Why does it rain in spring? When and why it rains: what determines its duration. Once again everything will be blamed on human activity
Rain is one of the most common weather phenomena. However, not everyone knows why it rains, even though teachers gave this information in elementary school. The global water cycle begins with heat. Under the scorching rays of the sun, liquid evaporates from the surfaces of reservoirs, rivers, seas and oceans. It turns into steam and rushes upward. In countries with high humidity, small bubbles can be easily noticed.
Reasons for appearance
The sciences that study any type of precipitation are called meteorology and climatology. They identify 4 main reasons:
- Elevated landforms.
- Ascending movement of air masses.
- The presence of water vapor, which contributes to the formation of precipitation in the form of rain.
- Meeting and interaction of cold and warm air flows.
You can conduct a small experiment at home and see clearly how the global water cycle occurs.
To do this, you need to take a small container, fill it with water and put it on the fire to boil. The pan must be covered with a transparent lid. As the liquid heats up, it will begin to turn into steam, and small droplets will begin to accumulate on the surface of the lid, and then fall back into the pan of boiling water and turn into steam again.
Rising movements
The sun's rays heat the earth, and the process of moisture evaporation begins. This happens not only with soil, but also with water surfaces. The evaporated liquid is in the air. According to the laws of physics, warm air moves to the upper layers of the atmosphere along with the water bubbles it contains.
Basic physical concepts- absolute humidity (the amount of steam that is currently contained in the air) and relative humidity (in relation to the humidity that is observed at a given temperature). The hotter the air, the more water vapor it contains.
All air currents contain moisture, but the higher it rises, the lower the air temperature becomes. It begins to condense and clouds appear in the sky. When the temperature reaches its lowest point and the cloud is no longer able to hold the amount of moisture it contains, it begins to rain.
The process is similar to what happens with rising air masses. The rule of precipitation formation only works if the water bubbles have somewhere to come from - from a leaf plate, water surface, freshly plowed soil, etc.
But if a person is, for example, in the Sahara Desert, the sun's rays will not cause rain, since the moisture has nowhere to come from.
Rain is the most common type of precipitation. Even in elementary school, students are told where rain comes from. But despite the availability of teacher explanations, many unclear “whys” remain. For example, why is a small cloud capable of pouring down torrents of rain, while black clouds pass by without even splashing? Why do drops come in different sizes and how are they formed?
Rain and the water cycle in nature
It all starts with warmth. Solar energy causes water to evaporate from the surfaces of oceans, lakes, seas, rivers, other bodies of water, soil and even plants. Turning into steam, it rises into the air. The force of the wind speeds up the process. Small water particles are not tangible. With high humidity (especially in the tropical zone), you can notice how the bubbles circle around, not descending, but, on the contrary, tending upward.
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Causes of rain (formation of precipitation)
Climatology and meteorology - sciences directly interested in any precipitation, identify 4 main reasons for the appearance of rain:
- Rising air movements
- The presence of water vapor in the air in quantities sufficient to form rain
- Meeting of warm and cold air currents
- Presence of elevated landforms
Rising air movements
The sun heats the earth's surface, and moisture begins to evaporate from it. The process of evaporation occurs not only directly from the soil, but also from the surface of the ocean, sea, lake, as well as from leaf blades and human skin. All the water that has evaporated is still in the air. But, in accordance with the laws of physics, the heated air begins to slowly rise upward. Along with all the water contained in it.
You need to remember important physical concepts - relative and absolute humidity. Absolute is the amount of water vapor that is already, at the moment, contained in the air. Relative humidity is the humidity that exists relative to what it could be at a given temperature. And the last physical law is that the higher the air temperature, the more water vapor it can hold.
There is already some moisture in the rising air currents. But as you move upward, the air temperature drops. Therefore, moisture begins to condense into clouds. When the temperature drops even lower and the cloud can no longer hold the amount of moisture it contains, the excess falls out as rain.
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The presence of water vapor in the air in quantities sufficient to form rain
The process is similar to the one described above, only with clarifications. The rule of rain formation works if water vapor has somewhere to come from - from the surface of freshly plowed soil, a river, a lake, or a leaf plate of green cabbage and spinach seedlings. And if we are in the center of the Sahara Desert, then there will be no moisture in the air, no matter how much the sun shines.
After the director of one of the American radio stations got wet to the skin, caught in the autumn rain, a “Weather Forecast” program appeared on the air, which had not previously existed. The information turned out to be relevant, because it is never a bad idea to find out whether it is worth taking an umbrella today and whether you need to leave the house, since, for example, in Portugal, rain and wind are a valid reason for not showing up at work.
Rain is a type of precipitation that falls mainly from nimbostratus and altostratus clouds in the form of water droplets with a diameter of 0.5 to 7 mm. Rain usually comes from mixed clouds containing supercooled droplets or ice crystals.
Raindrops fall after small spherical particles of water merge into larger ones, or when they freeze to an ice crystal. Unlike the generally accepted opinion, they do not have the shape of a teardrop, since they are flattened on the bottom side due to the pressure of the oncoming air flow.
At first, these droplets are light enough that the air allows them to remain in the cloud. Since inside the cloud they are constantly moving and colliding with each other, merging and increasing in size, they begin to gradually descend downwards, continuing to increase. This process continues until the water particles gain the required mass, allowing them to overcome air resistance and shed raindrops on the ground.
If water particles are in clouds, inside of which the temperature is high enough not to turn into ice crystals, the fusion of droplets with each other occurs constantly and extremely intensely. Rain does not come from them as often as from clouds where the temperature inside is below zero: in order to fall out of the cloud, ice crystals gain the necessary mass quite quickly.
If there is a very high difference in temperature between the cloud and the surface of the earth at this time, then the frozen crystals melt before reaching the earth's surface - and raindrops fall on the ground (the largest drops are obtained when hail melts).
Interestingly, the larger the precipitation drops, the heavier the rain, but it usually passes quite quickly. The speed of such precipitation can range from 9 to 30 m/s (usually this is typical for summer or spring rain). But if the raindrops turn out to be small, then such precipitation can last for several days and even weeks - the water flies to the ground “slowly”, at a speed of 2 to 6.6 m/s, which is typical for autumn rains.
Precipitation intensity
One of the important indicators of precipitation in nature is the recording of rain intensity - the volume of raindrops falling over a certain time.
The thickness of the rainwater layer is usually measured in millimeters: one millimeter of water layer is equal to one kilogram of raindrops falling on one square meter (precipitation intensity usually ranges from 1.25 mm/h to 100 mm/h). Considering the amount of precipitation that falls over a certain period of time, light, moderate and heavy rain are distinguished.
Cover precipitation
At a speed of 2.5 mm/h, light rain falls regardless of the time of year at above-zero temperatures in moderate and high latitudes from dark altostratus, nimbostratus and cumulonimbus clouds. Covering precipitation lasts from several hours to several weeks and covers a vast area. If precipitation of this type is prolonged, then it quite often harms nature: the humidity in the atmosphere increases greatly, and plants begin to rot due to oversaturation with moisture.
Drizzle
Moderate rain falls at a rate of 2.5 to 8 mm/h in the form of small droplets from stratus and stratocumulus clouds. These precipitations do not last long, from several hours to two days, their quantity is minimal, and therefore the rain does not have a negative impact on nature.
Rainfall
Rainfall is heavy rain with wind, which often falls in temperate latitudes, usually in the warm season. Such heavy rain is characterized by a high rate of precipitation (more than 8 mm/h) and a short duration, no more than a few hours. The exception is May rain, which can last up to three days, as well as rainfall that falls in tropical and equatorial latitudes. The rainy season here often lasts several months, and torrential rain falls almost non-stop with an intensity of 25-30 mm/min.
It should be noted that thunderstorms are often accompanied by heavy rain, so in such weather it is better to find shelter in order to avoid accidents. It is interesting that the occurrence of a thunderstorm is directly related to the Sun - in mid-latitudes such a natural phenomenon can be observed in the afternoon and very rarely before dawn.
In Europe, the heaviest rain fell in Germany in the twenties of the last century, when its indicators were 15.5 mm/min. As for the heaviest precipitation on a planetary scale, rain with an intensity of 38 mm/min was recorded in the lands of Guadeloupe.
Heavy rain is often accompanied by thunderstorms and gusty winds, which causes significant harm to both nature and humans. The consequences of such rain and wind are often landslides, floods, and soil erosion. Such weather conditions can cause human death and also cause an environmental disaster. When it comes to heavy torrential rain, it is not so much its duration that is important as its intensity: the more drops that fall, the more harmful the consequences will be.
Rainy season
There are areas on Earth where the greatest amount of precipitation falls. This phenomenon is known as the "rainy season" and can be observed in tropical and subtropical latitudes. The closer to the equator the rainy season, the more prolonged the precipitation, lasting from May to October. In tropical regions more distant from the equator, the rainy season consists of two periods and gives people a certain respite (the rain belt does not stand still and gradually moves following the zenith of the Sun from the northern to the southern tropics and back).
Tropical summer rain usually begins suddenly, and the raindrops, having formed one continuous stream, pour onto the ground in such a dense wall that at a distance of one meter little can be distinguished. As a result, precipitation of such intensity can not only completely flood cities and villages in a few hours, but also cause mudflows and floods.
It is interesting that for local residents the rainy season is a common occurrence; they have long been accustomed to such weather conditions and know how to act; for example, almost all houses in Thailand are built on stilts. That is why tourists are not recommended to visit equatorial and tropical countries during this period. Storms and hurricanes also occur quite often; in the Philippines alone, during one rainy season, about thirty hurricanes and storms fly over the country.
Precipitation in temperate latitudes
The further from the equator, the weaker the rainy season is, and in temperate latitudes it disappears altogether: precipitation here is evenly distributed throughout the year and its abundance depends not so much on the Sun as on the winds and mountain ranges. For example:
- Spring rain is typical for the entire territory of Europe and during the first two months the rains constantly alternate with the Sun. Showers often begin in the last days of spring;
- In Germany, warm rain can be observed throughout the summer. In Sweden, Denmark, the Netherlands, and in central and eastern Europe, August is considered one of the rainiest months;
- Autumn cold rain is observed in Norway, France, Italy and the Balkans in October and November, when warm weather gradually gives way to frost;
- Winter cold rain can be seen mainly in the south of Europe - in the Balkans, in the west and south of the Iberian Peninsula, but it is also common in the northern territories, for example, it often falls in Scotland and the Faroe Islands.
Rains and nature
The role of precipitation in the life of nature is difficult to overestimate, since it both gives life and takes it away. Rain and wind, forming squalls, thunderstorms, and hurricanes, can destroy houses, destroy crops, nullify all a person’s efforts and even deprive him of life or health. The consequences of heavy rainfall are often catastrophic.
Raindrops also give life: after rainfall, nature is renewed and comes to life. For example, all mushroom pickers look forward to mushroom rain. This is a drizzling warm rain that falls from clouds located low above the earth's surface during the period of mushroom growth. It is interesting that, unlike other precipitation, mushroom rain does not last long, raindrops wet the soil well, and all the mushrooms in the soil begin to grow extremely well.
Or snow. It goes on and on, but the weather is bad, it spoils the mood. Meanwhile, this is an interesting natural phenomenon that would be useful for everyone to study, because after becoming parents, people often hear such seemingly simple questions: “Why is it raining or the sun shining?” It is not necessary for little ones to explain everything in detail, but a six or seven year old child is already quite capable of understanding a serious explanation. So it is better to know the answer to the question that a child may ask when reminded about an umbrella and bad weather.
Many people know from their school chemistry course that water can exist in several states of aggregation: solid, liquid and gaseous. Moreover, it passes from liquid to gaseous state almost constantly and the more intensely, the higher its temperature. If you leave a puddle of water on the table, after a while it will dry out and evaporate. In the same way, it evaporates from rivers, lakes, from plant leaves, soil - from any surfaces. It got there from the lakes that were fed by the rain that had passed before. So this one turns into
But in nature, everything is balanced: both on the lid of a pan with boiling water and high in the troposphere, where the air temperature differs significantly from that observed near the ground, condensation forms, that is, drops of water. When they become very heavy, that is, a lot of them accumulate, form and then drops fall to the ground under the influence of gravity - it rains! The water collects in streams and rivulets, and eventually its remains can reach one of the oceans. Everything starts all over again. Of course, this process is described somewhat simplified, but without serious omissions.
This phenomenon is known as the water cycle or whirlpool in nature. However, the latter term is somewhat incorrect, since a whirlpool is usually called another phenomenon that has nothing to do with precipitation.
This whole short story explains why it rains. Sometimes it snows instead, these drops of water freeze and become snowflakes - ice crystals. Hail is an even more interesting phenomenon, it occurs when condensation, that is, water droplets collide with very cold air, then some of them can freeze, but not become snowflakes, but turn into hailstones. Large
Hail can form if there is strong air in the cloud, which prevents precipitation from falling for quite a long time. When this cold cloud collides with warmer air, a thunderstorm begins and hail falls. This phenomenon, however, should not be confused with snow pellets or rain and snow - they are significantly different.
After rain, especially if the weather is warm, even hot, you can see a rainbow. When the rain is mushroom, that is, the sun is not hidden behind the clouds, it can be seen directly during the rain. It appears when the sun shines through small droplets of evaporating or falling water. Children really like this beautiful natural phenomenon, so sometimes the question: “Why is it raining?” - you can even answer: “So that people can see the rainbow.”
Why does it rain? It is unlikely that a person will begin to ask this question if the sky outside the window has frowned, the first drops have fallen from it, but he urgently needs to leave the house. In this case, people simply take an umbrella and go about their business. But it is quite possible in moments of leisure, philosophizing and contemplation
think about why it rains. There are many constant processes going on in nature. One of them is its main participants: liquids of various kinds and the sun.
The luminary not only illuminates the earth, but also warms it. When water heats up, it transforms into another state - gaseous. Water vapor rises. The higher the vapors rise, the colder the air surrounds them. In these circumstances, the molecules are transformed into crystals during the process of condensation, which, when accumulated, form clouds and clouds. When they gain a lot of mass, their stability is disrupted. Cloud accumulations are no longer able to hold water, and drops begin to fall out of them. That's why it rains.
The water that falls on the surface of the earth either evaporates again, or seeps into the ground, or immediately enters the reservoir. In any case, the evaporation process begins again. It is infinite and, like everything ingenious, simple.
Usually determined by the temperature regime in the subcloud layer, the height of the clouds and their structure. As a rule, clouds carrying precipitation have a mixed composition: ice crystals and drops of cold water. Falling down from the total mass, this mixture is transformed in conditions of either warm or frosty air. If the temperature of the subcloud layer is positive, then raindrops reach the ground. If the parameters are negative, snow falls on the ground.
The lower layers of the atmosphere also play a role. If in summer clouds form very high above the ground, in conditions of negative temperatures, then the main composition of the mass consists of ice crystals. This means that snow flies out of the cloud into the subcloud layer. But as they pass through the warm air, the snowflakes melt. Then hail falls to the ground. If they manage to melt completely, then drops of water. That's why it snows, rains, hails.
In the summer - every schoolchild will answer this question. Because it's warm. But why does it rain in winter? It happens that atmospheric phenomena occur with a deviation (for various reasons) from the normal course of events. For example, in winter, mid-latitudes may be affected by warm cloud formations that form in a tropical region over an ocean or sea. In this case, a thaw begins, the previously fallen snow melts, and instead of snowflakes, rain falls on the ground.
This happens in the summer too. Masses of cold air are breaking through from the Arctic. The warm one is pushed back, but at the same time it forms with thick clouds. Rainfall can be extremely heavy. First it rains, then as the air cools it may start to hail or sleet. These precipitations can fall without a cold snap, but always in the presence of heavy clouds. If the front hovers over a certain area, the temperature of the atmosphere will drop even more, then real snow will fall on the ground.