scholarly journals Radiative Heating Rate Profiles over the Southeast Atlantic Ocean during the 2016 and 2017 Biomass Burning Seasons

2020 ◽  
Author(s):  
Allison B. Marquardt Collow ◽  
Mark A. Miller ◽  
Lynne C. Trabachino ◽  
Michael P. Jensen ◽  
Meng Wang
Keyword(s):  
Atlantic Ocean ◽  
Heating Rate ◽  
Biomass Burning ◽  
Radiative Heating ◽  
Aerosol Layer ◽  
Field Campaign ◽  
Cloud Structure ◽  
Ascension Island ◽  
Biomass Burning Aerosol ◽  
Aerosol Plume

Abstract. Marine boundary layer clouds, including the transition from stratocumulus to cumulus, are poorly represented in numerical weather prediction and general circulation models. Further uncertainties in the cloud structure arise in the presence of biomass burning carbonaceous aerosol, as is the case over the southeast Atlantic Ocean where biomass burning aerosol is transported from the African continent. As the aerosol plume progresses across the southeast Atlantic Ocean, radiative heating within the aerosol layer has the potential to alter the thermodynamic environment and therefore the cloud structure; however, this has yet to be quantified. The deployment of the First Atmospheric Radiation Measurement Mobile Facility (AMF1) in support of the Layered Atlantic Smoke Interactions with Clouds (LASIC) field campaign provided a unique opportunity to collect observations of cloud and aerosol properties during two consecutive biomass burning seasons during July through October of 2016 and 2017 over Ascension Island (7.96 S, 14.35 W). Using observed profiles of temperature, humidity, and clouds from the LASIC field campaign, alongside aerosol optical properties from the Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) as input for the Rapid Radiation Transfer Model (RRTM), profiles of the radiative heating rate due to aerosols and clouds were computed. Radiative heating is also assessed across the southeast Atlantic Ocean using an ensemble of back trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). Idealized experiments using RRTM with and without aerosols and a range of values for the single scattering albedo demonstrate that shortwave (SW) heating within the aerosol layer above Ascension Island can locally range between 2 and 8 K per day, though impacts of the aerosol can be felt elsewhere in the atmospheric column. SW radiative heating due to biomass burning aerosol is not balanced by additional longwave cooling, and the net radiative impact results in a stabilization of the lower troposphere. However, these results are extremely sensitive to the single scatter albedo and the height of the aerosol plume with respect to the inversion layer.

scholarly journals Radiative heating rate profiles over the southeast Atlantic Ocean during the 2016 and 2017 biomass burning seasons

2020 ◽  
Vol 20 (16) ◽  
pp. 10073-10090
Author(s):  
Allison B. Marquardt Collow ◽  
Mark A. Miller ◽  
Lynne C. Trabachino ◽  
Michael P. Jensen ◽  
Meng Wang
Keyword(s):  
Optical Properties ◽  
Atlantic Ocean ◽  
Biomass Burning ◽  
Single Scattering ◽  
Radiative Heating ◽  
Aerosol Layer ◽  
Aerosol Optical Properties ◽  
Ascension Island ◽  
Biomass Burning Aerosol ◽  
Aerosol Plume

Abstract. Marine boundary layer clouds, including the transition from stratocumulus to cumulus, are poorly represented in numerical weather prediction and general circulation models. Further uncertainties in the cloud structure arise in the presence of biomass burning carbonaceous aerosol, as is the case over the southeast Atlantic Ocean, where biomass burning aerosol is transported from the African continent. As the aerosol plume progresses across the southeast Atlantic Ocean, radiative heating within the aerosol layer has the potential to alter the thermodynamic environment and therefore the cloud structure; however, limited work has been done to quantify this along the trajectory of the aerosol plume in the region. The deployment of the first Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF1) in support of the Layered Atlantic Smoke Interactions with Clouds field campaign provided a unique opportunity to collect observations of cloud and aerosol properties during two consecutive biomass burning seasons during July through October of 2016 and 2017 over Ascension Island (7.96∘ S, 14.35∘ W). Using observed profiles of temperature, humidity, and clouds from the field campaign alongside aerosol optical properties from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), as input for the Rapid Radiation Transfer Model (RRTM), profiles of the radiative heating rate due to aerosols and clouds were computed. Radiative heating is also assessed across the southeast Atlantic Ocean using an ensemble of back trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Idealized experiments using the RRTM with and without aerosols and a range of values for the single-scattering albedo (SSA) demonstrate that shortwave (SW) heating within the aerosol layer above Ascension Island can locally range between 2 and 8 K d−1 depending on the aerosol optical properties, though impacts of the aerosol can be felt elsewhere in the atmospheric column. When considered under clear conditions, the aerosol has a cooling effect at the TOA, and based on the observed cloud properties at Ascension Island, the cloud albedo is not large enough to overcome this. Shortwave radiative heating due to biomass burning aerosol is not balanced by additional longwave (LW) cooling, and the net radiative impact results in a stabilization of the lower troposphere. However, these results are extremely sensitive to the single-scattering albedo assumptions in models.

scholarly journals Above Cloud Aerosol Optical Depth from airborne observations in the South-East Atlantic

2019 ◽  
Author(s):  
Samuel E. LeBlanc ◽  
Jens Redemann ◽  
Connor Flynn ◽  
Kristina Pistone ◽  
Meloë Kacenelenbogen ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biomass Burning ◽  
Aerosol Layer ◽  
The South ◽  
East Atlantic ◽  
Vertical Column ◽  
Biomass Burning Aerosol ◽  
Aerosol Plume

Abstract. The South-East Atlantic (SEA) is host to a climatologically significant biomass burning aerosol layer overlying marine stratocumulus. We present directly measured Above Cloud Aerosol Optical Depth (ACAOD) from the recent ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) airborne field campaign during August and September 2016. In our analysis, we use data from the Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) instrument and found an average ACAOD of 0.32 at 501 nm, with an average Ångström exponent (AE) of 1.71. The AE is much lower at 1.25 for the full column (including below cloud level aerosol), indicating the presence of large aerosol particles, likely marine aerosol, embedded within the vertical column. ACAOD is observed to be highest near coast at about 12° S, whereas its variability is largest at the southern edge of the average aerosol plume, as indicated by 12 years of MODIS observations. In comparison to MODIS derived ACAOD and long term fine-mode plume-average AOD, the directly-measured ACAOD from 4STAR is slightly lower than the ACAOD product from MODIS. The peak ACAOD expected from long term retrievals is measured to be closer to coast in 2016 at about 1.5°–4° W. By spatially binning the sampled AOD, we obtain a mean ACAOD of 0.37 for the SEA region. Vertical profiles of AOD showcase the variability of the altitude of the aerosol plume and its separation from cloud top. We measured larger AOD at high altitude near coast than farther from coast, while generally observing a larger vertical gap further from coast. Changes of AOD with altitude are correlated with a gas tracer of the biomass burning aerosol plume. Vertical extent of gaps between aerosol and cloud show a large distribution of extent, dominated by near zero gap. The gap distribution with longitude is observed to be largest at about 7° W, farther from coast than expected.

scholarly journals Above-cloud aerosol optical depth from airborne observations in the southeast Atlantic

2020 ◽  
Vol 20 (3) ◽  
pp. 1565-1590 ◽  
Author(s):  
Samuel E. LeBlanc ◽  
Jens Redemann ◽  
Connor Flynn ◽  
Kristina Pistone ◽  
Meloë Kacenelenbogen ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biomass Burning ◽  
Wide Distribution ◽  
Aerosol Layer ◽  
Modis Aod ◽  
First Results ◽  
Biomass Burning Aerosol ◽  
Aerosol Plume

Abstract. The southeast Atlantic (SEA) region is host to a climatologically significant biomass burning aerosol layer overlying marine stratocumulus. We present the first results of the directly measured above-cloud aerosol optical depth (ACAOD) from the recent ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) airborne field campaign during August and September 2016. In our analysis, we use data from the Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) instrument and found an average ACAOD of 0.32 at 501 nm (range of 0.02 to 1.04), with an average Ångström exponent (AE) above clouds of 1.71. The AE is much lower at 1.25 for the full column (including below-cloud-level aerosol, with an average of 0.36 at 501 nm and a range of 0.02 to 0.74), indicating the presence of large aerosol particles, likely marine aerosol, in the lower atmospheric column. The ACAOD is observed from 4STAR to be highest near the coast at about 12∘ S, whereas its variability is largest at the southern edge of the average aerosol plume, as indicated by 12 years of MODIS observations. In comparison to MODIS-derived ACAOD and long-term fine-mode plume-average AOD along a diagonal routine track extending out from the coast of Namibia, the directly measured ACAOD from 4STAR is slightly lower than the ACAOD product from MODIS. The peak ACAOD expected from MODIS AOD retrievals averaged over a long term along the routine diagonal flight track (peak of 0.5) was measured to be closer to coast in 2016 at about 1.5–4∘ E, with 4STAR ACAOD averages showing a peak of 0.42. When considering the full observation set over the SEA, by spatially binning each sampled AOD, we obtain a geographically representative mean ACAOD of 0.37. Vertical profiles of AOD showcase the variability in the altitude of the aerosol plume and its separation from the cloud top. We measured larger AOD at a high altitude near the coast than farther from the coast, while generally observing a larger vertical gap farther from the coast. Changes in AOD with altitude are correlated with carbon monoxide, a gas tracer of the biomass burning aerosol plume. Vertical extent of gaps between aerosol and cloud show a wide distribution, with a near-zero gap being most frequent. The gap distribution with longitude is observed to be largest at about 7∘ E, farther from coast than expected from previous studies.

scholarly journals Remote biomass burning dominates southern West African air pollution during the monsoon

2019 ◽  
Vol 19 (24) ◽  
pp. 15217-15234 ◽  
Author(s):  
Sophie L. Haslett ◽  
Jonathan W. Taylor ◽  
Mathew Evans ◽  
Eleanor Morris ◽  
Bernhard Vogel ◽  
...  
Keyword(s):  
Air Pollution ◽  
West Africa ◽  
Atlantic Ocean ◽  
Biomass Burning ◽  
West African ◽  
Small Scale ◽  
High Background ◽  
Accumulation Mode ◽  
Aerosol Loading ◽  
Biomass Burning Aerosol

Abstract. Vast stretches of agricultural land in southern and central Africa are burnt between June and September each year, which releases large quantities of aerosol into the atmosphere. The resulting smoke plumes are carried west over the Atlantic Ocean at altitudes between 2 and 4 km. As only limited observational data in West Africa have existed until now, whether this pollution has an impact at lower altitudes has remained unclear. The Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) aircraft campaign took place in southern West Africa during June and July 2016, with the aim of observing gas and aerosol properties in the region in order to assess anthropogenic and other influences on the atmosphere. Results presented here show that a significant mass of aged accumulation mode aerosol was present in the southern West African monsoon layer, over both the ocean and the continent. A median dry aerosol concentration of 6.2 µg m−3 (standard temperature and pressure, STP) was observed over the Atlantic Ocean upwind of the major cities, with an interquartile range from 5.3 to 8.0 µg m−3. This concentration increased to a median of 11.1 µg m−3 (8.6 to 15.7 µg m−3) in the immediate outflow from cities. In the continental air mass away from the cities, the median aerosol loading was 7.5 µg m−3 (5.9 to 10.5 µg m−3). The accumulation mode aerosol population over land displayed similar chemical properties to the upstream population, which implies that upstream aerosol is a significant source of aerosol pollution over the continent. The upstream aerosol is found to have most likely originated from central and southern African biomass burning. This demonstrates that biomass burning plumes are being advected northwards, after being entrained into the monsoon layer over the eastern tropical Atlantic Ocean. It is shown observationally for the first time that they contribute up to 80 % to the regional aerosol loading in the monsoon layer over southern West Africa. Results from the COSMO-ART (Consortium for Small-scale Modeling – Aerosol and Reactive Trace gases) and GEOS-Chem models support this conclusion, showing that observed aerosol concentrations over the northern Atlantic Ocean can only be reproduced when the contribution of transported biomass burning aerosol is taken into account. As a result, the large and growing emissions from the coastal cities are overlaid on an already substantial aerosol background. Simulations using COSMO-ART show that cloud droplet number concentrations can increase by up to 27 % as a result of transported biomass burning aerosol. On a regional scale this renders cloud properties and precipitation less sensitive to future increases in anthropogenic emissions. In addition, such high background loadings will lead to greater pollution exposure for the large and growing population in southern West Africa. These results emphasise the importance of including aerosol from across country borders in the development of air pollution policies and interventions in regions such as West Africa.

scholarly journals Vertical structure of biomass burning aerosol transported over the southeast Atlantic Ocean

2021 ◽  
Author(s):  
Harshvardhan Harshvardhan ◽  
Richard Ferrare ◽  
Sharon Burton ◽  
Johnathan Hair ◽  
Chris Hostetler ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
High Spectral Resolution ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Microphysical Properties ◽  
Stratocumulus Clouds ◽  
Fine Mode ◽  
Cloud Tops

Abstract. Biomass burning in southwestern Africa produces smoke plumes that are transported over the Atlantic Ocean and overlie vast regions of stratocumulus clouds. This aerosol layer contributes to direct and indirect radiative forcing of the atmosphere in this region, particularly during the months of August, September and October. There was a multi-year international campaign to study this aerosol and its interactions with clouds. Here we report on the evolution of aerosol distributions and properties as measured by the airborne high spectral resolution lidar (HSRL) during the ORACLES (Observations of Aerosols above Clouds and their intEractionS) campaign in September 2016. The NASA Langley HSRL-2 instrument was flown on the NASA ER-2 aircraft for several days in September 2016. Data were aggregated at two pairs of 2° × 2° grid boxes to examine the evolution of the vertical profile of aerosol properties during transport over the ocean. Results showed that the structure of the profile of aerosol extinction and microphysical properties is maintained over a one to two-day time scale. The fraction of aerosol in the fine mode between 50 and 500 nm remained above 0.95 and the effective radius of this fine mode was 0.16 μm from 3 to 5 km in altitude. This indicates that there is essentially no scavenging or dry deposition at these altitudes. Moreover, there is very little day to day variation in these properties, such that time sampling as happens in such campaigns, may be representative of longer periods such as monthly means. Below 3 km there is considerable mixing with larger aerosol, most likely continental source near land. Furthermore, these measurements indicated that there was a distinct gap between the bottom of the aerosol layer and cloud tops at the selected locations as evidenced by a layer of several hundred meters that contained relatively low aerosol extinction values above the clouds.

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 Biomass Burning Aerosol Heating Rates from the ORACLES 2016 and 2017 Experiments

2021 ◽  
Author(s):  
Sabrina P. Cochrane ◽  
K. Sebastian Schmidt ◽  
Hong Chen ◽  
Peter Pilewskie ◽  
Scott Kittleman ◽  
...  
Keyword(s):  
Heating Rate ◽  
Biomass Burning ◽  
Atmospheric Stability ◽  
Single Scattering ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Heating Rates ◽  
Water Vapor Absorption ◽  
Cloud Parameters ◽  
Cloud Properties

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 southeast 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 collocated and readily available. In this study, we derive heating rate profiles and curtains from aircraft measurements during the NASA ObseRvations of CLouds above Aerosols 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). The 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 Variability of aerosol vertical distribution in the Sahel

2010 ◽  
Vol 10 (7) ◽  
pp. 17609-17655 ◽  
Author(s):  
O. Cavalieri ◽  
F. Cairo ◽  
F. Fierli ◽  
G. Di Donfrancesco ◽  
M. Snels ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Biomass Burning ◽  
Seasonal Pattern ◽  
Dry Season ◽  
Satellite Observations ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Air Masses ◽  
Monsoon Flow ◽  
Biomass Burning Aerosol

Abstract. We present and discuss ground-based and satellite observations of aerosol optical properties over Sahelian Africa for the years 2006, 2007 and 2008. This study combines data acquired by three ground-based micro lidar systems located in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analysis (AMMA), by the AEROsol RObotic NETwork (AERONET) sun-photometers and by the space-based Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The 2006 seasonal pattern of the aerosols vertical distribution is presented. It shows the presence of aerosol mainly confined in the lower levels of the atmosphere during the dry season, with the aerosol layer increasing in vertical extension and absolute values in spring, reaching the largest values in summer in correspondence with a progressive clearing up of the atmosphere at the lowermost levels. Aerosol produced by biomass burning are observed mainly during the dry season, when north-easterly air masses pass over large biomass burning areas before recirculating over the measurement sites. This kind of aerosol is present mainly in layers between 2 and 6 km of altitude, although episodically it may show also below 2 km, as observed in Banizoumbou (Niger) in 2006. Biomass burning aerosol is also observed during spring when air masses originating from North and East Africa pass over sparse biomass burning sources, and during summer when biomass burning aerosol is transported from the southern part of the continent by the monsoon flow. The summer season on the whole is characterized by a large presence of desert dust along the entire Sahelian region, widespread in altitude with Aerosol Optical Depths above 0.2. The interannual variability in the three year monitoring period is not very significant. An analysis of the aerosol transport pathways, aiming at detecting the main source regions, revealed that air originated from the Saharan desert is present all year long and it is observed in the lower levels of the atmosphere at the beginning and at the end of the year. In the central part of the year it extends upward and the lower levels are less affected by air masses from Saharan desert when the monsoon flow carries inland air from the Guinea Gulf and Southern Hemisphere. Biomass burning is mainly confined in the higher layers and observable in winter and in autumn.

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