The dual-field-of-view polarization lidar technique: A new concept in monitoring aerosol effects in liquid-water clouds – Theoretical framework

Abstract

<jats:p>Abstract. In a series of two articles, a novel, robust, and practicable lidar approach is presented that allows us to derive microphysical properties of liquid-water clouds (cloud extinction coefficient, droplet effective radius, liquid-water content, cloud droplet number concentration) at a height of 50–100 m above cloud base. The temporal resolution of the observations is on the order of 30–120 sec. Together with the aerosol information (aerosol extinction coefficients, cloud condensation nucleus concentration) below the cloud layer, obtained with the same lidar, in-depth aerosol-cloud interaction studies can be performed. The theoretical background and the methodology of the new cloud lidar technique is outlined in this article (part 1), measurement applications are presented in an companion publication (part 2). The novel cloud retrieval technique is based on lidar observations of the volume linear depolarization ratio at two different receiver field-of-views (FOVs). Extensive simulations of lidar returns in the multiple scattering regime were conducted to investigate the capabilities of a dual-FOV polarization lidar to measure cloud properties and to quantify the information content in the measured depolarization features regarding the basic retrieval parameters (cloud extinction coefficient, droplet effective radius). Key simulation results and the developed overall data analysis scheme to obtain the aerosol and cloud products are presented. </jats:p>

Contrasting ice formation in Arctic clouds: surface coupled vs decoupled clouds

“…Liquid droplets on the other hand have a very low depolarization ratio. Within the liquid layer, however, the depolarization ratio increases strongly due to multiple scattering (Jimenez et al, 2020). The following classification was applied in the frame of the inspection of each individual profile: A depolarization ratio close to 0 accompanied with a strong lidar backscatter indicates the presence of spherical liquid-water droplets.…”

The dual-field-of-view polarization lidar technique: a new concept in monitoring aerosol effects in liquid-water clouds – case studies

“…There is still a strong request for the development of new and robust aerosol and cloud profiling techniques (Grosvenor et al, 2018). As a contribution to improved ACI field studies with a focus on liquid-water clouds, we offer a novel lidar measurement concept that permits continuous, vertically resolved observations of cloud-relevant aerosol properties below the cloud base, cloud microphysical properties in the lower part of the cloud layer, and the vertical wind component below and within the cloud parcels with a temporal resolution of 30-120 s. The methodological framework is presented in Part 1 (Jimenez et al, 2020). The selected measurement concept of combining aerosol lidar, cloud lidar, and wind Doppler lidar observations was already outlined and applied by Schmidt et al (2014Schmidt et al ( , 2015.…”

“…However, a fast lidar technique for cloud observation (day and night and with updraft-resolving temporal resolution) was introduced only recently (Jimenez et al, 2017(Jimenez et al, , 2018. In Part 1 (Jimenez et al, 2020), we presented the theoretical framework of the novel dual-field-of-view (dual-FOV) polarization lidar method, which allows us to derive microphysical properties of liquid-water clouds such as droplet number concentration N d , effective radius R e of the droplets, and liquidwater content w l as well as the cloud extinction coefficient α in the cloud base region at 50 to 100 m above the cloud base. Together with the recently developed method to derive height profiles of cloud condensations nuclei (CCN) concentrations (N CCN ) from aerosol extinction coefficients α par , measured with the same polarization lidar (Mamouri and Ansmann, 2016) below the cloud base, detailed studies of the impact of aerosol particles on the microphysical properties of droplets in the cloud base region of liquid-water cloud layers have become possible.…”

“…In Sect. 2, we briefly summarize the data analysis procedure to retrieve the aerosol and cloud parameters for in-depth ACI studies as extensively discussed and explained in Part 1 (Jimenez et al, 2020). Sect.…”

“…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 N d ) at a height of 50-100 m above the cloud base together with aerosol information (aerosol extinction coefficients, cloud condensation nuclei concentration N CCN ) 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).…”