Author(s): Yu Ohata; Takenobu Toyota; Alexander D. Fraser; Takayuki Shiraiwa
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Abstract: To clarify lake ice formation processes in mid-latitudes subject to significant snowfall and moderate air temperature, the properties of lake ice at Lake Abashiri in Hokkaido, Japan, were examined from field observations during the 2012/2013 and 2014/2015 ice seasons, and a one-dimensional thermodynamic model was developed based on the results. At all lake sites, the ice was composed of two distinct layers: a snow ice (SI) layer on top and a congelation ice (CI) layer below. The SI layer ranged from 29% to 73% of the total ice thickness, much greater than that in high-latitude lakes. In the model, the CI growth rate at the bottom was estimated using the traditional heat budget method, while the SI growth rate on top was calculated by assuming that the excessive snowfall, leading to a negative freeboard, is converted to SI by a reduction rate (β). By tuning the value ofβ, the model successfully reproduced the observational thicknesses of CI, SI and the break-up dates in both winters, showing the validity of this model to some extent. The numerical experiment with this model suggests that the role of snow may be to reduce the variability in total ice thickness caused by the change in meteorological conditions together with the SI growth. Furthermore, the model accurately reproduced break-up dates for the past 15 years (2000-2015) and ice thicknesses for the past 10years (2005-2015), as validated by NASA Moderate Resolution Imaging Spectrometer (MODIS) satellite images and records of lake ice thicknesses respectively. It is found from analysis with past meteorological data that ice thickness does not depend significantly on mean air temperature, but rather on mean snow depth due to SI thickness growth. In this paper, preliminary observational results on the SI formation processes will also be reported.
Year: 2016