Everything in St. Petersburg is anomalous warm winter(oh, I wish I could jinx it!), and I, quite tired from the two previous winter reconstructions of the events of the film “The Day After Tomorrow,” am incredibly happy about this. Moreover, a year ago, around this time, there was already a frost outside the window of -20°. Snowboarders and skiers will have artificial snow on the slopes, so they won’t be offended, but I can 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 get sweaty. And this is where two excellent sites with very accurate weather forecasts come to my aid. At one time, my friend helped me find them, but he doesn’t write on LiveJournal, so I’ll bring the light to the people. Those who know about them, do not rush to throw eggs at the button accordion, because many still go to the stupid and lying Gismeteo and Yandex to find out the weather.
At the bottom short review two excellent sites: RP5 And YR.no, as well as answers to several questions that may arise after getting to know them. If it seems like there are too many letters, just take into account my recommendations and believe that these two resources have never failed or deceived.
This site, a guest from Norway, unlike RP5, in addition to being very accurate forecasts has very beautiful design. There is no Russian language, however. But there is English (switches in the upper right corner).
Feature of the site - a bunch different ways 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 weather maps that change over time.
Personally, for me, the optimal and most understandable graph seems to be a moderately “loaded” graph, which can also acquire a line for pressure and a cloud diagram if you click on the Detailed button on the left, but this information seems unnecessary 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 their 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 publicly available in the system of free international exchange of weather 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 like in a particular place in the near future. It's just a matter of who can do it more accurately.
Q: It is not clear to me when precipitation is designated as 2 mm/6 hours. What to really expect?
A: Very easy to understand. Here's 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 - 10 liter bucket; 0.5 mm - half-liter bottle; 0.2 mm - a glass of water per 1 square. meter. Perhaps this explanation is not very solid, but it is 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. You can understand whether this umbrella is needed at all by these millimeters: 0.2-1 mm is very little, and most likely means heavy rain 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 the rain will continue to fall for a long time and everywhere.
Q: What rain, it’s winter here, 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 forecasts from 10 different sources could be averaged.
Yeah, someone has already done this
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 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, cover a 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 meet air masses with different temperatures and fall out of more warm 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 comes from moist air masses that form 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 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 and its formation
Precipitation does not fall from every cloud. Required condition 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 meet different temperatures and others 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 sinking, passing Mountain chain, it descends again and warms up, and relative humidity decreases, moving away from the saturation state.
According to the nature of the fallout, they are distinguished: rainfall (intense, short-lived, falling on non- large area) continuous precipitation (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 rain gauge differs from a rain gauge by special protection. Solid precipitation(snow, hail, cereals) are pre-melted. The amount of water entering the rain gauge is measured using a glass cylindrical vessel, the bottom area of which is 10 times less than the bottom area 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 2 mm high has fallen onto the surface of the Earth.
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
Geographical distribution of precipitation across 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 loss significant amount precipitation. Consequently, precipitation is distributed zonally.
IN equatorial belt falls out greatest number precipitation - 1000-2000 mm or more, since there all year round observed high temperatures, high evaporation and ascending air currents predominate.
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 westerly winds from the oceans prevail there throughout the year. 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.
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 the design of many different 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 pattern of heavy rain brings negative impacts on 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 diameter of the droplets 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 is 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 well-known methods is the use of pluviograph records, which was developed within the walls of the Academy of Public Utilities by 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 the summer season, near the oceans and windward sides of mountain ranges. Most often, heavy rainfall occurs in countries in the tropical and equatorial zones. 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 Barot 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. Such rainfalls are not observed on the territory of the Russian Federation. 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.
The amount of precipitation is one of the most important characteristics of the weather, along with air temperature, and, of course, knowing it for a certain area, you can predict the weather for the future, you can even track climate changes, if any. But how to measure precipitation?
With snow, everything is more or less simple: we take a ruler, immerse it in the snow to the ground - and get the amount of precipitation in millimeters. But this trick doesn’t work with rain! After all, water is immediately absorbed into the soil, and that which is not absorbed (say, gets on the asphalt) evaporates relatively quickly, so we won’t get accurate results this way, even if it comes to flooding... how to measure the amount of rain?
There are special devices for this.
One of them is a rain gauge. In fact, it is something like a bucket, only very large - 5 square meters in area. Rainwater enters such a vessel through a cone-shaped funnel - so that the wind does not distort the measurement results by blowing additional water into the vessel, or vice versa - blowing it out of there. This design is installed on a weather site at a height of 2 meters. Once a day, the collected rainwater from the rain gauge is poured into a graduated vessel and measured in millimeters. Every millimeter is a liter of precipitation per square meter.
There are also soil rain gauges, which are buried in the ground level with it, and also field rain gauges, which are graduated glass vessels that are placed in agricultural fields.
But it is not always and not everywhere possible to check the results once a day! In the taiga, tundra, mountains and other hard-to-reach places, you have to check the results once a week, or even ten days - during this time the water can evaporate and the result will be distorted. To operate in such extreme conditions, there are total precipitation gauges. In design, it differs little from a conventional rain gauge, but when it is installed, Vaseline oil is poured into it. As a result, when water is added to the vessel, petroleum jelly floats to the surface, covering its surface with a thin layer that prevents the water from evaporating, preserving it for measurement.
However, you can determine the amount of precipitation without approaching the device directly, if it is a radio precipitation gauge. Its sediment collection tank is installed in such a way that when filled, it turns over, the water is drained from it, and this activates a mechanism that turns on the radio transmitter. Its radio signal is recorded at the nearest weather station, or it is sent to a meteorological satellite.
Another instrument used by meteorologists to measure the amount of rain is a pluviograph. Rainwater is collected in a vessel with an area of 5 square meters. The bottom of the vessel is cone-shaped, and there are holes in it into which water drains and enters the chamber through a pipe. The chamber contains a hollow float connected to a metal rod. At the top of the rod there is a arrow on which the pen is mounted, and next to the camera there is a drum with paper tape. The water accumulating in the chamber raises the float, it sets the rod with the arrow in motion, and the pen draws a curve on the tape, which is used to determine the level of precipitation.