The western Baltic sea ice season in terms of a mass-related severity index: 1879-1992 - Part I. Temporal variability and association with the north Atlantic oscillation

Abstract

The variability of the severity of ice winters in the Western Baltic between 1879 and 1992 is statistically investigated using a time series of the accumulated areal ice volume (or V Al:) from the Baltic coast of Schleswig-Holstein. Lowpass filtering of the original time series shows the level of ice production in the mid 1980s to have been the same as that almost 100 years ago. A vivid interpretation is made possible of the variations in ice production by classifying V Al: according to ice winter severity types. The increased variability of ice production since the 1920s is seen in the more frequent occurrence both of very strong and weak ice winters, while moderate and strong ice winters have decreased. The time series of the accumulated areal ice volume is negatively correlated with a temporally corresponding series of the NAO winter index, a measure of the strength of the zonal atmospheric circulation above the North Atlantic. Pearson's correlation coefficient, rp =-0.47, exceeds the 99.9 % confidence limit. In addition, a contingency table analysis revealed that this inverse correlation is due to the preferential occurrence of (a) weak ice winters with strong westerlies (NAO winter index > 1) and (b) strong to very strong ice winters with weak westerlies (NAO winter index <-1).

Sea ice in the Baltic Sea – revisiting BASIS ice, a historical data set covering the period 1960/1961–1978/1979

“…This finding is in agreement with previous studies considering the relation between the NAO and ice extent (e.g. Tinz, 1996;Jevrejeva et al, 2003;Koslowski and Loewe, 1994). Note, however, that the relation between the NAO index and the ice extent is nonstationary (Omstedt and Chen, 2001), i.e.…”

“…The time period comprises the winters 1960/1961-1978/1979, a period known to feature high interannual variability, predominantly the effect of some particularly severe winters during the 1960s (e.g. Koslowski and Loewe, 1994). Figure 3 confirms the large interannual variability of the basin's ice coverage, which is consistent with previous studies (Leppäranta and Myrberg, 2009): maximum coverage reached during an annual cycle ranges from percentages as low as ≈ 15 up to almost 80 %.…”

Recent Change—Sea Ice

“…Meier and Kauker (2002) found that during two periods, around 1926 and 1966, the correlation increased simultaneously with improvements in the observation methods for MIB. Changes in the NAO-MIB relationship can, however, also be due to changes in the location of the atmospheric pressure patterns (Koslowski and Loewe 1994;Chen and Li 2004).…”

Severity of winter seasons in the northern Baltic Sea between 1529 and 1990: reconstruction and analysis

“…Tarand (1993 constructed time series of ice breakup in the port of Tallinn since 1501. Ice conditions in the western Baltic Sea have been analyzed in terms of a mass-related severity index by Koslowski & Loewe (1996) and Koslowski & Glaser (1995, 1999. Reconstruction of 7 types of winter severity was based on the accumulated areal ice volume along the German Baltic during 1501-1995.…”