Reduced ice sum

In 1947/48, the reduced ice sum was introduced for the evaluation of ice winter severity in the German coastal regions. It constitutes the arithmetic mean of days with ice recorded at the 13 ice climatological stations and characterises the extent and duration of ice occurrence. In the time since 1897, the reduced ice sum computed for the Baltic Sea coast has fluctuated between zero and maximally 98 days. The arithmetic mean is 21 days, and the median value 11 days.

Literature 
Büdel,  J., 1947: Der Eiswinter 1945/46 an den deutschen Küsten (Brit. Zone) im Vergleich zu den Eiswintern  1903/04 bis 1942/43. Unveröff. Wiss. Arb. Dt. Hydrogr. Inst. Nr. 34.  
Nusser, F., 1948: Die Eisverhältnisse des Winters 1947/48 an den deutschen Küsten. Dt. hydrogr. Z. 1, 149-156.