Watching weather changes is very exciting. The sun gives way to rain, the rain to snow, and gusty winds blow over all this variety. In childhood, this causes admiration and surprise, in older people - a desire to understand the mechanism of the process. Let's try to understand what shapes the weather and how atmospheric fronts are related to it.
Air mass boundary
In the usual perception, "front" is a military term. This is the edge on which the clash of enemy forces takes place. And the concept of atmospheric fronts is the boundaries of contact between two air masses that form over huge areas of the Earth's surface.
By the will of nature, man got the opportunity to live, evolve and populate ever larger territories. The troposphere, the lower part of the Earth's atmosphere, provides us with oxygen and is in constant motion. All of it consists of separate air masses, united by a common occurrence and similar indicators. Among the main indicators of these masses determine the volume, temperature, pressure and humidity. During the movement, different masses can approach and collide. However, they never lose their boundaries and do notare mixed with each other. Atmospheric fronts are areas where air masses touch and sharp weather surges occur.
A bit of history
The concepts of "atmospheric front" and "frontal surface" did not arise by themselves. They were introduced into meteorology by the Norwegian scientist J. Bjerknes. It happened in 1918. Bjerknes proved that atmospheric fronts are the main links in the atmospheric cycle in the high and middle layers. However, before the research of the Norwegian, back in 1863, Admiral Fitzroy suggested that violent atmospheric processes begin at the meeting places of air masses coming from different parts of the world. But at that moment, the scientific community did not pay attention to these observations.
The Bergen school, of which Bjerknes was a representative, not only carried out its own observations, but also brought together all the knowledge and assumptions expressed by earlier observers and scientists, and presented them in the form of a consistent scientific system.
By definition, the inclined surface, which is the transition area between different air flows, is called the frontal surface. But atmospheric fronts are a display of frontal surfaces on a meteorological map. Usually, the transition region of the atmospheric front is tied up near the surface of the Earth and rises up to those heights at which the differences between air masses are blurred. Most often, the threshold of this height is from 9 to 12 km.
Warm Front
Atmospheric fronts are different. They depend on direction.movement of warm and cold massifs. There are three types of fronts: cold, warm and occlusion, formed at the junction of various fronts. Let's take a closer look at what warm and cold atmospheric fronts are.
A warm front is a movement of air masses in which cold air gives way to warm air. That is, the air of a higher temperature, moving forward, is located in the territory where cold air masses dominated. In addition, it rises up along the transition zone. At the same time, the air temperature gradually decreases, due to which condensation of the water vapor in it occurs. This is how clouds form.
The main signs by which a warm atmospheric front can be identified:
- atmospheric pressure drops sharply;
- dew point rising;
- temperature rises;
- cirrus appears, then cirrostratus, and after high-stratus clouds;
- wind turns slightly to the left and becomes stronger;
- clouds become nimbostratus;
- Precipitation varies in intensity.
It usually warms up after the rain stops, but this does not last long, as the cold front moves very quickly and catches up with the warm atmospheric front.
Cold front
There is such a feature: a warm front is always inclined in the direction of movement, and a cold front is always inclined in the opposite direction. When fronts move, cold air wedges into warm air, pushing it up. Cold atmospheric fronts lead to a decrease in temperature and cooling over a large area. As the rising warm air masses cool, moisture condenses into clouds.
Main signs of a cold front:
- before the front, the pressure drops, behind the line of the atmospheric front it rises sharply;
- cumulus clouds form;
- a gusty wind appears, with a sharp change in direction clockwise;
- begins torrential rain with thunder or hail, the duration of precipitation is about two hours;
- temperature drops sharply, sometimes by 10°C at once;
- There are numerous clearings behind the atmospheric front.
Traveling through a cold front is no easy task for travelers. Sometimes you have to overcome whirlwinds and squalls in conditions of poor visibility.
Occlusion front
It has already been said that atmospheric fronts are different, if everything is more or less clear with warm and cold fronts, then the front of occlusions raises a lot of questions. The formation of such effects occurs at the junction of cold and warm fronts. The warmer air is forced upward. The main action occurs in cyclones at the moment when a more rapid cold front catches up with a warm one. As a result, atmospheric fronts move and three air masses collide, two cold and one warm.
The main signs by which you can determinefront of occlusions:
- clouds and patchy precipitation;
- abrupt changes in wind direction without much change in speed;
- smooth change in pressure;
- no sudden temperature changes;
- cyclones.
The occlusion front depends on the temperature of the cold air masses in front of it and behind it. Distinguish between cold and warm occlusion fronts. The most difficult conditions are observed at the moment of direct closure of the fronts. As warm air is forced out, the front is eroded and weather conditions improve.
Cyclone and anticyclone
Since the concept of "cyclone" was used in the description of the front of occlusions, it is necessary to tell what kind of phenomenon it is.
Due to the uneven distribution of air in the surface layers, zones of high and low pressure are formed. High pressure zones are characterized by excess air, low - insufficient air. As a result of the air flow between the zones (from excess to insufficient), wind is formed. A cyclone is an area of low pressure that draws, like a funnel, the missing air and clouds from areas where they are in excess.
Anticyclone is a high-pressure area that forces excess air into low-pressure areas. The main characteristic is clear weather, as clouds are also pushed out of this zone.
Geographic division of atmospheric fronts
Depending on the climatic zones over which atmospheric fronts form, theirgeographically divided into:
- Arctic, separating cold arctic air masses from temperate ones.
- Polar, between temperate and tropical masses.
- Tropical (trade wind), delimiting the tropical and equatorial zones.
Influence of underlying surface
The physical properties of air masses are affected by radiation and the type of the underlying surface of the Earth. Since the nature of such a surface can be different, the friction against it occurs unevenly. Difficult geographic topography can deform the atmospheric front line and change its effects. For example, there are known cases of destruction of atmospheric fronts when crossing mountain ranges.
Air masses and atmospheric fronts bring many surprises to forecasters. Comparing and studying the directions of movement of the masses and the vagaries of cyclones (anticyclones), they make graphs and forecasts that people use every day, without even thinking about how much work is behind it.
