Sudden stratospheric warming

The sudden stratospheric warming (english sudden stratospheric warming ) is a well-known since 1952, first described as a phenomenon Berlin by the Berlin meteorologist Richard Scherhag appearance in weather patterns in the stratosphere of the northern hemisphere.

Description

In the winter months forms in the polar stratosphere, due to the negative radiation balance in the polar region, a polar vortex out, strong westerly winds occur at its southern boundary. The temperatures in the lower stratosphere ( about 20 km altitude) are on average below -70 ° C. This structure is predominant in the winter average, but at irregular intervals, greatly disturbed every two years. With this strong heating (Major Warming ) the temperature of the stratosphere increases within a few days to more than 50 degrees and reaches higher values ​​than in more southern latitudes. Connected is this sudden warming with a reversal of the West in easterlies and hence a breakdown of the polar vortex. This is followed by an equally abrupt cooling.

The result of a sudden stratospheric warming is among other things a weakening of the pressure difference between the Iceland low and the Azores high. However, this determines the prevailing wind direction for Central Europe and thus whether the European winter cold or mild fails. A sudden stratospheric warming favors weather conditions that favor a penetration of cold continental air from the east to central Europe.

Causes

The cause of the irregularly occurring sudden stratospheric warming is considered the interaction between the North Atlantic, the troposphere and the stratosphere. An increased number of sudden stratospheric warming occurs when the heat flux is reinforced from the North Atlantic into the atmosphere.

Differentiation to similar phenomena

In meteorology, three forms of sudden stratospheric warming can be distinguished. In addition to the tangible as an anomaly in the weather Major Warming occur several times per winter on weaker stratospheric warmings ( Minor Warming ). These bring a temperature rise of at least 25 degrees within a week and can occur in all layers of the stratosphere. They have no effect on the stability of the polar vortex. As a final Warming is defined as the warming at the end of the winter March to May Here, the polar vortex breaks down to be restored together without then.

When Berlin 's phenomenon or Berlin phenomenon only Major Warming is called.