The role of snow in the thickening processes of lake ice at Lake Abashiri, Hokkaido, Japan

To clarify the properties of lake ice at mid-latitudes subject to moderate air temperature, heavy snow and abundant solar radiation even in winter, we conducted field observations at Lake Abashiri in Japan for three winters and developed a one-dimensional (1-D) thermo-dynamical ice growth model. Using this model with meteorological data-sets, we examined the role of snow in the ice thickening process, as well as the Lake Abashiri ice phenology (including the interannual trend) for the past 55 years to compare with high latitude lakes. The ice was composed of two distinct layers: a snow ice (SI) layer and a congelation ice layer. The SI layer occupied a much greater fraction of total ice thickness than that at high latitude lakes. In-situ observations served to demonstrate the validity of the model. Freeze-up and break-up dates supplied by satellite imagery enabled further model validation prior to the availability of field data (2000/01–2015/16). Based on both observations and numerical experiments, it was found that one important role of snow is to moderate the variability of ice thickness caused by changes in meteorological conditions. Furthermore, ice thickness is more sensitive to snow depth than air temperature. When applied to an extended 55-year period (1961/62–2015/16) for which local meteorological observations are available, the mean dates of freeze-up and break-up, ice cover duration and ice thickness in February were estimated to be 12 December (no significant trend), 17 April (−1.7 d/decade), 127 d (−2.4 d/decade) and 43 cm (−1.4 cm/decade). For this long-term period, while snow still played an important role in ice growth, the surface air temperature warming trend was found to be a strong factor influencing ice growth, as reported for the high latitude lakes.