EGU2020-8256, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-8256
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Possible albedo reduction due to light absorbing impurities in snowpack observed at various sites

Teruo Aoki1,2, Masashi Niwano2, Sumito Matoba3, Tomonori Tanikawa2, Yuji Kodama1, and Yoichiro Hirozawa4
Teruo Aoki et al.
  • 1National Institute of Polar Research, Arctic Environment Research Center, Tachikawa, Japan (aoki.teruo@nipr.ac.jp, kodama.yuji@nipr.ac.jp)
  • 2Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan (mniwano@mri-jma.go.jp, tanikawa@mri-jma.go.jp)
  • 3Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan (matoba@pop.lowtem.hokudai.ac.jp)
  • 4Toshiba Energy Systems & Solutions Corporation, Tokyo, Japan (yoyo.afro.709@outlook.jp)

Possible albedo reduction due to light absorbing impurities (LAI) in snowpack observed at various sites in the world are investigated. Reviewing previously measured black carbon (BC) concentrations, their values distribute in a range of 0.07-0.25 ppbw (ng of BC in g of snow) in Antarctica, 0.55-20 ppbw in Greenland Ice Sheet (GrIS), 4.4-87.6 ppbw for the other Arctic except GrIS, and 4-1221 ppbw for mid-latitudes. As albedo reduction rate by LAI depends on snow grain size, it is more enhanced by larger grain snow such as melt form (melting snow) than smaller grain snow such as precipitation particles (new snow). By assuming two typical snow grain radii rs = 1000 and 50 µm, respectively for those snow grain shapes, the albedo reduction as a function of BC concentration can be calculated with physically based snow albedo model. The result indicates that albedo in Antarctic snow is not affected by BC in any case of snow grain radius. In GrIS albedo reduction due to BC is small around 0.006 for rs = 50 µm (new snow) but it rises to 0.026 for rs = 1000 µm (melting snow), suggesting a few percent of albedo reduction could occur under warmer climate condition due to enhanced snow metamorphism. In the other Arctic except GrIS, the maximum albedo reductions for rs = 50 µm (1000 µm) are 0.015 (0.064) at the maximum BC concentration (87.6 ppbw). For. mid-latitudes, it is 0.070 (0.24) for rs = 50 µm (1000 µm) at the maximum BC concentration (1221 ppbw). These results mean albedo reduction in highly polluted area of mid-latitudes cannot be ignored even in case of new snow and is more serious for melting snow.

We have conducted energy budget and snow pit observations at Sapporo (43°N, 141°E, 15 m a.s.l), Japan since 2005. In addition, elemental carbon (EC~BC) and mineral dust concentrations in snowpack were also monitored for snow samples collected twice a week from 2007 by the thermal optical reflectance (TOT) method and gravimetric measurement of a filter. During 10 years from 2007 to 2017, the medians of EC and dust concentrations are 196 ppbw and 2700 ppbw, respectively. Using those data, contribution of LAI to albedo reduction and the radiative forcing (RF) were estimated. The 10-year-mean albedo reduction and RF due to BC+dust are 0.053 and +6.7 Wm-2, respectively, in which BC effect on albedo reduction is 5.6 times larger than dust. The albedo reduction by BC+dust for only melting period is 0.151, that is 4.8 times larger than that for accumulation period. The effect of LAI on albedo reduction is enhanced by snow grain growth as well as an increase of LAI in melting period compared to that for accumulation season.

How to cite: Aoki, T., Niwano, M., Matoba, S., Tanikawa, T., Kodama, Y., and Hirozawa, Y.: Possible albedo reduction due to light absorbing impurities in snowpack observed at various sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8256, https://doi.org/10.5194/egusphere-egu2020-8256, 2020

Comments on the presentation

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Presentation version 3 – uploaded on 03 May 2020
Revised a few words in p.2.
  • CC1: Comment on EGU2020-8256, Jessica McCarty, 04 May 2020

    I wanted to let the authors know that I really like and appreciate the uncertainty visualization on Slide 6 comparing SP-2 measurements to previous published estimates. 

    • AC1: Reply to CC1, Teruo Aoki, 04 May 2020

      Hi Jessica, Thanks for your comment. As mentioned in slide 6, there is a possibility of the improvement of BC pollution. However, some papers reported that BC concentrations measured by SP2 were lower than the optical method. As the snow areas measured with SP2 are presently limited, we have to confirm the accuracy with an intercomparison mentioned in slide 6.

Presentation version 2 – uploaded on 03 May 2020 , no comments
Outline on p.2 and page numbers were added on 3 May.
Presentation version 1 – uploaded on 01 May 2020 , no comments