A time series of over 100Â years of ice seasons on Lake Ladoga

Lake Ladoga ice conditions were examined for the period 1913-2015 based on weather data and Finnish ice data (1913-1937) and Soviet/Russian airborne and satellite surveys (1943-2015). The data from the time series included the evolution of the ice concentration each winter, and occasionally of ice thickness. The mean freezing and breakup dates were November 26 and May 15, respectively, and the annual frequency of complete freeze-over of the lake was 0.83. The ice may break up any time during winter and undergo rapid shifts. Therefore, the evolution of the concentration is an additional climatological property of ice cover, compressed into one index equal to the time integral of the ice concentration over the ice season. The period from 1990 to present was much milder than the preceding years. First-order analytic models fitted the data well. The evolution of ice conditions was synchronized with air temperature measurements from the Sortavala weather station on the northern coast of the lake. The increase in ice concentration depended on the accumulated freezing-degree-days (AFDD) and the hypsographic curve, while the ice thickness increased with the square root of AFDD. Vertical and lateral ice decreases during the breakup period were dictated by solar radiation and accumulated positive degree-days (APDD). These models provided an insight into the climatological properties of the time series.