Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Detection of Climate Change in the Baltic Sea Area Using Matching Pursuit
Christin Pettersen 1 , Anders Omstedt 1 , Harold O. Mofjeld 2 , James E. Overland 2 and Donald B.
Percival 3
1
Department of Oceanography, Earth Science Centre, Göteborg University, Box 460, SE-405 30 Göteborg, Sweden
2
Pacific Marine Environmental Laboratory /NOAA, Seattle, WA 98115-6349
3
Applied Physics Laboratory, Seattle, WA 98195-5640
chpe@oce.gu.se
1. Background
In this study we have been investigating different time series
describing ice and temperature, during the last 500 years.
The aim has been to describe the different centuries by
considering the links between the studied parameters. The
time series we have used show the time evolution of the date
for ice break-up as well as maximal ice cover and air
temperature, in and over the Baltic Sea area.
Figure 1. Map of the Baltic Sea showing the location
where the time series have been collected.
2. Data
The ice data used are of yearly resolution and stretches back
to at least the beginning of the 18 th century, with the longest
records covering the last 500 years, see fig 2. Air
temperature data are represented by records from Stockholm
and reconstructed data from Tallinn.
Figure 2. Time series describing ice used in the study, red
line is the 15 years running mean.
3. Method
The statistical method used in this study is matching pursuit.
Matching pursuit has shown to be very useful in detecting
abrupt changes or events in time series, Percival et al.,
(submitted), and therefore very interesting to use at
climatic time series. The idea behind the technique is to
make a large collection of time series vectors, a dictionary,
which could explain the time/frequency content of the
time series. A time series can then be projected against the
vectors in the dictionary and analysed.
In figure 3 we show the results from analysing the
maximal ice extent. The different steps show the order in
which the different vectors are picked out. In this case we
get a square wave oscillation as a first step.
Figure 3. Results from the matching pursuit analysis of
the maximal ice extent in the Baltic Sea.
4. Results
The outcome of the matching pursuit analyse strongly
support the occurrence of a regime shift in the end of the
19 th century. This shift is reported in other studies Omstedt
and Chen (2001) and is probably due to a change in the
large-scale atmospheric circulation associated with
increased low pressure circulation Omstedt et al. (2004).
References
Omstedt, A. and D. Chen, Influence of atmospheric
circulation on the maximum ice extent in the Baltic
Sea. J. Geophys. Res., 106 (C3), 4493-4500, 2001
Omstedt, A., C. Pettersen, J. Rodhe and P. Winsor, Baltic
Sea climate: 200 yr of data on air temperature, sea
level variation, ice cover, and atmospheric circulation,
Climate Research, 25, 3, 205-216, 2004
Percival, D.B., J.E. Overland and H.O. Mofjeld, Using
matching pursuit to assess atmospheric circulation
changes over the North Pacific. J. Climate. Submitted