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The ice winter of 2016/17 on the German North and Baltic Sea coasts with a brief de- scription of ice conditions in the entire Baltic Sea region Dr. Sandra Schwegmann [email protected] Dr. Jürgen Holfort [email protected] Bundesamt für Seeschifffahrt und Hydrographie, Eisdienst Neptunallee 5, Rostock 18057 Content Progression of the ice winter on the German North and Baltic Sea coasts ......................................................... 2 Weather conditions on the German coastal areas .......................................................................................... 2 Ice conditions on the German North and Baltic Sea coasts ............................................................................ 4 Navigational conditions on the German Baltic Sea coast ............................................................................... 6 Ice winter intensity .......................................................................................................................................... 6 Ice conditions in the western and southern Baltic Sea ........................................................................................ 9 Ice conditions in the northern Baltic Sea (north of 56°N) ................................................................................. 10 Maximum sea ice extent and maximum sea ice volume in the Baltic Sea ........................................................ 11 Literature ........................................................................................................................................................... 12 Appendix ........................................................................................................................................................... 14 Table A 1: Ice conditions at the German North Sea coast in the winter of 2016/17. .................................... 14 Table A 2: Ice conditions at the German Baltic Sea coast in the winter of 2016/17. .................................... 15 Figure A 1: Daily ice occurrence at the German North and Baltic Sea coast in the winter of 2016/17. ...... 16 New-ice cover in the port of Thiessow (Bay of Greifswald) on 11.02.2017 Courtesy of Frank Sakuth 1 Progression of the ice winter on the German North and Baltic Sea coasts Weather conditions on the German coastal areas In the winter 2016/2017, November was comparatively cold at the German coasts. Locally, temperatures dropped down to or slightly below the freezing point in the mid of the month. With monthly averages between 4°C and 6°C, air temperatures were well below the values for the usually used reference period 1961 – 1990 (Ch. Lefebvre, 2013) and even a bit lower for the current reference period (1981-2010, see reference periods in Tab. 1). In December air temperatures were, on the contrary, up to 2-3°C higher than the reference values (Tab. 2). The seasonal cooling of the air proceeded very slowly in December. Although light frost occurred occasionally, temperatures rose also up to 10°C. Northern Germany was influenced predominantly by high pressure systems by that time; mostly westerly to north-westerly winds transported mild air masses into the coastal regions. In the beginning of January, north-easterly winds brought a frost period - parallel to the big storm surges in the North and Baltic Seas - which lasted for few days. Afterwards the weather situation was unstable for the rest of the month with occasionally occurring frost periods (see Fig. 1). Table 1: Climatological mean of air temperatures (°C) in winter months on the German Baltic cost for the peri- od 1961-1990 (P1) and 1981-2010 (P2) exemplarily for Greifswald, Rostock-Warnemünde, Schleswig and Nor- derney (Data source: Deutscher Wetterdienst, www.dwd.de). Station November December January February March P1 P2 P1 P2 P1 P2 P1 P2 P1 P2 Greifswald 4,6 4,7 1,1 1,5 -0,6 0,7 0,0 1,1 2,7 3,7 Rostock-Warnemünde 5,3 5,5 1,9 2,3 0,2 1,4 0,7 1,7 3,1 4,1 Schleswig 4,9 5,0 1,7 2,0 0,3 1,3 0,6 1,4 2,8 3,7 Norderney 6,3 6,6 3,2 3,5 1,6 2,6 1,8 2,6 4,0 4,9 Table 2: Monthly mean air temperatures (°C) and their deviations from the reference period P2 (1981 – 2010) in °C for the winter 2016/2017 (Data source: Deutscher Wetterdienst, www.dwd.de). Station November December January February March Tair ΔTair Tair ΔTair Tair ΔTair Tair ΔTair Tair ΔTair Greifswald 4,0 -0,7 3,8 2,3 -0,2 -0,9 1,7 0,6 6,3 2,6 Rostock-Warnemünde 5,0 -0,5 4,8 2,5 1,1 -0,3 2,3 0,6 6,3 2,2 Schleswig 4,0 -1,0 4,7 2,7 1,1 -0,2 2,5 1,1 6,1 2,4 Norderney 5,8 -0,8 5,5 2,0 2,3 -0,3 3,1 1,3 7,2 2,3 In total, January was nevertheless a bit colder than normal. The first persistent frost period occurred only in February when the wind changed to easterly directions. Although February was warmer than normal, daily averaged air temperatures dropped below the freezing point permanently between the 7th and 14th of February. On the 15th of February the wind changed to westerly directions and the air became milder again. Afterwards, temperatures stayed above the freezing point for the rest of the season. Summarized, the winter of 2016/2017 consisted of one weak cold period from the beginning of January up to mid-February. Temperatures were not permanently below the freezing point during this period but varied around 0°C by few degree Celsius. The lowest values of the daily averaged temperatures lay between -3°C at the North Sea and up to -10°C at the Ger- man Baltic Sea (Fig. 2). 2 Greifswald Warnemünde Schleswig Norderney 12 10 8 6 4 °C 2 0 7.2. 7.3. -2 3.1. 17.1. 6.12. 10.1. 24.1. 31.1. 14.2. 21.2. 28.2. 14.3. 15.11. 22.11. 29.11. 13.12. 20.12. 27.12. -4 -6 -8 Figure 1: Daily averages of air temperatures in the winter 2016/17 (Data source: Deutscher Wetter- dienst, www.dwd.de/) exemplarily for Greifswald, Rostock-Warnemünde, Schleswig und Norderney. Air temperature 0 Oie -2 List Emden Arkona Tönning Hamburg Schleswig Norderney -4 Greifswald Warnemünde °C -6 -8 -10 2015/2016 2016/2017 -12 Figure 2: Lowest air temperatures along the German coasts, from the west to the east. Water temperatures dropped below the freezing point in the beginning of January in the inner waters of the German Baltic Sea coast except for the Schlei, where ice growth could already be observed mid-November for a few days. At the outer coastal part of the North and Baltic Seas, temperatures stayed above 0°C over the entire winter (see Fig. 3). 3 10.0 9.0 Karlshagen 0,5 m Karnin 0,5 m Barhöft 0,5 m Stahlbrode 0,5 m 8.0 07:00 MEZ 07:00 MEZ 07:00 MEZ 07:00 MEZ 7.0 6.0 5.0 °C 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 3.1. 7.2. 7.3. 6.12. 10.1. 17.1. 24.1. 31.1. 14.2. 21.2. 28.2. 14.3. 20.12. 22.11. 29.11. 13.12. 27.12. 15.11. 10.0 9.0 Büsum(Schleuse) 1,5m Brunsbüttel 1,0m Blankenese 1,0m Norderney 1,5m 08:00 MEZ 08:00 MEZ 07:00 MEZ ca. 14:00 MEZ 8.0 7.0 6.0 5.0 °C 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 7.2. 3.1. 7.3. 6.12. 10.1. 17.1. 24.1. 31.1. 14.2. 21.2. 28.2. 14.3. 22.11. 29.11. 13.12. 20.12. 27.12. 15.11. 10.0 9.0 Koserow WDFÜ 1,5 m Sassnitz 1,5 m Warnemünde WDFÜ 1,5 m Travemünde 1,5 m 8.0 07:00 MEZ 07:00 MEZ 07:00 MEZ 07:00 MEZ 7.0 6.0 5.0 °C 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 3.1. 7.2. 7.3. 24.1. 6.12. 10.1. 17.1. 31.1. 14.2. 21.2. 28.2. 14.3. 22.11. 29.11. 13.12. 20.12. 27.12. 15.11. Figure 3: Water temperatures of the German coastal waters. Data sources: Karlshagen, Karnin, Barhöft, Stahlbrode, Koserow, Sassnitz and Warnemünde – WSA Stralsund; Travemünde – WSA Lübeck; Büsum – Schleuse Büsum; Blankenese - Institut für Hygiene und Umwelt; Norderney – Deutscher Wetterdienst; Brunsbüttel – WSA Brunsbüttel. Ice conditions on the German North and Baltic Sea coasts The ice winter of 2016/17 consisted of three ice periods at the German North Sea coast: the first ice occurred in the beginning of January. Afterwards, there was a short ice period in mid- January and a further one in February. At the German Baltic Sea coast, ice growth took place for three times between mid-November and beginning of December, but only for few days in each period. In the beginning of January, a permanent ice cover formed regionally between 5th of January and 24th of February. The evolution of the ice winter 2016/2017 is 4 shown in Figure A1 in the appendix. Table A1 and A2 of the appendix summarize the most important ice parameters for the season. Figure 4: Ice conditions in Thiessow at the time of maximum ice extent on the German Baltic Sea coast. Courtesy of Frank Sakuth. The initial ice formation started on the 12th November on the river Schlei. In fact, this was the earliest seasonal ice formation since 1984, when the first ice was discovered in Warthe on the 1st of November. The former earliest ice formation on the river Schlei took place on the 17th November 1993. At the North Sea, ice had initially formed in Emden on the 3rd January and in Tönning on the 5th January. In Tönning ice could be found temporarily until the 16th February. At the Baltic Sea, ice persisted locally until the 24th February.