Author(s): Juho Jakkila; Matti Lepparanta; Toshiyuki Kawamura; Kunio Shirasawa
Linked Author(s): Matti Leppäranta
Keywords: No keywords
Abstract: The heat budget of Lake Paajarvi, located in Southern Finland, was studied basing on field experiment in winter 2003-2004. The data includes meteorological observations, under-ice temperature and current measurements and ice and snow thickness observations. Additional field measurements were done in April 2006 for examining radiative transfer through the ice cover. The obtained data was used for studying the heat exchange at the ice-water interface. Turbulent heat flux from the water was calculated using under-ice water current and temperature measurements. Penetration of shortwave radiation through the ice cover was examined by diffuse attenuation coefficients determined for snow and different ice layers. Heat fluxes at the ice bottom were compared to the heat budget terms at the surface of the ice cover. The main term of the surface heat budget during winter months was longwave radiation loss, which was balanced by heat release from the ice growth and heat flux from the water. In April shortwave radiation became the dominant term of the surface heat budget and penetrated radiation heated the under ice water causing convective currents. Warming of under ice water and convective currents increased the average heat flux from the water from 12 to 20 W/m2. The increasing amount of penetrated radiation during the melting season heated up the water temperature of the whole lake evenly to 3 ºC already before ice break-up. The penetrated radiation has thus important impact on springtime overturn and the water quality of the lake during the melting season.
Year: 2008