In most parts of European Russia, summer is over. Everyone who cares about the weather is wondering: what will winter be like? Is it possible to make a prediction now, and if so, what kind?
One of the key factors that determine the nature of winter is polar vortex (area of low pressure in the troposphere and stratosphere above the North Pole, which is most intense in the cold half of the year).
polar vortex – low pressure area above the North Pole. As a rule, the polar vortex is formed in the cold semester under conditions of limited inflow of solar heat. The boundary of the circular vortex at large latitudes is surrounded by a zone of strong pre-spherical winds (jet flows). In the undisturbed state it has a normal shape, close to the oval.
A well-developed polar vortex indicates a large temperature difference between south and north. The greater the contrast, the stronger the westerly air flow that surrounds it.
As you know, the main source of heat is the Sun. Its rays bring more heat to the tropics and less to the polar regions. According to the laws of physics, hot air rushes north. The Coriolis force deflects it to the right, to the east. This is how western transport is shaped.
It carries warm Atlantic air to the continent. As a result, winter has a mild European character.
If the polar vortex is underdeveloped or even split, then we have a Russian winter. In this case, favorable conditions are created to prevent western transport over the Arctic and Scandinavia.
Blockade cyclones weaken and even reverse the normal circulation of the atmosphere, with the result that cold air masses from the Arctic and Siberia spread to the territory of European Russia.
The temperature difference between south and north for European Russia is expressed by the index north atlantic oscillation (ΝΑΟ – English. North Atlantic oscillation). This indicator represents the pressure difference between the Azores and Iceland.
The North Atlantic oscillation is a large-scale fluctuation of atmospheric pressure between the Azores and the Icelandic Recession. The North Atlantic oscillation is quantified by the index. In the positive phase, there is high activity of storms in the North Atlantic, which determine the unstable, stormy and wet weather in Northern Europe. Cyclones are raging in a negative phase in Southern Europe and the Mediterranean Sea. In the north of the continent the frequency of cold air inflows from the north and northeast is increasing.
Right now the index ΝΑΟ negative, ie the atmospheric pressure difference is small or even negative. This is due to the positive temperature anomalies operating in the North and East Atlantic.
The contribution of the ocean can be appreciated El Niιοo – South Oscillation (ENSO – English. El Niιοo / La Niιαa — Southern Oscillation). Its positive phase (the El Nino episode) contributes to the strengthening of the patrol vortex. This is the phase we are in right now.
The Southern Oscillation is the atmospheric component of the El Niιοo natural phenomenon. Represents the cyclical fluctuations of atmospheric pressure in the equatorial zone of the Pacific Ocean. The magnitude of the oscillation is expressed by the south oscillation index. The index is calculated from the difference in atmospheric pressure between Tahiti (French Polynesia) and Darwin (Australia).
However, according to the forecast, autumn and winter ENSO enters the neutral phase. In the future, it is possible to go into the cold phase (La Niña episode). Subsequently, temperature contrasts between south and north will weaken, and as a result, high-pressure exclusion zones may become wedged in western transport.
The last important factor is almost two-year wind cycle in the equatorial stratosphere (QBO – English. Quasi Biennial Oscillation).
The almost two-year cycle of stratospheric winds is characteristic of the general circulation of the atmosphere in the equatorial latitudes. It is characterized by the fact that at altitudes of 20-35 km, for about a year, the winds blow from west to east and during the next year – from east to west. The natural phenomenon is more intense in the equatorial zone, up to about 10 degrees latitude on both sides of the equator. The average duration of the cycle is 26 months. The peculiarity is that each new circle first appears in the upper layers, at a level of about 35 km, and gradually spreads downwards. At the borders of the tropics and middle latitudes, the phenomenon disappears.
With a positive phase QBOwhat is observed now is the winds of the western district. By transferring the atmosphere to medium and large latitudes, they enhance the polar vortex. hesitation QBO correlates quite well with the corresponding phase ENSOwhich, according to the forecast, may become negative this winter as well.
Now consider the factors that have a minor effect on the polar vortex. These are the solar activity, the snow cover (accumulated in Siberia in late autumn) and the oscillation of the Arctic.
Let’s start with the last one. Arctic Oscillation (JSC – English. Arctic Oscillation) is expressed by the index JSC.
Arctic Oscillation characterizes the form of atmospheric circulation in the polar and middle latitudes. Arctic oscillation is measured using the arctic oscillation index. The Arctic Fluctuation Index can be negative or positive. The negative phase of Arctic Oscillation is characterized by increased atmospheric pressure in the polar regions and decreased atmospheric pressure in the 45th parallel of the northern latitude. During the negative phase, cold air penetrates the middle latitudes of Europe and southern cyclones cause storms in the Mediterranean basin. The positive phase results in opposite conditions, leading Atlantic cyclones across large latitudes and producing wetter and milder weather in Northern Europe and drier and warmer weather in Southern Europe.
The index describes the large-scale distribution of atmospheric pressure in the Aleutian Islands, Iceland and the Bay of Biscay. Index JSC It turns out positive if the air pressure is higher in the south than in the north, and negative if it is vice versa. positive indicator JSC speaks of the prevalence of western transport. Usually phases ΝΑΟ and ΑΟ race.
Snow cover in Siberia in late autumn is considered a strong argument in favor of a cold winter. In this case, a steady cold anticyclone forms over the snowy area. Winds blowing from the area can spread the cold for several weeks to the British Isles and the Mediterranean Sea. But there is an important feature! Under conditions of a well-developed polar vortex and active western transport, such an anticyclone is not easy to form.
Solar Activity has an even more complex relationship. It changes every 11 years. There is a solar minimum at the moment. This means that the Earth receives a little less energy than usual. Physically it is. But the atmosphere, and especially the stratosphere, tends to balance. The reduction of heat inflow is compensated by waves and disturbances that disrupt the normal circulation of stratospheric winds (QBO). This seemingly insignificant factor can tilt the scales in the other direction.
So, we looked at all the factors. But it has not yet received an answer to the main question: what will winter be like?
If you approach it strictly scientifically, then it is clear that nothing is clear – relationships are so complicated and confusing. Even when analyzed a posteriori, the answer is never clear.
However, from the very complex description, we have drawn two main conclusions:
- ENSO and QBO will become neutral at the end of 2019 – beginning of 2020 and in the future will go into a negative phase.
- Temperatures above zero at sea level in the Atlantic will remain significant, especially in early winter.
As a result, the polar vortex will weaken. This can lead to an increased frequency of meridional processes, including prolonged cold air invasions from the Arctic and Siberia.