Polar depressions are natural formations. It is not so easy to foresee and identify such natural systems with the help of ordinary meteorological messages. Therefore, they pose a threat to sailors, air carriers and other active human activities in the northern regions. How unpredictable and dangerous the polar depression is, what kind of phenomenon it is, let's look at it step by step.
Discovery history
A polar depression is a phenomenon that refers to a relatively small-scale weather system that is short-lived and characterized by low pressure. It forms over the oceans in both hemispheres on the side of the main polar front. In early studies, it was assumed that the main cause of its occurrence is thermal instability. But this statement turned out to be very far from reality. Later, the formation conditions were studied. For the first time this type of natural system was discovered on meteorological images, which became available in the 60s of the last century.
Bat high latitudes, experts have definitely identified a whole host of vortex clouds. They were traced over ice-free areas of the seas mentioned above, over Labrador, and also over the bays of Alaska. It is noted that the polar depression dissipates quite rapidly when it comes to land. The northern counterparts of Antarctic cyclones are usually weaker, because they experience temperature fluctuations along the entire continent. Although sometimes even within the Southern Ocean one can observe the dynamism of this phenomenon.
Satellite images suggest that the polar depression is characterized by a variety of cloud forms, which can form in a spiral pattern from cloud bands enveloping the center, or closer to the polar front take the form of a comma. Strictly speaking, the degree of danger of a given weather phenomenon, its intensity and speed of propagation also depend on the structure.
Shaping mechanism
When a wave begins to develop on the polar front, contributing to the penetration of a tropical stream into the air mass medium, a polar depression is formed. Considering the eastward movement of the system, the warm cyclone whose air is trying to displace the cold one is different from the opposite one, which follows it and rolls under the sun-warmed masses. The result of such a movement of opposite elements is a decrease in pressure on the surface, the center of which is surrounded by isobars that are blown across by the wind.
Howconsequently, the air moves towards the core of the depression upwards and spirals overnight. As this process develops, the cold front approaches the warm front, which leads to the occlusion phase. Despite the presence of low-temperature air above and cyclonic movements indicated by isobars and wind direction, there is one frontal contrast on the surface in the form of a dividing line between incoming flows located in the rear region of the depression. This results in a transformation in the front. Depending on the essence of the processes that determine such a metamorphosis, occlusion is either cold or warm. The external manifestation of the cyclone on land depends on this.
Lifetime
The period of existence of this kind of weather system depends on how long the potential energy has to transform into kinetic energy. The polar depression collapses when the contrast of low and high pressure disappears between the air layers located in the neighborhood. Its rapid weakening occurs when it moves over the ice surface or when land approaches. Given the direct relationship with the rise of air and powerful winds, it can significantly affect the weather.
Impact on weather
As the air from warm fronts rises gradually until it reaches stability, stratus cloud forms form. If cirrus clouds appear in the sky, then a warm front is nearby. As it approaches, the clouds become lower and more massive. Often, layering portends light rain over time.turning into heavy rain. And by lunchtime, you can already expect a sunny sky in a cumulus frame.
The arrival of a cold front dramatically changes the weather. In the sky, cumulonimbus clouds appear, similar to towers, bringing, as a rule, heavy showers and thunderstorms. Suddenly the wind direction changes to north or northwest. The storm situation develops unexpectedly and in a short period.
What's the difference?
What is the difference between the frontal depression of the Southern Hemisphere and its counterpart in the Northern? Almost nothing, although there is one important dividing line. In the first case, the wind on a warm front turns from north to northwest, and on a cold front - from west to southwest, in the second case, the movement occurs in the same way as the hands on a clock. But the peculiarity is that each polar depression is an individual phenomenon, that is, there is no idealized model that can describe it.
Predictability
It is possible to make a weather forecast in frontal depressions on the condition that a significant area is covered by synoptic observations. For example, for the European part of the mainland, the study area should expand to the west, including the adjacent areas of the Atlantic. After all, such natural systems usually have a speed of 1000 km per day. If observations are made in the upper layers of the atmosphere, this will greatly facilitate the work on the forecast in the sector where the cyclone is located.
Quite common when frontal depressionsunite in large families, involving secondary formations in movement around the main stream. The most common are those that appear at 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.
