Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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- 124 - Long-term Changes in Cyclone Trajectories in Northern Europe Mait Sepp 1 , Piia Post 2 and Jaak Jaagus 1 1 Department of Geography, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia, maitmss@ut.ee 2 Department of Environmental Physics, University of Tartu, Tähe 4, 51014 Tartu, Estonia 1. Introduction The Global warming has been detected during the 20 th century (Houghton et al., 2001). The warming has been significant also in the Northern Europe, including Estonia. Annual mean air temperature in Tartu (Estonia) has increased by 0.7°C during the 20 th century. The most remarkable warming in Estonia (by 1.7°C according to linear trend) has taken place in the second half of the century. Statistically significant trends in surface air temperature have been observed in winter and especially in spring. The highest increase in monthly mean temperature has occurred in March when mean temperature has risen up to 5°C during 1951-2000 (Jaagus, 2004). The climatic conditions in Northern Europe are much warmer then in Siberia or Canada at the same latitudes. The main source of heat in Europe during the cold season is the Atlantic Ocean. Heat of the Atlantic is transported to the European inland by atmospheric circulation. Westerly airflow transports warm and moist maritime air as far to the east as to the Urals. There are many ways to investigate the essence and changes of atmospheric circulation. One of the most popular approaches is to use circulation indices as the North Atlantic Oscillation (NAO) indices (Hurrell 1995, Jones et al. 1997) and the Arctic Oscillation (AO) index (Thompson, Wallace, 1998). On the other hand a number of subjective classifications of circulation types have been worked out. The most prominent of them are the Grosswetterlagen system (Gerstengarbe et al. 1993), and the classifications elaborated by Dzerdzeevskij (1968), Vangengeim and Girs (Girs, 1971) and Lamb (1972). Numerous studies have demonstrated that there is a strong correlation between variability of atmospheric circulation and air temperature in Europe, especially in Northern Europe (Hurrell 1995, Post et al., 2002; Sepp, Jaagus, 2002). Both circulation indices and types are generalizations of circulation processes and do not allow to make a detailed analyses. Circulation forms join together genetically similar (cyclonic or anticyclonic) elementary circulation processes. But the actual position of ridges and lows may be different over a geographical location, which affects air temperature differently, especially in spring and autumn. For example, depending on the trajectory of cyclones, warm Atlantic or cold Arctic air may be transported into Estonia. Therefore, it is important to investigate changes in cyclonic activity and in cyclone trajectories. The first attempt to investigate storm tracks over Europe was made by van Bebber in 1882. He analyzed the movement of depressions during 1876-80 and found five major tracks (Barry, Perry, 1973). In the Soviet Union, Krichak (1956) investigated trajectories of lows and highs during the period 1930 - 1954 and distinguished ten main tracks. Gulev et al. (2001) analyzed Northern Hemisphere winter cyclone activity using NCEP/NCAR 6-hourly reanalysis data for the period 1958 - 1999 using software presented in Grigoriev et al. (2000). They concluded that the total number of winter cyclones has decreased by 12 cyclones per decade on the Northern Hemisphere in years 1948-1999. Over the Atlantic Ocean, the number of cyclones has decreased in mid latitudes but significantly decreased in the region of the Icelandic minimum and in the European Arctic till the early 1970s. A significant upward trend (14 cyclones per decade) took place over Arctic from the late 1970s to 1990s. In the 1980s and 1990s, intense cyclones become more frequent while the number of weak cyclones has decreased (Gulev et al., 2001). Two hypotheses how the warming can be caused: 1) Due to the increase in frequency of deep and long-living cyclones, climate conditions in Northern Europe have become more maritime because the increased number of cyclones have moved inland of Northern Europe; 2) There have been changes in frequency of cyclone trajectories. Probably, cyclones in Northern Europe prefer more northern tracks and less the southern ones. That causes a strong advection of mild and moist air into Northern Europe. Our task is to track the cyclones in the Atlantic-European sector of the Northern Hemisphere and answer to these abovementioned questions. 2. Data and preliminary results At our disposal is the database of Northern Hemispheric cyclones (Gulev, et al., 2001) and software presented in Grigoriev et al. (2000). Changes in frequency and trajectories of cyclones in the Atlantic-European sector (30W-45E, 35N–75N) of the Northern Hemisphere for the period 1948 - 2000 are analyzed. The number of cyclones for the Atlantic-European sector is calculated (Figure 1). During years 1948 – 2000 the total number of cyclones has decreased over this area what coincides also with the results of Gulev et al. (2001). The breaking point in cyclonic activity at the beginning of 1970s can easily be followed. Number of cyclones 625 575 525 475 1948 1958 1968 1978 1988 1998 Years Figure 1. Time series of the total number of cyclones (with linear trend line) in Atlantic-European sector (30W - 45E, 35N-75N) for period 1948-2000. To concentrate more to the changes in cyclone activity over Northern Europe, cyclones in circles with radii 500, 1000, 1500 and 2000 km are counted (Figure 2). The center of those circles was chosen at 60 N, 22.5 E. All four lines look
similar: the locations of main minima and maxima coincide for all lines. In the Northern Europe region the decreasing trend after 1970s is smaller than over the whole Atlantic- European region, resulting for the time period 1948-2000 in a slight increase for the cyclones frequency (about 10 cyclones for selected 53-years period). Trend lines for frequency of cyclones in all 4 circles show a slight increase of number of cyclones reaching to the Northern Europe. Number of cyclones 450 400 350 300 250 200 150 100 50 0 1948 1958 1968 1978 1988 1998 Years 2000 1500 1000 500 Figure 2. Time series of the total number of cyclones whose centres are less distant from 60N, 22.5E than 500, 1000, 1500 and 2000 km, respectively. Linear trend lines are also included. 3. Acknowledgements We like to thank Olga Zolina (University of Bonn) for making available Northern Hemisphere cyclones database. The work is partly sponsored by Estonian Science Foundation grant 5786. References Barry, R. G. and Perry, A. H. Synoptic Climatology Methods and Applications. Methuen & Co Ltd, 1973 Dzerdzeevskij B.L.Cirkuljacionnyje mehanizmy v atmosfere severnogo polušarija v XX stoletii. Inst. Geogr. AN SSSR, Moscow, 1968 (in Russian) Gerstengarbe F.W., Werner P.C., Busold W., Rüge U., Wegener K.-O.: Katalog der Grosswetterlagen Europas nach Paul Hess und Helmuth Brezowsky 1881-1992. Bericht des Deutschen Wetterdienstes Nr. 113, 4th edn., Deutscher Wetterdienst, Offenbach am Main, 249 pp, 1993 Girs A.A. Mnogoletnije kolebanija atmosfernoj cirkuljacii i dolgosročnyje gidrometeorologičeskije prognozy. Gidrometeoizdat, Leningrad, 280 pp, 1971 (in Russian) Grigoriev, S., Gulev, S. K., Zolina, O., Innovative software facilitates cyclone tracking and analysis. EOS ,Vol. 81, No. 16, April 18, 2000 Gulev, S.K., Zolina, O., Grigoriev, S., Extratropical cyclone variability in the Northern Hemisphere winter - 125 - from the NCEP/NCAR reanalysis data. Climate Dynamics, Vol. 17, pp. 795-809, 2001 Houghton, J.T. et al. (eds.), Climate change 2001: The scientific basis. Third Assessment Report of IPCC. Cambridge University Press, 2001 Hurrell J.W. Decadal trends in the North Atlantic Oscillation and relationships to regional temperature and precipitation. Science, vol 269, pp. 676–679, 1995 Jaagus, J., Climatic changes in Estonia during the second half of the 20 th century in relationship with changes in large-scale atmospheric circulation, Theor. Appl. Climatol., (submitted), 2004 Jones P. D., Jónsson T. & Wheeler D. Extension to the North Atlantic Oscillation using early instrumental pressure observations from Gibraltar and South-West Iceland. Int. J. Climatol., Vol 17, pp. 1433–1450, 1997 Krichak, O. G., Sinopticheskaja meteorologija. Gidrometeoizdat, Leningrad, 1956 (in Russian) Lamb H.H. British Isles weather types and a register of the daily sequence of circulation pattern 1861-1971. Geophys. Mem. 116, 85 pp. 1972 Post, P., Truija, V., Tuulik, J., Circulation weather types and their influence on temperature and precipitation in Estonia. Boreal Env. Res., Vol 7, pp. 281–289, 2002 Sepp, M., Jaagus, J., Frequency of circulation patterns and air temperature variations in Europe. Boreal Env. Res., Vol. 7, pp. 273–279, 2002 Thompson D.W.J. & Wallace J.M.. The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., Vol 25, pp. 1297-1300, 1998
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Fourth Stu
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Preface The 4 th Study</str
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- I - Table of Abstracts Title Auth
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- III - Sensitivity in Calculation
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- V - Parameter Estimation of the S
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- VII - The Realism of the ECHAM5.2
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Adam, W. K. .......................
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- 1 - Activities of the GEWEX Hydro
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eference site archive (Cabauw, Neth
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- 5 - Remote Sensing of Atmospheric
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minute averages around the satellit
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- 9 - Precipitation Type Statistics
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- 11 - Assimilation of New Land Sur
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Multichannel Microwave Radiometer f
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output has been processed in an equ
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height dependence of the Z-R-relati
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- 19 - CERES and Surface Radiation
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- 21 - Coastal Wind Mapping from Sa
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- 23 - Clouds and Water Vapor over
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- 25 - Broadband Cloud Albedo from
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- 27 - Observation of Clouds and Wa
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shows a ground-track of the vessel
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- 31 - Determination and Comparison
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- 33 - Spatial Variability of Snow
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- 35 - EVA-GRIPS: Regional Evaporat
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- 37 - LITFASS-2003 - A Land Surfac
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-39- Calibrated Surface Temperature
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- 41 - The Marine Boundary Layer -
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- 43 - Characteristics of the Atmos
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Figure 2. Surface stress from two d
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During the experiment the water was
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While the number of smallest drops
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SCANDIA will not be supported any l
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- 53 - Relationships Between Precip
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- 55 - Analysis of the Role of Atmo
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- 57 - Meteorological Peculiarities
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Baltic Sea Inflow Events Jan Piechu
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- 61 - The Different Baltic Inflows
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- 63 - Observations of Turbulent Ki
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- 65 - The Influence of Synoptic Si
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-67- Improved Method for the Determ
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-69- The Helicopter-Borne Turbulenc
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- 71 - CEOP Reference Site Data fro
Page 89 and 90: - 73 - The BALTEX Hydrological Data
Page 91 and 92: - 75 - Hydrological and Hydrochemic
Page 93 and 94: -77- Sea-level Monitoring at MARNET
Page 95 and 96: 1 0.8 0.6 0.4 0.2 GO(CLD-M) ERA40 S
Page 97 and 98: Figure 2. Monhly mean values of lat
Page 99 and 100: In the case of an ideal fit, the co
Page 101 and 102: - 85 - Influence of Atmospheric For
Page 103 and 104: The largest inter-annual variabilit
Page 105 and 106: References Andrejev, O, Sokolov, A.
Page 107 and 108: On the other hand, if the stratific
Page 109 and 110: Cyberska 1989, Cyberska and Krzymin
Page 111 and 112: - 95 - Continental-Scale Water-Bala
Page 113 and 114: - 97 - ICTS (Inter-CSE Transferabil
Page 115 and 116: The subsurface flow calculation is
Page 117 and 118: functions only data with higher qua
Page 119 and 120: - 103 - Modelling the Impact of Ine
Page 121 and 122: - 105 - Objective Calibration of th
Page 123 and 124: - 107 - Validation of Boundary Laye
Page 125 and 126: - 109 - Simulated Dynamical Process
Page 127 and 128: spreads along isobaths (fig.2). As
Page 129 and 130: than the precipitation pattern of J
Page 131 and 132: Figure 2. Long-term variability in
Page 133 and 134: obvious from temperature charts. Ho
Page 135 and 136: shortening of the winter seasons by
Page 137 and 138: Maximum 5 day precipitation (mm) Nu
Page 139: scale parameters the correlation be
Page 143 and 144: - 127 - Storminess on the Western C
Page 145 and 146: - 129 - Trends in Wind Speed over t
Page 147 and 148: - 131 - Wind Energy Prognoses for t
Page 149 and 150: - 133 - Detection of Climate Change
Page 151 and 152: Figure 3. Cross section of salinity
Page 153 and 154: of 35 m/s up to 3 hours. Data on wi
Page 155 and 156: Figure 2. Time series of Mean Sea L
Page 157 and 158: - 141 - Calculation and Forecast of
Page 159 and 160: - 143 - An Overview of Long-Term Ti
Page 161 and 162: - 145 - Baltic Sea Saltwater Inflow
Page 163 and 164: - 147 - Significance of Feedback in
Page 165 and 166: Lindström, G., Johansson, B., Pers
Page 167 and 168: - 151 - Air-Sea Fluxes Including Mo
Page 169 and 170: - 153 - The Realism of the ECHAM5.2
Page 171 and 172: - 155 - Figure 3. Accumulated total
Page 173 and 174: Figure 2. Example for Fourier decom
Page 175 and 176: Figure1. Modeled percent volume cha
Page 177 and 178: conditions even more challenging th
Page 179 and 180: surface heat fluxes close to zero.
Page 181 and 182: - 165 - Figure 1. Modeled seasonal
Page 183 and 184: - 167 - Present-Day and Future Prec
Page 185 and 186: - 169 - Extreme Precipitation on a
Page 187 and 188: at the stations Pärnu (Estonia) an
Page 189 and 190: 6. Results There are many possible
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and vegetation, and to derive the h
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The structure of water bodies cadas
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Figure 1. The area of Gdańsk subje
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- 181 - Climate and Water Resources
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- 183 - Generating Synthetic Daily
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The evapotranspiration is affected
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Model parameters and coefficients:
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3. Hydrodynamic model of nutrient l
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No. 15: Minutes of 8 th Meeting of
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Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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