Observing wind, aerosol particles, cloud and precipitation: Finland's new ground-based remote-sensing network

Abstract

The Finnish Meteorological Institute, in collaboration with the University of Helsinki, has established a new ground-based remote-sensing network in Finland. The network consists of five topographically, ecologically and climatically different sites distributed from southern to northern Finland. The main goal of the network is to monitor air pollution and boundary layer properties in near real time, with a Doppler lidar and ceilometer at each site. In addition to these operational tasks, two sites are members of the Aerosols, Clouds, and Trace gases Research InfraStructure Network (ACTRIS); a <i>K</i>_a-band Doppler cloud radar at Sodankylä will provide cloud retrievals within CloudNet, and a multi-wavelength Raman lidar, POLLY^XT (POrtabLe Lidar sYstem eXTended), in Kuopio provides optical and microphysical aerosol properties through EARLINET (European Aerosol Research Lidar Network to Establish an Aerosol Climatology). Three C-band weather radars are located in the Helsinki metropolitan area and are deployed for operational and research applications. We carried out two inter-comparison campaigns to investigate the Doppler lidar performance. The aims of the campaigns were to compare the backscatter coefficient and retrieved wind profiles, and to optimise the lidar sensitivity through adjusting the telescope focus and data-integration time to ensure enough signals in low-aerosol-content environments. The wind profiles showed good agreement between different lidars. However, due to inaccurate telescope focus setting and varying receiver sensitivity, backscatter coefficient profiles showed disagreement between the lidars. Harsh Finnish winters could pose problems, but, due to the built-in heating systems, low ambient temperatures had no, or only a minor, impact on the lidar operation: including scanning-head motion. However, accumulation of snow and ice on the lens has been observed, which can lead to formation of a water/ice layer thus attenuating the signal inconsistently. Thus, care must be taken to ensure continuous snow removal

An Overview of the Urban Boundary Layer Atmosphere Network in Helsinki

“…Novel scanning strategies may enable the study of estimates of a horizontal transect of horizontal wind vectors (Wood et al 2013b), turbulent mixing and dynamics of the ABL (Barlow et al 2011), and sensible heat and momentum flux (Collier et al 2005). Performance of the lidar was investigated during a 2-week intercomparison campaign in Helsinki (Hirsikko et al 2013) against FMI's other Doppler lidars showing good agreement for the wind vector profiles. From 2013 onward, these ABL wind and aerosol profiles will be complemented with a radio acoustic sounding system (SODAR-RASS) instrument for temperature and wind profiles.…”

Atmospheric Boundary Layer Classification With Doppler Lidar

“…After the background correction, new measurement uncertainties are derived from the corrected signal (O'Connor et al, ; Rye & Hardesty, ), which will then propagate through to the products derived from the lidar signal and radial Doppler velocity. Profiles of calibrated attenuated backscatter coefficient ( β ) are also derived (Westbrook et al, ), if the telescope function is known (Hirsikko et al, ).…”

“…The Halo lidar, operated by the Finnish Meteorological Institute, has been operating continuously at the station since 2013, following the operational scanning strategy outlined in Hirsikko et al (). The scanning sequence for this period comprised the following: VAD scan at 30° elevation from horizontal with 23 beams (excluding one blocked beam) every 30 min, three‐beam Doppler beam swinging (DBS) scan at 70° elevation every 30 min, and range height indicator scan and custom sector scan every 30 min with slightly varying integration times.…”

Inadvertent Localized Intensification of Precipitation by Aircraft

“…To investigate what role supercooled liquid cloud layers play in forming LIP, a Doppler lidar and satellite data were used in addition to the radar observations to study several cases from 2009–2013. The Halo Doppler lidar, located in Kumpula, operates at a wavelength of 1.5 μm and provides vertical profiles of attenuated backscatter coefficient, Doppler velocity, and the depolarization ratio with high spatial and temporal resolution (Hirsikko et al, ). These parameters were used to detect the presence and location of the lowest supercooled liquid layer using the method described in Hogan et al () and corroborated with low values of the depolarization ratio, as discussed in section .…”