scholarly journals Aerosol above-cloud direct radiative effect and properties in the Namibian region during the AErosol, RadiatiOn, and CLOuds in southern Africa (AEROCLO-sA) field campaign – Multi-Viewing, Multi-Channel, Multi-Polarization (3MI) airborne simulator and sun photometer measurements

2021 ◽  
Vol 21 (10) ◽  
pp. 8233-8253
Author(s):  
Aurélien Chauvigné ◽  
Fabien Waquet ◽  
Frédérique Auriol ◽  
Luc Blarel ◽  
Cyril Delegove ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Southern Africa ◽  
Single Scattering ◽  
Visible Range ◽  
Radiative Effect ◽  
Field Campaign ◽  
Airborne Measurements ◽  
Cloud Properties ◽  
Fine Mode ◽  
Sun Photometer

Abstract. We analyse the airborne measurements of above-cloud aerosols from the AErosol, RadiatiOn, and CLOuds in southern Africa (AEROCLO-sA) field campaign performed in Namibia during August and September 2017. The study aims to retrieve the aerosol above-cloud direct radiative effect (DRE) with well-defined uncertainties. To improve the retrieval of the aerosol and cloud properties, the airborne demonstrator of the Multi-Viewing, Multi-Channel, Multi-Polarization (3MI) satellite instrument, called the Observing System Including PolaRisation in the Solar Infrared Spectrum (OSIRIS), was deployed on-board the SAFIRE (Service des Avions Français Instrumentés pour la Rechercheen Environnement) Falcon 20 aircraft during 10 flights performed over land, over the ocean, and along the Namibian coast. The airborne instrument OSIRIS provides observations at high temporal and spatial resolutions for aerosol above clouds (AACs) and cloud properties. OSIRIS was supplemented with the Photomètre Léger Aéroporté pour la surveillance des Masses d'Air version 2 (PLASMA2). The combined airborne measurements allow, for the first time, the validation of AAC algorithms previously developed for satellite measurements. The variations in the aerosol properties are consistent with the different atmospheric circulation regimes observed during the deployment. Airborne observations typically show strong aerosol optical depth (AOD; up to 1.2 at 550 nm) of fine-mode particles from biomass burning (extinction Ångström exponent varying between 1.6 and 2.2), transported above bright stratocumulus decks (mean cloud top around 1 km above mean sea level), with cloud optical thickness (COT) up to 35 at 550 nm. The above-cloud visible AOD retrieved with OSIRIS agrees within 10 % of the PLASMA2 sun photometer measurements in the same environment. The single scattering albedo (SSA) is one of the most influential parameters on the AAC DRE calculation that remains largely uncertain in models. During the AEROCLO-sA campaign, the average SSA obtained by OSIRIS at 550 nm is 0.87, which is in agreement within 3 %, on average, with previous polarimetric-based satellite and airborne retrievals. The strong absorption of the biomass burning plumes in the visible range is generally consistent with the observations from the Aerosol Robotic Network (AERONET) ground-based sun photometers. This, however, shows a significant increase in the particles' absorption at 440 nm in northern Namibia and Angola, which indicates more absorbing organic species within the observed smoke plumes. Biomass burning aerosols are also vertically collocated, with significant amounts of water content up to the top of the plume at around 6 km height in our measurements. The detailed characterization of aerosol and cloud properties, water vapour, and their uncertainties obtained from OSIRIS and PLASMA2 measurements allows us to study their impacts on the AAC DRE. The high-absorbing load of AAC, combined with high cloud albedo, leads to unprecedented DRE estimates, which are higher than previous satellite-based estimates. The average AAC DRE calculated from the airborne measurements in the visible range is +85 W m−2 (standard deviation of 26 W m−2), with instantaneous values up to +190 W m−2 during intense events. These high DRE values, associated with their uncertainties, have to be considered as new upper cases in order to evaluate the ability of models to reproduce the radiative impact of the aerosols over the southeastern Atlantic region.

scholarly journals Aerosol and cloud properties in the Namibian region during AEROCLO-sA field campaign: 3MI airborne simulator and sun-photometer measurements

2020 ◽  
Author(s):  
Aurélien Chauvigné ◽  
Fabien Waquet ◽  
Frédérique Auriol ◽  
Luc Blarel ◽  
Cyril Delegove ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Climate Models ◽  
Single Scattering ◽  
Visible Range ◽  
Field Campaign ◽  
Airborne Measurements ◽  
Aerosol Forcing ◽  
Cloud Properties ◽  
Multi Wavelength ◽  
Sun Photometer

Abstract. We analyse of the airborne measurements of above-cloud aerosols from the AEROCLO-sA field campaign performed in Namibia during August and September 2017. To improve the retrieval of the aerosol and cloud properties, the airborne demonstrator of the Multi-viewing, Multi-channel, Multi-polarization (3MI) satellite instrument, called OSIRIS, was deployed on-board the Safire Falcon 20 aircraft during 10 flights performed over land, over the ocean and along the Namibian coast. The airborne instrument OSIRIS provides observations at high temporal and spatial resolutions for AAC and cloud properties, with well-defined uncertainties. OSIRIS was supplemented with the airborne multi-wavelength sun-photometer PLASMA2. The application of the algorithm developed for the POLDER spaceborne instrument in the visible range to the OSIRIS measurements allowed to characterise the Aerosol Above Cloud (AAC) properties. The variations of the aerosol properties are consistent with the different atmospheric circulation regimes observed during the deployment. Airborne observations typically a show strong Aerosol Optical Depth (AOD, up to 1.2 at 550 nm) of fine mode particles from biomass burning (extinction Angström exponent varying between 1.6 and 2.2), transported above a stratocumulus deck (cloud top around 1 km above mean sea level) with Cloud Optical Thickness (COT) up to 35 at 550 nm. The above-cloud visible AOD retrieved with OSIRIS agrees within 10 % with the PLASMA2 sun-photometer measured in the same environment. The AEROCLO-sA campaign-average Single Scattering Albedo (SSA) obtained by OSIRIS at 550 nm is 0.87. The strong absorption of the biomass burning plumes in the visible is consistent with the observations from the AERONET ground-based sun-photometers. The latter indicate a significant increase of the absorption at 440 nm, showing possible additional presence of absorbing organic species within the smoke plumes. Biomass burning aerosols are also vertically collocated with significant amounts of water content up to the top of the plume around 6 km height. The average AAC Direct Radiative Effect (DRE) calculated from the airborne measurements in the visible range is +85 W m−2 (standard deviation of 26 W m−2) with instantaneous values up to +200 W m−2 during intense events. Combination between water vapour and the strong positive aerosol forcing over the region explains possible feedbacks on cloud development. This new set of data represents a new opportunity to better constrain climate models and to study aerosol–cloud–radiation interactions over the South-East Atlantic region.

scholarly journals Remote sensing of soot carbon – Part 1: Distinguishing different absorbing aerosol species

2015 ◽  
Vol 15 (9) ◽  
pp. 13607-13656 ◽  
Author(s):  
G. L. Schuster ◽  
O. Dubovik ◽  
A. Arola
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Iron Oxide ◽  
South America ◽  
Biomass Burning ◽  
Southern Africa ◽  
Refractive Indices ◽  
Carbonaceous Aerosols ◽  
Fine Mode ◽  
Soot Carbon

Abstract. We describe a method of using the aerosol robotic network (AERONET) size distributions and complex refractive indices to retrieve the relative proportion of carbonaceous aerosols and iron oxide minerals. We assume that soot carbon has a spectrally flat refractive index, and that enhanced imaginary indices at the 440 nm wavelength are caused by brown carbon or hematite. Carbonaceous aerosols can be separated from dust in imaginary refractive index space because 95% of biomass burning aerosols have imaginary indices greater than 0.0042 at the 675–1020 nm wavelengths, and 95% of dust has imaginary refractive indices of less than 0.0042 at those wavelengths. However, mixtures of these two types of particles can not be unambiguously partitioned on the basis of optical properties alone, so we also separate these particles by size. Regional and seasonal results are consistent with expectations. Monthly climatologies of fine mode soot carbon are less than 1.0% by volume for West Africa and the Middle East, but the southern Africa and South America biomass burning sites have peak values of 3.0 and 1.7%. Monthly-averaged fine mode brown carbon volume fractions have a peak value of 5.8% for West Africa, 2.1% for the Middle East, 3.7% for southern Africa, and 5.7% for South America. Monthly climatologies of iron oxide volume fractions show little seasonal variability, and range from about 1.1 to 1.7% for coarse mode aerosols in all four study regions. Finally, our sensitivity study indicates that the soot carbon retrieval is not sensitive to the component refractive indices or densities assumed for carbonaceous and iron oxide aerosols, and differs by only 15.4% when these parameters are altered from our chosen baseline values. The associated soot carbon absorption aerosol optical depth (AAOD) does not vary at all when these parameters are altered, however, because the retrieval is constrained by the AERONET optical properties.

scholarly journals Retrieval of UV-Visible aerosol absorption using AERONET and OMI-MODIS synergy: Spatial and temporal variability across major aerosol environments

2021 ◽  
Author(s):  
Vinay Kayetha ◽  
Omar Torres ◽  
Hiren Jethva
Keyword(s):  
Single Scattering ◽  
Visible Range ◽  
Spatial And Temporal Variability ◽  
Ozone Monitoring Instrument ◽  
Data Set ◽  
Airborne Measurements ◽  
Aerosol Absorption ◽  
Uv Visible ◽  
Aerosol Types ◽  
Total Column

Abstract. Measuring spectral aerosol absorption remains a challenging task in aerosol studies, especially in the UV region, where the ground and airborne measurements are sparse. In this research, we introduce an algorithm that synergizes ground measurements with satellite observations for the derivation of spectral single scattering albedo (SSA, ωo) of aerosols in the UV to visible range (340–670 nm). The approach consists in explaining satellite measured near-UV radiances (340, 354 and 388 nm) by the Ozone Monitoring Instrument (OMI), and visible radiances (466 and 646 nm) by MODerate Imaging Spectrometer (MODIS), in terms of ground-based Aerosol Robotic Network (AERONET) measurements of total column extinction aerosol optical depth (AOD, τ), and retrieved total column wavelength dependent SSA using radiative transfer calculations. Required information on aerosol particle size distribution is taken from an AERONET-based climatology specifically developed for this project. This inversion procedure is applied over 110 AERONET sites distributed worldwide, for which continuous, long-term AERONET measurements are available. Using the derived data set we present seasonal and regional climatology of ωo(λ) for carbonaceous, dust and urban/industrial aerosol types. The UV-Visible spectral dependence of ωo obtained for the three major aerosol types from the synergy algorithm is found to be consistent with the in situ measurements reported in the literature. A comparison to standard AERONET SSA product at 646 nm shows absolute differences within 0.03 (0.05) for 40 % (59 %) of the compared observations. The derived aerosol ωo(λ) data set provides a valuable addition to the existing aerosol absorption record from AERONET by extending the absorption retrieval capability to the near-UV region. The combined UV-Visible data set, in addition to improving our understanding of spectral aerosol absorption properties, also offers wavelength-dependent dynamic aerosol absorption models for use in the satellite-based aerosol retrieval algorithms.

scholarly journals Biomass burning aerosol heating rates from the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) 2016 and 2017 experiments

2022 ◽  
Vol 15 (1) ◽  
pp. 61-77
Author(s):  
Sabrina P. Cochrane ◽  
K. Sebastian Schmidt ◽  
Hong Chen ◽  
Peter Pilewskie ◽  
Scott Kittelman ◽  
...  
Keyword(s):  
Heating Rate ◽  
Biomass Burning ◽  
Atmospheric Stability ◽  
Single Scattering ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Heating Rates ◽  
Water Vapor Absorption ◽  
Cloud Properties ◽  
Southeastern Atlantic

Abstract. Aerosol heating due to shortwave absorption has implications for local atmospheric stability and regional dynamics. The derivation of heating rate profiles from space-based observations is challenging because it requires the vertical profile of relevant properties such as the aerosol extinction coefficient and single-scattering albedo (SSA). In the southeastern Atlantic, this challenge is amplified by the presence of stratocumulus clouds below the biomass burning plume advected from Africa, since the cloud properties affect the magnitude of the aerosol heating aloft, which may in turn lead to changes in the cloud properties and life cycle. The combination of spaceborne lidar data with passive imagers shows promise for future derivations of heating rate profiles and curtains, but new algorithms require careful testing with data from aircraft experiments where measurements of radiation, aerosol, and cloud parameters are better colocated and readily available. In this study, we derive heating rate profiles and vertical cross sections (curtains) from aircraft measurements during the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project in the southeastern Atlantic. Spectrally resolved irradiance measurements and the derived column absorption allow for the separation of total heating rates into aerosol and gas (primarily water vapor) absorption. The nine cases we analyzed capture some of the co-variability of heating rate profiles and their primary drivers, leading to the development of a new concept: the heating rate efficiency (HRE; the heating rate per unit aerosol extinction). HRE, which accounts for the overall aerosol loading as well as vertical distribution of the aerosol layer, varies little with altitude as opposed to the standard heating rate. The large case-to-case variability for ORACLES is significantly reduced after converting from heating rate to HRE, allowing us to quantify its dependence on SSA, cloud albedo, and solar zenith angle.

scholarly journals Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

2015 ◽  
Vol 15 (8) ◽  
pp. 4179-4196 ◽  
Author(s):  
F. Peers ◽  
F. Waquet ◽  
C. Cornet ◽  
P. Dubuisson ◽  
F. Ducos ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Case Studies ◽  
Biomass Burning ◽  
Optical Thickness ◽  
Single Scattering ◽  
Original Method ◽  
Saharan Dust ◽  
Radiative Effect ◽  
Cloud Optical Thickness ◽  
The Mean

Abstract. This study presents an original method to evaluate key parameters for the estimation of the direct radiative effect (DRE) of aerosol above clouds: the absorption of the the cloud albedo. It is based on multi-angle total and polarized radiances both provided by the A-train satellite instrument POLDER – Polarization and Directionality of Earth Reflectances. The sensitivities brought by each kind of measurements are used in a complementary way. Polarization mostly translates scattering processes and is thus used to estimate scattering aerosol optical thickness and aerosol size. On the other hand, total radiances, together with the scattering properties of aerosols, are used to evaluate the absorption optical thickness of aerosols and cloud optical thickness. The retrieval of aerosol and clouds properties (i.e., aerosol and cloud optical thickness, aerosol single scattering albedo and Ångström exponent) is restricted to homogeneous and optically thick clouds (cloud optical thickness larger than 3). In addition, a procedure has been developed to process the shortwave DRE of aerosols above clouds. Three case studies have been selected: a case of absorbing biomass burning aerosols above clouds over the southeast Atlantic Ocean, a Siberian biomass burning event and a layer of Saharan dust above clouds off the northwest coast of Africa. Besides these case studies, both algorithms have been applied to the southeast Atlantic Ocean and the results have been averaged during August 2006. The mean DRE is found to be 33.5 W m−2 (warming). Finally, the effect of the heterogeneity of clouds has been investigated and reveals that it affects mostly the retrieval of the cloud optical thickness and not greatly the aerosols properties. The homogenous cloud assumption used in both the properties retrieval and the DRE processing leads to a slight underestimation of the DRE.

scholarly journals Airborne measurements of carbonaceous aerosols in southern Africa during the dry biomass burning season

2003 ◽  
Vol 108 (D13) ◽  
pp. n/a-n/a ◽  
Author(s):  
Thomas W. Kirchstetter ◽  
T. Novakov ◽  
Peter V. Hobbs ◽  
Brian Magi
Keyword(s):  
Biomass Burning ◽  
Southern Africa ◽  
Carbonaceous Aerosols ◽  
Airborne Measurements ◽  
Dry Biomass

scholarly journals Aircraft and ground measurements of dust aerosols over the west African coast in summer 2015 during ICE-D and AER-D

2018 ◽  
Vol 18 (5) ◽  
pp. 3817-3838 ◽  
Author(s):  
Dantong Liu ◽  
Jonathan W. Taylor ◽  
Jonathan Crosier ◽  
Nicholas Marsden ◽  
Keith N. Bower ◽  
...  
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Single Scattering ◽  
Effective Diameter ◽  
Radiative Effects ◽  
Airborne Measurements ◽  
Cloud Properties ◽  
The Uk ◽  
Santiago Island

Abstract. During the summertime, dust from the Sahara can be efficiently transported westwards within the Saharan air layer (SAL). This can lead to high aerosol loadings being observed above a relatively clean marine boundary layer (MBL) in the tropical Atlantic Ocean. These dust layers can impart significant radiative effects through strong visible and IR light absorption and scattering, and can also have indirect impacts by altering cloud properties. The processing of the dust aerosol can result in changes in both direct and indirect radiative effects, leading to significant uncertainty in climate prediction in this region. During August 2015, measurements of aerosol and cloud properties were conducted off the coast of west Africa as part of the Ice in Cloud Experiment – Dust (ICE-D) and AERosol properties – Dust (AER-D) campaigns. Observations were obtained over a 4-week period using the UK Facility for Atmospheric Airborne Measurements (FAAM) BAe 146 aircraft based on Santiago Island, Cabo Verde. Ground-based observations were collected from Praia (14∘57′ N, 23∘29′ W; 100 m a.s.l.), also located on Santiago Island. The dust in the SAL was mostly sampled in situ at altitudes of 2–4 km, and the potential dust age was estimated by backward trajectory analysis. The particle mass concentration (at diameter d = 0.1–20 µm) decreased with transport time. Mean effective diameter (Deff) for supermicron SAL dust (d = 1–20 µm) was found to be 5–6 µm regardless of dust age, whereas submicron Deff (d = 0.1–1 µm) showed a decreasing trend with longer transport. For the first time, an airborne laser-induced incandescence instrument (the single particle soot photometer – SP2) was deployed to measure the hematite content of dust. For the Sahel-influenced dust in the SAL, the observed hematite mass fraction of dust (FHm) was found to be anti-correlated with the single scattering albedo (SSA, λ = 550 nm, for particles d < 2.5 µm); as potential dust age increased from 2 to 7 days, FHm increased from 2.5 to 4.5 %, SSA decreased from 0.97 to 0.93 and the derived imaginary part (k) of the refractive index at 550 nm increased from 0.0015 to 0.0035. However, the optical properties of Sahara-influenced plumes (not influenced by the Sahel) were independent of dust age and hematite content with SSA ∼ 0.95 and k ∼ 0.0028. This indicates that the absorbing component of dust may be source dependent, or that gravitational settling of larger particles may lead to a higher fraction of more absorbing clay–iron aggregates at smaller sizes. Mie calculation using the measured size distribution and size-resolved refractive indices of the absorbing components (black carbon and hematite) reproduces the measured SSA to within ±0.02 for SAL dust by assuming a goethite ∕ hematite mass ratio of 2. Overall, hematite and goethite constituted 40–80 % of the absorption for particles d < 2.5 µm, and black carbon (BC) contributed 10–37 %. This highlights the importance of size-dependent composition in determining the optical properties of dust and also the contribution from BC within dust plumes.

scholarly journals Radiative budget in the presence of multi-layered aerosol structures in the framework of AMMA SOP-0

2008 ◽  
Vol 8 (4) ◽  
pp. 12461-12528 ◽  
Author(s):  
J.-C. Raut ◽  
P. Chazette
Keyword(s):  
Biomass Burning ◽  
Asymmetry Parameter ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Accurate Determination ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Visible Range ◽  
Atmospheric Measurements ◽  
Dust Aerosols

Abstract. This paper presents radiative transfer calculations performed over Niamey in the UV-Visible range over the period 26th January – 1st February during the African Multidisciplinary Monsoon Analysis (AMMA) international program. Climatic effects of aerosols along the vertical column have required an accurate determination of their optical properties, which are presented in for a variety of instrumented platforms: Ultralight aircraft, Facility for Airborne Atmospheric Measurements (FAAM) research aircraft, AERONET station. Measurements highlighted the presence of a multi-layered structure of mineral dust located below and biomass-burning particles in the more elevated layers. Radiative forcing was affected by both the scattering and absorption effects governed by the aerosol complex refractive index (ACRI). The best agreement between our results and AERONET optical thicknesses, ground-based extinction measurements and NO2 photolysis rate coefficient was found using the synergy between all the instrumented platforms. The corresponding averaged ACRI were 1.53 (±0.04)–0.047i (±0.006) and 1.52 (±0.04)–0.008i (±0.001) for biomass-burning and mineral dust aerosols, respectively. Biomass-burning aerosols were characterized by single-scattering albedo ranging from 0.78 to 0.82 and asymmetry parameter ranging from 0.71 to 0.73. For dust aerosols, single-scattering albedo (asymmetry parameter) ranged from 0.9 to 0.92 (0.73 to 0.75). The solar energy depletion at the surface is shown to be ~ −21.2 (±1.7) W/m2 as a daily average. At the TOA, the radiative forcing appeared slightly negative but very close to zero (~ −1.4 W/m2). The corresponding atmospheric radiative forcing was found to be ~19.8 (±2.3) W/m2. Mineral dust located below a more absorbing layer act as an increase in surface reflectivity of ~3–4%. The radiative forcing is also shown to be highly sensitivity the optical features of the different aerosol layers (ACRI, optical thickness and aerosol vertical distribution).

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