What is the polar depression?
Polar depressions are spontaneous formations. Such natural systems can not be envisaged and identified using conventional meteorological messages is not so simple. Therefore, they pose a threat to seafarers, air carriers and other active human activities in the northern regions. How unpredictable and dangerous the polar depression is, what this phenomenon is, let's look at it in stages.
History of detection
Polar depression is a phenomenon thatrefers to a weather system of relatively small scales, which is short-lived and characterized by low pressure. It is formed over the oceans in both hemispheres on the side of the main polar front. In earlier studies, it was assumed that the main cause of its occurrence was thermal instability. But this statement was very far from reality. Later, the formation conditions were studied. This type of natural system was first discovered on meteorological images, which became available in the 60s of the last century.
In the high latitudes, specialists were definitelya whole set of vortex clouds. They were traced over the ice-free sections of the above-mentioned seas, over Labrador, and also in the bays of Alaska. It is noted that the polar depression is rapidly dissipated when it comes to land. The northern colleagues of the Antarctic cyclones are usually weaker, because they are experiencing different temperatures throughout the continent. Although sometimes, even within the Southern Ocean, one can observe the dynamism of this phenomenon.
Satellite imagery suggests thatpolar depression is characterized by a variety of cloud forms that can be formed spirally from the cloud strips enveloping the center, or closer to the polar front take the image of a comma. Strictly speaking, the degree of danger of the given weather phenomenon, its intensity and speed of distribution also depends on the structure.
Mechanism of formation
When the polar front begins to developA wave contributing to the penetration of the tropical stream into the air mass environment forms a polar depression. Given the eastward progress of the system, the warm cyclone, whose air is trying to force out the cold, is different from the opposite one, which follows it and rides under the masses heated by the sun. The result of this displacement of the opposite elements is a decrease in pressure on the surface, the center of which is surrounded by isobars, which are blown by the wind across.
As a consequence, air moves to the coredepression up and spiral overnight. As this process develops, the cold front approaches warm, leading to an occlusion phase. Despite the presence of low-temperature air at the top and cyclonic movements, indicated by the isobars and wind direction, there is one front contrast on the surface in the form of a dividing line between the incoming streams located in the rear area of the depression. This leads to a transformation in the front. Depending on the nature of the processes that determine this metamorphosis, the occlusion is either cold or warm. On this depends the external manifestation of the cyclone on land.
Time of existence
The period of existence of this kind of weather systemdepends on how long the potential energy has to be transformed into kinetic energy. The polar depression is destroyed when the low and high pressure contrast disappears between the air layers located in the neighborhood. Its rapid attenuation occurs when the ice surface is displaced or when land is approaching. Given the direct relationship with the rise of air and powerful winds, it is able to significantly affect the weather.
As the air of warm fronts risesGradually, until it reaches stability, layered cloud forms are formed. If crescent clouds appear in the sky, it means that the warm front is near. As it approaches, the clouds become lower and more massive. Often stratification predicts a shallow rain with time passing into a heavy downpour. And by lunchtime one can already expect a sunny sky in a cumulus frame.
The arrival of the cold front dramatically changes the weather. In the skies there are cumulonimbus clouds, like towers, which, as a rule, bring abundant downpours and thunderstorms. Suddenly, the direction of the wind changes to the north or north-west. The storm situation is developing unexpectedly and in a short period.
What's the Difference?
What is the difference between the frontal depression of the Southhemisphere from a similar in the North? Almost nothing, although there is one important dividing line. In the first case, the wind on the warm front turns from north to north-west, and on the cold front - from west to south-west, in the second - the movement occurs in the same way as the hands on the clock. But the peculiarity is that every polar depression is an individual phenomenon, that is, there is no idealized model that can describe it.
Possibility of forecasts
Make weather forecasts in frontaldepression is possible on the condition that a significant area is covered by synoptic observations. For example, for the European part of the continent, the study area should expand to the west, including the adjacent areas of the Atlantic. After all, usually such natural systems have a speed of 1000 km per day. If observations are made in the upper atmosphere, this will greatly facilitate the work on the forecast in the sector where the cyclone is located.
It is quite common when the frontalDepressions combine into large families, involving secondary formations in motion around the main stream. The most common are those that appear on the edge of cold air. Each next representative of such a conditional family is located along a trajectory closer to the equator than its predecessor.