The boehm wind or bohemian wind is a katabatic fall wind that occurs in eastern Bavaria , eastern Upper Franconia, the Vogtland , the Ore Mountains , Upper Lusatia , the Sudeten and the Austrian granite and gneiss highlands. It is gusty, dry and associated with low temperatures. Bohemian wind often brings slightly dusty, misty air from the Bohemian Basin .
The Bohemian wind is the result of a high pressure area that lies above the Bohemian Basin , so that the air close to the ground tends to flow into the surrounding areas with lower air pressure.
The effect is particularly pronounced in the winter half-year, when there is a high over Central and Eastern Europe for a long time and cold air increasingly collects in the Bohemian Basin. Since cold air is heavier than warm, the air pressure near the ground rises over Bohemia - a small cold peak forms . Most of the time, fog-like clouds with cloudy views prevail over Bohemia . In the northern and western environs of Bohemia (Silesia, Saxony, Bavaria), a cold air lake cannot develop as clearly due to the orography ; the air pressure here is somewhat lower.
The peripheral mountains, which surround Bohemia on three sides, prevent the heavier cold air from flowing away to the south, west and north; Pressure compensation is only possible where these mountains have passages or breakthrough valleys. There the air mass lying in Bohemia flows as a cold “Bohemian wind” into the surrounding area.
How high the layer of cold air above Bohemia reaches into the atmosphere also plays a role. It is usually delimited by an inversion at a height of 700 to 900 m . If a mountain ridge or pass is at the height of this inversion, the Bohemian wind is particularly strong here.
The strength of the wind is different. While it can occur at lower altitudes and in the summer months with wind force 4 to 6, wind force 10 and more is also possible in pass and ridge locations as well as in the winter half year. Agricultural crops suffer due to the dryness of the wind. The persistence of the current in the winter months leads to snow drifts and heavy frost in the affected areas .
The Bohemian wind lasts as long as the high altitude stays above the Bohemian Basin, which can take one to three weeks in winter. Approaching warm fronts usually do not yet cause a change in weather, as their force is not sufficient to remove the air mass near the ground. On the contrary, they lead to the deterioration of conditions in Bohemia (snowfall and black ice rain ). Only a strong cold front is able to mix the layer of air close to the ground and clear away the cold. Then the Bohemian wind also goes out.
In rare cases, the Bohemian wind also sets in without a pronounced cold air lake in Bohemia. This is the case when a small-scale low from Bavaria or Baden-Württemberg moves directly north; the east to south-east current prevailing from its front side literally sucks air out of the Bohemian Basin. The Bohemian wind only lasts until the core of the low has crossed the Thuringian Forest or South Hesse, and in this case has more characteristics of the foehn . However, this type of weather rarely occurs.
Saxony is separated from Bohemia by the Ore Mountains and the Lusatian Mountains . While the high altitudes of the central Ore Mountains over 1000 m are hardly affected by the Bohemian wind, as they lie above the inversion above Bohemia, the lower altitudes of the Eastern Ore Mountains (700 to 900 m crest height) often suffer from Bohemian wind in winter; If the inversion over Bohemia hangs just above the mountain ridge, it acts like a "Föhndüse" and leads to wind force 10 to 12 in the ridge area. In the Lusatian Mountains, valley areas running through from south to north are primarily affected. A positive effect is when a high with a core lies over Poland or the Baltic States, so that a southeastern current over Saxony also sets in at higher altitudes.
Between about 1965 and 1990 the air pollution (sulfur dioxide, hydrocarbon compounds, soot, dust) from the industrial area in northwest Bohemia around Chomutov , Most and Teplice caused extensive tree death in the Ore Mountains with the south-east wind coming in from Bohemia.The smell of the exhaust gases could sometimes still be heard in the lower ones Perceive the locations of the Ore Mountains. After stricter environmental regulations came into effect in the Czech Republic after 1990, the situation has improved significantly, but there is still an odor pollution in the Ore Mountains and Vogtland with Bohemian winds .
The main points of occurrence of the Bohemian wind are (from west to east):
- the valley of the upper White Elster from Bad Elster down to Plauen ,
- The ridge of the Osterzgebirge between Zinnwald and Bielatal ,
- The Saxon Elbe Valley as far as Dresden ,
- The upper Spreetal near Bautzen ("If the wind doesn't know where, then it blows over Budissin"),
- The upper Neisse valley in the Liberec - Zittau - Görlitz area ("Görlitzer Wind").
The Polish-Czech border area is formed by the contiguous mountain wall of the Jizera Mountains, the Giant Mountains and the Glatzer Mountains. The main points of the Bohemian wind are here (from west to east):
- The upper Neisse valley in the Liberec - Zittau - Görlitz area ,
- the Wittig / Smědá / Witka valley between Hejnice and Frýdlant in the Jizera Mountains,
- the north-facing valleys of the headwaters of the Bóbr on the eastern edge of the Giant Mountains,
- the valley of the Glatzer Neisse in the Glatzer Kessel ,
- the Moravian Gate .
The boehm wind often dominates the areas of Eastern Bavaria for days in summer and winter . When this wind blows in summer, it usually brings a longer period of nice weather with it, even if the constant breeze is a bit fresh.
In winter it is often unbearable, as it brings with it more continental and therefore colder air masses . Not least because of this wind, the Bavarian part of the area it sweeps has the nickname "Bavarian Siberia". If a high has built up east of the Fichtelgebirge and Elstergebirge and the Bavarian and Upper Palatinate Forest in Bohemia ( Czech Republic ) and a low west of it on the Bavarian side or north on the Saxon side , an atmospheric pressure equalization takes place from east to west ( gradient force ) or North. At first a completely normal wind , it gains more and more speed on its way across the Bohemian-Bavarian border mountains. Last but not least, this fall wind is like a loud howling storm that can even reach hurricane strength. At the same time it seems to have an even greater destructive power in the valleys, in which it gets a kind of suction effect, than up on the heights. In 1987 the Bohemian wind caused damage of ten million DM in a single night in the forests of Eastern Bavaria. The whole thing occurs preferentially as a partial aspect of an increased Eastern influence in Central Europe and thus an increased Arctic Oscillation (AO), while the west wind drift is often only weak throughout Europe, i.e. the index of the North Atlantic Oscillation (NAO) is small and this system is therefore weaker than is normal.
When the Böhm wind whistles for days in winter over the heights down into the valleys on the Bavarian side, the snow drifts that it creates within a few minutes often lead to severe obstructions to road traffic. The worst affected are valleys that stretch from west to east (e.g. Cham-Further Senke , valleys of Pfreimd , Ilz and Regen ). Since the ridge layers protrude above the Bohemian cold air layer, there is often sunshine with weak wind and temperatures around freezing point at the same time .
The Böhmwind, which can be felt from Hof , in the north of Eastern Bavaria, to the area north of Passau , has also found expression in popular culture . In the Bavarian Forest people danced after a local man named “Bohemian Wind” and in folk songs he blew the “Waaz” ( wheat ) or even a Bohemian carter .
In the poem The Bohemian Forest by Georg Britting are the verses
"Often there is a wind,
from the Bohemian,
and the winter is long,
and the summer is heavy.
Of the green and the gold
that rolls down the top."
The Bohemian Wind is also featured in a folk music song.
The Bohemian wind has also found its way into proverbs. In the Ore Mountains, for example, the expression “It is like the Bohemian wind” is often used to describe a very stubborn or penetrating person. This is also due to the frequency and duration of the weather phenomenon.
In the granite and gneiss highlands north of the Danube - the Upper Austrian Mühlviertel and the Lower Austrian Waldviertel - the Bohemian wind or Böhmwind (both expressions are common) is a cold north to northeast wind. The phenomenon occurs in all northern locations, but is mainly limited to the later winter months from January to April. This wind is cutting cold, strong to stormy, and leads to widespread snowdrifts. It is one of the factors for the - by Austrian standards - harsh climate of the granite and gneiss highlands, but in extreme cases it can penetrate into the foothills of the Alps .
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