Precipitation- water in a liquid or solid state, falling out of clouds or deposited from the air on earth surface.
Rain
Under certain conditions, cloudy drops begin to merge into larger and heavier ones. They can no longer be held in the atmosphere and fall to the ground in the form rain.
Hail
It happens that in summer the air rises quickly, picks up rain clouds and carries them to a height where the temperature is below 0 °. Raindrops freeze and fall out as hail(fig. 1).
Rice. 1. Origin of the city
Snow
In winter, in temperate and high latitudes, precipitation falls in the form snow. Clouds at this time do not consist of water droplets, but of the smallest crystals - needles, which, joining together, form snowflakes.
Dew and frost
Precipitation falling on the earth's surface not only from clouds, but also directly from the air is dew and frost.
The amount of precipitation is measured by a rain gauge or a rain gauge (Fig. 2).
Rice. 2. The structure of the rain gauge: 1 - outer body; 2 - funnel; 3 - container for collecting oxen; 4 - dimensional tank
Classification and types of precipitation
Precipitation is distinguished by the nature of precipitation, origin, physical condition, seasons of precipitation, etc. (Fig. 3).
By the nature of precipitation, precipitation is heavy, heavy and drizzling. Heavy rainfall - intense, short, cover a small area. Overhead precipitation - medium intensity, uniform, long-term (can last for days, capturing large territories). Drizzling precipitation - fine-droplet precipitation falling on an insignificant area.
Precipitation is distinguished by origin:
- convective - characteristic of the hot zone, where heating and evaporation are intense, but often occur in the temperate zone;
- frontal - are formed when two air masses meet with different temperatures and fall out of the warmer air. Typical for temperate and cold zones;
- orographic - fall on the windward slopes of the mountains. They are very abundant if the air comes from the side. warm sea and has a high absolute and relative humidity.
Rice. 3. Types of precipitation
Comparing on climate map the annual amount of atmospheric precipitation in the Amazonian lowland and in the Sahara desert, one can be convinced of their uneven distribution (Fig. 4). How can this be explained?
Precipitation brings wet air masses forming over the ocean. This is clearly illustrated by the example of territories with a monsoon climate. The summer monsoon brings a lot of moisture from the ocean. And there are continuous rains over land, like on the Pacific coast of Eurasia.
Constant winds also play big role in the distribution of precipitation. For example, trade winds blowing from the continent bring dry air to northern Africa, where the largest desert in the world, the Sahara, is located. Western winds bring rains to Europe from the Atlantic Ocean.
Rice. 4. Average annual distribution of precipitation on the Earth's land
As you already know, sea currents affect precipitation in the coastal parts of the continents: warm currents contribute to their appearance (Mozambique current off the eastern coast of Africa, Gulf Stream off the coast of Europe), cold ones, on the contrary, prevent precipitation (Peruvian current off the western coast of South America) ...
The relief also affects the distribution of precipitation, for example, the Himalayan mountains do not allow wet winds blowing from the Indian Ocean to the north. Therefore, their southern slopes sometimes receive up to 20,000 mm of precipitation per year. Wet air masses, rising along the slopes of mountains (ascending currents of air), are cooled, saturated, and precipitation falls out of them. The territory north of the Himalayan mountains resembles a desert: only 200 mm of precipitation falls there per year.
There is a relationship between the belts and the amount of precipitation. At the equator - in the belt low pressure- constantly heated air; rising up, it cools and saturates. Therefore, many clouds form in the equator area and there are heavy rains. There is a lot of rainfall in other areas as well. the globe where low pressure prevails. Wherein great importance has an air temperature: the lower it is, the less precipitation falls.
Downward air currents prevail in high pressure belts. As the air sinks, it heats up and loses its saturation state. Therefore, at latitudes of 25-30 °, precipitation is rare and in small quantities. There is also little rainfall in high pressure areas near the poles.
Absolute maximum precipitation registered on about. Hawaii (Pacific Ocean) - 11,684 mm / year and Cherrapunji (India) - 11,600 mm / year. The absolute minimum is in the Atacama Desert and in the Libyan Desert - less than 50 mm / year; sometimes precipitation does not fall for years at all.
The characteristic of the moistening of the territory is moisture factor- the ratio of annual precipitation and evaporation for the same period. The moisture coefficient is designated by the letter K, the annual precipitation is by the letter O, and the evaporation is by I; then K = O: I.
The lower the moisture coefficient, the drier the climate. If the annual amount of precipitation is approximately equal to the evaporation rate, then the moisture coefficient is close to unity. In this case, moisture is considered sufficient. If the moisture index is more than one, then the moisture excess, less than one - insufficient. With a humidification coefficient less than 0.3, humidification is considered meager... Areas with sufficient moisture include forest-steppe and steppe, areas with insufficient moisture - deserts.
Precipitation refers to water that falls from the atmosphere onto the earth's surface. Atmospheric precipitation also has a more scientific name - hydrometeors.
They are measured in millimeters. To do this, measure the thickness of the water that has fallen to the surface using special devices - rain gauges. If you need to measure the water column over large areas, then meteorological radars are used.
On average, our Earth receives almost 1000 mm of precipitation annually. But it is quite predictable that the amount of moisture deposited depends on many conditions: climate and weather regime, terrain and proximity to water bodies.
Types of precipitation
Water from the atmosphere falls onto the earth's surface, being in two of its states - liquid and solid. According to this principle, all atmospheric precipitation is usually divided into liquid (rain and dew) and solid (hail, frost and snow). Let's consider each of these types in more detail.
Liquid precipitation
Liquid precipitation falls on the ground in the form of water droplets.
Rain
Evaporation from the surface of the earth, water in the atmosphere collects into clouds, which consist of the smallest droplets, ranging in size from 0.05 to 0.1 mm. These tiny droplets in the clouds merge with each other over time, becoming larger in size and noticeably heavier. Visually, this process can be observed when the snow-white cloud begins to darken and grow heavier. When there are too many such drops in a cloud, they fall on the ground in the form of rain.
Summer it's raining in the form of large drops. They remain large because the heated air rises from the ground. It is these ascending streams that do not allow the drops to break into smaller ones.
But in spring and autumn, the air is much cooler, so the rains are drizzling during these seasons. Moreover, if it rains from stratus clouds, it is called overburden, and if drops begin to fall from kunevo-rainy clouds, then the rain turns into a downpour.
Every year, almost 1 billion tons of water is poured on our planet in the form of rain.
It is worth highlighting in a separate category drizzle... This type of precipitation also falls from stratus clouds, but its drops are so small, and their speed is so negligible that the water droplets seem to be suspended in the air.
Dew
Another type of liquid precipitation that falls at night or early in the morning. Dew droplets are formed from water vapor. During the night, this vapor cools down, and the water turns from a gaseous state into a liquid one.
The most favorable conditions for dew formation are clear weather, warm air and almost complete absence of wind.
Solid precipitation
We can observe solid precipitation during the cold season, when the air cools to such an extent that the water droplets in the air freeze.
Snow
Snow, like rain, is formed in a cloud. Then, when the cloud enters the air stream, in which the temperature is below 0 ° C, the water droplets in it freeze, become heavy and fall to the ground in the form of snow. Each droplet solidifies in the form of a kind of crystal. Scientists say that all snowflakes have a different shape and it is simply impossible to find the same.
By the way, snowflakes fall very slowly, as they are almost 95% air. For the same reason, they are white. And the snow crunches underfoot because crystals break. And our ears are able to pick up this sound. But for the fish it is a real torment, since snowflakes falling on the water emit a high-frequency sound that the fish hear.
Hail
falls only in the warm season, especially if it was very hot and stuffy the day before. The heated air rushes upward in strong currents, carrying away the evaporated water. Heavy cumulus clouds form. Then, under the influence of ascending currents, water droplets in them become heavy, begin to freeze and become overgrown with crystals. These lumps of crystals rush to the ground, increasing in size along the way due to merging with drops of supercooled water in the atmosphere.
It should be borne in mind that such ice "snowballs" rush to the ground with incredible speed, and therefore hail is able to break through slate or glass. The hail does a lot of damage agriculture, therefore, the most "dangerous" clouds, which are ready to burst into hail, are dispersed with the help of special cannons.
Frost
Hoarfrost, like dew, is formed from water vapor. But in the winter and autumn months when it is already cold enough, water droplets freeze and therefore fall out in the form of a thin layer of ice crystals. And they do not melt because the earth is cooling down even more.
Rainy seasons
In the tropics and very rarely in temperate latitudes, there comes a time of year when it falls out of proportion a large number of precipitation. This period is called the rainy season.
In countries located in these latitudes, there is no harsh winters... But spring, summer and autumn are incredibly hot. During this hot period, a huge amount of moisture accumulates in the atmosphere, which then pours out in the form of prolonged rains.
In the equator zone, the rainy season occurs twice a year. And in the tropical zone, south and north of the equator, this season happens only once a year. This is due to the fact that the rain belt gradually runs from south to north and vice versa.
In St. Petersburg, everything portends an abnormally warm winter (oh, I shouldn't jinx it!), And I'm pretty tired of the two previous winters, reconstructions of the events of the film "The Day After Tomorrow", I'm incredibly happy about it. Moreover, a year ago about this time outside the window was already frost -20 °. Snowboarders and skiers will have artificial snow on the slopes, so they will not be offended, and I can live well without it.
But while the weather shakes around zero, every morning for me turns into a dilemma: what to wear so as not to freeze and evaporate. And this is where two excellent sites with very accurate weather forecasts come to my rescue. At one time, my friend helped me find them, but he does not write in LJ, so I will carry the light to the people. Anyone who knows about them, do not rush to throw eggs at the button accordion, because many still go to the stupid and lying Gismeteo and Yandex for the weather.
Below is a small overview of two great sites: RP5 and YR.no, as well as answers to several questions that may arise after getting to know them. If it seems that there are too many letters, just take note of my recommendations and believe that these two resources have never failed or deceived.
This site, a guest from Norway, unlike RP5, in addition to very accurate forecasts, has a very beautiful design. True, there is no Russian language. But there is English (switchable in the upper right corner).
A feature of the site is a bunch of different ways of providing information, from simple forecasts-tables familiar from Yandex for 9 days in advance (it is worth noting that the decoding is still very detailed), and ending with graphs and weather maps that change over time.
For me personally, the optimal and most understandable is the moderate "workload" of the graph, which can also acquire a pressure line and a cloud diagram if you click on the Detailed button on the left, but this information seems redundant to me. The blue bars on the time axis are again the precipitation level in millimeters.
Now I will answer a couple of questions that may arise after reading these sites:
Q: Where do the British and Norwegians get information about our weather? Our hydrometeorological center probably knows better!
A: Not at all. Both the Hydrometeorological Center and everyone else know exactly the same thing about the actual weather. All information is collected by ground-based meteorological stations and is laid out for public access in the system of free international exchange of meteorological data. Now anyone who has a supercomputer with a thousand or two processors can take this data, process it and try to predict what the weather will be in one place or another in the near future. It's only up to those who manage to do it more accurately.
Q: I don't understand when precipitation is designated as 2 mm / 6 hours. What can you really expect?
A: Very easy to understand. WP5 explains it this way:
"The ratio is straight: 1 mm corresponds to 1 liter per 1 square meter. That is, 12 mm is a large 12-liter bucket; 10 mm is a 10-liter bucket; 0.5 mm is a half-liter bottle; 0.2 mm is a glass of water per 1 square meter. meter. Perhaps this explanation is not very solid, but understandable. "
This opens up new horizons compared to those weather forecasts, where rain, regardless of the predicted intensity, is indicated by a droplet, or an umbrella. It is possible to understand whether this umbrella is needed at all by these millimeters: 0.2-1 mm is very small, and most likely means heavy rains in some places (that is, all 10 millimeters will fall on 10% of the city, and the sun will shine over the remaining 90%) ... And 4-10 mm is already an impressive amount, smeared over a huge area, and most likely it will rain for a long time and everywhere.
Q: What a rain, we have winter, frost -30! How to measure snow in millimeters?
A: Just multiply by 10. 1 millimeter of precipitation equals a 1-centimeter snowdrift.
Q: It would be great if the forecasts from 10 different sources could be averaged.
Aha, someone already before that
Average annual rainfall is an important part of climate data — one that is recorded using a variety of methods.
Precipitation (most often includes snow, hail, sleet and rain, and other types of water falling to the ground) are measured in units over a period of time.
In the United States, precipitation is usually reported in inches over a 24 hour period. This means that if one inch of rain falls in a 24 hour period and the water does not soak into the ground and flow down after the storm, there would be a layer of one inch of water covering the ground.
Low-tech rainfall measurement uses a flat-bottomed, straight-sided container (eg a coffee cylinder). While a cylinder can help you determine if precipitation is one or two inches of rain, it is difficult for them to measure small amounts of precipitation.
Weather watchers use more sophisticated instruments known as rain gauges and tipping buckets to measure rainfall more accurately. Rain gauges have wide openings at the top for rainfall. The rain is directed into a narrow tube one-tenth the diameter of the top of the throat. Because the pipe is thinner than the top of the funnel, the units are farther apart than they would be on a ruler, and one hundredth (1/100 or 0.01) inch accurate measurements are possible. When there is less than 0.01 inches of rain, that amount is called a rain footprint.
A bucket equipped with a sensor records precipitation readings on a rotating drum or electronically. It has a funnel like a simple rain gauge, but the funnels lead to two tiny buckets. The two buckets are balanced and each has a 0.01 inch volume of water. When a bucket is full, the bottom of the bucket is emptied, while the other bucket is filled with rainwater. Each tip of the bucket triggers a device to record an increase of 0.01 inches of rain.
Snowfall is measured in two ways. First, it is a simple measurement of the layer of snow on the ground with a stick, marked with the units of measurement. The second measurement determines the equivalent amount of water per unit of snow. To obtain this ratio, the snow must be collected and melted into the water. Typically, 10 inches of snow produces one inch of water. However, this may apply to loose, fluffy snow, although just 2-4 inches of wet, compacted snow can provide an inch of water.
Wind, buildings, trees, terrain, and other factors can alter the amount of rainfall, and this snowfall is usually measured from obstacles. The 30-year average annual rainfall is used to determine the average annual rainfall for a specific location.
The amount of precipitation is of constant interest to those who monitor the weather. It would seem that the forecast is 10-15 mm, and on the streets there is knee-deep snow or huge puddles. To make it easier for you to navigate the forecasts, we have prepared information on measuring the amount of precipitation.
Meteorologists distinguish between two concepts: the height of the snow cover and the amount of precipitation. What we see on the street after a snowfall is the height of the snow cover, which sometimes reaches 50 cm, although the amount of precipitation in this case can be no more than 20 mm. One millimeter of snowfall is equivalent to 1-1.5 cm of snow depth, depending on the structure of the snow.
According to meteorological guidance, a millimeter of precipitation is one liter of water per square meter. All meteorological stations have precipitation buckets, from which, at 9 and 21 o'clock GMT, precipitation is poured into a special vessel, by which their amount is measured. Solid precipitation - snow, hail - is melted, and then experts measure the resulting water.
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