Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Table 1. Monthly trends of the mean wind speed, m·s -1 ·year -1
Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Utö
Hanko
Inkoo
Kotka
Kalbådagrund
Kunda
Pakri
Vilsandi
0.04
0.01
0.02
0.05
-0.04
-0.01
-0.05
-0.01
0.04
0.02
0.03
0.07
0.07
-0.01
-0.05
0.03
0.02
0
0.01
0.05
0.07
-0.03
-0.07
0
0.02
0.01
0.01
0.03
0.01
-0.03
-0.07
-0.03
This fact is extremely interesting if we keep in mind that
according to, e.g., Orviku et al. (2003) the frequency of
storms has increased over the same decades. Since the
storms occur mostly during the cold period in the area in
question, this should result in an opposite tendency.
Notice that the detected feature is also different from the
general tendency of restoring of the storm- and waveclimate
to the level that was typical at the beginning of
the 20 th century (WASA Group 1994) .
The same procedure was applied to the late winter data.
Coupling February and March gave us a data set where a
statistically significant (at the 0.1 level) positive trend of
the mean wind speed was detected with a slope of 0.070.
Such an increase in the surface wind speed can be
attributed to the recently detected changes in the largescale
circulation (Keevallik 2003). Namely, both, zonal
and meridional components of the wind velocity vector
at the 850 hPa isobaric level clearly increased.
Moreover, the wind speed at 850 hPa level during 1966-
1997 showed a significant trend with the slope of 0.066
in February. In March the trend was weaker but also
positive.
0.02
0
0
0.03
0.01
-0.03
-0.06
-0.01
4. Conclusions
1) Trends in the wind speed are different at the
northern and southern coasts of the Gulf of Finland. The
wind speed increased at the Finnish coast and decreased
(at least during the second half of the year) in the centre
of the gulf and at the Estonian coast.
2) The increase in the wind speed during late winter
and early spring can be attributed to the changes in the
large-scale circulation over this area.
3) The decrease of the average wind speed in autumn
and early winter is in an amazing contradiction with the
generally recognised fact that the frequency of storms
has increased during the same period.
Acknowledgments
The authors are deeply grateful to the Finnish
Meteorological Institute (Contract 8/410/03, in the
framework of the project “Reconstruction of the wind
regime of Gulf of Finland") and Estonian Meteorological
and Hydrological Institute for presenting the wind data.
Financial support from ETF (Grant 5762) is gratefully
appreciated.
0.02
-0.01
0.01
0.03
0.01
-0.02
-0.04
-0.01
0.02
0
0.02
0.04
0.04
-0.02
-0.05
-0.03
0.02
-0.01
0
0.02
-0.06
-0.02
-0.06
-0.01
0.01
-0.01
-0.01
0.02
-0.05
-0.05
-0.09
-0.06
0.02
0
0.02
0.06
-0.03
-0.04
-0.09
-0.01
0.02
0
0.02
0.04
-0.06
-0.04
-0.11
-0.07
0.03
0
0.01
0.04
-0.03
-0.04
-0.09
-0.02
References
Jaagus, J. Climate change tendencies in Estonia in
relation with changes in atmospheric circulation
during the second half of the 20 th century.
Publicationes Instituti Geographici Universitatis
Tartuensis 93, 62-78, 2003
Keevallik, S. Changes in spring weather conditions and
atmospheric circulation in Estonia (1955-1995).
International Journal of Climatology 23, 263-270,
2003
Niros, N., T. Vihma, J. Launiainen. Marine meteorological
conditions and air-sea exchange processes
over the northern Baltic Sea in 1990s. Geophysica
38, 59-87, 2002
Orviku, K., J. Jaagus, A. Kont, U. Ratas, R. Rivis.
Increasing activity of coastal processes associated
with climate change in Estonia. Journal of Coastal
Research 19, 364-375, 2003
WASA Group. Comment on ``Increases in Wave
Heights over the North Atlantic: A Review of the
Evidence and some Implications for the Naval
Architect'' by N Hogben. Transactions of the Royal
Institute of Naval Architects 137, 107-110, 1994.