Characterization of Arctic aerosol and optically-thin clouds from the middle troposphere to the lower stratosphere by means of lidar backscatter and depolarization ratio

Aerosols and high altitude clouds in the Arctic have an important role in the radiative energy budget by influencing the net gain or loss of radiative heat.  Similarly, aerosols are the main nucleation source for the formation of high altitude clouds and responsible to alter cloud properties. Ground-based lidar systems are well-suited for the investigation of aerosol and optically-thin clouds due to their temporal scales and high vertically-resolved information. In remote locations with challenging environments like the Arctic, however,  ground-based lidars are scarce mainly due to their typical high maintenance requirements. To overcome this limitation, a compact mobile Rayleigh-Mie-Resonance lidar has been recently developed as part of the European Lidar Array for Atmospheric Climate Monitoring (EULIAA) project. The EULIAA-IR1 is a Doppler infrared (770 nm wavelength) mobile, compact (1 m³) and highly autonomous lidar. The EULIAA-IR1 lidar senses the atmosphere by three line of sights and is capable to cover the atmosphere from 4 km to at least 50 km.  The lidar’s high resolution Doppler spectra at three field of views has been conceived to allow the retrieval profiles of the wind components, particle (Mie scattering) and molecular (Rayleigh scattering) unattenuated backscatter coefficient, with depolarization capabilities for zenith observations, as well as stratospheric temperature profiles.

The EULIAA-IR1 system has been deployed to the first of a series of field campaigns ranging from high latitudes to the tropics within the framework of the EULIAA project. The high latitude campaign is taken place at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) located at 69.3° North and 16.0° East on top of the Ranman montain (379 m.a.s.l.) at Andøya, Norway. The EULIAA-IR1 lidar started operation at ALOMAR since end of October 2025, where persistent aerosol layers up to about 20 km and optically thin clouds up to 10 km have been systematically observed. The EULIAA-IR1 observations of aerosols and thin clouds are here presented to assess thresholds of backscatter coefficient and depolarization ratio (δ) to characterize and distinguish aerosols and thin clouds which have been previously reported by other lidar systems. We use the lidar slant observations to extend the characterization of the aerosol layers and their dynamics based on the meridional and zonal wind components obtained by the lidar. Moreover, we show how the EULIAA-IR1’s retrieved vertical wind component provides an insight on the interaction at the cloud mixing layer (top and bottom edges), where the complex interplay between aerosols and clouds takes place.

With this contribution we demonstrate the EULIAA-IR1system data pipeline to provide near-real-time retrieval products to different data dissemination platforms and meteorological agencies for data assimilation purposes, which is one of the goals of the EULIAA project.