Satellite inference of water vapor and aerosol-above-cloud combined effect on radiative budget and cloud top processes in the Southeast Atlantic Ocean

Deaconu, Lucia; Ferlay, Nicolas; Waquet, Fabien; Peers, Fanny; Thieuleux, F.; Goloub, Philippe

doi:10.5194/acp-2019-189

Cited by 4 publications

(9 citation statements)

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“…The mean AEROCLO-sA instantaneous DRE value is +85 W m -2 for AAC. Our observations are in agreement with previous studies indicating a strong positive aerosol forcing over the region (De Graaf et al, 2019b, 2020 with possible feedbacks on cloud development due to both aerosol and water vapour combined 440 radiative effects (Deaconu et al, 2019). However, the aerosol DRE on the AEROCLO-sA region is higher than the mean DRE observed in the southern Atlantic region, mainly because of the exceptional atmospheric conditions sampled during the flights (high loads of absorbing aerosols and high cloud albedo).…”

supporting

confidence: 92%

“…The highest column concentrations of water vapour (up to 2.4 g cm -2 ) are observed for the two flights of 8 September. This correlation could be explained by the meteorological conditions, which would be responsible for the simultaneous transport of aerosols and water vapour (Adebiyi et al, 2015, Deaconu et al, 2019, or by the wood moisture emitted in tropical area, biomass burning can also generate water vapour (Betts and Silva Dias, 2010;Sena et al, 2013). The variability observed in the relationship between AOD and water vapour through PLASMA2 measurements could also be the result of https://doi.org/10.5194/acp-2020-992 Preprint.…”

Section: Integrated Water Contentmentioning

confidence: 99%

“…It shows that the method allows to robustly model the selected data within the measurements noise. For these values of scattering angles, the sensitivity of polarization to cloud microphysics is minimized and the cloud droplet effective radius is assumed to be equal to 10 microns, which is the mean value for the stratocumulus clouds observed over 180 the domain of interest (Deaconu et al, 2019).…”

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confidence: 99%

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

Chauvigné

Waquet

Auriol

et al. 2020

Preprint

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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.

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supporting

confidence: 92%

Section: Integrated Water Contentmentioning

confidence: 99%

mentioning

confidence: 99%

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

Chauvigné

Waquet

Auriol

et al. 2020

Preprint

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“…As a consequence, boundary layer relative humidity is preserved and cloud coverage maintained. This could lead to an increase of LWP, optically thicker clouds, and therefore an additional cooling semi-direct effect -potentially of comparable magnitude to the warming BBA direct radiative effect, resulting in both the sign and the magnitude of the total BBA radiative effect remaining unclear (Deaconu et al, 2019;Sakaeda et al, 2011;Wilcox, 2010Wilcox, , 2012. Previous efforts https://doi.org/10.5194/acp-2020-532 Preprint.…”

Section: Introductionmentioning

confidence: 99%

The significant role of biomass burning aerosols in clouds and radiation in the South-eastern Atlantic Ocean

Che

Stier

Gordon

et al. 2020

Preprint

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Abstract. The South-eastern Atlantic Ocean (SEA) is semi-permanently covered by one of the most extensive stratocumulus cloud decks on the planet and experiences about one-third of the global biomass burning emissions from the southern Africa savannah region during the fire season. To get a better understanding of the impact of these biomass burning aerosols on clouds and radiation balance over the SEA, the latest generation of the UK Earth System Model (UKESM1) is employed. Measurements from the CLARIFY and ORACLES flight campaigns are used to evaluate the model, demonstrating that the model has good skill in reproducing the biomass burning plume. To investigate the underlying mechanisms in detail, the effects of biomass burning aerosols on the clouds are decomposed into radiative effects (via absorption and scattering) and microphysical effects (via perturbation of cloud condensation nuclei (CCN) and cloud microphysical processes). The July–August means are used to characterise aerosols, clouds and the radiation balance during the fire season. Results show around 68 % of CCN at 0.2 % supersaturation in the SEA domain can be attributed to biomass burning. The absorption effect of biomass burning aerosols is the most significant in affecting clouds and radiation. Near the continent it increases the maximum supersaturation diagnosed by the activation scheme, while further from the continent it reduces the altitude of the maximum supersaturation. As a result, the cloud droplet number concentration shows a similar pattern. The microphysical effect of biomass burning aerosols decreases the maximum supersaturation and increases the cloud droplets concentration over the ocean; however, this change is relatively small. The liquid water path is also significantly increased over the SEA (mainly caused by the absorption effect of biomass burning aerosols) when biomass burning aerosols are above the stratocumulus cloud deck. The microphysical pathways lead to a slight increase in the liquid water path over the ocean. These changes in cloud properties indicate the significant role of biomass burning aerosols on clouds in this region. Among the effects of biomass burning aerosols on radiation balance, the semi-direct radiative effects (rapid adjustments induced by biomass burning aerosols radiative effects) have a dominant cooling impact over the SEA, which offset the warming direct radiative effect (radiative forcing from biomass burning aerosol–radiation interactions). However, the magnitude and the sign of the semi-direct effects are dependent on the relative location of biomass burning aerosols and clouds. The net biomass burning aerosols radiative effect shows a negative cooling effect in the SEA, indicating the significant role of biomass burning aerosols in affecting the regional radiation balance and climate.

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“…Shortwave-absorbing aerosols above the southeast Atlantic overlay and mix in with one of the earth's largest stratocumulus deck from July through October. Many studies highlight the presence and radiative impact of the absorbing aerosol in the free troposphere (Waquet et al, 2013;Peers et al, 2015;Das et al, 2017;Sayer et al, 2019;Peers et al, 2019;Deaconu et al, 2019), and indeed recent aircraft measurements confirm this for the month of September (LeBlanc et al, 2019;Cochrane et al, 2019).…”

Section: Introductionmentioning

confidence: 95%

Low cloud reduction within the smoky marine boundary layer and the diurnal cycle

Zhang

Zuidema

2019

Preprint

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Abstract. Previous observational studies of the southeast Atlantic emphasize an increase in the stratocumulus cloud cover when shortwave-absorbing aerosols are present in the free-troposphere. Recent field measurements at Ascension Island (8&#176;&#8201;S, 14.5&#176;&#8201;W) reveal that smoke is also often present in the marine boundary layer, most evident in August when the smoke is highly absorbing of sunlight, the boundary layer is deeper, the cloud-top inversion is weaker, and a climatologically lower cloud fraction eases penetration of the sunlight to the surface, compared to later months. In these conditions, the low cloud cover decreases further with enhanced smoke loadings, reflecting a boundary layer semi-direct effect that is a positive feedback. The low cloud cover reduction is particularly pronounced in the afternoon, although the cloud liquid water path is more strongly reduced at night. The daily-mean surface-based mixed layer is warmer by approximately 0.5&#8201;K when more smoke is present in the boundary layer, with a warming peak in the late afternoon when the cloud cover reduction is largest. After sunset, sub-cloud moisture accumulates throughout the night, increasing the moisture stratification with the cloud layer. This increase in boundary layer decoupling is consistent with reduced turbulence. A new observation is that in the sunlit morning hours, the smokier boundary layer deepens by approximately 200&#8201;m, and both the liquid water paths and cloud top heights increase. We speculate this reflects radiatively-induced vertical ascent originating from within a well-mixed smoke-filled sub-cloud layer. Overall, the reduction in daytime low cloud decreases the top-of-atmosphere all-sky albedo, despite an increase in the top-of-atmosphere direct aerosol radiation of ~&#8201;6.5&#8201;W&#8201;m2 between the (most-least) smoky tercile composites. A convolving meteorological influence is also apparent near the cloud top, in that, although the free troposphere is also often smoky in August, the associated above-cloud potential temperatures are often cooler, rather than warmer, and better-mixed. The cooling weakens the inversion beyond that expected from the warming of the boundary layer and further encourages entrainment of more smoke into the already smoky boundary layer, increasing the longevity of the boundary layer smoke events. The free-tropospheric winds are also typically stronger and more easterly. More smoke appears to settle into the sub-cloud layer during the day than at night when it is smoky, speculated to reflect a deeper daytime sub-cloud layer facilitating entrainment, when the nighttime stratification does not.

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Satellite inference of water vapor and aerosol-above-cloud combined effect on radiative budget and cloud top processes in the Southeast Atlantic Ocean

Cited by 4 publications

References 50 publications

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

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

The significant role of biomass burning aerosols in clouds and radiation in the South-eastern Atlantic Ocean

Low cloud reduction within the smoky marine boundary layer and the diurnal cycle

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