Author response to reviewers on egusphere-2023-2412

Published: March 1, 2024

Abstract. The springtime atmosphere over the southeast Atlantic Ocean (SEA) is subjected to a consistent layer of biomass burning (BB) smoke from widespread fires on African continent. An elevated humidity signal co-incident with this layer, consistently proportional amount present. combined and BB aerosol has potentially significant radiative dynamic impacts. Here we use aircraft-based observations NASA ORACLES (ObseRvations Aerosols above CLouds their intEractionS) deployments in conjunction reanalyses characterize co-variations smoke. observed plume-vapor relationship, its agreement ERA5 CAMS reanalyses, persists across all observations, although magnitude relationship varies as season progresses. Water vapor well-represented by while tends underestimate carbon monoxide especially under high BB. While optical depth (AOD) generally overestimated relative AOD, show between CO extinction, demonstrating utility tracer understanding vertical distribution. We next k-means clustering examine multi-year seasonal patterns distributions. identify canonical profile types CO, allowing us changes atmospheric structures, impacts, they covary. Predominant vary spatiotemporally SEA region through season. With work, establish framework for more complete analysis broader dynamical effects humid aerosols SEA.

Language: Английский

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Vertical structure of a springtime smoky and humid troposphere over the southeast Atlantic from aircraft and reanalysis

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(13), P. 7983 - 8005

Published: July 12, 2024

Abstract. The springtime atmosphere over the southeast Atlantic Ocean (SEA) is subjected to a consistent layer of biomass burning (BB) smoke from widespread fires on African continent. An elevated humidity signal coincident with this layer, consistently proportional amount present. combined and BB aerosol has potentially significant radiative dynamic impacts. Here, we use aircraft-based observations NASA ORACLES (ObseRvations Aerosols above CLouds their intEractionS) deployments in conjunction reanalyses characterize covariations across SEA. observed plume–vapor relationship, its agreement European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, persists all observations, although magnitude relationship varies as season progresses. Water vapor well represented by reanalyses, while CAMS tends underestimate carbon monoxide especially under high BB. While optical depth (AOD) generally overestimated relative AOD, show between (CO) extinction, demonstrating utility CO tracer understanding vertical distribution. We next k-means clustering examine multi-year seasonal patterns distributions. identify canonical profile types CO, allowing us changes atmospheric structures, impacts they covary. profiles range both total water concentration structure, primarily vary terms maximum concentration, similar structures each. distribution spatiotemporally SEA region through season, ranging largely one type northeast southwest more evenly distributed multiple where air masses meet middle These distributions follow transport humid, smoky source (greatest influence SEA) (increasing decreasing respectively). With work, establish framework complete analysis broader dynamical effects humid aerosols

Language: Английский

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More biomass burning aerosol is being advected westward over the southern tropical Atlantic since 2003

EarthArXiv (California Digital Library), Journal Year: 2024, Volume and Issue: unknown

Published: July 26, 2024

Each year, agricultural fires in southern continental Africa emit approximately one third of the world’s biomass burning aerosol. This is advected westward by prevailing circulation winds over a subtropical stratocumulus cloud deck. The radiative effects from aerosol and aerosol-cloud interactions impact regional circulations hydrology. Here we examine how changes coupled African earth system past 20 years southeast Atlantic. We combine satellite-derived burned area datasets with ECMWF-reanalysis carbon monoxide, black carbon, meteorology season (May-October) Africa. begins May woody savannas northwest shifts to open savanna grassland southeast, small (less than 1 km2) contributing significantly total area. More are occurring middle overall shorter, corroborated reanalysis monoxide fields. Significantly increased free tropospheric winds, shifted southward, transport smoke further southwest advection shift south Atlantic high an increase low fraction on edge While emissions sources have not changed significantly, pathway, attributed increasing surface temperatures tropical expansion, combined altered distribution, explain radiation balance has more top-of-atmosphere cooling recent decades.

Language: Английский

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

Atmospheric chemistry and physics, Journal Year: 2022, Volume and Issue: 22(15), P. 9859 - 9876

Published: Aug. 3, 2022

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 indirect radiative forcing atmosphere this region particularly during months August, September, October. There was a multi-year international campaign study its interactions with Here, we report on evolution distributions properties as measured by airborne high spectral resolution lidar (HSRL-2) ORACLES (Observations Aerosols above Clouds their intEractionS) September 2016. The NASA Langley HSRL-2 instrument flown ER-2 aircraft for several days Data were aggregated at two pairs 2∘ × grid boxes examine vertical profile transport ocean. Results showed structure extinction microphysical is maintained 1 2 d timescale. In 3–5 km altitude range, 95 % contributed particles 0.05–0.50 µm radius size range having an average effective 0.16 µm. indicates there essentially no scavenging or dry deposition these altitudes. Moreover, very little day-to-day variation properties, such time sampling happens campaigns may be representative longer periods monthly means. Below 3 km, considerable mixing larger aerosol, most likely continental source near land. Furthermore, measurements indicated often distinct gap between bottom cloud tops selected locations evidenced hundred meters contained relatively low values

Language: Английский

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Response to reviewers of acp-2022-501

Published: Feb. 1, 2023

Abstract. Aerosol over the remote southeastern Atlantic is some of most sunlight-absorbing aerosol on planet: in situ free-tropospheric single-scattering albedo at 530 nm wavelength (SSA_{530 nm}) ranges from 0.83 to 0.89 within ORACLES (ObseRvations Aerosols above CLouds and their intEractionS) aircraft flights late August–September. Here we seek explain low SSA. The SSA depends strongly black carbon (BC) number fraction, which 0.15 0.4. Low organic (OA)-to-BC mass ratios 8–14 modified combustion efficiency values >0.975 point indirectly dry, flame-efficient primarily grass fuels, with back trajectories ending miombo woodlands Angola. youngest aerosol, aged 4–5 d since emission, occupied top half a 5 km thick plume sampled directly west Angola vertically consistent class="inline-formula">BC:ΔCO (carbon monoxide) ratio, indicating homogenization source emissions. younger transported more quickly off continent by stronger winds, overlaid older, slower-moving larger mean particle size fraction BC-containing particles. This ongoing gas condensation coagulation smaller non-BC particles upon volumes class="inline-formula">OA:BC older were smaller, attributed evaporation following fragmentation, instead dilution or thermodynamics. CLARIFY (CLoud–Aerosol–Radiation Interaction Forcing: Year 2017) campaign aerosols that had traveled further reach Ascension Island. reported higher BC fractions, lower ratios, yet absorption coefficients compared this study's. Values one 2017 flight, held midway Island, are intermediate, confirming long-range changes. Overall data continuing oxidation through fragmentation releasing subsequently enter phase, reducing OA mass, rather than support best fit: SSA${}_{\mathrm{530}\mathrm{nm}}=\mathrm{0.801}+\mathrm{0055}\cdot \left(\mathrm{OA}:\mathrm{BC}\right)$ (r=0.84). fires southern Africa emit approximately one-third world's carbon; emitted distinct other regional smoke emissions, composition needs be represented appropriately realistically depict radiative effects.

Language: Английский

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