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, convective, frontal and orographic precipitation are distinguished by origin.

Convective precipitation is typical for the hot zone, where during the year there is intense heating, water evaporation, and the ascending movement of warm and humid air predominates. 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 meet. Typical frontal precipitation is observed in the temperate and cold zones.

Orographic precipitation falls on the windward slopes of mountains, especially high ones, since they also cause the air to rise upwards. Having lost moisture and descending, bypassing the mountain range, it again descends and warms up, and the relative humidity decreases, moving away from the saturation state.

By the nature of the fallout, they distinguish: heavy rainfall (intense, short, falling over a small area); heavy rainfall (medium intensity, uniform, long - can last the whole day, often fall over a large area); precipitation, drizzling (characterized as if small droplets suspended in the air).

Precipitation measurement

Precipitation is measured in terms of the thickness of the water layer in millimeters that would result from precipitation on a horizontal surface in the absence of evaporation and infiltration 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 rain gauge differs from a rain gauge in special protection. Solid precipitation (snow, hail, cereals) is pre-melted. into the rain gauge, 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 rainfall measurements are summarized for each month and output the monthly and then the annual rainfall. The longer the observation is, the more accurately it is possible to calculate the average monthly and, accordingly, the average annual rainfall for this observation site. Lines on a map connecting points with the same amount of precipitation in millimeters for a certain period of time (for example, a year) are called isohieta.

Distribution of precipitation on the surface of the globe

The geographical 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, the distribution of land and sea, and ocean currents. The most important among them is the air temperature, which determines the intensity of evaporation and the amount of air evaporation (the amount of moisture in millimeters of a layer of water that can evaporate in a certain place in a year).

In "cold latitudes, evaporation is negligible, it had evaporation, since cold air can contain a small amount of water vapor. And although the relative humidity of the air can be quite high, when a small amount of vapor condenses, a meager amount of precipitation falls. In the hot zone, the opposite phenomenon is observed: a large Evaporation and high evaporability, and, consequently, the absolute humidity of the air cause a significant amount of precipitation to fall.Consequently, atmospheric precipitation is distributed zonally.

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

In tropical latitudes, the amount of precipitation decreases to 300-500 mm, and in the interior desert regions of the continents - less than 100 mm. The reason for this is the dominance here of high pressure and downward air currents, while heating up and moving away from the state of saturation. Here only on the eastern coasts of the continents, which

flowing with warm currents, heavy rainfall occurs, especially in summer.

In temperate latitudes, the amount of precipitation again increases to 500-1000 m. Most of them fall on the western coasts of the continents, since western winds from the oceans prevail there during the year. Warm currents and mountainous terrain also contribute to more precipitation here.

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

However, the amount of precipitation does not yet determine the conditions of moisture. The nature of moisture is expressed by the coefficient of moisture - the ratio of precipitation to evaporation over the same period. That is, K \u003d O / B, where K is the moisture coefficient, O is the amount of precipitation, B is the amount of evaporation. If K = 1, then humidification is adequate, K> 1 - 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 average annual rainfall is an important part of climate data - those recorded using various methods.

Precipitation (most often includes snow, hail, sleet, and other forms of water falling on the ground) is measured in units over a specified period of time.

In the United States, precipitation is usually presented in inches per 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.

For Low Tech rainfall measurements, a container with a flat bottom and straight sides (e.g. a coffee cylinder) is used. While a cylinder can help you determine if a rainfall 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 tip buckets to measure precipitation 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 neck. Because the pipe is thinner than the top of the funnel, the units are farther apart than they would be on a ruler, and accurate one-hundredth (1/100 or 0.01) of an inch measurements are possible. When the rate is less than 0.01 inches of rain, this amount is called the "footprint" of rain.

A bucket fitted 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 0.01 inch of water. When a bucket is full, its bottom 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 units of measure. The second measurement determines the equivalent amount of water per unit of snow. To obtain this coefficient, the snow must be collected and melted into water. Typically, 10 inches of snow produces one inch of water. However, this may apply to loose, fluffy snow, although as little as 2-4 inches of wet, compacted snow can produce an inch of water.

Wind, buildings, trees, terrain and other factors can change the amount of precipitation, and such snowfall is usually measured from obstacles. The thirty-year mean annual rainfall is used to determine the average annual rainfall for a particular location.

Popular meteorology and climatology

1 millimeter of rain is 1 liter per square meter
(units of anomalous rain and anomalous snow)

Weather forecast, weather news: record rainfall, extreme rainfall, 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 this is only 7.5 liters of water (kilograms) per square meter.

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

Snow piled up measured by snow gauges in centimeters and meters, and the water content in the snow - the snow is simply melted and the volume of water obtained from melting is measured.

A snowfall of 10-20 centimeters of snow is not something extreme, 10-20 centimeters fell overnight - this is 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).

Snow on the roofs is successfully kept with slopes of 60 degrees and the wind blows and slaps it. But it can be an avalanche. So it remains to be seen which roof is better - flat or steep. The snow load on the roof (the snow is rammed by the wind!) may well be 0.5 tons per square meter (1 meter vertically). Therefore, the collapse of the roof under the snow - old roofs or new roofs (on which they saved a lot - materials were replaced), balconies are 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 the snow that has fallen is melted. 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. Is the increase in snow cover in the weather forecast 2 times less? This is taking into account the fact that the snow is slightly rammed by the wind.

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

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 a rain the water increased by 1 centimeter, then 10 millimeters of precipitation fell. That is, the rain poured water 10 liters 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 wait for flooding in low places.

Precipitation observations, examples of precipitation

Winter precipitation, photo

Location: 10 kilometers from Varna (Bulgaria)

Summer precipitation, photo

Location: city of Burgas on the Black Sea, Bulgaria

More related articles
Causes of natural disasters

Rain and its characteristics

Rain is precipitation that falls from clouds in the form of water droplets. In this case, the diameter of one drop can vary from 0.5 to 7 mm. Rain with droplets of small diameter is called drizzle, and large drops, as a rule, fall during showers. Important characteristics of precipitation data are intensity, duration and frequency.

Rainfall intensity is the layer or volume of rainfall that falls in a given unit of time. This indicator can have a value ranging from 0.25 mm/h to 100 mm/h.

It should be noted that the intensity of rain is an important indicator of precipitation. Registration and calculation of the indicator is necessary for the design of many different systems and structures. The design of sewer systems, many engineering structures, and agricultural drainage depend on the average monthly rainfall. Even the device of the roof, the angle of its slope is largely determined by precipitation.

Types of rain

Rain according to its nature can be divided into the following main types:

1. Drizzling rain

With such precipitation, the amount of rainfall is minimal, the drops have the smallest diameter. And the rain intensity does not exceed 0.01 mm/min. Drizzle does not bring any special impacts on nature, agriculture. More it causes a certain mood in a person, causing a desire to sit at home under a warm blanket.

2. Incessant rain

In such a situation, dark clouds with rain cover the sky, and they can spread for many kilometers. Precipitation falls for several hours, days, and even weeks. The intensity of such rains is not great, it exceeds the drizzle by about 4-6 times, however, the protracted nature allows saturating the air with moisture, increasing the total humidity. The continuous pattern of continuous rain brings a negative impact on agriculture. Due to oversaturation with moisture, the plants begin to rot, the crop can be ruined.

3. Shower

It is heavy rain that starts suddenly. Quite often it is accompanied by squally winds and thunderstorms. The droplet diameter at such atmospheric precipitation has a maximum value, and the intensity exceeds 1 mm/min. lasting for several hours, serious damage can be caused to the entire area, and not just to agricultural land.

A downpour can cause phenomena such as flooding, landslides, soil erosion. At the same time, it is worth considering that it is the intensity of the rain, and not its duration, that is more important. A large amount of rain falling in a short period of time causes a greater effect than prolonged, but less intense precipitation.

Determination of rain intensity

To determine the intensity of rain, there are various methods for calculating it. One of the most well-known methods is the use of pluviograph records, which was developed within the walls of the Academy of Public Utilities K.D. Pamfilova. The pluviograph is a self-recording device, which consists of three main components: a mechanism for measuring rain, a system for collecting precipitation, and a recorder of precipitation over time.

Intensimeters are also used to directly measure the intensity of rain itself.

The most intense rains

The greatest is observed in the summer season, near the oceans and windward sides of mountain ranges. Most often, heavy showers are shed in the countries of the tropical and equatorial belts. Record intensities are inherent in convective (or thunderstorm) showers that pour over the tropical part of Central America.

Such precipitation is characterized by short duration, large-diameter drops, a small coverage area, and it starts and ends abruptly. A more extensive capture of the territory is inherent in frontal showers. They last from several hours to several days, but they are less intense.

The heaviest downpour was recorded in November 1970, when water flows with an intensity of 38 mm / min fell at the Baro station in Guadeloupe. Prior to that, the record had been held by a rainstorm that hit Unionville, USA in July 1956. Then the rain intensity was 31 mm/min. More such heavy precipitation was not observed, and today these two records remain the only and exceptional ones.

To do this, you can compare with other indicators of the parameter. Thus, the heaviest rain in Europe was observed in 1920 in Germany, when its value was 15.5 mm / min. On the territory of the Russian Federation, such showers are not observed. Most often, the intensity of rain does not exceed 5 mm/min.

Rains of strong intensity, as a rule, are short-lived. However, even a few minutes is sometimes enough to cause significant damage to the inhabitants of settlements. If the downpour continues for several hours, then the consequences become more serious.