Baltic Sea Cooling

How the early cooling of the Baltic paved the way for the extreme war winter of 1939/40 (2_17)

Extract from: “Climate Change & Naval War," pp. 87 - 96 Baltic Sea paved way for extreme winter (2_17) Preamble    Introduction    The Baltic Sea            The navy starts the war at Gdynia    General developments    Background to the two following winters     Historical List    LITERATURE

Preamble

Baltic Sea, in terms of size, is a mere ‘drop’ in the world’s oceans but due to its strategic location and specific features, acts as a ‘significant’ force affecting the weather of those countries surrounding it. It is an excellent location to study climatology as mentioned by the Russian scientist Kuznetzow-Ugamski in 1933: “The study of climatology is especially relates to study atmospheric processes developed near the surface of the earth-crust. It is not only an atmospheric process as such, but a very peculiar climatic process, which is the result of thermo-dynamical fluctuations of the same atmosphere, influenced by the ‘underlying surface’ of the earth. The same atmospheric (synoptically) process, in diverse localities may have several local peculiarities, more or less specific to every one of given regions, with regard to form of relief, width and distribution of water-basins, and characteristics of vegetation etc.”  (Lit.: Blüthgen, Geographie, p.13)[1]

Introduction

In this study Baltic Sea is given the same climatic importance as given to the North Sea, insofar as the former plays a key role in determining winter conditions in Northern Europe. Therefore full reference is made to the relevant paper: North Sea cooling (2_16). Further, the Baltic Sea has features that are very different from those of the North Sea. Some of these most significant aspects, relevant to the situation in the autumn of 1939, will be briefly discussed in the next section.  Thereafter, main military activities and meteorological events relevant to the issue, will be mentioned and analysed, even though this is not always done in a chronological order. ‘List of historical Events from September 1939 – March 1940’ given at the end of this paper refers to most relevant or interesting events only.

To aid understanding, it seems reasonable to give some early attention to the Historical List below, the special study on the Finland-Russian war in December (2_41) and other papers on naval activities in 1939:  Sea war events (2_13), Sea mines (2_14), and Depth charging (2_32). A similar approach is adopted with regard to ice conditions in the Baltic. While some general situations of ice cover in winter of1939/40 will be discussed here, icing of Baltic Sea during the three winters from 1939 to 1942 will be dealt with elsewhere. (3_11), (3_24). After all, icing of the Baltic Sea during winter of 1939/40 was the severest in many decades and together with following winters constitutes core evidence to suggest that the war machinery certainly caused climatic changes observed since start of WWII.

Baltic Sea – Physical features and Winter Climate

Total area of Baltic Sea is 400,000 square kilometres with an average depth of 55m including the Gulf of Bothnia (55-294m) and the Gulf of Finland (lower than 30m). Southern Baltic, except Gdynia Bight (114m), is less then 50m deep. Climatically the most important feature of this sea is a high mountain ridge from north to south Norway with a height of 2,500m. Behind this barrier, continental and polar air have much easier access than in areas where Atlantic air travels east at a low elevation level.  This frequently guarantees mild summers to Baltic countries by significantly delaying arrival of continental winter conditions. The mountain ridgealso prevents heavy winter conditions by preventinginvasion of Arctic air masses with very high surface fluxes of sensitive heat and moisture that can reach conditions common to those, which exist in the Arctic (Lit.: Raschke[2]. Therei s hardly any other sea in the northern hemisphere, which can convincingly demonstrate theimportance of heat storage and release process as the Baltic Sea. Actually, very cold conditions cannot prevail on sea and in nearby coastal areas over a longer period as long as the sea is open and not iced.  Icing is a very critical point in the regional climatology. Every sea area covered with ice loses ten times less energy to the atmosphere than an open sea area (Lit.: Finnish Institute)[3]. The importance of heat flux can be clearly demonstrated by temperature data records that show that winter average at the seaside is considerably higher than further inland, whereby the temperature sometimes decreases in great leaps, i.e. by 1°C per 50 km or more, depending upon distance from the coast. From mid September to the end of February, when air is colder than the sea water,  water temperature decreases between 13°C and 15°C, which is significantly more than that of the North Sea (9.5-11.5°C). This actually means that the surface temperatures with an average ranging between 0C° (north) and 3C° (south) in January quickly come close to zero. Heat stored at lower levels exists but is negligible. Deeper waters, 80 metres and below, have just 4-5°C, while the water column above varies according to the seasons (Lit.: Magaard)[4]. These temperature changes through the seasons are effective from surface to about 80m depth. While surface water reaches its peak temperature by the end of August, lower levels may reach its peak later on (e.g. 40m, with 10°C in late October). All activities that took place at sea in September thus could have forced considerable warm water masses to greater depths, which may have delayed the icing process by days or even weeks.

The navy starts the war at Gdynia. – Attack and defence in the South Eastern Baltic

German Navy assembled within sight of Gdynia at dawn on September 1, 1939 with a fleet of about 40 ships. At 4:45 a.m. battleship Schleswig-Holsteini started shelling Westernplatte with big calibre guns. After 13 days of pounding shells from sea to land and coastal batteries shooting at the armada of naval ships out in the Baltic, Gdynia fell. Thereafter, other positions along the Polish coast were shelled fiercely from the seas making their defences in vain. With the shelling of Hela (Gdanska Bight) by two German battleships from September 25-27, the last Polish coastal defence position was silenced (Lit.: Rohwer, Chronik)[5]. Within four weeks, the Germans had brought the entire Southern Baltic coast under their sole control. How much of the several thousands of tons of ammunition fired exploded on or under the sea surface is difficult to assess. Substantial areas of sea affected was certainly stirred and mixed heavily.

Heavy exchange of shelling for almost four weeks at a sea area with depths down to 114 metres could have severely altered  temperature compositions, normally ranging from 17° C at surface, to 4°C at bottom at the end of August (at 20m ~14°C; at 30m ~8°C, at 40m ~6°C). It would be a miracle if heavy shelling had not forced warm water into much deeper water layers and colder water to the upper layers. Under such circumstances it seems totally unavoidable that since the start of war considerable parts of the south-eastern Baltic must have had much lower water temperatures than usual. Following evidences suggest this: (1) freezing temperature at Rügenwalde (about 150 west of Gdynia) on the September 26, and on October 4,1939 at Königsberg/Kaliningrad (see below: Events), (2) icing of the sea at Gdanska Bight started by mid December, which although early, does not indicate any extreme situation. This could have been due to the fact that masses of surface water, forced into greater depths in September, may have returned back to surface at a later time. In this respect it should be noted that icing process started earlier in North Germany (see below: Events, Dec. 18 – 28) and along the southern Baltic coast (early Jan. 40), while the Gulf of Finland was still open as far as Pellinki, until January 17, 1940, when icing started very rapidly. (Lit.: Palosuo)[6]

All waters along Southern Baltic coast were put under severe stress from September 1, 1939 onwards. German Navy was navigating the waters extensively. They used these waters to train tens of thousands of their naval personnel, including firing by guns into designated sea areas. Many mine fields had been laid to west of the Island of Rügen and Trelleborg.  Danish government had also arranged for laying of mine fields in the three navigation channels of Copenhagen (NYT, 03 September, 1939). Eventhough water is shallower west of Gdanska Bight, the war could have had a considerable impact on the southern section of the Baltic Sea as explained.

An indication of the impact on weather exerted by all these activities is the early icing in Western Baltic (since December 18) and its lasting longer than usual, until end of March, 1940. In addition, water modification in the Southern Baltic would certainly have contributed to weather changes in the sameway as in the North Sea, (North Sea cooling,2_16), particularly in supporting a ‘corridor’ of increased continental air pressure, (Lost West Drift, 2_12), which culminated in a lasting independent cold air plug close to the southernBaltic Sea for six weeks; see below: Events, 15 January, 1940; (Lit.: Palosuo)[7].

General developments until end of the year 1939

Baltic had not seen any war activities as mentioned in the previous section or any obviously erratic or unusual weather behaviour until Russia invaded Finland on November 30, 1939. Traffic at sea was certainly several times higher than in previous years. Besides, Swedes laid mines and Navy of the Soviet Union was active in Baltic countries. A number of cyclones entered the sea from North, while some of those, which had originated in the Adriatic Sea, were blocked south of the Polish border. All above circumstances cannot necessarily be regarded as ‘usual behaviour’. But investigating them in detail is not the aim of this paper. Secondly a ‘clash’ between a military and meteorological chain of events erupted with the war in Finland. The first big ‘clash’ should be attributed to the ‘Rain Making’ in Western Europe, (Rain-Making 1939; 2_31), although ‘closing’ of the west drift (Lost West Drift 2_12) can hardly be ignored as a very early contribution either.

Extraordinary developments in the high North during December 1939 have been studied elsewhere, (Russian-Finnish war,2_41). How many unusual meteorological events are necessary as sufficient proof, that war changed weather? Here are some of the events: On November 30, 1939 the Red Army attacked Finland at a number of locations along a 2,000 km long border, running north–south, from the Barents Sea to a point east of Vyborg. Red Army strengths was 300.000 men and more. On December 1, the Red Army bombed cities; on December 2, snow started falling; on December 4, “blinding snowstorms” affected fighting; and the first cold period lasted from December 7-15. When weather had cleared for the first time after two weeks, this improvement in weather was immediately utilised for intensive bombing and fighting missions on 19. Second extreme cold wave entered the scene on the next day. “The Russian drive was stalled in the far north by blizzards and temperatures 25 degrees below zero (minus 31° C). (NYT, 21 December 1939). This was only the beginning and it became much worse. Unbelievably extreme weather conditions were reported, (Russian-Finnish war, 2_41) .However, as much as there is no political excuse for the invasion of Finland, it would be wrong to call the Russian decision to invade Finland in early December ill judged. Actually, according to all indications available at that time, there was nothing to suggest that such a thing would happen. Neither was there any precedent indicating that it could happen so suddenly and so early. Normally, average temperature in December in Murmansk is about -10°C; and average low temperature there in December is -13°C; which is still much warmer than -35°C reported in December 1939 (NYT, 25 December 1939). A selection of numerous naval and military activities in the northern Baltic Sea that presumably played a major role in relatively late icing of the Gulf of Finland is listed in the relevant paper, (Russian-Finnish war, 2_41),while the main conditions in regard to icing in the winter of 1939/40 is dealt with in the next paragraph.

Baltic had not been covered with as much ice since 1893. Coverage 1939/40 was tremendous exceptional. Ice did not start retreating until around March 8, 1940. Conditions for building up of ice differed in three ways from the average of previous years.  1) Even though ice started to form in the very North very early, solid ice developed at usual time; 2) Ice formation started at first in the southern Baltic Sea, and 3) Icing in the Gulf of Finland followed rapidly with a cold wave of 14 –24 January 1940 (Lit.: Jurva, p.22)[8]. In the South, at Greifswald Bodden (an open bight SE of the island of Rügen), icing started on December 18, 1939, solid ice remained in place without any interruption until April 4, 1940, and last ice disappeared on April 11, 1940,(Lit.: Blüthgen)[9].  In Hanko/Finland (at the west entrance to Gulf of Finland), icing started on December 27, 1939; solid ice formed on January 4, 1940; end of ice came on May 7, 1940.; at almost the same time as Helsinki (Lit.: Jurva, p.48)[10]. However, on January 15, 1940 the Gulf of Finland was still open as far East as the median of Pellinki. In the Gulf of Bothnia, sea was also open in most parts. Ice then formed rapidly (Lit.: Palosuo)[11]. Just to remind. Although the Gulf of Bothnia is far in the North it is with over 200 metres –in the Baltic Sea area -the deepest water, holding considerable heat for considerable time even in cold winters. A ‘ice-bridge’ between Turku and the island of Åland formed on January 6/7, 1940, which is about 2 ½ weeks earlier than usual (Lit.: Jurva)[12].

There is no other valid explanation for any deviation in weather from earlier averages than the war activities at sea. Most of the factors relevant to Baltic Sea are the long open sea areas in the Gulf of Finland, a clear indication that, due to military activities a high mixing of water took place preventing formation of ice. On the other hand, early formation of the ‘ice bridge’ showed that water of that area had already cooled enough to freeze, in this case, more than two weeks earlier than a place like Hanko, less than 100 kms away.    

Background to two following winters and the summary

Being land locked and located in the far north, Baltic Sea is particularly sensitive to water heat. This became very obvious during the next winter of 1940/41 when, during initial months of the war, sea was not made a battle ground. Winter cold centre shifted ‘a little bit’ further west to Skagerrak and South Norway region, (Arctic by occupation, 3_11). The Baltic Sea’s climatic sensitivity in the events of  ‘turning the water about’, became particularly obvious in the war winter of 1941/42, when the navy battled with the Baltic Fleet for supremacy over sea from summer of 1941 until winter of 1941/42, (Baltic battle field,3_21). It was colder than even during the Little Ice Age, (Stockholm’s record, 3_23). Baltic Sea was used as a great style field for experiment on anthropogenic climatic forcing. It proved to work after four months of naval activities in 1939.

‘‘List of Historical Events from September 1939 – March 1940’;

Note: This list is not a complete one. Its aim is to show certain contributions or indications to weather making process and highlightsome of the recorded weather conditions, as far as theymay relate to the extraordinary situation

24 September 1939; Snowfall in Baltic countries. A low pressure (1,000mb) originated in the western part of the Gulf of Finland, with wind force 6-8 Beaufort near Sundsval and Åland Island (Lit.:Seewarte)

26 September 1939; Temperatures: at Rügenwalde (small city at the Baltic coast, 150 km west of Gdynia) on the 26 September: -0.4°C; on 27^th, +1.5°C; in Koenigsberg/Kaliningrad, 25-27^th, (+2.5° C to +1.6°C). Putbus (Rügen), 24-29^th  (+5.2°C to + 3.8°C). (Lit.: Witterungsbericht).

27 September 1939; Hamburg –2.5°C; (Lit.: Seewarte)

11 October 1939; A high pressure over Finland brings cold air of arctic origin to East of Germany, Koenigsberg - 3°C average. Within the range of this cold air first light snow occurred in the Gdynia Bight.  Actually, Koenigsberg had already experienced -1°C on 04 Oct., (Lit.:Witterungsbericht)

Mid-October 1939: Some lakes and rivers froze in Northern and middle of Norrland, as well asin NW of Svealand, high in the North, which usually happens only towards end of the month. (Lit.: Statens)

01 November 1939; Together with the first snow showers in the eastern Baltic, cold air had been carried as far as the line Bohemia – Helgoland Bight. (Lit.: Seewarte)..

19 November 1939; Danish Light vessel Anholt Knob (Kattegat) reported snow fall (Lit.: Forklaring )

26 November 1939; Danish Light vessel Anholt Knob (Kattegat) reported snow fall (Lit.: Forklaring )

01 December 1939; First appearance of ice in the Baltic was indicated by reported withdrawal of Helsinki Light Vessel from its station. (Lit.: Frankcom, Ice)

04 December 1939; Navigation closed at Kotka (Gulf of Finland). (Lit.: Frankcom, Ice)

07 –15 December; Light vessel ‘Skagens Rev’ reported frost on 6 days during 7-15 Dec. (Lit. Forklaring)

08 December 1939; Navigation closed at Kalix, Northern port in Gulf of Bothnia (Lit.: Frankcom, Ice).

11 December 1939; Navigation closed at Oulu. Last vessel sailed December 7. (Lit.: Frankcom, Ice))

17 December 1939; In Hamburg temperature sank to minus °7C, (Lit.: Seewarte).

18 – 31 December 1939; In Denmark, sea water temperatures dropped to below zero degree Celsius (selection): Aalborg 5 days (max low -1.6°C);  Rodby Havn 7 days (max low. –0.6°C); Fredrikssund 7 days (max low. -1.8°C); Klinth Havn 3 days (max low. -0.5°C).  (Lit.: Forklaring). December mean temperaturesat 08 a.m. for all Danish coastal stations are between +1.7°C and + 5°C.

19 December 1939; Ice, which was reported in Kiel Channel (from Elbe to Kiel), Lübeck and Travemünde, remainedfor almost three months(Lit DHI-Eisbeobachtung)

19 December 1939; Navigation closed to several ports in Gulf of Bothnia, except with icebreaker assistance until end of December or middle of January (Lit: Frankcom, Ice).

21 December 1939; Ice reported in Schlei (north of Kiel), was to stay until 31 March 1940,  (Lit .:DHI-Eisbeobachtung)

26 – 31 December 1939; Most Danish light vessels reported permanent frost (max -6.3° Lappegrund).

27 December 1939; Reported from Tallinn that Leningrad harbour was closed owing to ice (Lit.: Frankcom, Ice)..

28 December 1939; Ice which was reported in Flensburg (at Danish border) lasted till28 March 1940, (Lit.: DHI-Eisbeobachtung)

2 January; Narva and several other Estonian ports report fast ice; navigation closed. (Lit.: Frankcom, Ice).

9 January 1940; Heavy ice in Riga –navigation only possible for powerful steamers. (Lit.: Frankcom, Ice).

13 January 1940; Gulf of Bothnia. A minesweeper and two patrol boats dropped depth bombs in an attempt to cripple a Russian submarine, which had trailed small Finnish steamer, Bore, through the international water of the Gulf of Bothnia.  (NYT, 14 January 1940)  

15 January 1939(39 or 40?); Palosuo’s meteorological assessment (Lit.: Palosuo, A Treatise; pp.92-93) reads: By 15 January, the atmospheric pressure in Greenland had reached a remarkably high level. As a low pressure simultaneously prevailed in Central Russia very cold air began to flow westward at high speed from the northern side of this low pressure, and a very severe frosty period began in the region of the Baltic. The outbreak of cold air resulted in an independent cold air plug (“Kaltluftpfropfen”) in Germany which persisted in the area for nearly a week. The cold air plug in the German area began to move on January 24 towards the Baltic region from where, reinforced, it pushed back to German territory on February 7. OnFebruary 12, its centre was in the region of Hamburg, from where, moving slowly, it arrived in East Germany about February 20.

17 January 1940; Heavy fast ice recorded at Tallinn and Riga (Lit.: Frankcom, Ice)

17 January 1940; Copenhagen harbour full of firm thick ice. Extremely difficult conditions reported for shipping in all Danish waters. 23° frost reported during the night in Denmark. Baltic Sea frozen over as far as can be seen from Danish coast.

18 January 1940; Heavy ice reported in the sea off Riga and in Tallinn (Lit.: Frankcom, Ice)

By middle of January 1940 the first severe cold spell was firmly established. Regarding the winter conditions in Europe, see: Winter 1939-40 (2_11).

LITERATURE:

Blüthgen, Joachim (Geographie); ‘Geographie der winterlichen Kaltlufteinbrüche in Europa’, Hamburg 1940, p. 13; Blüthgen citied the reproduced text from: Kuznetzow-Ugamski, I.N. Tschto takoje klimat? Journal geofiski 1933, III, S. 249-262 (russ.).

Blüthgen, Joachim; ‘Die Eisverhältnisse der Küstengewässer von Mecklenburg-Vorpommern’, Remagen 1954; Tab.2 (p.143).

DHI-Eisbeobachtung; Deutsches Hydrographisches Institut, ‚Eisbeobachtungen’, Nr.17,  Hamburg 1961

Finnish Institute of Marine Research; M.Leppäranta et.al; “Phases of the ice season in the Baltic Sea’ No. 254, Suppl.2; Helsinki 1988

Forklaring til Nautisk-meteorologiske Observationer, Copenhagen

Frankcom, C. E. N.; ‘Ice conditions in the Baltic and Danube Areas December 1^st 1939 to January 23^rd 1940’, in: The Meteorological Magazine, Vol.75, February 1940, pp. 1-8.

Jurva, Risto and Palosuo, Eric; ‘Die Eisverhältnisse in den Finnland umgebenden Meeren in den Wintern 1938 –45 und die Baltischen Eiswochen in den Wintern 1938 –39’, Helsinki 1959

Magaard, L. und G.Rheinheimer, G. (ed); Meereskunde der Ostsee’, Berlin 1974, p. 51.

Palosuo, Erkki; ‚A Treatise on severe ice conditions in the central Baltic’, Fennia 77 No.1, Helsinki 1953. p.92.

Raschke, E. (ed); ‘Scientific plan for the Baltic Sea Experiment (Baltex)’; Geesthacht sec. Ed. 1994, p.11)

Rohwer, Juergen and Huemmelchen, Gerhard; ‚Chronik des Seekrieges 1939-1945’ Oldenburg/Hamburg, 1968. The material is also available in German under: --www.wlb-stuttgart.de (Marine), Württembergische Landesbibliothek, Stuttgart.

Statens Meteorologisk-Hydrografiska Anstalt, ‚Arsbok I, 1939’, Månadsöversikt över Vänderlek och Vattentillgång ,  Argang 21 (Oktober 1939), Stockholm 1940

Seewarte:  refers to the official daily weather charts of the  “Deutsche Seewarte, Abteilung: Wetterdienst” (under the supervision of the ‘Reichsminister Luftfahrt’), with detailed weather observation and weather forecast and weather analysis, section “Witterungsübersicht”. 

Witterungsbericht; ‘Deutscher Witterungsbericht’, until 1939 (including) in: Zeitschrift „Wirtschaft und Statistik“, by Statistischen Reichsamt (publ), since 1940 as ‚Deutscher Witterungsbericht 1940-1944’, Deutscher Wetterdienst in der US-Zone, Bad Kissing, 1948.