December 2, 2011 – PARIS – Climatology, there are several indices or indicators that quantify the climate anomalies of pressure, wind and temperatures in some regions (for the atmosphere but also to the ocean). These anomalies are associated with natural oscillations whose frequency can vary from several months to several decades, and sometimes almost a century. These are the natural variability (including solar activity is also included) who are responsible for “change” climate as it is wrongly described in most media. The climate has indeed never been stable in the past. It went through phases of warming (as the Medieval Warm Period between the tenth and the fourteenth century) and then by cooling phases (such as the Little Ice Age from the late sixteenth century and the nineteenth century). Since the beginning of this fall, the temperatures of the atmosphere in the stratosphere (20 to 50 km altitude) began to fall over the North Pole. This decrease is quite usual in this season as well as the polar vortex weakening in summer, then re-forms in winter as the sun’s influence is diminishing. However, the current temperatures have gone below the average climate, indicating a strong enhancement of the vortex. It is customary to quantify the intensity of the strengthening of the polar vortex by a climatic index called Arctic Oscillation (AO), which measures the pressure difference between Greenland and the middle latitudes (about 45 ° North). The higher the value of AO is high (positive values so) over the vortex is strong and vice versa. Yet the intensity of the polar vortex partly determines the position of the jet stream. There is a persistent anomaly in the equatorial stratosphere winds since last winter. This anomaly is associated with the quasi-biennial oscillation mentioned above which, as its name suggests, at a frequency of about 24 to 30 months. During this period, winds in the middle stratosphere are now accelerating towards the west (called a westerly QBO phase), and sometimes accelerating to the east (from east QBO phase).
We thus understand better why the circumstances of the next few days will promote the development of frequent depressions. This is even more rapid and intense that the jet stream is powerful: in extreme cases, it is called “weather bomb” to describe these storms suddenly exploding a few hours before landfall, generating widespread destruction of property and life. This was the case of Lothar and Martin storms that occurred in December 1999. In this context, a strong storm, named “Berit” has already swept the weekend Norway, causing millions of euros in damage. The winds had blown close to 140-150 km / h, lifting heavy seas with waves of 6 to 10 meters away several people who were near the coast. Finally, the cumulative rainfall amounted to almost 100 mm in places. A second storm occurred last night between Iceland and the British Isles. Dubbed “Zafer” by the German weather service, it concerned Ireland and the UK before weakening towards the Norwegian Sea. It generated sales of close to 140-150 km / h on the hills of Highlands (northwest Scotland) and more generally from 70 to 100 km / h on the rest of the UK and Ireland. The sea is removed with the palm of 5 to 8 m making conditions even more dangerous near the coast. A very disturbed rail will fall into place between the south of Iceland and Central Europe. Along the rail (formed by the jet stream), a new depression will emerge, deepening into a very short period of time and resulting in real weather bomblets. These storms, more violent than Zafer, Saturday and Sunday will affect the regions of northern Europe from the British Isles, the Benelux, Germany, Poland and a number of other neighboring countries- it is difficult to list at the moment due to the still large uncertainty about the path of these storms. Similarly, the exact violence of these phenomena needs to be clarified in the coming days. Other very shallow depressions are expected next week but should cover regions with latitudes north. The situation in northern Europe looks very hectic in the coming days with frequent notice of gale and storm, with sea conditions very degraded (Wed strong to very strong) in the North Atlantic, North Sea and Norwegian Sea. Rainfall will be locally supported. Cold air tumbling to the back of these disturbances will cause some heavy snowfall from northern Ireland, Scotland, Scandinavia and Russia, also with snow in the mountains both in France or Central Europe. In short, a time more season. This could then remain a part of next week due to the blockage caused by the maintenance of high pressure over the North Atlantic and the persistence of a strong polar vortex over the Arctic. –Meteo Consult.fr translated