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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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, while large droplets usually fall during showers. Important characteristics of precipitation data are intensity, duration and frequency.
Rain rate 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 is worth noting that rain intensity is an important indicator of precipitation. Registration and calculation of the indicator is necessary for designing a set various systems and structures. The design of sewer systems, many engineering structures, and drainage of farmland depends on the average monthly rainfall. Even the structure of the roof and the angle of its slope are 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 rain that falls is minimal, the drops have the smallest diameter. And the rain intensity does not exceed 0.01 mm/min. Drizzle does not cause any special impacts on nature or agriculture. More than anything, it evokes 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 occurs for several hours, days, or even weeks. The intensity of such rains is not great, exceeding drizzle by about 4-6 times, but their prolonged nature allows them to saturate the air with moisture, increasing the overall humidity. The continuous nature of heavy rain brings negative impact for agriculture. Due to oversaturation with moisture, plants begin to rot and the harvest may be ruined.
3. Shower
This is heavy rain that starts suddenly. Quite often it is accompanied by squally winds and thunderstorms. The droplet diameter during such precipitation has a maximum value, and the intensity exceeds 1 mm/min. lasting for several hours can cause serious damage to the entire area, not just agricultural land.
Rainfall can cause phenomena such as flooding, landslides, and soil erosion. It is worth considering that it is the intensity of the rain, and not its duration, that has more important. A large amount of rain falling in a short period of time has a greater impact 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 known methods is the use of pluviograph records, which was developed within the Academy utilities K.D. Pamfilova. A pluviograph is a self-recording instrument that consists of three main components: a mechanism for measuring rain, a system for collecting precipitation, and a recorder of precipitation amounts over time.
Intensimeter instruments are also used to directly measure the intensity of rain.
The most intense rains
The greatest is observed in summer season, near oceans and windward sides of mountain ranges. Most often, heavy rainfall occurs in tropical and equatorial belts. Record intensities are characteristic of convective (or thunderstorm) showers that occur in the tropical part of Central America.
Such precipitation is characterized by its short duration, droplets of large diameter, small coverage area, and abruptly begin and end. A more extensive coverage of the territory is characteristic of frontal showers. They last from several hours to several days, but they are less intense.
The heaviest rainfall was recorded in November 1970, when water flows with an intensity of 38 mm/min hit the Baro station in Guadeloupe. Previously, the record belonged to a rainstorm that occurred in Unionville in the USA in July 1956. Then the rain intensity was 31 mm/min. Such heavy precipitation has never been observed again, and today these two records remain the only and exceptional ones.
To do this, you can compare it 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. In the territory Russian Federation such showers are not observed. Most often, the rain intensity does not exceed 5 mm/min.
Heavy rainfall usually does not last long. However, even a few minutes are sometimes enough to cause significant damage to residents of populated areas. If the rain continues for several hours, then the consequences become more serious.
Precipitation- water in a liquid or solid state that falls from clouds or settles from the air onto 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 time in moderate and high latitudes precipitation falls in the form 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, captivating small area.Cover precipitation - medium intensity, uniform, long-term (can last for days, capturing 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 air masses meet 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 to climate map the annual amount of precipitation in the Amazonian lowland and the Sahara Desert, one can be convinced of its uneven distribution (Fig. 4). What explains this?
Precipitation brings wet air masses, forming over the ocean. This is clearly seen in the example of territories with 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 (the Mozambique Current off the eastern coast of Africa, the Gulf Stream off the coast of Europe), cold weather, on the contrary, prevents 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 north to pass through. Indian Ocean. 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 the belt low pressure— 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 belts high pressure 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.
Atmospheric precipitation is the name given 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 water that has fallen to the surface using special instruments - precipitation gauges. If you need to measure the water thickness over large areas, then weather radars are used.
On average, our Earth receives almost 1000 mm of precipitation annually. But it is quite predictable that the amount of moisture that falls depends on many conditions: climate and weather conditions, terrain and proximity to water bodies.
Types of precipitation
Water from the atmosphere falls onto the earth's surface, being in its two 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 look at each of these types in more detail.
Liquid precipitation
Liquid precipitation falls to the ground in the form of water droplets.
Rain
Evaporating from the surface of the earth, water in the atmosphere collects in clouds, which consist of tiny droplets, ranging in size from 0.05 to 0.1 mm. These miniature 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 become heavier. When there are too many such drops in a cloud, they fall to the ground in the form of rain.
In summer It is raining in the form of large drops. They remain large because heated air rises from the ground. These rising jets prevent the drops from breaking into smaller ones.
But in spring and autumn the air is much cooler, so at these times of the year the rain is drizzling. Moreover, if the rain comes from stratus clouds, it is called cover clouds, and if drops begin to fall from nimbus clouds, then the rain turns into downpour.
Every year, almost 1 billion tons of water fall on our planet in the form of rain.
IN separate category worth highlighting drizzle. This type of precipitation also falls from stratus clouds, but the droplets are so small and their speed is so negligible that the water droplets appear 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. Overnight, this steam cools, and the water turns from a gaseous state into a liquid.
The most favorable conditions for dew formation: clear weather, warm air and almost complete absence wind.
Solid precipitation
We can observe solid precipitation in the cold season, when the air cools to such an extent that water droplets in the air freeze.
Snow
Snow, like rain, forms in a cloud. Then, when the cloud enters a stream of air in which the temperature is below 0°C, the water droplets in it freeze, become heavy and fall to the ground as snow. Each droplet solidifies into a kind of crystal. Scientists say that all snowflakes have different shapes and it is simply impossible to find identical ones.
By the way, snowflakes fall very slowly, since they are almost 95% air. For the same reason they white. And the snow crunches underfoot because the crystals are breaking. And our hearing is able to catch this sound. But for the fish it’s a real torment, since snowflakes falling on the water emit a high-frequency sound that the fish hear.
hail
only appears in warm time year, especially if the day before it was very hot and stuffy. The heated air rushes upward in strong currents, carrying with it the evaporated water. Heavy Cumulus clouds. Then, under the influence of rising currents, the water droplets in them become heavier, 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 must be taken into account that such icy “snowballs” rush to the ground with incredible speed, and therefore hail is capable of breaking through slate or glass. Hail causes great damage agriculture, therefore, the most “dangerous” clouds that are ready to burst into hail are dispersed with the help of special guns.
Frost
Frost, like dew, is formed from water vapor. But in the winter and autumn months, when it is already quite cold, the water droplets freeze and therefore fall out in the form of a thin layer of ice crystals. But they don’t melt because the earth is cooling even more.
Rainy seasons
In the tropics and very rarely in temperate latitudes, there comes a time of year when there is an excessive amount of rainfall. a large number of precipitation. This period is called the rainy season.
In countries located in these latitudes, there are no severe 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 region, the rainy season occurs twice a year. And in tropical zone, south and north of the equator, such a season occurs only once a year. This is due to the fact that the rain belt gradually runs from south to north and back.