Effects of black carbon and Icelandic dust on snow albedo, melt and density

• Main Author: Meinander, Outi
• Other Authors: Nilson, Tiit, University of Helsinki, Faculty of Biological and Environmental Sciences, Department of Environmental Sciences, Finnish Meteorological Institute, Helsingin yliopisto, bio- ja ympäristötieteellinen tiedekunta, ympäristötieteiden laitos, Helsingfors universitet, bio- och miljövetenskapliga fakulteten, miljövetenskapliga institutionen, de Leeuw, Gerrit, Kauppi, Pekka
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2016
• Subjects: Environmental Sciences; Arctic; Sodankylä; albedo; black carbon
• Online Access: http://hdl.handle.net/10138/167780

Light-absorbing impurities in the cryosphere are of hydrological, environmental and climatic importance. The wet and dry deposition of black carbon (BC), organic carbon (OC), and dust particles affect the optical properties and melt of snow and ice. In the Arctic region, the climatic effects are amplified, and surface albedo feedback is often cited as the main contributor. The aim of this thesis is to fill in some of the gaps in our knowledge of the effects of BC, OC, and Icelandic dust on snow in the European Arctic through a series of field and laboratory experiments and an analysis of the resulting data, including modeling. The thesis presents a new hypothesis on the snow density effects of light-absorbing impurities, an important quantity for climate modeling and remote sensing. Three processes are suggested to explain the proposed BC density effect . Experimental results show that dirty snow releases melt water quicker than cleaner snow. The albedo of natural seasonally melting snow in Sodankylä, north of the Arctic Circle, is found to be asymmetric with respect to solar midday, thus indicating a change in the properties of the snow. The radiative transfer modeling results show that the observed solar zenith angle asymmetry results in a 2-4 % daily error for satellite snow albedo estimates. Surface albedo model results indicate that the biggest snow albedo changes due to BC are expected in the ultraviolet (UV) part of the electromagnetic spectrum. The albedo of natural seasonal snow measured in Sodankylä, is found to be lower than expected. Solar UV and visible (VIS) albedo values of 0.6-0.8 in the accumulation period and 0.5-0.7 during melting are observed. The low albedo values are explained to be due to large snow grain sizes up to ~ 3 mm in diameter, meltwater surrounding the grains and increasing the effective grain size, and absorption caused by impurities in the natural snow (87 ppb BC and 2894 ppb OC). The BC contents of the surface snow layer at the Sodankylä Arctic Research Center, Finland, is ...