We have already talked more than once about precipitation, its quantity and types. But it would be nice to understand this issue in more detail - it is very important!

All water falling from clouds in the form of rain, snow or any other form is called precipitation. Their quantity is measured in millimeters of the thickness of the layer of water that they would form on the surface of the earth if they did not spread, seep or evaporate. This quantity is measured over a specific period of time - per day, month or year.

To measure the amount of precipitation, rain gauges are used - reservoirs (usually metal barrels) into which precipitation falling over a certain area is collected (for example, using a funnel with an area of ​​one square meter). At the end of the observation period, the amount of water accumulated in the reservoir is measured and converted into units of thickness of the corresponding layer.

Instrument for measuring precipitation

For example, if 200 liters of water have accumulated, this means that the layer thickness will be 200,000 cubic centimeters / 10,000 square centimeters = 20 centimeters = 200 millimeters.

But water can evaporate from a barrel, too? Of course, especially in hot weather. And if our rain gauge is installed somewhere far from housing, and meteorologists come to it only once a month to find out how much precipitation has fallen in this place, are they mistaken? No, and to avoid mistakes, they came up with a funny way. A little oil (for example, machine oil) is poured into the barrel. It is lighter than water and therefore, when water enters the barrel, it spreads over its surface, forming a thin film. And an oil film of negligible thickness hides the water underneath.

Why are precipitation different?

Under certain conditions, water vapor in the air begins to turn into water - condense. At the same time, small droplets of water appear, still so light that they do not fall to the ground, but already so large that they can be seen. Fog or clouds appear. Further events can develop in different ways.

Typically, raindrops are about one millimeter in size, less often up to five millimeters. This happens because large drops in flight are crushed into smaller ones. The formation of large droplets is associated not with the process of steam condensation, but with the process of sticking together of small cloud droplets. In addition, if water droplets and ice crystals simultaneously appear in a cloud, crystals (snowflakes) grow while the droplets evaporate.

If the air under the cloud has a temperature lower than HC, snowflakes reach the earth's surface. In the warm air they melt, turning into raindrops. In the mountains you can often see how it rains in the valleys, and the peaks are simultaneously covered with snow.

Associated with this phenomenon is an important geographical concept - the snow line (or border). This is the name for the altitudinal level above which temperatures are so low that the accumulation of snow and other solid precipitation prevails over evaporation and melting. The existence of a snow line determines the height of glaciers in the mountains. Above the equator, it is located at an altitude of about 4,600 meters above sea level (and only high mountains, like Kilimanjaro, reach it), in the Arctic it drops to 200–500 meters (and glaciers form even on very low mountains, such as Byrranga), and in Antarctica it drops to sea level (and ice shelves form, as in the Ross Sea).

One of the most dangerous species precipitation – freezing rain. It is usually observed when a warm atmospheric front approaches during the cold season. First, snowflakes form in the stratus clouds above the front. When they enter warm air, they melt, and the resulting droplets fall into the cold ground layers of air. If the temperature here is not very low, they reach the ground without freezing. But when they get on cold pavements, branches, wires, etc., they freeze on them with a crust. ice. If the air under the front is very cold, the drops freeze in flight, forming cereal(ice balls less than five millimeters in diameter) or hail(balls are more than five millimeters). Hailstones can reach the size of an orange, and the largest measured, which fell on September 3, 1970 in Kansas, weighed up to 750 grams and had a circumference of up to 0.5 meters! In India, in the New Delhi region, in April 1888, 246 people were killed by hail.

Precipitation- water in a liquid or solid state that falls from clouds or settles from the air onto the earth's surface.

Rain

Under certain conditions, cloud droplets begin to merge into larger and heavier ones. They can no longer stay in the atmosphere and fall to the ground in the form rain.

hail

It happens that in summer the air quickly rises, picks up rain clouds and carries them to a height where the temperature is below 0°. Raindrops freeze and fall as hail(Fig. 1).

Rice. 1. Origin of the hail

Snow

In winter, in temperate and high latitudes, precipitation falls in the form of snow. Clouds at this time do not consist of water droplets, but of tiny crystals - needles, which, joining together, form snowflakes.

Dew and frost

Precipitation falling onto 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 precipitation gauge or rain gauge (Fig. 2).

Rice. 2. Structure of the rain gauge: 1 - outer casing; 2 - funnel; 3 - container for collecting oxen; 4-dimensional tank

Classification and types of precipitation

Precipitation is distinguished by the nature of precipitation, by origin, by physical state, by seasons of precipitation, etc. (Fig. 3).

According to the nature of precipitation, precipitation can be torrential, heavy and drizzling. Rainfall - intense, short-lived, cover a small area. Cover precipitation - medium intensity, uniform, long-lasting (can last for days, covering large areas). Drizzle - fine precipitation falling over a small area.

Precipitation is classified according to its 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 meet air masses with different temperatures and fall out of warmer air. Characteristic 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 high absolute and relative humidity.

Rice. 3. Types of precipitation

Comparing the annual amount on the climate map atmospheric precipitation in the Amazonian lowland and in the Sahara desert, one can see their uneven distribution (Fig. 4). What explains this?

Precipitation comes from moist air masses that form over the ocean. This is clearly seen in areas with a monsoon climate. The summer monsoon brings a lot of moisture from the ocean. And there are continuous rains over the land, as on the Pacific coast of Eurasia.

Constant winds also play a big role in the distribution of precipitation. Thus, trade winds blowing from the continent bring dry air to northern Africa, where the largest desert in the world is located - the Sahara. Western winds bring rain from the Atlantic Ocean to Europe.

Rice. 4. Average annual distribution of precipitation on Earth's land

As you already know, sea currents affect precipitation in the coastal parts of continents: warm currents contribute to their appearance (Mozambique Current off the eastern coast of Africa, Gulf Stream off the coast of Europe), cold currents, on the contrary, prevent precipitation (Peruvian Current off the western coast of South America) .

Relief also affects the distribution of precipitation, for example, the Himalayan mountains do not allow moist winds blowing from the Indian Ocean to pass to the north. Therefore, on their southern slopes sometimes up to 20,000 mm of precipitation falls per year. Moist air masses, rising along the mountain slopes (ascending air currents), cool, become saturated, and precipitation falls from 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 belts and precipitation. At the equator - in a low pressure zone - there is constantly heated air; rising upward, it cools and becomes saturated. Therefore, in the equator region there are many clouds and heavy rainfall. A lot of precipitation also falls in other areas of the globe where low pressure prevails. Wherein great importance has an air temperature: the lower it is, the less precipitation falls.

In high pressure belts, downward air currents predominate. As the air descends, it heats up and loses the properties of its saturation state. Therefore, at latitudes 25-30° precipitation occurs rarely and in small quantities. Areas of high pressure near the poles also receive little precipitation.

Absolute maximum precipitation registered on o. Hawaii ( Pacific Ocean) - 11,684 mm/year and in Cherrapunji (India) - 11,600 mm/year. The absolute minimum - in the Atacama Desert and the Libyan Desert - less than 50 mm/year; Sometimes there is no precipitation at all for years.

The moisture content of the area is characterized by humidification coefficient— the ratio of annual precipitation and evaporation for the same period. The humidification coefficient is denoted by the letter K, the annual amount of precipitation by the letter O, and evaporation by the letter I; then K = O: I.

The lower the humidification coefficient, the drier the climate. If the annual precipitation is approximately equal to evaporation, then the humidification coefficient is close to unity. In this case, hydration is considered sufficient. If the moisture index is greater than one, then the moisture excessive, less than one -insufficient. When the humidification coefficient is less than 0.3, humidification is considered meager. Zones with sufficient moisture include forest-steppes and steppes, and zones with insufficient moisture include deserts.

Popular meteorology and climatology

1 millimeter of precipitation is 1 liter per square meter
(units for abnormal rain and abnormal snow)

Weather forecast, meteorological news: record precipitation, extreme precipitation, snow hell

Snowfall, winter - 10-15 centimeters of snow falls per day. How is snow measured? In two quantities - in the increase in the thickness of the snow cover and in millimeters of water. If 15 centimeters of snow piled up, then that’s only 7.5 liters of water (kilograms) per square meter.

Snow thickness (snow height) for middle latitudes of 1-1.5 meters is not surprising; snow up to 2-4 meters in the mountains is the normal precipitation for the temperate climate zone.

There's a lot of snow is measured by snow measuring rods in centimeters and meters, and the water content in the snow - the snow is simply melted and the volume of water resulting from melting is measured.

A snowfall of 10-20 centimeters of snow is not something extreme; 10-20 centimeters fell overnight - it was normal snowfall.

Freshly fallen snow has a density of only about 50 kg/cubic meter; during a snowstorm, the density of snow is up to 120-180 kilograms per cubic meter. Well-packed snow has a density of up to 0.5 (tons per cubic meter).

The snow on the roofs successfully stays on slopes that are steep and 60 degrees, the wind blows it and slaps it down. But it could cause an avalanche. So it is still unknown which roof is better - flat or steep. The snow load on the roof (snow compacted by the wind!) may well be 0.5 tons per square meter (1 meter vertically). Therefore, the collapse of a roof under the snow - old roofs or new roofs (on which they saved a lot - they replaced the materials), balconies - is not uncommon.

Weather news: "up to 10-15 mm of precipitation will fall, more than a quarter of the January norm. The increase in snow cover may be 7-15 cm."
10 millimeters of precipitation is a layer of water if you melt the fallen snow. Freshly fallen snow is 20 times looser than water (20 times less dense), therefore, the weather forecast promises 20-30 fluffy snow, if there is no wind. The increase in snow cover in the weather forecast is 2 times less? This takes into account the fact that the snow is slightly compacted by the wind.

Weather forecast, meteorological news: record rain, thunderstorm, prolonged extreme precipitation, abnormal rains

Precipitation measurement - rain gauge, precipitation gauge, pluviograph.

Millimeters of precipitation is the amount of water height if it did not flow anywhere. For example, if after rain the water increased by 1 centimeter, then 10 millimeters of precipitation fell. That is, the rain poured 10 liters of water per square meter. This is average heavy rain, nothing extreme.

But when the soil can no longer absorb water or has not yet thawed and there is nowhere to drain, then expect flooding in low places.

Precipitation observations, precipitation examples

Winter precipitation, photo

Location: 10 kilometers from Varna (Bulgaria)

Summer precipitation, photo

Place: Burgas city on the Black Sea, Bulgaria

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Atmospheric precipitation and its formation

Precipitation does not fall from every cloud. A prerequisite for the formation of precipitation is the simultaneous presence of water in the air in solid, liquid and gaseous states, sometimes in mixed clouds. This only happens when the cloud rises and cools. Therefore, by origin, convective, frontal and orographic precipitation are distinguished.

Convective precipitation is characteristic of the hot zone, where intense heating and evaporation of water occur throughout the year, and the ascending movement of warm and humid air. In summer, such processes often occur in the temperate zone.

Frontal precipitation is formed when two air masses with different temperatures and other physical properties. Typical frontal precipitation is observed in temperate and cold zones.

Orographic precipitation occurs on the windward slopes of mountains, especially high ones, since they also force the air to flow upward. Having lost moisture and descending, passing the mountain range, it descends again and warms up, and the relative humidity decreases, moving away from the saturation state.

According to the nature of the fallout, they are distinguished: rainfall (intense, short-lived, falling over a small area); heavy rainfall (medium intensity, uniform, long-lasting - can last a whole day, often falls over a large area); precipitation, drizzling (characterized by small droplets suspended in the air).

Precipitation measurement

The amount of precipitation is measured by the thickness of the layer of water in millimeters that could be formed as a result of precipitation on a horizontal surface in the absence of evaporation and seepage into the soil. To measure the amount of precipitation, a rain gauge is used (a metal cylinder 40 cm high and a cross-sectional area of ​​500 cm2 with an inserted diaphragm to prevent evaporation). A precipitation gauge differs from a rain gauge by special protection. Solid precipitation (snow, hail, graupel) is preliminarily melted. The amount of water that enters in a rain gauge, is measured using a glass cylindrical vessel, the bottom area of ​​which is 10 times less than the area of ​​the bottom of the rain gauge. So, when the layer of water drained from the rain gauge at the bottom of the vessel is 20 mm, this means that a layer of water with a height of 2 mm.

All precipitation measurements are summarized for each month and output monthly and then annual precipitation. The longer the observation, the more accurately it is possible to calculate the average monthly and, accordingly, average annual precipitation for this observation location. Lines on a map connecting points with the same amount of precipitation in millimeters over a certain period of time (for example, a year) are called isohyets.

Distribution of precipitation on the surface of the globe

The geographic distribution of precipitation over the earth's surface depends on the combined action of many factors: temperature, evaporation, air humidity, cloudiness, atmospheric pressure, prevailing winds, distribution of land and sea, ocean currents. The most important among them is air temperature, on which the intensity of evaporation and the amount of air evaporation depend (the amount of moisture in millimeters of water layer that can evaporate in a certain place in a year).

In “cold latitudes, evaporation was insignificant, evaporation was observed, since cold air can contain a low content of water vapor. And although the relative humidity of the air can be quite high, when a small amount of vapor condenses, a negligible amount of precipitation falls. In the hot zone, the opposite phenomenon is observed: a large evaporation and high volatility, and, consequently, absolute humidity air causes significant amounts of precipitation. Consequently, precipitation is distributed zonally.

In the equatorial belt it falls greatest number precipitation - 1000-2000 mm or more, since there all year round There are high temperatures, high evaporation and ascending air currents prevail.

In tropical latitudes, the amount of precipitation decreases to 300-500 mm, and in the interior desert areas of the continents it is less than 100 mm. The reason for this is the dominance of high pressure and downward air flows, which heat up and move away from the saturation state. Here only on the eastern coasts of the continents that

carried by warm currents, there is heavy precipitation, especially in summer.

IN temperate latitudes the amount of precipitation increases again to 500-1000 m. Most of it falls on the western coasts of the continents, since they prevail there throughout the year westerly winds from the oceans. Warm currents and mountainous terrain also contribute to greater precipitation here.

In the polar regions, precipitation is only 100-200 mm, which is due to the low moisture content in the air, despite heavy cloudiness.

However, the amount of precipitation does not yet determine the moisture conditions. The nature of moistening is expressed by the moistening coefficient - the ratio of precipitation to evaporation for the same period. That is, K = O / B, where K is the humidification coefficient, O is the amount of precipitation, B is the amount of evaporation. If K = 1, then the moisture is adequate, K> 1 is excessive, K<1 - недостаточное, а К <0,3 - бедное. Коэффициент увлажнения определяет тип природно-растительных зон: при избыточном и достаточном увлажнении и достаточный, количества тепла произрастают леса; недостаточное, близкий к единице, увлажнение характерно для лесостепи, саванн; несколько больше 0,3 - луговых и сухих степей; бедное - для полупустынь и пустынь.

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 there is knee-deep snow or huge puddles on the streets. To make it easier for you to navigate the forecasts, we have prepared information on measuring precipitation.

Meteorologists distinguish between two concepts: the depth of 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 may be no more than 20 mm. One millimeter of fallen snow is equivalent to 1-1.5 cm of snow depth, depending on the structure of the snow.

According to meteorological instructions, a millimeter of precipitation is one liter of water per square meter. At all weather stations there are precipitation measuring buckets, from which, at 9 and 21 o'clock GMT, precipitation is poured into a special vessel, by which its quantity is measured. Solid precipitation - snow, hail - is melted, and then specialists measure the resulting water.