Abstract
Abstract. In a companion article (Jimenez et al., 2020), we introduced a new lidar method to derive microphysical properties of liquid-water clouds (cloud extinction coefficient, droplet effective radius, liquid-water content, cloud droplet number concentration Nd) at a height of 50–100 m above the cloud base together with aerosol information (aerosol extinction coefficients, cloud condensation nuclei concentration NCCN) below the cloud layer so that detailed studies of the influence of given aerosol conditions on the evolution of liquid-water cloud layers with high temporal resolution solely based on lidar observations have become possible now. The novel cloud retrieval technique makes use of lidar observations of the volume linear depolarization ratio at two different receiver field of views (FOVs). In this article, Part 2, the new dual-FOV polarization lidar technique is applied to cloud measurements in pristine marine conditions at Punta Arenas in southern Chile. A multiwavelength polarization Raman lidar, upgraded by integrating a second polarization-sensitive channel to permit depolarization ratio observations at two FOVs, was used for these measurements at the southernmost tip of South America. Two case studies are presented to demonstrate the potential of the new lidar technique. Successful aerosol–cloud-interaction (ACI) studies based on measurements with the upgraded aerosol–cloud lidar in combination with a Doppler lidar of the vertical wind component could be carried out with 1 min temporal resolution at these pristine conditions. In a stratocumulus layer at the top of the convective boundary layer, we found values of Nd and NCCN (for 0.2 % water supersaturation) ranging from 15–100 and 75–200 cm−3, respectively, during updraft periods. The studies of the aerosol impact on cloud properties yielded ACI values close to 1. The impact of aerosol water uptake on the ACI studies was analyzed with the result that the highest ACI values were obtained when considering aerosol proxies (light-extinction coefficient αpar or NCCN) measured at heights about 500 m below the cloud base (and thus for dry aerosol conditions).
Highlights
Numerous details and aspects of aerosol–cloud interaction (ACI) are not well understood and not well considered and parameterized in weather and climate models
In Part 1 (Jimenez et al, 2020), we presented the theoretical framework of the novel dual-field-of-view polarization lidar method, which allows us to derive microphysical properties of liquid-water clouds such as droplet number concentration Nd, effective radius Re of the droplets, and liquidwater content wl as well as the cloud extinction coefficient α in the cloud base region at 50 to 100 m above the cloud base
Cout is obtained under the assumption that the volume depolarization ratios for FOVin and FOVout are equal under clear-sky conditions
Summary
Numerous details and aspects of aerosol–cloud interaction (ACI) are not well understood and not well considered and parameterized in weather and climate models. The new dual-FOV polarization lidar technique can be implemented in widespread aerosol polarization lidars (of, e.g., EARLINET) with near-range and far-range receiver telescopes, as will be discussed below, and can contribute to the long-term monitoring of droplet microphysical properties in the lower part of liquid-water clouds within network structures. In this second article (Part 2), we apply the new dual-FOV polarization lidar technique to recent aerosol and cloud observations at Punta Arenas, Chile, discuss the cloud retrieval uncertainties, compare the results with independent alternative cloud observations, and highlight the new potential of the lidar technique to significantly contribute to atmospheric and climate research in the field of ACI.
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