Abstract. To study the feasibility of a fluorescence lidar for aerosol characterization, the fluorescence channel is added to the LILAS multiwavelength Mie–Raman lidar of Lille University, France. A part of the fluorescence spectrum induced by 355 nm laser radiation is selected by the interference filter of 44 nm bandwidth centered at 466 nm. Such an approach has proved to have high sensitivity, allowing fluorescence signals from weak aerosol layers to be detected and the fluorescence backscattering coefficient from the ratio of fluorescence and nitrogen Raman backscatters to be calculated. Observations were performed during the November 2019–February 2020 period. The fluorescence capacity (ratio of fluorescence to elastic backscattering coefficients), measured under conditions of low relative humidity, varied in a wide range, being the highest for the smoke and the lowest for the dust particles. The results presented also demonstrate that the fluorescence measurements can be used for monitoring the aerosol inside the cloud layers.

This paper presents an 8-year (2005-2012 inclusive) study of the marine aerosol distribution and variability over the Southern Indian Ocean, precisely in the area {10 • S−40 • S ; 50 • E−110 • E} which has been identified as one of the most pristine regions of the globe. A large dataset made of satellite data (POLDER, CALIOP), AERONET measurements at Saint-Denis (French Reunion Island) and model reanalysis (MACC), has been used. In spite of a positive bias of about 0.05 between the AOD (aerosol optical depth) given by POLDER and MACC on one hand and the AOD measured by AERONET on the other hand, consistent results about the aerosol distribution and variability over the area considered have been obtained. First, aerosols are mainly confined below 2 km asl (above sea level) and are dominated by sea salt, especially in the center of the area of interest, with AOD 0.1. This zone is the most pristine and is associated to the Mascarene anticyclone position. There, the direct radiative effect is assessed around −9 W m −2 at TOA (top of the atmosphere) and probability density functions of the AODs are leptokurtic lognormal functions without * .

The main object of this paper is to emphasize that clouds-the nonprecipitating component of condensed atmospheric water-can produce a strong attenuation at operational microwave frequencies, although they present a low reflectivity preventing their radar detection. By way of a simple and realistic model, simulations of radar observations through warm precipitating targets are thus presented in order to quantify cloud attenuation. Simulations concern an airborne radar oriented downward and observing precipitation at four frequencies: 3, 10, 35, and 94 GHz. Two cases are first considered: a convective cell (vigorous cumulus congestus plus rain) and a stratiform one (nimbostratus plus drizzle) superimposed on the previous one. Other simulations are then performed on different types of cumulus (congestus, mediocris, and humilis) with various thicknesses characterized, in a microphysical sense, by their maximum liquid water content.Simulations confirm the low cumulus reflectivity ranging from Ϫ45 dBZ for the weakest cumulus (i.e., the humilis one) to Ϫ5 dBZ for the strongest one (i.e., the vigorous cumulus congestus). It reaches Ϫ35 dBZ for the nimbostratus cloud. On the other hand, cumulus attenuation [precisely path-integrated cloud attenuation (PICA)] is not negligible and, depending on the frequency, can be very strong: the higher the frequency, the stronger the PICA. At 3 GHz, the far less attenuated frequency, PICA for the vigorous cumulus congestus alone in the convective cell (embedded into the stratiform background) is on the order of 1.2 dB (1.5 dB) at 10 GHz, 16 dB (20 dB) at 35 GHz, and 80 dB (100 dB) at 94 GHz. For weaker cumulus, PICA is lower but, in certain cases, significant. All these results mean that it is necessary to be very careful about radar measurements if reliable information on precipitation-for example, the precipitation rate R-has to be deduced, particularly at high operational frequencies.