16 Dec 2021
16 Dec 2021
Status: a revised version of this preprint is currently under review for the journal ACP.

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

Harshvardhan Harshvardhan1, Richard Ferrare2, Sharon Burton2, Johnathan Hair2, Chris Hostetler2, David Harper2, Anthony Cook2, Marta Fenn3, Amy Jo Scarino3, Eduard Chemyakin3, and Detlef Müller4 Harshvardhan Harshvardhan et al.
  • 1Purdue University, West Lafayette, IN, United States
  • 2NASA Langley Research Center, Hampton, VA, United States
  • 3Science Systems and Applications, Inc./NASA Langley Research Center, Hampton, VA, United States
  • 4University of Hertfordshire, Hatfield, Hertfordshire, United Kingdom

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.

Harshvardhan Harshvardhan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-846', Anonymous Referee #1, 03 Jan 2022
    • AC1: 'Reply on RC1', Harshvardhan Harshvardhan, 17 Jan 2022
  • RC2: 'Comment on acp-2021-846', Anonymous Referee #2, 04 Jan 2022

Harshvardhan Harshvardhan et al.

Harshvardhan Harshvardhan et al.


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Short summary
The evolution of aerosol in biomass burning smoke plumes that travel over marine clouds off the Atlantic coast of Central Africa was studied using measurements made by a lidar mounted on a high-altitude aircraft. The main finding was that the physical properties of aerosol do not change appreciably once the plume has left land and travels over the ocean over a time scale of one to two days. Almost all particles in the plume are of radius less than one micron and spherical in shape.