Philippe Royer

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

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.

Springtime major pollution events by aerosol over Paris Area: from a case study to a multi-annual analysis

A study of the intense spring pollution events occurring between 2007 and 2016 on the Paris Area is presented using ground-based and spaceborne measurements. Emphasis is placed on 2011 where data included ground-based lidar measurements. This last period corresponds with the highest regional pollution levels of the past decade. The information threshold (daily average of PM10 > 50 μg m-3) was exceeded 16 times, whilst the alert threshold (daily average of PM10 > 80 μg m-3) was exceeded twice. The information (alert) threshold exists to protect the most fragile people (the entire population). Ground-based and spaceborne measurements demonstrate the benefit of their synergy as each is representative of specific space and time scales. The operational products of the spaceborne instruments Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) and the Moderate Resolution Imaging Spectroradiometer (MODIS) are used. For 2011, CALIOP vertical profiles are inversed to assess the backscatter to extinction ratio, which is then successfully compared with similar results derived from the CALIOP operational products, a ground-based lidar and sunphotometers. The aerosols are identified to be polluted continental and polluted dust aerosols following the criteria used for the inversion of the CALIOP profiles. Aerosol typing is consistent between the ground-based and spaceborne lidars, demonstrating the importance of CALIOP for other years where the ground-based lidar was not in operation. The main pollution sources responsible for the spring aerosol pollution, occurring during anticyclonic meteorological conditions, are identified as coming from Western Europe: Benelux, Rhine-Ruhr Area and the Lorraine Area.

Simulation of Doppler Lidar Measurement Range and Data Availability

AbstractThe measurement range of a coherent wind Doppler lidar (CWDL) along a laser beam is the maximum distance from the lidar where wind speed data are accurately retrieved. It means that, at this distance, a sufficient number of emitted laser photons are backscattered and received by the lidar. Understanding of the propagation of the laser through the atmosphere, and particularly the backscattering and extinction processes from aerosols, is therefore important to estimate the metrological performances of a CWDL instrument. The range is directly related to specific instrument characteristics and atmospheric content, such as the aerosols type, size, and density distributions. Associated with the measurement range is the notion of data availability, which can be defined, at a given range and over a time period, as the percentage number of data retrieved correctly by the CWDL over the total number of measurement attempts.This paper proposes a new approach to predict the CWDL data availability and range of ...