Watching the weather change is very exciting. The sun gives way to rain, rain to snow, and gusty winds blow over all this diversity. In childhood, this causes admiration and surprise, among older people - the desire to understand the mechanism of the process. Let's try to understand what forms the weather and how atmospheric fronts are associated with this.
Air mass boundary
In the usual perception, “front” is a military term. This is the line on which the clash of enemy forces takes place. And the concept of atmospheric fronts is the boundary of the contact of two air masses that are formed over huge areas of the Earth’s surface.
By the will of nature, man got the opportunity to live, evolve and populate all large territories. The troposphere - the lower part of the Earth's atmosphere - provides us with oxygen and is in continuous motion. All of it consists of individual air masses, united by a common occurrence and similar indicators. Among the main indicators of these masses, volume, temperature, pressure and humidity are determined. During movement, various masses can come together and collide. However, they never lose their borders and do not mix with each other. Atmospheric fronts are areas where air masses come into contact and sudden weather surges occur.
A bit of history
The concepts of “atmospheric front” and “frontal surface” did not arise on their own. They were introduced into meteorology by the Norwegian scientist J. Björknes. It happened in 1918. Björknes proved that atmospheric fronts are the main links in the atmospheric cycle in the high and middle layers. However, before the studies of the Norwegian, back in 1863, Admiral Fitzroy suggested that violent atmospheric processes begin at the places where air masses coming from different parts of the world meet. But at that moment, the scientific community did not pay attention to these observations.
The Bergen school, of which Björknes was a representative, not only made 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, an inclined surface representing a transition region between different air flows is called a frontal surface. But atmospheric fronts are a mapping of frontal surfaces onto a meteorological map. Usually, the transitional region of the atmospheric front is tied at the surface of the Earth and rises up to those heights at which the differences between the air masses are eroded. Most often, the threshold of this height is from 9 to 12 km.
Warm front
Atmospheric fronts are different. They depend on the direction of movement of warm and cold massifs. Three types of fronts are distinguished: cold, warm, and occlusion formed at the junction of various fronts. Let us consider in more detail 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, air of higher temperature, advancing, 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 there is a condensation of the water vapor in it. This is how clouds form.
The main signs by which you can determine a warm atmospheric front:
- atmospheric pressure drops sharply;
- dew point increases;
- air temperature rises;
- cirrus, then cirrostratus, and then - highly stratus clouds appear;
- the wind turns slightly to the left and becomes stronger;
- the clouds become layered rain;
- precipitation of varying intensity.
Usually, after the precipitation stops, it gets warmer, but it does not last long, because the cold front moves very quickly and catches up with a warm atmospheric front.
Cold front
This feature is observed: a warm front is always tilted in the direction of movement, and a cold front is in the opposite direction. When the fronts move, cold air wedges into warm air, pushing it up. Cold atmospheric fronts lead to lower temperatures and cooling in a large area. As cooling of the rising warm air masses, moisture condenses into clouds.
The main signs by which you can determine 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;
- Heavy rain begins with a thunderstorm or hail, the duration of precipitation is about two hours;
- the temperature drops sharply, sometimes by 10 ° C immediately;
- Numerous clarifications are observed behind the atmospheric front.
For travelers, going through a cold front is not an easy test. Sometimes it is necessary to overcome vortices and squalls in conditions of poor visibility.
Occlusal front
It has already been said that atmospheric fronts are different, if everything is clear with warm and cold, the front of occlusions raises a lot of questions. The formation of such effects occurs at the junction of cold and warm fronts. Warmer air is forced up. 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 determine the front of occlusions:
- Cloud cover and rainfall;
- sudden changes in wind direction without a strong change in speed;
- smooth pressure change;
- lack of sharp temperature changes;
- cyclones.
The front of occlusions depends on the temperature of the cold air masses in front of him and beyond his line. Distinguish between cold and warm fronts of occlusions. The most difficult conditions are observed at the moment of direct closure of the fronts. As the warm air is forced out, the front erodes, weather conditions improve.
Cyclone and anticyclone
Since the term “cyclone” was used in the description of the occlusal front, it is necessary to tell what kind of phenomenon it is.
Due to the uneven distribution of air in the surface layers, high and low pressure zones are formed. High pressure zones are characterized by excess air, low - by insufficient quantity. As a result of the flow of air between the zones (from excess to insufficient), wind is formed. A cyclone is a low-pressure section that draws, as in a funnel, the missing air and clouds from zones where they are in excess.
An anticyclone is a section with high pressure that displaces excess air into low pressure zones. The main characteristic is clear weather, as the clouds from this zone are also crowded out.
Geographical separation of atmospheric fronts
Depending on the climatic zones over which atmospheric fronts are formed, they are divided according to geographical feature into:
- Arctic, separating cold arctic air masses from moderate ones.
- Polar, located between moderate and tropical masses.
- Tropical (trade wind), delimiting the tropical and equatorial zones.
The influence of the underlying surface
The physical properties of air masses are affected by radiation and the type of underlying surface of the Earth. Since the nature of such a surface can be different, the friction against it occurs unevenly. Complex geographic relief can deform the line of the atmospheric front and change its effects. For example, cases of the destruction of atmospheric fronts during handling through mountain ranges are known.
Air masses and atmospheric fronts bring weather forecasters a lot of surprises. Comparing and studying the directions of mass movement 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.