Baltic Sea Ice Climate Workshop 2005
80
(10 km )
Reconstruction of Annual Maximum Ice Extent
in the Baltic Sea 1660-2005
Lars Axel! and Katarina Lindquist
Swedish Meteorological and Hydrological Institute. Sweden
Figure 1. Annual maximum ice extent based on proxy data and ice charts.
Data used in the reconstruction:
•Swedish and Finnish ice charts:
1961-2005
•coastal observations: 1871—1990
•Stockholm winter (DJF) air temperature:
1756-1990
•Uppsala winter (DJF) air temperature:
1722-1990
•Central England winter (DJF) air
temperature: 1660—1990
Consolidation method:
•all proxy-based ice extents weighted as
Aj = W t Aj, + W 2 A j2 + ...
where w f is the weight corresponding to
the nth reconstruction
•weights calculated according to
w- l = Y E i /E j
j
where E'¡ 2 are the mean-square errors
Regression methods:
•calibration period: 1961—1990
•ice charts used as reference
•regression of winter air temperature T w
against ice charts: Aj=c 0 + c,T„
•c 0 and c, calculated for calibration period
for each temperature data set
•Aj calculated for period 1660—1960
•regression of coastal observations s yi
against ice charts: A t = S p a,
where j denotes year, i denotes the
number of the coastal station, and a i is the
ice area associated with coastal station i
•a t is calculated with a least-squares
technique for the calibration period
•Aj calculated for period 1871—1960
Figure 2. Calculated trends over moving 30-year
windows. Mann-KendaFs test was
applied on test time series B J =A J -aAj_ l , where
a is the autocorrelation for time lag 1 year
[i.e. con-(A r A jA )\. Significant trends (95%
C.I.) coloured red.
SWEDISH MARITIME
ADMINISTRATION
http://www.sjofartsverket.se/
Sponsored by the Swedish Maritime Administration: www.sjofartsverket.se
Contact person: Lars Axell e-mail: Lars.Axell@smhi.se
http:// www.smhi.se/
