Marine and biomass burning aerosols in the southern Indian Ocean: Retrieval of aerosol optical properties from shipborne lidar and Sun photometer measurements

Abstract

[1] We document aerosol extinction properties in the southern Indian Ocean. A unique data set of shipborne measurements has been collected with a dual Rayleigh-Mie lidar aboard the research vessel Marion Dufresne during two campaigns: one around Madagascar during the Southern Hemisphere late summer and one close to the Kerguelen Islands during the biomass burning (BB) season. During this latter, a layer containing a mix of BB and marine aerosols extending up to ∼3 km above mean sea level (amsl) has been observed from [31°S, 69°E] to [24°S, 59°E]. Both vertical structure and aerosol optical properties have been retrieved from the inversion of the lidar signals. Sun photometer-derived aerosol optical thickness (AOT) at 355 nm is used to constrain the lidar inversion. We obtain a mean integrated value of backscatter-to-extinction ratio (BER) (extinction-to-backscatter ratio, or so-called lidar ratio, LR) of 0.039 ± 0.009 sr −1 (26 ± 6 sr) and 0.021 ± 0.006 sr −1 (48 ± 12 sr) for the marine aerosols layer, and for the mixing between BB and marine aerosols with an uncertainty of 0.009 sr −1 (6 sr) and 0.004 sr −1 (9 sr), respectively. Lidar calibration is used to inverse data without any simultaneous Sun photometer measurements (as nighttime data), and the temporal evolution of the optical properties and vertical extension of the BB aerosol plume is documented. The presence of BB aerosols is in agreement with Lagrangian model GIRAFE v3 (reGIonal ReAl time Fire plumEs) simulations, which show the South American and Southern African BB origin of the encountered aerosol layer.

Impact of the Generation and Activation of Sea Salt Aerosols on the Evolution of Tropical Cyclone Dumile

“…However, because of the large predominance of natural aerosols (sea salts and dust), it was assumed that Dumile evolved in a clean maritime environment. This is supported by the conclusions of Duflot et al (), who found a clean maritime environment in this region out of the biomass burning season (July–October).…”

Radiative effect of aerosols above the northern and southern Atlantic Ocean as determined from shipborne lidar observations

“…Dubovik et al [] presented asymmetry parameters from 0.47 for smoke particles and 0.75 for marine particles in the wavelength range from 440 to 1020nm. In our simplified approach, we defined a SSA of 0.9 and an asymmetry parameter of 0.62 for the free‐tropospheric aerosol which represents a compromise between the main observed and reported free‐tropospheric aerosol types over the Atlantic, dust and smoke, respectively [ Reid et al , ; Tesche et al , ; Yu et al , ; Duflot et al , ; Kanitz et al , ; Preißler et al , ]. An overview of the idealized aerosol conditions is shown in Figure .…”

Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution?

“…12c and d. Duflot et al (2011) present MOPITT (Measurement of Pollution in the Troposphere) CO distributions observed over Réunion source regions. During June-August 2007, elevated CO over Réunion is linked to high-CO regions at 250 hPa over South America, the South Atlantic and southern Africa as well as southeast Asia and Indonesia.…”