Lidar characterization of the Arctic atmosphere during ASTAR 2007: four cases studies of boundary layer, mixed-phase and multi-layer clouds

Abstract

Abstract. During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR), which was conducted in Svalbard in March and April 2007, tropospheric Arctic clouds were observed with two ground-based backscatter lidar systems (micro pulse lidar and Raman lidar) and with an airborne elastic lidar. In the time period of the ASTAR 2007 campaign, an increase in low-level cloud cover (cloud tops below 2.5 km) from 51% to 65% was observed above Ny-Ålesund. Four different case studies of lidar cloud observations are analyzed: With the ground-based Raman lidar, a layer of spherical particles was observed at an altitude of 2 km after the dissolution of a cloud. The layer probably consisted of small hydrated aerosol (radius of 280 nm) with a high number concentration (around 300 cm −3 ) at low temperatures (−30 • C). Observations of a boundary layer mixedphase cloud by airborne lidar and concurrent airborne in situ and spectral solar radiation sensors revealed the localized process of total glaciation at the boundary of different air masses. In the free troposphere, a cloud composed of various ice layers with very different optical properties was detected by the Raman lidar, suggesting large differences of ice crystal size, shape and habit. Further, a mixed-phase double layer cloud was observed by airborne lidar in the free troposphere. Local orography influenced the evolution of this cloud. The four case studies revealed relations of cloud properties and specific atmospheric conditions, which we plan to use as the base for numerical simulations of these clouds.

Local ice formation via liquid water growth in slowly ascending humid aerosol/liquid water layers observed with ground‐based lidars and radiosondes

“…With the further cloud development and substantial ice formation (close to a rainfall), the relationship between cloud layer and inversion layer became complicated. In our examples of ice formation, the freezing temperatures were −3 to −8°C which are obviously higher than the reported results from the earlier observations [ Ansmann et al ., ; de Boer et al ., ; Hoffmann et al ., ; Lampert et al ., ; Seifert et al ., ]. Accordingly, what our lidars observed were the suspended ice crystals rather than falling ice virga.…”

AMALi – the Airborne Mobile Aerosol Lidar for Arctic research

“…The influence of the atmospheric state was found to be substantial, e.g. even in the free troposphere, multi-layer clouds formed by a disturbance of the wind field near Svalbard (Lampert et al, 2010). Mixed-phase clouds in the lower troposphere were observed during airborne AMALi measurements and allowed to guide the aircraft into areas within these clouds for measuring in situ their microphysical parameters (Stachlewska, 2006b;Stachlewska et al, 2006c;Gayet et al, 2007).…”

Lidar Measurements of the Vertical Distribution of Aerosol Optical and Physical Properties over Central Asia

“…In the beginning of the episode ( Figure 5(a)), moderate values of DR 532 = (0.05-0.1) were observed, indicating particles with a general spherical shape due to the high relative humidity, and/or the particles were small in comparison to the 532 nm laser wavelength. On 06 June ( Figure 5(b)), a simultaneous increase in (an increase of more than 50) and DR 532 was observed in an aerosol layer at 5.0-7.0 km that may have resulted from multiple scattering due to the penetration of laser radiation into an optically dense cloud [20]. Mineral particles exposed to increased relative humidity (RH > 80%) can act as condensation nuclei, causing clouds to form.…”