Which means 1 5 mm of precipitation. How to measure precipitation Methods for measuring precipitation. Weather forecast, weather news: record rainfall, extreme rainfall, snow hell
The amount of precipitation is of constant interest to those who follow the weather. It would seem that the forecast is 10-15 mm, and on the streets - 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 can be no more than 20 mm. One millimeter of fallen snow is equivalent to 1-1.5 cm of snow cover height, depending on the snow structure.
According to meteorological guidance, a millimeter of precipitation is one liter of water per square meter. At all weather stations there are rain gauge buckets, from which, at 9 and 21 hours 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.
Precipitation- water in a liquid or solid state, falling out of clouds or deposited from the air on the earth's surface.
Rain
Under certain conditions, cloud drops begin to merge into larger and heavier ones. They can no longer be retained 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 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 the smallest crystals - needles, which, when combined together, form snowflakes.
dew and frost
Precipitation that falls 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 rain gauge (Fig. 2).
Rice. 2. The structure of the rain gauge: 1 - outer case; 2 - funnel; 3 - a container for collecting oxen; 4 - measuring tank
Classification and types of precipitation
Precipitation is distinguished by the nature of precipitation, by origin, by physical condition, seasons of precipitation, etc. (Fig. 3).
According to the nature of the precipitation, there are torrential, continuous and drizzling. Rainfall - intense, short, capture a small area. Overhead precipitation - medium intensity, uniform, long (can last for days, capturing large areas). Drizzling precipitation - fine-drop precipitation falling over a small area.
By origin, precipitation is distinguished:
- convective - characteristic of the hot zone, where heating and evaporation are intense, but often occur in the temperate zone;
- frontal - formed when two air masses with different temperatures meet and fall out of warmer air. Characteristic for temperate and cold zones;
- orographic - fall on the windward slopes of mountains. They are very abundant if the air comes from the warm sea and has a high absolute and relative humidity.
Rice. 3. Types of precipitation
Comparing the annual amount of precipitation in the Amazonian lowland and in the Sahara Desert on the climate map, one can be convinced of their uneven distribution (Fig. 4). What explains this?
Precipitation is brought by moist air masses that form over the ocean. This is clearly seen in the example of territories with a monsoon climate. The summer monsoon brings a lot of moisture from the ocean. And over land there are continuous rains, as on the Pacific coast of Eurasia.
Constant winds also play a large role in the distribution of precipitation. Thus, the 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 rain from the Atlantic Ocean to Europe.
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 influences the distribution of precipitation, for example, the Himalayan mountains do not allow moist winds blowing from the Indian Ocean to the north. Therefore, up to 20,000 mm of precipitation sometimes falls a year on their southern slopes. Humid air masses, rising along the slopes of the mountains (ascending air currents), cool, saturate, 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 rainfall. At the equator - in the low pressure belt - constantly heated air; as it rises, it cools and becomes saturated. Therefore, in the region of the equator, a lot of clouds form and there are heavy rains. A lot of precipitation also falls in other areas of the globe where low pressure prevails. At the same time, air temperature is of great importance: the lower it is, the less precipitation falls.
Downward air currents predominate in high pressure belts. The air, descending, heats up and loses the properties of the state of saturation. Therefore, at latitudes of 25-30 °, precipitation is rare and in small quantities. High-pressure areas near the poles also receive little precipitation.
Absolute maximum precipitation registered on about. Hawaii (Pacific Ocean) - 11,684 mm / year and Cherrapunji (India) - 11,600 mm / year. Absolute minimum - in the Atacama Desert and the Libyan Desert - less than 50 mm / year; sometimes precipitation does not fall at all for years.
The moisture content of an area is moisture factor- the ratio of annual precipitation and evaporation for the same period. The moisture coefficient is denoted by the letter K, the annual rainfall is denoted by the letter O, and the evaporation rate is denoted by I; then K = O: I.
The lower the humidity coefficient, the drier the climate. If the annual precipitation is approximately equal to evaporation, then the moisture coefficient is close to unity. In this case, moisture is considered sufficient. If the moisture index is greater than one, then the moisture excess, less than one - insufficient. If the moisture coefficient is less than 0.3, moisture is considered meager. Zones with sufficient moisture include forest-steppes and steppes, while zones with insufficient moisture include deserts.
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
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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 the water that falls from the clouds in the form of rain, snow or any other, is called precipitation. Their number 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 and evaporate. This quantity is measured over a certain period of time - per day, month or year.
To measure the amount of precipitation, rain gauges are used - tanks (usually metal barrels) into which precipitation is collected that falls on a certain area (for example, using a funnel with an area of \u200b\u200bone square meter). At the end of the observation period, the amount of water accumulated in the reservoir is measured and converted into units of the thickness of the corresponding layer.
Precipitation measuring instrument
For example, if 200 liters of water have accumulated, this means that the thickness of the layer will be 200,000 cubic centimeters / 10,000 square centimeters = 20 centimeters = 200 millimeters.
But after all, water can evaporate from a barrel, can't it? Of course, especially in hot weather. And if our rain gauge is installed somewhere far from home, and meteorologists come to him only once a month - to find out how much precipitation fell in this place - are they wrong? No, and in order not to be mistaken, they came up with an amusing 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 water underneath.
Why is precipitation different?
Under certain conditions, water vapor in the air begins to turn into water - to 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 may develop in different ways.
Typically, raindrops are about one millimeter in size, less often up to five millimeters. This is because large droplets break up into smaller ones in flight. The formation of large droplets is associated not with the process of vapor condensation, but with the process of adhesion of small cloud droplets. In addition, if water droplets and ice crystals appear simultaneously in the cloud, crystals (snowflakes) grow while the droplets evaporate.
If the air under the cloud has a temperature lower than (GS), snowflakes reach the earth's surface. In warm air, they melt, turning into raindrops. In the mountains, one can often observe how it rains in the valleys, and the peaks are covered with snow at the same time.
An important geographical concept is associated with this phenomenon - the snow line (or border). This is the name given to the altitude 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 the appearance 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 the Antarctic, it drops to sea level (and ice shelves form, as in the Ross Sea).
One of the most dangerous types of precipitation is freezing rain. It is usually observed during the onset of a warm atmospheric front in the cold season. First, snowflakes form in stratus clouds above the front. Once in the warm air, they melt, and the resulting droplets fall into the cold surface layers of air. If the temperature here is not very low, they reach the ground without freezing. But, having got on cold pavements, branches, wires, etc., they freeze on them with a crust ice. If the air under the front is very cold, the droplets freeze in flight, forming groats(ice balls less than five millimeters in diameter) or hail(balls larger than five millimeters). Hailstones can reach the size of an orange, and the largest of those 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.
In St. Petersburg, everything portends an abnormally warm winter (oh, I wouldn’t jinx it!), And I, rather tired of the two previous winters-reconstructions of the events of the film “The Day After Tomorrow,” are incredibly happy about this. Moreover, a year ago, at about this time, it was already -20 ° outside the window. Snowboarders and skiers will be covered with artificial snow on the slopes, so they will not be offended, but I live well without it.
But while the weather is shaking around zero, every morning turns into a dilemma for me: what to wear so as not to freeze and not to sweat. And that's where two great sites come to my rescue with very accurate weather forecasts. At one time, my friend helped me find them, but he does not write in LiveJournal, so I will carry the light to the people. Who knows about them, do not rush to throw eggs at the button accordion, because many still go to obtuse and lying Gismeteo and Yandex for the weather.
Below is a small overview of two great sites: WP5 and YR.no, as well as answers to a few 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. The Russian language, however, is not. But there is English (switches in the upper right corner).
The peculiarity of the site is a bunch of different ways of providing information, ranging from simple forecast 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 meteorological maps that change over time.
For me personally, the optimal and most understandable is a moderately "busy" graph, which can also acquire a line for pressure and a cloud chart 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 level of precipitation in millimeters.
Now I will answer a couple of questions that may arise after reading these sites:
Q: How do the British and Norwegians get information about our weather? Our hydrometeorological center certainly 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 weather stations and made available to the public in the system of free international exchange of meteorological data. Now, anyone with a supercomputer with a thousand or two processors can take this data, process it, and try to predict what the weather will be like in this or that place 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 referred to as 2 mm/6 hours. What to expect really?
A: It is very easy to understand. Here is how RP5 explains it:
"The ratio is direct: 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 such an 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 drop, or an umbrella. It is possible to understand whether this umbrella is needed at all precisely by these millimeters: 0.2-1 mm is very small, and most likely means heavy rains in 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, spread 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: Simply multiply by 10. 1 millimeter of precipitation equals 1 centimeter snowdrift.
Q: It would be great if we could average forecasts from 10 different sources.
Yeah, someone already before