Matti Leppäranta was born 1950 in Helsinki, Finland. He received MSc degree in mathematics in 1976 and PhD degree in geophysics (sea ice) in 1981 in the University of Helsinki. He has worked as a research physicist in the Finnish Institute of Marine Research in 1975–1991 except for a post doc period in Cold Regions Research and Engineering Laboratory, Hanover, NH in 1983–1984. Since 1992 he has been a professor in geophysics in the University of Helsinki, from 2018 as an emeritus. In the university period he has made long-term visits to Hokkaido University, Japan and Dalian University of Technology, China and acted as a regular visiting teacher in Universitetstudiene i Svalbard (UNIS) and St. Petersburg State University, Russia. He is also an adjunct professor in University of Oulu, Finland, University of Sherbrooke, Québec, Canada, and Polar Research Institute of China, Shanghai.

The scientific research of Matti Leppäranta has been around geophysics of sea ice and lake ice, covering their structure and morphology, remote sensing, thermodynamics, dynamics, and environmental and climate questions. He organized with IAPSO Sea Ice Commission an International Summer School on Physics of Ice-covered Seas in 1994. He has given sea ice dynamics lectures in several advanced study institutes and published the books The drift of sea ice (2005) and Physical oceanography of the Baltic Sea (2009, with Kai Myrberg, and Freezing of lakes and physics of their ice cover (2015). The sea ice and lake ice books are available for their second editions (2011 and 2023) and Chinese translations (2017 and 2024). Matti Leppäranta has been a member of IAPSO Sea Ice Commission, International Glaciological Society Board, and IAHR Ice Committee with a chair in 2014–2018.

Lake Ice Melting, Deterioration and Break-up

Matti Leppäranta

University of Helsinki, Yliopistonkatu 4, 00100 Helsinki, Finland

This presentation provides an overview of lake ice decay from field data, modelling, and climatological perspective. The time scale of the decay is one month for half meter thick seasonal lake ice. Field data of this period is limited because it is dangerous to work on a weakening ice cover, and modelling efforts suffer from good validation data as well as from parameterization problems. Remote sensing methods suffer from the co-presence of liquid water with ice.

Lake ice decay is a chaotic process where lake ice thermal, radiative and mechanical processes drive ice loss and deterioration in intense interaction. Starting from a solid ice layer, melting at the ice surface and bottom decrease ice thickness while internal melting increases the porosity and, consequently, the strength of the ice. Melting of lake ice is driven primarily by solar radiation, and complications arise from large variability of albedo and light transmittance of ice in the decay period. Melting increases at the bottom of the ice since a fraction of the solar radiation transmitted through ice returns there.

In time series analysis and ice climatology a common approach has been to estimate the melting using the positive degree-days of air temperature. This is motivated by the correlation of air temperature to many melting factors, but to include properly for the role of the solar radiation, a latitude dependent term must be added to the picture. In extreme polar conditions, ice maybe melted by solar radiation alone with no significant degree-days. The climate sensitivity of ice decay and break-up is primarily in the maximum annul ice thickness and snow accumulation on ice.