Classification of precipitation. By appearance precipitation are divided into liquid, solid and terrestrial.
Liquid precipitation includes:
rain – precipitation in the form of drops of various sizes with a diameter of 0.5–7 mm;
drizzle - small droplets with a diameter of 0.05–0.5 mm, seemingly in suspension.
Solid sediments include:
snow – ice crystals that form various kinds of snowflakes (plates, needles, stars, columns) 4–5 mm in size. Sometimes snowflakes are combined into snow flakes, the size of which can reach 5 cm or more;
snow pellets - precipitation in the form of opaque spherical grains of white or matte white (milky) color with a diameter of 2 to 5 mm;
ice pellets are solid particles that are transparent on the surface and have an opaque, matte core in the center. The diameter of the grains is from 2 to 5 mm;
hail – more or less large pieces of ice (hailstones), having a spherical or irregular shape and a complex internal structure. The diameter of hailstones varies within a very wide range: from 5 mm to 5–8 cm. There are cases when hailstones weighing 500 g or more fell.
If precipitation does not fall from clouds, but is deposited from atmospheric air on the surface of the earth or on objects, then such precipitation is called ground precipitation. These include:
dew - tiny drops of water that condense on the horizontal surfaces of objects (decks, boat covers, etc.) due to radiation cooling them on clear cloudless nights. A slight wind (0.5–10 m/s) promotes the formation of dew. If the temperature of horizontal surfaces is below zero, then under similar conditions water vapor sublimates on them and frost forms - a thin layer of ice crystals;
liquid deposit – tiny drops of water or a continuous film of water, formed in cloudy and windy weather on the windward predominantly vertical surfaces of cold objects (walls of superstructures, protective devices of winches, cranes, etc.).
glaze is an ice crust that forms when the temperature of these surfaces is below 0 °C. In addition, a hard coating may form on the surfaces of the vessel - a layer of crystals densely or densely sitting on the surface or a thin continuous layer of smooth transparent ice.
Into the foggy frosty weather in low winds, granular or crystalline frost may form on the vessel's rigging, ledges, cornices, wires, etc. Unlike frost, rime does not form on horizontal surfaces. The loose structure of frost distinguishes it from solid plaque. Granular frost is formed at air temperatures from –2 to – 7 ° C due to freezing of supercooled fog droplets, and crystalline frost, which is white precipitate from crystals of a fine structure, is formed at night with a cloudless sky or thin clouds from particles of fog or haze at temperatures from –11 to –2 ° C and above.
According to the nature of precipitation, precipitation is divided into shower, heavy and drizzling.
Rainfall falls from cumulonimbus (thunderstorm) clouds. In summer it is large drops of rain (sometimes with hail), and in winter it is heavy snowfall with frequent changes shapes of snowflakes, snow or ice grains. Precipitation occurs from nimbostratus (summer) and altostratus (winter) clouds. They are characterized by small fluctuations in intensity and long duration of fallout.
Drizzle falls from stratus and stratocumulus clouds in the form of small drops with a diameter of no more than 0.5 mm, descending at very low speeds.
Based on intensity, precipitation is divided into strong, moderate and light.
Clouds and precipitation.
Upper level clouds.
Cirrus (Ci)- Russian name feathery, individual tall, thin, fibrous, white, often silky clouds. Their fibrous and feathery appearance is due to the fact that they are composed of ice crystals.
Cirrus appear in the form of isolated bunches; long, thin lines; feathers like smoke torches, curved stripes. Cirrus clouds can appear in parallel bands that cross the sky and appear to converge on a single point on the horizon. This will be the direction to the area low pressure. Because of their height, they become illuminated earlier than other clouds in the morning and remain illuminated after the Sun has set. Cirrus generally associated with clear weather, but if they are followed by lower and denser clouds, then there may be rain or snow in the future.
Cirrocumulus (Cc) , the Russian name for cirrocumulus, are tall clouds made up of small white flakes. Usually they do not reduce illumination. They are placed in the sky in separate groups of parallel lines, often like ripples, similar to sand on the coast or waves on the sea. Cirrocumulus are composed of ice crystals and are associated with clear weather.
Cirrostratus (Cs), The Russian name is cirrostratus - thin, white, high clouds, sometimes covering the sky completely and giving it a milky tint, more or less distinct, reminiscent of a thin tangled network. The ice crystals they are made of refract light to form a halo with the Sun or Moon at the center. If the clouds subsequently thicken and lower, precipitation can be expected in about 24 hours. These are the clouds of a warm front system.
Upper level clouds do not produce precipitation.
Mid-level clouds. Precipitation.
Altocumulus (Ac), Russian name altocumulus,- middle-tier clouds, consisting of a layer of large individual spherical masses. Altocumulus (Ac) are similar to the upper level clouds of sirrocumulus. Since they lie lower, their density, water content and the size of individual structural elements are greater than those of sirrocumulus. Altocumulus (Ac) can vary in thickness. They can range from blinding white if they are illuminated by the Sun to dark gray if they cover the entire sky. They are often mistaken for stratocumulus. Sometimes individual structural elements merge and form a series of large swells, like ocean waves, with stripes of blue sky between them. These parallel stripes differ from cirrocumulus in that they appear on the palate in large dense masses. Sometimes altocumulus appear before a thunderstorm. As a rule, they do not produce precipitation.
Altostratus (As) , Russian name altostratified, - middle-tier clouds that look like a gray fibrous layer. The Sun or Moon, if visible, appears as if through frosted glass, often with crowns around the star. Halos do not form in these clouds. If these clouds thicken, lower, or turn into low ragged Nimbostratus, then precipitation begins to fall from them. Then you should expect prolonged rain or snow (for several hours). In the warm season, drops from altostratus, evaporating, do not reach the surface of the earth. IN winter time they can produce significant snowfalls.
Low level clouds. Precipitation.
Stratocumulus (Sc) Russian name stratocumulus– low clouds that look like soft, gray masses, like waves. They can be formed into long, parallel shafts similar to altocumulus. Sometimes precipitation falls from them.
Stratus (St), The Russian name is stratified - low, homogeneous clouds resembling fog. Often their lower boundary is at an altitude of no more than 300 m. The curtain of dense stratus gives the sky a hazy appearance. They can lie on the very surface of the earth and are then called fog. Stratus can be dense and transmit sunlight so poorly that the Sun is not visible at all. They cover the Earth like a blanket. If you look from above (having broken through the thickness of the clouds on an airplane), they are dazzlingly white illuminated by the sun. Strong wind sometimes tears the stratus into shreds, called stratus fractus.
Lungs can fall out of these clouds in winter ice needles, and in the summer - drizzle– very small droplets suspended in the air and gradually settling. Drizzle comes from continuous low stratus or from those lying on the surface of the Earth, that is, from fog. Fog is very dangerous in navigation. Freezing drizzle can cause icing on the boat.
Nimbostratus (Ns) , Russian name for stratostratus, - low, dark. Stratus, shapeless clouds, almost uniform, but sometimes with damp patches at the base. Nimbostratus usually cover vast territories measured in hundreds of kilometers. Throughout this vast territory there is simultaneously snow or rain. Precipitation falls for long hours (up to 10 hours or more), drops or snowflakes are small in size, the intensity is low, but during this time a significant amount of precipitation can fall. They are called cover. Similar precipitation may also fall from Altostratus, and sometimes from Stratocumulus.
Clouds of vertical development. Precipitation.
Cumulus (Cu) . Russian name cumulus, - dense clouds formed in vertically rising air. As the air rises, it cools adiabatically. When its temperature reaches the dew point, condensation begins and a cloud appears. Cumulus have a horizontal base, convex upper and lateral surfaces. Cumulus appear as separate flakes, and never cover the palate. When the vertical development is small, the clouds look like tufts of cotton wool or cauliflower. Cumulus are called "fair weather" clouds. They usually appear by midday and disappear by evening. However, Cu can merge with altocumulus, or grow and turn into thunderous cumulonimbus. Cumulus are distinguished by high contrast: the white, illuminated by the Sun, and the shadow side.
Cumulonimbus (Cb), Russian name cumulonimbus, - massive clouds of vertical development, rising in huge columns to great heights. These clouds start at the very lower tier and extend to the tropopause, and sometimes extend into the lower stratosphere. They are taller than the most high mountains on the ground. Their vertical thickness is especially great in equatorial and tropical latitudes. The upper part of Cumulonimbus is composed of ice crystals, often stretched by the wind in an anvil shape. At sea, the top of the cumulonimbus can be visible at a great distance, when the base of the cloud is still below the horizon.
Cumulus and cumulonimbus are called clouds of vertical development. They are formed as a result of thermal and dynamic convection. On cold fronts, cumulonimbus arise as a result of dynamic convection.
These clouds can appear in the cold air at the rear of the cyclone and at the front of the anticyclone. Here they are formed as a result of thermal convection and give, accordingly, intramass, local rainfall. Cumulonimbus and associated showers over the oceans occur more often at night, when the air above the water surface is thermally unstable.
Particularly powerful cumulonimbus develop in the intertropical convergence zone (near the equator) and in tropical cyclones. Associated with cumulonimbus are: atmospheric phenomena like rain showers, snow showers, snow pellets, thunderstorms, hail, rainbows. It is with cumulonimbus that tornadoes (tornadoes), the most intense and most often observed in tropical latitudes, are associated.
Shower rain (snow) characterized by large drops (snow flakes), sudden onset, sudden end, significant intensity and short duration (from 1-2 minutes to 2 hours). Rain showers in summer are often accompanied by thunderstorms.
Ice grains It is a hard, opaque piece of ice up to 3 mm in size, moist on top. Ice pellets fall with heavy rain in spring and autumn.
Snow pellets has the appearance of opaque soft grains of white branches from 2 to 5 mm in diameter. Snow pellets are observed when the wind is squally. Snow pellets are often observed simultaneously with heavy snow.
hail falls only in the warm season exclusively during showers and thunderstorms of their most powerful cumulonimbus and usually lasts no more than 5-10 minutes. These are pieces of ice with a layered structure, about the size of a pea, but there are also many larger sizes.
Other precipitation.
Precipitation in the form of drops, crystals or ice on the surface of the Earth or objects is often observed, not falling from clouds, but precipitating from the air under a cloudless sky. This is dew, frost, frost.
Dew drops that appear on the deck at night in summer. At negative temperatures it forms frost. Frost - ice crystals on wires, ship equipment, racks, yards, masts. Frost forms at night, more often when there is fog or haze, at air temperatures below -11°C.
Ice an extremely dangerous phenomenon. It is an ice crust that results from the freezing of supercooled fog, drizzle, raindrops or droplets on supercooled objects, especially on windward surfaces. A similar phenomenon occurs from splashing or flooding of the deck. sea water at negative air temperatures.
Determining cloud height.
At sea, cloud heights are often determined approximately. This is a difficult task, especially at night. The height of the lower base of vertical clouds (any variety of cumulus), if they were formed as a result of thermal convection, can be determined from psychrometer readings. The height to which the air must rise before condensation begins is proportional to the difference between the air temperature t and the dew point td. At sea, this difference is multiplied by 126.3 to obtain the height of the lower boundary of the cumulus clouds N in meters. This empirical formula looks like:
H = 126.3 ( t – t d ). (4)
The height of the base of lower layer stratus clouds ( St, Sc, Ns) can be determined using empirical formulas:
H = 215 (t – t d ) (5)
H = 25 (102 - f); (6)
Where f – relative humidity.
Visibility. Fogs.
Visibility it's called maximum distance horizontally, in which an object can be clearly visible and recognized in daylight. In the absence of any impurities in the air, it is up to 50 km (27 nautical miles).
Visibility is reduced due to the presence of liquid and solid particles in the air. Visibility is impaired by smoke, dust, sand, and volcanic ash. This occurs when there is fog, smog, haze, or precipitation. The visibility range decreases due to splashes in the sea in stormy weather with a wind force of 9 or more (40 knots, about 20 m/s). Visibility becomes worse during low, continuous clouds and at dusk.
Haze
Haze is a clouding of the atmosphere due to solid particles suspended in it, such as dust, as well as smoke, burning, etc. With severe haze, visibility decreases to hundreds, and sometimes to tens of meters, as in dense fog. Haze is usually a consequence of dust (sand) storms. Even relatively large particles are lifted into the air by strong winds. This is a typical phenomenon of deserts and plowed steppes. Large particles spread in the lowest layer and settle near their source. Small particles are carried over long distances by air currents, and due to air turbulence they penetrate upward to a considerable height. Fine dust remains in the air for a long time, often in the complete absence of wind. The color of the Sun becomes brownish. The relative humidity during these events is low.
Dust can be transported over long distances. It was celebrated in the Greater and Lesser Antilles. Dust from the Arabian deserts is carried by air currents into the Red Sea and the Persian Gulf.
However, during haze, visibility is never as bad as during fog.
Fogs. General characteristics.
Fogs pose one of the greatest dangers to navigation. They are responsible for many accidents, human lives, and sunken ships.
Fog is said to occur when horizontal visibility, due to the presence of droplets or water crystals in the air, becomes less than 1 km. If visibility is more than 1 km, but not more than 10 km, then such a decrease in visibility is called haze. Relative humidity during fog is usually more than 90%. Water vapor itself does not reduce visibility. Visibility is reduced by water droplets and crystals, i.e. water vapor condensation products.
Condensation occurs when the air is oversaturated with water vapor and the presence of condensation nuclei. Above the sea it is mainly small particles of sea salt. Supersaturation of air with water vapor occurs when the air is cooled or in cases of additional supply of water vapor, and sometimes as a result of mixing of two air masses. In accordance with this, fogs are distinguished cooling, evaporation and mixing.
Based on intensity (based on the visual range D n), fogs are divided into:
strong D n 50 m;
moderate 50 m<Д n <500 м;
weak 500 m<Д n < 1000 м;
heavy haze 1000 m<Д n <2000 м;
light haze 2000 m<Д n <10 000 м.
Based on their state of aggregation, fogs are divided into droplet-liquid, icy (crystalline) and mixed. Visibility conditions are worst in icy fogs.
Cooling mists
Water vapor condenses as the air cools to its dew point. This is how cooling fogs are formed - the largest group of fogs. They can be radiative, advective and orographic.
Radiation mists. The Earth's surface emits long-wave radiation. During the day, energy losses are offset by the arrival of solar radiation. At night, radiation causes the Earth's surface temperature to drop. On clear nights, the cooling of the underlying surface occurs more intensely than in cloudy weather. The air adjacent to the surface also cools. If the cooling is to the dew point and below, then dew will form in calm weather. A weak wind is required for fog to form. In this case, as a result of turbulent mixing, a certain volume (layer) of air is cooled and condensation forms in this layer, i.e. fog. Strong wind leads to mixing of large volumes of air, dispersion of condensate and its evaporation, i.e. to the disappearance of the fog.
Radiation fog can extend up to a height of 150 m. It reaches its maximum intensity before or shortly after sunrise, when the minimum air temperature occurs. Conditions necessary for the formation of radiation fog:
High air humidity in the lower layers of the atmosphere;
Stable stratification of the atmosphere;
Partly cloudy or clear weather;
Light wind.
The fog disappears as the earth's surface warms up after sunrise. The air temperature rises and the droplets evaporate.
Radiation mists above the water surface are not formed. Daily fluctuations in the temperature of the water surface, and therefore the air, are very small. The temperature at night is almost the same as during the day. Radiative cooling does not occur, and there is no condensation of water vapor. However, radiation fogs can cause problems in navigation. In coastal areas, fog, as a single whole, flows with cold, and therefore heavy, air onto the water surface. This can also be amplified by the night breeze from land. Even clouds formed at night over elevated coasts can be carried by the night breeze to the surface of the water, as is observed on many coasts of temperate latitudes. The cloud cap from the hill often flows down, covering the approaches to the shore. More than once this led to a collision between ships (port of Gibraltar).
Advection fogs. Advective fogs result from the advection (horizontal transfer) of warm, moist air onto a cold underlying surface.
Advective fogs can simultaneously cover vast horizontal spaces (many hundreds of kilometers), and vertically extend up to 2 kilometers. They do not have a daily cycle and can exist for a long time. Over land at night they intensify due to radiation factors. In this case, they are called advective-radiative. Advective fogs also occur with significant winds, provided that the air stratification is stable.
These fogs are observed over land in the cold season when relatively warm and humid air enters it from the water surface. This phenomenon occurs in Foggy Albion, Western Europe, and coastal areas. In the latter case, if fogs cover relatively small areas, they are called coastal.
Advective fogs are the most common fogs in the ocean, occurring near the coasts and in the depths of the oceans. They always stand above cold currents. In the open sea, they can also be found in warm sectors of cyclones, in which air is transported from warmer areas of the ocean.
They can be found off the coast at any time of the year. In winter, they form over land and can partially slide to the water surface. In summer, advective fogs occur off the coast in cases where warm, moist air from the continent, in the process of circulation, passes to a relatively cold water surface.
Signs of the imminent disappearance of advective fog:
- change in wind direction;
- disappearance of the warm sector of the cyclone;
- it started to rain.
Orographic fogs. Orographic fogs or slope fogs are formed in mountainous areas with a low-gradient baric field. They are associated with the valley wind and are observed only during the day. The air rises up the slope with the valley wind and is cooled adiabatically. Once the temperature reaches the dew point, condensation begins and a cloud forms. For residents of the slope it will be fog. Sailors can encounter such fogs off the mountainous coasts of islands and continents. Fogs can obscure important landmarks on the slopes.
Mists of evaporation
Condensation of water vapor can occur not only as a result of cooling, but also when the air is oversaturated with water vapor due to evaporation of water. The evaporating water should be warm and the air cold, the temperature difference should be at least 10 °C. Cold air stratification is stable. In this case, an unstable stratification is established in the lowest driving layer. This causes a large amount of water vapor to flow into the atmosphere. It will immediately condense in the cold air. A fog of evaporation appears. Often it is small vertically, but its density is very high and, accordingly, visibility is very poor. Sometimes only the masts of the ship stick out from the fog. Such fogs are observed over warm currents. They are characteristic of the Newfoundland region, at the junction of the warm Gulf Stream and the cold Labrador Current. This is an area of heavy shipping.
In the Gulf of St. Lawrence, fog sometimes extends vertically up to 1500m. At the same time, the air temperature can be below 9°C below zero and the wind is almost gale force. The fog in such conditions consists of ice crystals and is dense with very poor visibility. Such dense sea fogs are called frost smoke or arctic frost smoke and pose a serious danger.
At the same time, with unstable air stratification, there is a slight local hovering of the sea, which does not pose a danger to navigation. The water seems to be boiling, streams of “steam” rise above it and immediately dissipate. Such phenomena occur in the Mediterranean Sea, off Hong Kong, in the Gulf of Mexico (with the relatively cold north wind “Norther”) and in other places.
Mixing mists
Fog can also form when two air masses mix, each of which has high relative humidity. The reservoir may be oversaturated with water vapor. For example, if cold air meets warm and humid air, the latter will cool at the mixing boundary and fog may appear there. Fog ahead of a warm front or occluded front is common in temperate and high latitudes. This mixing fog is known as frontal fog. However, it can also be considered as evaporation fog, since it occurs when warm droplets evaporate in cold air.
Mixing fogs form at the edge of ice and above cold currents. An iceberg in the ocean can be surrounded by fog if there is enough water vapor in the air.
Geography of fogs
The type and shape of clouds depend on the nature of the prevailing processes in the atmosphere, the season of the year and the time of day. Therefore, much attention is paid to observations of the development of clouds over the sea when sailing.
There are no fogs in the equatorial and tropical regions of the oceans. It’s warm there, there are no differences in temperature and air humidity day and night, i.e. There is almost no daily variation of these meteorological quantities.
There are a few exceptions. These are vast areas off the coast of Peru (South America), Namibia (South Africa) and off Cape Guardafui in Somalia. In all these places it is observed upwelling(rising of cold deep waters). Warm, moist air from the tropics flows over cold water and forms advective fog.
Fogs in the tropics can occur near continents. Thus, the port of Gibraltar has already been mentioned; fog is possible in the port of Singapore (8 days a year); in Abidjan there are up to 48 days of fog. Their greatest number is in the Bay of Rio de Janeiro - 164 days a year.
In temperate latitudes, fogs are a very common phenomenon. Here they are observed off the coast and in the depths of the oceans. They occupy vast territories and occur in all seasons of the year, but are especially frequent in winter.
They are also typical for polar regions near the boundaries of ice fields. In the North Atlantic and the Arctic Ocean, where the warm waters of the Gulf Stream penetrate, there is constant fog during the cold season. They are often found at the ice edge in summer.
Fogs most often occur at the junction of warm and cold currents and in places where deep water rises. The frequency of fogs is also high along the coasts. In winter, they occur when warm, moist air advects from the ocean onto land, or when cold continental air flows down onto relatively warm water. In the summer, air from the continent hitting the relatively cold water surface also produces fog.
Atmospheric precipitation is water in liquid and solid state that falls from clouds and precipitates from the air.
Types of precipitation
There are different classifications for precipitation. A distinction is made between blanket precipitation, which is associated with warm fronts, and rainfall, which is associated with cold fronts.
Precipitation is measured in millimeters - the thickness of the layer of fallen water. On average, high latitudes and deserts receive about 250 mm of precipitation per year, and the globe as a whole receives about 1,000 mm of precipitation per year.
Measuring precipitation is essential for any geographic research. After all, precipitation is one of the most important links in moisture circulation on the globe.
The defining characteristics for a particular climate are considered to be the average monthly, annual, seasonal and long-term amount of precipitation, its daily and annual cycle, its frequency and intensity.
These indicators are extremely important for most sectors of the national (agricultural) economy.
Rain is liquid precipitation - in the form of drops from 0.4 to 5-6 mm. Raindrops can leave a mark in the form of a wet spot on a dry object, or on the surface of water - in the form of a diverging circle.
There are different types of rain: freezing rain, freezing rain and sleet. Both freezing rain and ice rain fall at subzero air temperatures.
Supercooled rain is characterized by liquid precipitation, the diameter of which reaches 5 mm; After this type of rain, ice may form.
And freezing rain is represented by precipitation in a solid state - these are ice balls with frozen water inside. Snow is precipitation that falls in the form of flakes and snow crystals.
Horizontal visibility depends on the intensity of snowfall. A distinction is made between sleet and sleet.
The concept of weather and its features
The state of the atmosphere in a particular place at a particular time is called weather. Weather is the most variable phenomenon in the environment. It will start to rain, then the wind will start, and after a few hours the sun will shine and the wind will subside.
But even the variability of weather has its own patterns, despite the fact that the formation of weather is influenced by a huge number of factors.
The main elements characterizing the weather include the following meteorological indicators: solar radiation, atmospheric pressure, air humidity and temperature, precipitation and wind direction, wind strength and cloudiness.
If we talk about weather variability, then most often it changes in temperate latitudes - in regions with a continental climate. And the most stable weather occurs in polar and equatorial latitudes.
Changes in weather are associated with changes in seasons, that is, changes are periodic, and weather conditions repeat over time.
Every day we observe the daily change in weather - night follows day, and for this reason weather conditions change.
Climate concept
The long-term weather pattern is called climate. Climate is determined in a specific area - thus, the weather pattern must be stable for a certain geographical location.
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 air masses with different temperatures meet and fall out of the 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 warm sea and has high absolute and relative humidity.
Rice. 3. Types of precipitation
By comparing the annual amount of precipitation on the climate map in the Amazonian Lowland and in 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 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. At the same time, air temperature is of great importance: 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.
Water molecules continuously evaporate from the surface of lakes, seas, rivers and oceans - enter the atmosphere, where they are converted into water vapor, and then into various types of precipitation. There is always water vapor in the air, which is usually impossible to see, but the humidity of the air depends on the amount of it.
Air humidity varies in all regions of the globe; in hot weather it increases when evaporation from the surface of reservoirs into the atmosphere increases. Low humidity is usually found over desert areas because there is little water vapor, so the air in deserts is very dry.
Water vapor goes through many tests before falling to the ground in the form of rain, snow or frost.
The surface of the earth is heated by the sun's rays, and the resulting heat is transferred to the air. Since heated air masses are much lighter than cold ones, they rise. Tiny water droplets that formed in the air continue to travel along with it into in the form of precipitation.
Types of precipitation, fog and clouds.
To imagine how further transformation of water vapor occurs in the atmosphere, you can conduct a fairly simple experiment. You need to take a mirror and bring it closer to the spout of a boiling kettle. After a few seconds, the cool surface of the mirror will fog up, then large water drops will form on it. The released steam turned into water, which means that a phenomenon called condensation occurred.
A similar phenomenon occurs with water vapor at a distance of 2-3 km from the earth. Since the air at this distance is colder than near the surface of the earth, steam condenses in it and water droplets are formed, which can be observed from the ground in the form of clouds.
When flying on an airplane, you can see how clouds sometimes appear below the aircraft. Or you can even find yourself among the clouds if you climb a high mountain in low clouds. At this moment, surrounding objects and people will turn into invisible beings, swallowed up by a thick veil of fog. Fog is the same clouds, but only located near the earth's surface.
If the drops in the clouds begin to grow and become heavier, then the snow-white clouds gradually darken and turn into clouds. When heavy drops are no longer able to stay in the air, then rain pours from thunderclouds onto the ground. in the form of precipitation.
Dew and frost as types of precipitation.
Near bodies of water in summer, a lot of steam forms in the air and it becomes highly saturated with water pores. With the onset of night, coolness comes and at this time less steam is required to saturate the air. Excess moisture condenses on the ground, leaves, grass and other objects, and such type of precipitation called dew. Dew can be observed in the early morning, when transparent small drops are visible covering various objects.
With the arrival of late autumn, the temperature overnight can drop below 0°C, then dew drops freeze and turn into amazing transparent crystals called frost.
In winter, ice crystals freeze and settle on window glass in the form of frosty patterns of extraordinary beauty. Sometimes frost simply covers the surface of the earth, like a thin layer of snow. The fantastic patterns formed by frost are best seen on rough surfaces, such as:
- tree branches;
- loose ground surface;
- wooden benches.
Snow and hail as types of precipitation.
Hail is the name given to irregularly shaped pieces of ice that fall to the ground with rain in the summer. There is also “dry” hail, which falls without rain. If you carefully cut a hailstone, you will see on the cut that it consists of alternating opaque and transparent layers.
When air currents carry water vapor to a height of about 5 km, then droplets of water begin to settle on the dust particles, and they instantly freeze. The resulting ice crystals begin to increase in size, and when they reach a large weight, they begin to fall. But a new stream of warm air emanates from the ground and it returns them back to the cold cloud. The hailstones begin to grow again and try to fall, this process is repeated several times, and as soon as they gain a sufficiently heavy weight they fall to the ground.
The size of these types of precipitation(hailstones) usually range from 1 to 5 mm in diameter. Although there have been cases when the size of hailstones exceeded a chicken egg, and the weight reached approximately 400-800 g.
Hail can cause great damage to agriculture; it damages vegetable gardens and crops, and also leads to the death of small animals. Large hailstones can damage cars and even pierce aircraft skins.
To reduce the likelihood of hail falling on the ground, scientists are constantly developing new substances that, using special rockets, are thrown into thunderclouds and thus disperse them.
With the arrival of winter, the earth is enveloped in a snow-white blanket consisting of tiny ice crystals called snow. Due to low temperatures, water droplets freeze and ice crystals form in the clouds, then new water molecules attach to them and, as a result, a separate snowflake is born. All snowflakes have six corners, but the patterns woven on them by frost differ from each other. When snowflakes are exposed to wind currents, they stick together and form snow flakes. Walking through the snow in frosty weather, we often hear crunching noises under our feet; these are ice crystals breaking in the snowflakes.
Such types of precipitation, as snow brings many problems, traffic on roads becomes difficult due to snow, power lines break under its weight, and melting snow leads to floods. But due to the fact that the plants are covered with a blanket of snow, they are able to withstand even severe frosts.
These are products of condensation of water vapor that fall from clouds in the form of rain, snow, cereals, hail, or settle from the air onto the earth's surface as dew, hoarfrost, and frost. They are all called hydrometeors. The transition of water vapor into a liquid or solid state occurs when the air is saturated with vapor. In this case, an excessive amount of water vapor is released in the form of water droplets or ice crystals. A necessary condition is the presence of condensation nuclei, tiny grains of dust, each of which is covered with a film of water. This is how a droplet appears. In the absence of dust particles for air supersaturated with vapors, air molecules become condensation nuclei.
The smallest droplets of water (with a diameter of 0.05 to 0.1 mm) seem to float in the air. Every drop of water or every ice crystal is supported by rising air currents; Because of this, the clouds remain at a certain height. Colliding, the droplets in the cloud connect, their mass increases, and they fall to the ground - small drops in the form of drizzle (up to 0.5 mm in diameter), and large ones fall as rain. The stronger the rising air streams, the larger the falling drops should be. Therefore, in the summer, when the iriseschmic air is heated and rapidly rises, large-droplet rains usually fall (the diameter of the drops is up to 6-7 mm), and in the spring and especially in the fall - drizzling rains.
Clouds are formed not only during air convection, when their cumulus accumulations occur, but also in cases when air flows with unequal temperatures move one above the other, for example, warm air over cold air or vice versa. When air masses in which vapor is close to saturation are mixed, stratus clouds appear. Based on their composition, clouds are divided into water, ice and mixed. Water droplets formed around condensation nuclei in the cloud often remain at temperatures below zero in a supercooled but liquid state (even at a temperature of -20 ° C). Some of the droplets turn into snowflake ice crystals. From a water cloud it becomes mixed. Connecting with each other, snowflakes fall into snow flakes. Supercooled drops of water often turn into small ice spherical formations (spherocrystals), which fall out of the atmosphere in the form of grains with a diameter of 1 to 15 mm.
The city goes through a more complex path of formation. By breaking a hailstone, you can easily verify that it has a layered structure - in the center there is an ice spherocrystal in a thin shell of loose ice, then an ice shell, then loose again, etc. This indicates that after the formation of the central spherocrystal and it was repeatedly dropped into cloud and rose by ascending vertical air currents, taking on a layered structure and increasing in size. Hailstones are the size of a pigeon's egg, and sometimes larger (hailstones of 1 and even 2 kg are known).
The shape of the clouds is varied and changeable. But they can still be grouped into several types. The nature of the clouds determines what kind of precipitation may fall (rain, hail), and even their quantity. An international classification of clouds has been developed based on their appearance and the height of their location.
There are three tiers of height, for which certain types of clouds are most characteristic. The lower tier is from the Earth's surface up to 2 km. Stratus clouds, stratocumulus, and nimbostratus are common for it. The middle tier is from 2 to 4 km in high latitudes of the globe; towards the equator it expands from 2 to 8 km. Altostratus and altocumulus clouds predominate here. The upper tier is in high latitudes from 3 to 8 km, in middle latitudes - up to 13, and in low latitudes - from b to 18 km. It is characterized by cirrus, cirrocumulus, and cirrostratus clouds.
Certain types of clouds from one tier penetrate into others, for example, altostratus - from the middle tier to the upper, nimbostratus - from the lower to the middle, and cumulus and cumulonimbus, which often give showers with thunderstorms, can have a base in the lower and a top in the upper tier (their height reaches 9 km).
There are three main types of clouds: cirrus, cumulus, and stratus. The remaining forms are their combinations.
The degree to which the sky is covered with clouds is called cloudiness; it is assessed on a 10-point scale or as a percentage. The height and speed of movement of clouds are measured with a special device - a nephoscope. Clouds can tell us about upcoming weather. For example, if cirrus clouds appeared high in the sky, and then the clouds began to cover the sky, then it is very likely that it will rain after a while. When high clouds move first and are replaced by increasingly lower clouds, it means that a front of warm air mass is approaching, at the border with which rain is common. There are other signs of approaching bad weather: groups of clouds increase, become denser, and descend; clouds move quickly, becoming heavier and lower; isolated swirling clouds merge and descend; cloud bases darken and become flat; Around noon, bulky, powerful clouds appear at high altitudes.
Signs of good weather: morning fog dissipates before noon; the number of clouds gradually decreases, their bases rise higher and higher; a layer of stratus clouds breaks through to reveal a clear, cloudless sky.
However, it is unlikely that there are completely reliable weather harbingers: after all, they differ in different areas and are associated not only with the local situation, but also with external influences, from more or less remote areas.
The nature of precipitation is very diverse and is determined by many conditions - time of year and day, temperature in the lower layers of the troposphere, air movement (calm, light, strong wind, etc.).
Rains can be short-term and prolonged, drizzle and torrential, and precipitation in solid form - snowfall, pellets, hail.
The amount of precipitation is measured by a precipitation gauge and is equal to the layer of water in millimeters over a certain time; solid sediments are melted and also measured as a layer of water. From observations over many years, the average amount of precipitation per year is calculated.
Ground precipitation, unlike precipitation from the free atmosphere, occurs in the form of dew, frost, frost, and ice in cases where warmer, moist air comes into contact with the surface of cooled objects and water condenses on them. Dew usually forms in clear weather after sunset with the rapid cooling of blades of grass, leaves, thin branches, and grains of soil. Surface air, in contact with them, cools and reaches the dew point. The amount of dew depends on the degree of air humidity and the cooling of objects. When the air temperature is below zero, it is not water droplets that form on the surface of objects, but ice-frost crystals. Over time, it can build up, forming a layer of ice. On cold days with persistent fog, loose ice is deposited on objects; increasing due to small ice crystals floating in the air, it forms a beautiful fluffy coating - frost. Sometimes its mass is so great that tree branches break under its weight, telegraph and electrical wires break.
When it warms up, a moist wind blows across cold objects, causing water or ice to form on them. This often happens in the mountains, where the ice crust reaches tens of centimeters. After severe frosts, a layer of transparent ice, or glaze, forms on the surface of the soil, roads, on the walls of houses, and on trees. It also occurs from rain, the drops of which freeze in a layer of cold surface air. Terrestrial precipitation accounts for a small proportion of total precipitation.
The distribution of precipitation over the Earth's surface is uneven and is determined by many conditions. The main share of water vapor enters the atmosphere from the World Ocean. It also receives the bulk of precipitation. The greatest amount of precipitation is in the equatorial zone - from 1500 to 2000 mm per year, the least - in the high latitudes of the Arctic and Antarctic - 200-300 mm. Little precipitation falls in the zone of high atmospheric pressure (20-40°). In the zones of temperate latitudes there is more precipitation than near the tropics and in the polar regions - up to 600-1000 mm. The amount of precipitation on land is greatly influenced by its proximity to the seas and sea currents: warm ones increase them, cold ones decrease them. An important factor is air currents. For example, the west of Eurasia (up to the Urals), where air transport from the Atlantic dominates, is more humidified than Siberia and Central Asia. Relief plays a big role. On the slopes of mountain ranges facing moist winds from the ocean, moisture falls noticeably more than on the opposite ones - this is clearly visible in the Cordillera of America, on the southern spurs of the Himalayas (here the Cherrapunji region is the rainiest - up to 12 thousand mm per year), on the eastern slopes of the mountains of the Far East, etc. On maps, points with the same amount of precipitation are connected by lines - and zogiet.
In some places there is a lot of precipitation, but little moisture evaporates - excessive moisture; in other places there is little precipitation and high evaporation (for example, in deserts). The humidification coefficient shows the ratio of the amount of precipitation to the amount that can evaporate from a given area over a certain period of time (for example, a year): K=(R/E)x100%, where R is precipitation, E is the amount of evaporation. Thus, K shows how much precipitation in a given location compensates for possible evaporation from the open water surface. The value of this coefficient in the forest zone is 1.0-1.5, in the forest-steppe - 0.6-1.0, in the steppe - 0.8-0.6, in the semi-desert - 0.1 - 0.3, in the desert - less than 0.1. In other words, in the forest zone there is more precipitation than can evaporate - excessive moisture, in the steppes K less than one - insufficient moisture; In deserts, precipitation makes up a small proportion of evaporation—humidification is negligible.
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