The CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) measurement campaign

Haywood, Jim M.; Abel, Steven J.; Barrett, Paul A.; Bellouin, Nicolas; Blyth, Alan; Bower, Keith; Brooks, M. E.; Carslaw, K. S.; Che, Haochi; Coe, Hugh; Cotterell, Michael I.; Crawford, Ian; Cui, Zhiqiang; Davies, Nicholas W.; Dingley, Beth; Field, Paul R.; Formenti, Paola; Gordon, Hamish; Graaf, M. de; Herbert, Ross; Johnson, Ben; Jones, Anthony C.; Langridge, Justin M.; Malavelle, Florent; Partridge, Daniel G.; Peers, Fanny; Redemann, J.; Stier, Philip; Szpek, Kate; Taylor, Jonathan; Watson-Parris, Duncan; Wood, Robert; Wu, Huihui; Zuidema, Paquita

doi:10.5194/acp-21-1049-2021

Cited by 87 publications

(87 citation statements)

References 140 publications

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“…Keil and Haywood, 2003). While lidar retrievals of aerosols above cloud have been available for some time from the active CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) instrument (Hu et al, 2007;Chand et al, 2008;Liu et al, 2015), retrievals of aerosols from passive instrumentation have also been developed. Studies based on the OMI (Ozone Monitoring Instrument; Torres et al, 2012; de Graaf et al, 2019), SCIAMACHY (SCanning Imaging Absorption SpectroMeter for Atmospheric CHar-tographY; de Graaf et al, 2012), MODIS (MODerate resolution Imaging Spectroradiometer; Jethva et al, 2013;Meyer et al, 2015;Sayer et al, 2016) and POLDER (POLarization and Directionality of the Earth's Reflectances; Waquet et al, 2013;Peers et al, 2015) satellite instruments have already demonstrated the potential of retrieving both cloud properties and above-cloud aerosol optical thickness (AOT) from passive sensors or deriving the direct radiative effect of aerosols above clouds.…”

Section: Introductionmentioning

confidence: 99%

Observation of absorbing aerosols above clouds over the south-east Atlantic Ocean from the geostationary satellite SEVIRI – Part 2: Comparison with MODIS and aircraft measurements from the CLARIFY-2017 field campaign

et al. 2021

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Abstract. To evaluate the SEVIRI retrieval for aerosols above clouds presented in Part 1 of the companion paper, the algorithm is applied over the south-east Atlantic Ocean during the CLARIFY-2017 field campaign period. The first step of our analysis compares the retrieved aerosol and cloud properties against equivalent products from the MODIS MOD06ACAERO retrieval (Meyer et al., 2015). While the correlation between the two satellite retrievals of the above-cloud aerosol optical thickness (AOT) is good (R = 0.78), the AOT retrieved by SEVIRI is 20.3 % smaller than that obtained from the MODIS retrieval. This difference in AOT is attributed mainly to the more absorbing aerosol model assumed for the SEVIRI retrieval compared to MODIS. The underlying cloud optical thickness (COT) derived from the two satellites is in good agreement (R = 0.90). The cloud droplet effective radius (CER) retrieved by SEVIRI is consistently smaller than MODIS by 2.2 µm, which is mainly caused by the use of different spectral bands of the satellite instruments. In the second part of our analysis, we compare the forecast water vapour profiles used for the SEVIRI atmospheric correction as well as the aforementioned aerosol and cloud products with in situ measurements made from the Facility for Airborne Atmospheric Measurements (FAAM) aircraft platform during the CLARIFY-2017 campaign. Around Ascension Island, the column water vapour used to correct the SEVIRI signal is overestimated by 3.1 mm in the forecast compared to that measured by dropsondes. However, the evidence suggests that the accuracy of the atmospheric correction improves closer to the African coast. Consistency is observed between the SEVIRI above-cloud AOT and in situ measurements (from cavity ring-down spectroscopy instruments) when the measured single-scattering albedo is close to that assumed in the retrieval algorithm. On the other hand, the satellite retrieval overestimates the AOT when the assumed aerosol model is not absorbing enough. Consistency is also found between the cloud properties retrieved by SEVIRI and the CER measured by a cloud droplet probe and the liquid water path derived from a microwave radiometer. Despite the instrumental limitations of the geostationary satellite, the consistency obtained between SEVIRI, MODIS and the aircraft measurements demonstrates the ability of the retrieval in providing additional information on the temporal evolution of the aerosol properties above clouds.

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Section: Introductionmentioning

confidence: 99%

Observation of absorbing aerosols above clouds over the south-east Atlantic Ocean from the geostationary satellite SEVIRI – Part 2: Comparison with MODIS and aircraft measurements from the CLARIFY-2017 field campaign

et al. 2021

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“…The large uncertainty in aerosol climate forcing in the SE Atlantic was the impetus for the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project, funded through the NASA Earth Venture Suborbital (EVS-2) program , as well as complementary campaigns (Zuidema et al, 2016;Formenti et al, 2019;Haywood et al, 2021). The ORACLES project explicitly measured aerosol properties necessary to calculate the direct aerosol radiative effect (DARE).…”

Section: Introductionmentioning

confidence: 99%

“…The WRF-CAM5 and GEOS models are included because they were used for aerosol and meteorological forecasting during the ORACLES campaign. Similarly, the UM-UKCA modeling team participated in the U.K. CLARIFY (Cloud-Aerosol-Radiation Interactions and Forcing) campaign, which deployed out of Ascension Island (Figure 1) in 2017 (Haywood et al, 2021). In 2016 both ORACLES and the French AEROCLO-SA (AEROsol radiation and CLOuds in 110 Southern Africa; Formenti et al, 2019) campaign deployed out of Walvis Bay, Namibia, with the latter focusing on nearcoast aerosols.…”

Section: Introductionmentioning

confidence: 99%

Modeled and observed properties related to the direct aerosol radiative effect of biomass burning aerosol over the Southeast Atlantic

Doherty¹,

Saide²,

Zuidema³

et al. 2021

Preprint

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Abstract. Biomass burning smoke is advected over the southeast Atlantic Ocean between July and October of each year. This smoke plume overlies and mixes into a region of persistent low marine clouds. Model calculations of climate forcing by this plume vary significantly, in both magnitude and sign. The NASA EVS-2 (Earth Venture Suborbital-2) ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project deployed for field campaigns off the west coast of Africa in three consecutive years (Sept., 2016; Aug., 2017; and Oct., 2018) with the goal of better characterizing this plume as a function of the monthly evolution, by measuring the parameters necessary to calculate the direct aerosol radiative effect. Here, this dataset and satellite retrievals of cloud properties are used to test the representation of the smoke plume and the underlying cloud layer in two regional models (WRF-CAM5 and CNRM-ALADIN) and two global models (GEOS and UM-UKCA). The focus is on comparisons of those aerosol and cloud properties that are the primary determinants of the direct aerosol radiative effect, and on the vertical distribution of the plume and its properties. The representativeness of the observations to monthly averages are tested for each field campaign, with the sampled mean aerosol light extinction generally found to be within 20 % of the monthly mean at plume altitudes. When compared to the observations, in all models the simulated plume is too vertically diffuse, has smaller vertical gradients, and, in two of the models (GEOS and UM-UKCA), the plume core is displaced lower than in the observations. Plume carbon monoxide, black carbon, and organic aerosol masses indicate under-estimates in modeled plume concentrations, leading in general to under-estimates in mid-visible aerosol extinction and optical depth. Biases in mid-visible single scatter albedo are both positive and negative across the models. Observed vertical gradients in single scatter albedo are not captured by the models, but the models do capture the coarse temporal evolution, correctly simulating higher values in October (2018) than in August (2018) and September (2017). Uncertainties in the measured absorption Ångstrom exponent were large but propagate into a negligible (<4 %) uncertainty in integrated solar absorption by the aerosol and therefore in the aerosol direct radiative effect. Model biases in cloud fraction, and therefore the scene albedo below the plume, vary significantly across the four models. The optical thickness of clouds is, on average, well simulated in the WRF-CAM5 and ALADIN models in the stratocumulus region and is under-estimated in the GEOS model; UM-UKCA simulates significantly too-high cloud optical thickness. Overall, the study demonstrates the utility of repeated, semi-random sampling across multiple years that can give insights into model biases and how these biases affect modeled climate forcing. The combined impact of these aerosol and cloud biases on the direct aerosol radiative effect (DARE) is estimated using a first-order approximation for a sub-set of five comparison gridboxes. A significant finding is that the observed gridbox-average aerosol and cloud properties yield a positive (warming) aerosol direct radiative effect for all five gridboxes, whereas DARE using the gridbox-averaged modeled properties ranges from much larger positive values to small, negative values. It is shown quantitatively how model biases can offset each other, so that model improvements that reduce biases in only one property (e.g., single scatter albedo, but not cloud fraction) would lead to even greater biases in DARE. Across the models, biases in aerosol extinction and in cloud fraction and optical depth contribute the largest biases in DARE, with aerosol single scatter albedo also making a significant contribution.

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“…The ORACLES campaign looks into aerosol-cloud interactions over the southeast Atlantic throughout the majority (August 2017, September 2016 and October 2018) of the biomass burning season (Zuidema et al, 2016;Cochrane et al, 2019;Pistone et al, 2019). CLouds and Aerosol Radiative Impacts and Forcing for Year 2017 (CLARIFY-2017) aimed to better represent the radiative and microphysical properties of stratocumulus clouds as they transition to cumulus clouds (Haywood et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Impacts of aerosols produced by biomass burning on the stratocumulus‐to‐cumulus transition in the equatorial Atlantic

Ajoku

Miller

Norris

2021

Atmospheric Science Letters

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The impact of aerosols produced by biomass burning on the stratocumulus-tocumulus transition (SCT) in the equatorial Atlantic is studied using satellitebased and reanalysis data for the month of June. The month of June is highlighted because it represents monsoon onset as well as the largest sea surface temperature gradient in the summer, which is the peak season of tropical African biomass burning. Boundary layer deepening and increasing temperatures put the location of the SCT within the Gulf of Guinea. Satellite retrievals indicate that the bulk of aerosols occur near 1,500 m in altitude, either above or below the boundary layer depending on latitudinal position. Changes in smoke loading over the Gulf of Guinea due to greater transport from southern Africa leads to increases in low-level cloud cover above cloud decks and decreases when mixed within the boundary layer. Further south, we find significant changes to temperature, cloud top height, tropospheric stability and moisture availability near maximum aerosol loading. In addition, changes in vertical velocity during dirty conditions further reinforce changes in tropospheric stability. These effects combine to shorten the SCT in space during increased aerosol loading episodes.

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The CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) measurement campaign

Cited by 87 publications

References 140 publications

Observation of absorbing aerosols above clouds over the south-east Atlantic Ocean from the geostationary satellite SEVIRI – Part 2: Comparison with MODIS and aircraft measurements from the CLARIFY-2017 field campaign

Observation of absorbing aerosols above clouds over the south-east Atlantic Ocean from the geostationary satellite SEVIRI – Part 2: Comparison with MODIS and aircraft measurements from the CLARIFY-2017 field campaign

Modeled and observed properties related to the direct aerosol radiative effect of biomass burning aerosol over the Southeast Atlantic

Impacts of aerosols produced by biomass burning on the stratocumulus‐to‐cumulus transition in the equatorial Atlantic

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