attributed to enhanced longwave atmospheric cooling from clouds that counters shortwave atmospheric warming by dust surrounding Nadine, suggesting that aerosol–cloud interactions are a more significant influence on Nadine’s track than aerosol–radiation interactions. These findings demonstrate that tropical systems, specifically their track, can be impacted by dust interaction with the atmosphere.

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Vertical wind velocity measurements using a five-hole probe with remotely piloted aircraft to study aerosol–cloud interactions

Atmospheric Measurement Techniques ◽

10.5194/amt-11-2583-2018 ◽

2018 ◽

Vol 11 (5) ◽

pp. 2583-2599 ◽

Cited By ~ 8

Author(s):

Radiance Calmer ◽

Gregory C. Roberts ◽

Jana Preissler ◽

Kevin J. Sanchez ◽

Solène Derrien ◽

...

Keyword(s):

Wind Velocity ◽

Vertical Wind ◽

Cloud Base ◽

Velocity Measurements ◽

Atmospheric Research ◽

Aerosol Cloud ◽

Remotely Piloted Aircraft ◽

Wind Velocities ◽

Aerosol Cloud Interactions ◽

Vertical Wind Velocity

Abstract. The importance of vertical wind velocities (in particular positive vertical wind velocities or updrafts) in atmospheric science has motivated the need to deploy multi-hole probes developed for manned aircraft in small remotely piloted aircraft (RPA). In atmospheric research, lightweight RPAs (< 2.5 kg) are now able to accurately measure atmospheric wind vectors, even in a cloud, which provides essential observing tools for understanding aerosol–cloud interactions. The European project BACCHUS (impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) focuses on these specific interactions. In particular, vertical wind velocity at cloud base is a key parameter for studying aerosol–cloud interactions. To measure the three components of wind, a RPA is equipped with a five-hole probe, pressure sensors, and an inertial navigation system (INS). The five-hole probe is calibrated on a multi-axis platform, and the probe–INS system is validated in a wind tunnel. Once mounted on a RPA, power spectral density (PSD) functions and turbulent kinetic energy (TKE) derived from the five-hole probe are compared with sonic anemometers on a meteorological mast. During a BACCHUS field campaign at Mace Head Atmospheric Research Station (Ireland), a fleet of RPAs was deployed to profile the atmosphere and complement ground-based and satellite observations of physical and chemical properties of aerosols, clouds, and meteorological state parameters. The five-hole probe was flown on straight-and-level legs to measure vertical wind velocities within clouds. The vertical velocity measurements from the RPA are validated with vertical velocities derived from a ground-based cloud radar by showing that both measurements yield model-simulated cloud droplet number concentrations within 10 %. The updraft velocity distributions illustrate distinct relationships between vertical cloud fields in different meteorological conditions.

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Investigating the sensitivity to resolving aerosol interactions in downscaling regional model experiments with WRFv3.8.1 over Europe

Geoscientific Model Development ◽

10.5194/gmd-13-2511-2020 ◽

2020 ◽

Vol 13 (6) ◽

pp. 2511-2532

Author(s):

Vasileios Pavlidis ◽

Eleni Katragkou ◽

Andreas Prein ◽

Aristeidis K. Georgoulias ◽

Stergios Kartsios ◽

...

Keyword(s):

Solar Radiation ◽

Statistical Significance ◽

Regional Climate ◽

The Black Sea ◽

Radiative Effect ◽

Surface Solar Radiation ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions ◽

The Impact ◽

Aerosol Radiative

Abstract. In this work we present downscaling experiments with the Weather Research and Forecasting model (WRF) to test the sensitivity to resolving aerosol–radiation and aerosol–cloud interactions on simulated regional climate for the EURO-CORDEX domain. The sensitivities mainly focus on the aerosol–radiation interactions (direct and semi-direct effects) with four different aerosol optical depth datasets (Tegen, MAC-v1, MACC, GOCART) being used and changes to the aerosol absorptivity (single scattering albedo) being examined. Moreover, part of the sensitivities also investigates aerosol–cloud interactions (indirect effect). Simulations have a resolution of 0.44∘ and are forced by the ERA-Interim reanalysis. A basic evaluation is performed in the context of seasonal-mean comparisons to ground-based (E-OBS) and satellite-based (CM SAF SARAH, CLARA) benchmark observational datasets. The impact of aerosols is calculated by comparing it against a simulation that has no aerosol effects. The implementation of aerosol–radiation interactions reduces the direct component of the incoming surface solar radiation by 20 %–30 % in all seasons, due to enhanced aerosol scattering and absorption. Moreover the aerosol–radiation interactions increase the diffuse component of surface solar radiation in both summer (30 %–40 %) and winter (5 %–8 %), whereas the overall downward solar radiation at the surface is attenuated by 3 %–8 %. The resulting aerosol radiative effect is negative and is comprised of the net effect from the combination of the highly negative direct aerosol effect (−17 to −5 W m−2) and the small positive changes in the cloud radiative effect (+5 W m−2), attributed to the semi-direct effect. The aerosol radiative effect is also stronger in summer (−12 W m−2) than in winter (−2 W m−2). We also show that modelling aerosol–radiation and aerosol–cloud interactions can lead to small changes in cloudiness, mainly regarding low-level clouds, and circulation anomalies in the lower and mid-troposphere, which in some cases, mainly close to the Black Sea in autumn, can be of statistical significance. Precipitation is not affected in a consistent pattern throughout the year by the aerosol implementation, and changes do not exceed ±5 % except for the case of unrealistically absorbing aerosol. Temperature, on the other hand, systematically decreases by −0.1 to −0.5 ∘C due to aerosol–radiation interactions with regional changes that can be up to −1.5 ∘C.

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Droplet Clustering in Shallow Cumuli: The Effects of In–Cloud Location and Aerosol Number Concentration

10.5194/acp-2018-772 ◽

2018 ◽

Author(s):

Dillon S. Dodson ◽

Jennifer D. Small Griswold

Keyword(s):

Pair Correlation ◽

Cloud Droplet ◽

Number Concentration ◽

Atmospheric Composition ◽

Cloud Base ◽

Arrival Times ◽

Remotely Piloted Aircraft ◽

Aerosol Number Concentration ◽

Aerosol Cloud Interactions ◽

Lifetime Effects

Abstract. Aerosol–cloud interactions are complex, including albedo and lifetime effects that cause modifications to cloud characteristics. With most cloud–aerosol interactions focused on the previously stated phenomena, there has been no in–situ studies that focus explicitly on how aerosols can affect droplet clustering within clouds. This research therefore aims to gain a better understanding of how droplet clustering within cumulus clouds can be influenced by in–cloud droplet location (cloud edge vs. center) and aerosol number concentration. The pair–correlation function (PCF) is used to identify the magnitude of droplet clustering from data collected onboard the Center for interdisciplinary Remotely–Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft, flown during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS). Time stamps (at 10−4 m spatial resolution) of cloud droplet arrival times were measured by the Artium Flight Phase–Doppler Interferometer (PDI). Using four complete days of data with 81 non–precipitating cloud penetrations organized into two flights of low (L1, L2) and high (H1, H2) pollution data shows more clustering near cloud edge as compared to cloud center for all four cases. Low pollution clouds are shown to have enhanced overall clustering, with flight L2 being solely responsible for this enhanced clustering. Analysis suggests cloud age plays a larger role in the clustering amount experienced than the aerosol number concentration, with dissipating clouds showing increased clustering as compared to growing or mature clouds. Results using a single, vertically developed cumulus cloud demonstrate more clustering near cloud top as compared to cloud base.

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Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-4115-2009 ◽

2009 ◽

Vol 9 (12) ◽

pp. 4115-4129 ◽

Cited By ~ 21

Author(s):

N. Unger ◽

S. Menon ◽

D. M. Koch ◽

D. T. Shindell

Keyword(s):

Air Quality ◽

Wet Deposition ◽

Wide Spectrum ◽

Surface Ozone ◽

Tropospheric Chemistry ◽

Atmospheric Composition ◽

Sulfate Production ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions ◽

The Impact

Abstract. The development of effective emissions control policies that are beneficial to both climate and air quality requires a detailed understanding of all the feedbacks in the atmospheric composition and climate system. We perform sensitivity studies with a global atmospheric composition-climate model to assess the impact of aerosols on tropospheric chemistry through their modification on clouds, aerosol-cloud interactions (ACI). The model includes coupling between both tropospheric gas-phase and aerosol chemistry and aerosols and liquid-phase clouds. We investigate past impacts from preindustrial (PI) to present day (PD) and future impacts from PD to 2050 (for the moderate IPCC A1B scenario) that embrace a wide spectrum of precursor emission changes and consequential ACI. The aerosol indirect effect (AIE) is estimated to be −2.0 Wm−2 for PD-PI and −0.6 Wm−2 for 2050-PD, at the high end of current estimates. Inclusion of ACI substantially impacts changes in global mean methane lifetime across both time periods, enhancing the past and future increases by 10% and 30%, respectively. In regions where pollution emissions increase, inclusion of ACI leads to 20% enhancements in in-cloud sulfate production and ~10% enhancements in sulfate wet deposition that is displaced away from the immediate source regions. The enhanced in-cloud sulfate formation leads to larger increases in surface sulfate across polluted regions (~10–30%). Nitric acid wet deposition is dampened by 15–20% across the industrialized regions due to ACI allowing additional re-release of reactive nitrogen that contributes to 1–2 ppbv increases in surface ozone in outflow regions. Our model findings indicate that ACI must be considered in studies of methane trends and projections of future changes to particulate matter air quality.

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The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation

Annales Geophysicae ◽

10.1007/s00585-996-0845-5 ◽

1996 ◽

Vol 14 (8) ◽

pp. 845-852 ◽

Cited By ~ 3

Author(s):

P. F. Coley ◽

P. R. Jonas

Keyword(s):

Solar Radiation ◽

Monte Carlo Model ◽

Liquid Water Content ◽

Cloud Fraction ◽

Cloud Layer ◽

Shortwave Radiation ◽

Transmission Properties ◽

Droplet Concentration ◽

The Impact ◽

Side Illumination

Abstract. The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.

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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 ◽

Aerosol Cloud Interactions

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.

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The impact of atmospheric mineral aerosol deposition on the albedo of snow and sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-23131-2015 ◽

2015 ◽

Vol 15 (16) ◽

pp. 23131-23172

Author(s):

M. L. Lamare ◽

J. Lee-Taylor ◽

M. D. King

Keyword(s):

Optical Properties ◽

Sea Ice ◽

Atmospheric Aerosols ◽

Aerosol Deposition ◽

Shortwave Radiation ◽

Radiative Transfer Model ◽

Transfer Model ◽

Polar Regions ◽

Polar Snow ◽

The Impact

Abstract. Knowledge of the albedo of polar regions is crucial for understanding a range of climatic processes that have an impact on a global scale. Light absorbing impurities in atmospheric aerosols deposited on snow and sea ice by aeolian transport absorb solar radiation, reducing albedo. Here, the effects of five mineral aerosol deposits reducing the albedo of polar snow and sea ice are considered. Calculations employing a coupled atmospheric and snow/sea ice radiative-transfer model (TUV-snow) show that the effects of mineral aerosol deposits is strongly dependent on the snow or sea ice type rather than the differences between the aerosol optical characteristics. The change in albedo between five different mineral aerosol deposits with refractive indices varying by a factor of 2 reaches a maximum of 0.0788, whereas the difference between cold polar snow and melting sea ice is 0.8893 for the same mineral loading. Surprisingly, the thickness of a surface layer of snow or sea ice loaded with the same mass-ratio of mineral dust has little effect on albedo. On the contrary, multiple layers of mineral aerosols deposited during episodic events evenly distributed play a similar role in the surface albedo of snow as a loading distributed throughout, even when the layers are further apart. The impact of mineral aerosol deposits is much larger on melting sea ice than on other types of snow and sea ice. Therefore, the higher input of shortwave radiation during the summer melt cycle associated with melting sea ice accelerates the melt process.

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Daytime low-level clouds in West Africa – occurrence, associated drivers, and shortwave radiation attenuation

Earth System Dynamics ◽

10.5194/esd-11-1133-2020 ◽

2020 ◽

Vol 11 (4) ◽

pp. 1133-1152

Author(s):

Derrick K. Danso ◽

Sandrine Anquetin ◽

Arona Diedhiou ◽

Kouakou Kouadio ◽

Arsène T. Kobea

Keyword(s):

Solar Radiation ◽

West Africa ◽

Moisture Flux ◽

Heat Fluxes ◽

Occurrence Frequency ◽

Shortwave Radiation ◽

High Attenuation ◽

Low Level ◽

Class 1 ◽

The Impact

Abstract. This study focuses on daytime low-level clouds (LLCs) that occur within the first 2 km of the atmosphere over West Africa (WA). These daytime LLCs play a major role in the earth's radiative balance, yet their understanding is still relatively low in WA. We use the state-of-the-art ERA5 dataset to understand their occurrence and associated drivers as well as their impact on the incoming surface solar radiation in the two contrasting Guinean and Sahelian regions of WA. The diurnal cycle of the daytime occurrence of three LLC classes namely No LCC, LLC Class-1 (LLCs with lower fraction), and LLC Class-2 (LLCs with higher fraction) is first studied. The monthly evolutions of hourly and long-lasting LLC (for at least 6 consecutive hours) events are then analyzed as well as the synoptic-scale moisture flux associated with the long-lasting LLC events. Finally, the impact of LLC on the surface heat fluxes and the incoming solar irradiance is investigated. During the summer months in the Guinean region, LLC Class-1 occurrence is low, while LLC Class-2 is frequent (occurrence frequency around 75 % in August). In the Sahel, LLC Class-1 is dominant in the summer months (occurrence frequency more than 80 % from June to October); however the peak occurrence frequency of Class-2 is also in the summer. In both regions, events with No LLC do not present any specific correlation with the time of the day. However, a diurnal evolution that appears to be strongly different from one region to the other is noted for the occurrence of LLC Class-2. LLC occurrence in both regions is associated with high moisture flux driven by strong southwesterly winds from the Gulf of Guinea and significant background moisture levels. LLC Class-2 in particular leads to a significant reduction in the upward transfer of energy and a net downward energy transfer caused by the release of large amounts of energy in the atmosphere during the cloud formation. In July, August, and September (JAS), most of the LLC Class-2 events may likely be the low-level stratiform clouds that occur frequently over the Guinean region, while they may be deep convective clouds in the Sahel. Additionally, LLC Class-2 causes high attenuation of the incoming solar radiation, especially during JAS, where about 49 % and 44 % of the downwelling surface shortwave radiation is lost on average in Guinea and the Sahel, respectively.

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