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 mixed-phase 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.
Highlights
The Arctic is a sensitive indicator of climate change due to a large number of special interactions and feedback mechanisms (Curry et al, 1996)
In this article we present case studies of tropospheric Arctic clouds observed by lidar technique during the ASTAR 2007 campaign and analyze them in the context of the
4 Summary: Arctic clouds observed by lidar technique
Summary
The Arctic is a sensitive indicator of climate change due to a large number of special interactions and feedback mechanisms (Curry et al, 1996). Gayet et al (2007) observed the feeder-seeder effect, i.e. ice crystals and drizzle particles falling out of a cirrus cloud layer into a stratiform layer of liquid cloud droplets. The local and temporary radiative forcing of mixed-phase clouds may differ significantly depending on solar zenith angle, surface albedo, cloud geometry, cloud optical thickness and the partitioning of liquid and ice water in the clouds (Harrington, 1999; Vavrus, 2004). Arctic haze consists of anthropogenic aerosol transported into the Arctic region in spring time from polluting sources at southern latitudes It can reach high optical depth values up to 0.3 at 532 nm wavelength over Spitsbergen (Herber et al, 2002) and significantly influences the radiation budget
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