Meteorology and climatology. Meteorology and climatology Rotation of the Earth around its axis
Geography and climate
Mumbai (Bombay)- a city in western India, the center of the state of Maharashtra. The name Bombay was official until 1995. Mumbai, translated from the Maharati language, means “mother.” The area of the city is 603.4 km². It is the most populous city in India.
There are three lakes in the city: Tulsi, Powai and Vihar; the city itself is located at the mouth of the Ulhas River.
Mumbai's topography is varied: mangrove swamps border it, the rugged coastline is indented by bays and numerous streams. The soil near the sea is sandy, in some places clayey and alluvial. The territory of Mumbai belongs to seismically dangerous zones.
You can get to Mumbai by plane to Chhatrapati Shivaji Airport, which is 28 km from the city. The railway network and bus service are developed.
Mumbai is located in the subequatorial zone. There are two climatic seasons: dry and wet. Dry season lasts from December to May, humidity at this time is moderate. January and February are the coldest months. Lowest recorded temperature: +10 °C.
The wet season lasts from June to November. The strongest monsoons occur from June to September. The average temperature at this time is +30 °C. The best time The best time to visit Mumbai is from November to February.
The city expands towards Solsett Island, and the official urban area (since 1950) stretches from south to north, from the fort to the town of Thane. In the northern part of Bombay there are the Trombay nuclear research center, the Institute of Technology (1961-1966, built with the help of the USSR), oil refineries, chemical plants, machine-building plants, and thermal power plants.
The city has announced the construction of the second tallest building in the world, India Tower. This building is due to be completed by 2016.
mass media
In Mumbai, newspapers are published in English (Times of India, Midday, Aftonun, Asia Age, Economic Times, Indian Express), Bengali, Tamil, Marathi, Hindi. There are television channels in the city (more than 100 per different languages), radio stations (8 stations broadcast in the FM range and 3 in AM).
Climatic conditions
The city is located in the subequatorial zone. There are two distinct seasons: wet and dry. The rainy season lasts from June to November, with particularly intense monsoon rains occurring from June to September, causing high humidity in the city. The average temperature is about 30 °C, temperature fluctuations from 11 °C to 38 °C, record sharp changes were in 1962: 7.4 °C and 43 °C. The amount of annual precipitation is 2200 mm. There was especially a lot of precipitation in 1954 - 3451.6 mm. The dry season from December to May is characterized by moderate humidity. Due to the predominance of cold north wind January and February are the coldest months; the absolute minimum in the city was +10 degrees.
| Climate of Mumbai | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Index | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | But I | Dec | Year |
| Absolute maximum, °C | 40,0 | 39,1 | 41,3 | 41,0 | 41,0 | 39,0 | 34,0 | 34,0 | 36,0 | 38,9 | 38,3 | 37,8 | 41,3 |
| Precipitation rate, mm | 1 | 0,3 | 0,2 | 1 | 11 | 537 | 719 | 483 | 324 | 73 | 14 | 2 | 2165 |
| Average minimum, °C | 18,4 | 19,4 | 22,1 | 24,7 | 27,1 | 27,0 | 26,1 | 25,6 | 25,2 | 24,3 | 22,0 | 19,6 | 23,5 |
| Average temperature, °C | 23,8 | 24,7 | 27,1 | 28,8 | 30,2 | 29,3 | 27,9 | 27,5 | 27,6 | 28,4 | 27,1 | 25,0 | 27,3 |
| Water temperature, °C | 26 | 25 | 26 | 27 | 29 | 29 | 29 | 28 | 28 | 29 | 28 | 26 | 28 |
| Absolute minimum, °C | 8,9 | 8,5 | 12,7 | 19,0 | 22,5 | 20,0 | 21,2 | 22,0 | 20,0 | 17,2 | 14,4 | 11,3 | 8,5 |
| Average maximum, °C | 31,1 | 31,4 | 32,8 | 33,2 | 33,6 | 32,3 | 30,3 | 30,0 | 30,8 | 33,4 | 33,6 | 32,3 | 32,1 |
The content of the article
METEOROLOGY AND CLIMATOLOGY. Meteorology is the science of the Earth's atmosphere. Climatology is a branch of meteorology that studies the dynamics of changes in the average characteristics of the atmosphere over any period - a season, several years, several decades, or over a longer period. Other branches of meteorology are dynamic meteorology (the study of the physical mechanisms of atmospheric processes), physical meteorology (the development of radar and space-based methods for studying atmospheric phenomena) and synoptic meteorology (the science of patterns of weather change). These sections overlap and complement each other.
CLIMATE.
A significant portion of meteorologists are involved in weather forecasting. They work for government and military organizations and private companies that provide forecasts for aviation, agriculture, construction and the navy, and also broadcast them on radio and television. Others monitor pollution levels, provide consultations, teach, or do research. Electronic equipment is becoming increasingly important in meteorological observations, weather forecasting and scientific research.
PRINCIPLES OF STUDYING WEATHER
Temperature, atmospheric pressure, air density and humidity, wind speed and direction are the main indicators of the state of the atmosphere, and additional parameters include data on the content of gases such as ozone, carbon dioxide, etc. Characteristics the physical body is the temperature, which increases with increasing internal energy of the environment (for example, air, clouds, etc.) if the energy balance is positive. The main components of the energy balance are heating through the absorption of ultraviolet, visible and infrared radiation; cooling due to infrared radiation; heat exchange with the earth's surface; the acquisition or loss of energy during the condensation or evaporation of water, as well as during the compression or expansion of air. Temperature can be measured in degrees Fahrenheit (F), Celsius (C), or Kelvin (K). The lowest possible temperature, 0° Kelvin, is called “absolute zero.” Different temperature scales are interconnected by the following relations:
F = 9/5 C + 32; C = 5/9 (F – 32) and K = C + 273.16,
where F, C and K respectively denote the temperature in degrees Fahrenheit, Celsius and Kelvin. The Fahrenheit and Celsius scales coincide at the point –40°, i.e. –40° F = –40° C, which can be checked using the above formulas. In all other cases, temperatures in degrees Fahrenheit and Celsius will differ. In scientific research, the Celsius and Kelvin scales are commonly used.
Atmospheric pressure at each point is determined by the mass of the overlying air column. It changes if the height of the air column above a given point changes. The air pressure at sea level is approx. 10.3 t/m2. This means that the weight of a column of air with a horizontal base of 1 square meter at sea level is 10.3 tons.
Air density is the ratio of the mass of air to the volume it occupies. The density of air increases when it is compressed and decreases when it expands.
Temperature, pressure and air density are related to each other by the equation of state. Air is pretty much like " ideal gas", for which, according to the equation of state, temperature (expressed in Kelvin scale) multiplied by density and divided by pressure is a constant.
According to Newton's second law of motion (law of motion), changes in wind speed and direction are caused by forces acting in the atmosphere. These are the force of gravity, which holds the layer of air near the earth's surface, the pressure gradient (the force directed from an area of high pressure to an area of low) and the Coriolis force. Coriolis force influences hurricanes and other large-scale weather conditions. The smaller their scale, the less significant this power is for them. For example, the direction of rotation of a tornado (tornado) does not depend on it.
WATER VAPOR AND CLOUDS
Water vapor is water in a gaseous state. If the air is unable to hold more water vapor, it becomes saturated, and then water from the exposed surface stops evaporating. The content of water vapor in saturated air is closely dependent on temperature and with its increase by 10 ° C it can increase no more than twice.
Relative humidity is the ratio of the amount of water vapor actually contained in the air to the amount of water vapor corresponding to the saturation state. The relative humidity of the air near the earth's surface is often high in the morning when it is cool. As temperature rises, relative humidity usually decreases, even if the amount of water vapor in the air changes little. Suppose that in the morning at a temperature of 10 ° C the relative humidity was close to 100%. If the temperature drops during the day, water will condense and dew will form. If the temperature rises, for example to 20 ° C, the dew will evaporate, but the relative humidity will be only approx. 50%.
Clouds arise when water vapor in the atmosphere condenses, forming either water droplets or ice crystals. Clouds form when water vapor rises and cools past its saturation point. As air rises, it enters layers of increasingly lower pressure. Unsaturated air cools by about 10° C with every kilometer of rise. If air with a relative humidity of approx. 50% will rise more than 1 km, cloud formation will begin. Condensation first occurs at the base of the cloud, which grows upward until the air no longer rises and therefore cools. In summer, this process can be easily seen in the example of lush cumulus clouds with a flat base and a top that rises and falls with the movement of air. Clouds also form in frontal zones when warm air slides upward, moving over cold air, and at the same time cools to a state of saturation. Cloudiness also occurs in areas of low pressure with rising air currents.
Fog is a cloud located near the earth's surface. It often descends to the ground on quiet, clear nights, when the air is moist and the earth's surface cools, radiating heat into space. Fog can also form when warm, moist air passes over a cold surface of land or water. If cold air is above the surface of warm water, a fog of evaporation appears right before your eyes. It often forms in the morning late autumn over the lakes, and then it seems that the water is boiling.
Condensation is a complex process in which microscopic particles of airborne impurities (soot, dust, sea salt) serve as condensation nuclei around which water droplets form. The same nuclei are necessary for freezing water in the atmosphere, since very clean air in their absence, water droplets do not freeze to temperatures of approx. –40° C. The ice formation core is a small particle, similar in structure to an ice crystal, around which a piece of ice is formed. It is quite natural that airborne ice particles are the best nuclei for ice formation. The role of such nuclei is also played by the smallest clay particles; they acquire special significance at temperatures below –10°–15° C. Thus, a strange situation is created: water droplets in the atmosphere almost never freeze when the temperature passes through 0° C. For them Freezing requires significantly lower temperatures, especially if there are few ice nuclei in the air. One way to stimulate precipitation is to spray silver iodide particles - artificial condensation nuclei - into clouds. They help tiny droplets of water freeze into ice crystals that are heavy enough to fall as snow.
The formation of rain or snow is a rather complex process. If the ice crystals inside the cloud are too heavy to remain suspended in the updraft, they fall as snow. If the lower layers of the atmosphere are warm enough, snowflakes melt and fall to the ground as raindrops. Even in summer in temperate latitudes, rain usually originates in the form of ice floes. And even in the tropics, rain falling from cumulonimbus clouds begins with ice particles. Convincing evidence that ice exists in the clouds even in summer is hail.
Rain usually comes from “warm” clouds, i.e. from clouds with temperatures above freezing. Here are small droplets carrying charges opposite sign, are attracted and merge into larger drops. They can increase so much that they become too heavy, are no longer supported in the cloud by updrafts and rain down.
The basis of modern international classification clouds was founded in 1803 by the English amateur meteorologist Luke Howard. It uses Latin terms to describe the appearance of clouds: alto - high, cirrus - cirrus, cumulus - cumulus, nimbus - rain and stratus - stratus. Various combinations of these terms are used to name the ten main forms of clouds: cirrus - cirrus; cirrocumulus – cirrocumulus; cirrostratus – cirrostratus; altocumulus – altocumulus; altostratus – highly layered; nimbostratus – nimbostratus; stratocumulus – stratocumulus; stratus – layered; cumulus - cumulus and cumulonimbus - cumulonimbus. Altocumulus and altostratus clouds are located higher than cumulus and stratus clouds.
The lower tier clouds (stratus, stratocumulus and nimbostratus) consist almost exclusively of water, their bases are located up to an altitude of approximately 2000 m. Clouds spreading along the earth's surface are called fog.
The bases of mid-level clouds (altocumulus and altostratus) are found at altitudes from 2000 to 7000 m. These clouds have temperatures from 0 ° C to -25 ° C and are often a mixture of water droplets and ice crystals.
The upper level clouds (cirrus, cirrocumulus and cirrostratus) usually have fuzzy outlines because they consist of ice crystals. Their bases are located at altitudes of more than 7000 m, and the temperature is below –25° C.
Cumulus and cumulonimbus clouds are clouds of vertical development and can extend beyond one layer. This is especially true for cumulonimbus clouds, the bases of which are only a few hundred meters from the earth's surface, and the tops can reach heights of 15–18 km. In the lower part they consist of water droplets, and in the upper part they consist of ice crystals.
CLIMATE AND CLIMATE FORMING FACTORS
The ancient Greek astronomer Hipparchus (2nd century BC) conditionally divided the Earth's surface with parallels into latitudinal zones, differing in the height of the midday position of the Sun on the longest day of the year. These zones were called climates (from the Greek klima - slope, originally meaning "inclination of the sun's rays"). Thus, five climatic zones were identified: one hot, two temperate and two cold, which formed the basis of geographical zonation globe.
For more than 2000 years, the term “climate” was used in this sense. But after 1450, when Portuguese sailors crossed the equator and returned to their homeland, new facts emerged that required a revision of classical views. Among the information about the world acquired during the discoverers’ travels were the climatic characteristics of the selected zones, which made it possible to expand the term “climate” itself. Climatic zones were no longer just mathematically calculated areas of the earth's surface based on astronomical data (i.e., hot and dry where the Sun rises high, and cold and damp where it is low, and therefore does not warm well). It was discovered that climatic zones do not simply correspond to latitudinal zones, as previously thought, but have very irregular outlines.
Solar radiation, general atmospheric circulation, geographic distribution of continents and oceans, and major landforms are the main factors influencing land climate. Solar radiation is the most important factor climate formation and will therefore be considered in more detail.
RADIATION
In meteorology, the term "radiation" refers to electromagnetic radiation, which includes visible light, ultraviolet and infrared radiation, but does not include radioactive radiation. Each object, depending on its temperature, emits different rays: less heated bodies are mainly infrared, hot bodies are red, hotter bodies are white (i.e., these colors will prevail when perceived by our vision). Even hotter objects emit blue rays. The hotter an object is, the more light energy it emits.
In 1900, German physicist Max Planck developed a theory explaining the mechanism of radiation from heated bodies. This theory, for which in 1918 he was awarded Nobel Prize, became one of the cornerstones of physics and laid the foundation for quantum mechanics. But not all light radiation is emitted by heated bodies. There are other processes that cause luminescence, such as fluorescence.
Although the temperature inside the Sun is millions of degrees, the color of sunlight is determined by the temperature of its surface (about 6000 ° C). An electric incandescent lamp emits light rays, the spectrum of which is significantly different from the spectrum of sunlight, since the temperature of the filament in the light bulb ranges from 2500 ° C to 3300 ° C.
The predominant type of electromagnetic radiation from clouds, trees or people is infrared radiation, invisible to the human eye. It is the main way of vertical exchange of energy between the earth's surface, clouds and atmosphere.
Meteorological satellites are equipped with special instruments that take pictures in infrared rays emitted into outer space by clouds and the earth's surface. Clouds that are colder than the Earth's surface emit less radiation and therefore appear darker in infrared light than the Earth. The great advantage of infrared photography is that it can be carried out around the clock (after all, clouds and the Earth emit infrared rays constantly).
Insolation angle.
The amount of insolation (incoming solar radiation) changes over time and from place to place in accordance with the change in the angle at which the sun's rays strike the Earth's surface: the higher the Sun is overhead, the larger it is. Changes in this angle are determined mainly by the Earth's revolution around the Sun and its rotation around its axis.
The Earth's revolution around the Sun
wouldn't have of great importance, if the earth's axis were perpendicular to the plane of the earth's orbit. In this case, at any point on the globe at the same time of day, the Sun would rise to the same height above the horizon and only small seasonal fluctuations in insolation would appear, caused by changes in the distance from the Earth to the Sun. But in fact, the earth's axis deviates from the perpendicular to the orbital plane by 23° 30º, and because of this, the angle of incidence of the sun's rays changes depending on the position of the Earth in orbit.
For practical purposes, it is convenient to assume that the Sun moves north during the annual cycle from December 21 to June 21 and south from June 21 to December 21. At local noon on December 21, along the entire Southern Tropic (23° 30° S), the Sun “stands” directly overhead. At this time in Southern Hemisphere the sun's rays fall at the greatest angle. This moment in the Northern Hemisphere is called the “winter solstice.” During an apparent northward shift, the Sun crosses the celestial equator on March 21 (spring equinox). On this day, both hemispheres receive the same amount of solar radiation. The most northern position, 23° 30° N. (Northern Tropic), the Sun reaches June 21st. This moment, when the sun's rays fall at the greatest angle in the Northern Hemisphere, is called the summer solstice. On September 23, at the autumn equinox, the Sun crosses the celestial equator again.
The inclination of the earth's axis to the plane of the earth's orbit causes changes not only in the angle of incidence of the sun's rays on earth's surface, but also the daily duration of sunshine. At the equinox, the duration of daylight on the entire Earth (except for the poles) is 12 hours; in the period from March 21 to September 23 in the Northern Hemisphere it exceeds 12 hours, and from September 23 to March 21 it is less than 12 hours. North 66° 30° s .sh. (Arctic Circle) from December 21, the polar night lasts around the clock, and from June 21, daylight continues for 24 hours. At the North Pole, polar night occurs from September 23 to March 21, and polar day from March 21 to September 23.
Thus, the cause of two clearly defined cycles of atmospheric phenomena - annual, lasting 365 1/4 days, and daily, 24-hour - is the rotation of the Earth around the Sun and the tilt of the Earth's axis.
The amount of solar radiation arriving per day at the outer boundary of the atmosphere in the Northern Hemisphere is expressed in watts per square meter horizontal surface (i.e. parallel to the earth's surface, not always perpendicular to the sun's rays) and depends on the solar constant, the angle of inclination of the sun's rays and the length of the day (Table 1).
| Table 1. ARRIVAL OF SOLAR RADIATION TO THE UPPER BOUNDARY OF THE ATMOSPHERE (W/m2 per day) | ||||||||||
| Latitude, °N | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
| 21st of June | 375 | 414 | 443 | 461 | 470 | 467 | 463 | 479 | 501 | 510 |
| 21 December | 399 | 346 | 286 | 218 | 151 | 83 | 23 | 0 | 0 | 0 |
| Average annual value | 403 | 397 | 380 | 352 | 317 | 273 | 222 | 192 | 175 | 167 |
It follows from the table that the contrast between summer and in winter amazing. On June 21 in the Northern Hemisphere, the insolation value is approximately the same. On December 21, there are significant differences between low and high latitudes, and this is the main reason that the climatic differentiation of these latitudes in winter is much greater than in summer. Atmospheric macrocirculation, which depends mainly on differences in atmospheric heating, is better developed in winter.
The annual amplitude of the solar radiation flux at the equator is quite small, but increases sharply towards the north. Therefore, other than that equal conditions The annual temperature range is determined mainly by the latitude of the area.
The rotation of the Earth around its axis.
The intensity of insolation anywhere in the world on any day of the year also depends on the time of day. This is explained, of course, by the fact that in 24 hours the Earth rotates around its axis.
Albedo
– the fraction of solar radiation reflected by an object (usually expressed as a percentage or fraction of a unit). The albedo of freshly fallen snow can reach 0.81; the albedo of clouds, depending on the type and vertical thickness, ranges from 0.17 to 0.81. Albedo of dark dry sand is approx. 0.18, green forest - from 0.03 to 0.10. The albedo of large water areas depends on the height of the Sun above the horizon: the higher it is, the lower the albedo.
The Earth's albedo, along with the atmosphere, changes depending on cloud cover and the area of snow cover. Of all the solar radiation reaching our planet, approx. 0.34 is reflected into outer space and lost to the Earth-atmosphere system.
Absorption by the atmosphere.
About 19% of solar radiation reaching the Earth is absorbed by the atmosphere (according to average estimates for all latitudes and all seasons). IN upper layers In the atmosphere, ultraviolet radiation is absorbed mainly by oxygen and ozone, and in the lower layers, red and infrared radiation (wavelength more than 630 nm) is absorbed mainly by water vapor and to a lesser extent by carbon dioxide.
Absorption by the Earth's surface.
About 34% of direct solar radiation arriving at the upper boundary of the atmosphere is reflected into outer space, and 47% passes through the atmosphere and is absorbed by the earth's surface.
The change in the amount of energy absorbed by the earth's surface depending on latitude is shown in table. 2 and is expressed in terms of the average annual amount of energy (in watts) absorbed per day by a horizontal surface with an area of 1 sq.m. The difference between the average annual arrival of solar radiation to the upper boundary of the atmosphere per day and the radiation received on the earth's surface in the absence of clouds at different latitudes shows its losses under the influence of various atmospheric factors (except cloudiness). These losses account for approximately one-third of incoming solar radiation everywhere.
| Table 2. AVERAGE ANNUAL RECEIPT OF SOLAR RADIATION ON A HORIZONTAL SURFACE IN THE NORTHERN HEMISPHERE (W/m2 per day) |
||||||||||
| Latitude, °N | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
| Arrival of radiation at the outer boundary of the atmosphere | 403 | 397 | 380 | 352 | 317 | 273 | 222 | 192 | 175 | 167 |
| The arrival of radiation on the earth's surface under clear skies | 270 | 267 | 260 | 246 | 221 | 191 | 154 | 131 | 116 | 106 |
| The arrival of radiation on the earth's surface under average cloudiness | 194 | 203 | 214 | 208 | 170 | 131 | 97 | 76 | 70 | 71 |
| Radiation absorbed by the earth's surface | 181 | 187 | 193 | 185 | 153 | 119 | 88 | 64 | 45 | 31 |
The difference between the amount of solar radiation arriving at the upper boundary of the atmosphere and the amount of its arrival on the earth’s surface during average cloudiness, due to radiation losses in the atmosphere, significantly depends on geographical latitude: 52% at the equator, 41% at 30° N. and 57% at 60° N. This is a direct consequence of the quantitative change in cloud cover with latitude. Due to the characteristics of atmospheric circulation in the Northern Hemisphere, the amount of clouds is minimal at a latitude of approx. 30° The influence of cloudiness is so great that the maximum energy reaches the earth's surface not at the equator, but in subtropical latitudes.
The difference between the amount of radiation arriving at the earth's surface and the amount of absorbed radiation is formed only due to albedo, which is especially large at high latitudes and is due to the high reflectivity of snow and ice cover.
Of all the solar energy used by the Earth-atmosphere system, less than one third is directly absorbed by the atmosphere, and the bulk of the energy it receives is reflected from the earth's surface. Most solar energy comes to areas located at low latitudes.
Earth's radiation.
Despite the continuous flow of solar energy into the atmosphere and onto the earth's surface, the average temperature of the Earth and atmosphere is fairly constant. The reason for this is that almost the same amount of energy is emitted by the Earth and its atmosphere into outer space, mainly in the form of infrared radiation, since the Earth and its atmosphere is much cooler than the Sun, and only a small fraction is in the visible part of the spectrum. The emitted infrared radiation is recorded by meteorological satellites equipped with special equipment. Many satellite weather maps shown on television are infrared images and show the heat emitted by the earth's surface and clouds.
Heat balance.
As a result of complex energy exchange between the earth's surface, atmosphere and interplanetary space, each of these components receives on average as much energy from the other two as it loses itself. Consequently, neither the earth's surface nor the atmosphere experiences any increase or decrease in energy.
GENERAL CIRCULATION OF THE ATMOSPHERE
Due to the peculiarities of the relative position of the Sun and the Earth, the equatorial and polar regions, equal in area, receive completely different quantities solar energy. Equatorial regions receive more energy than polar regions, and their water areas and vegetation absorb more of the incoming energy. In the polar regions there is a high albedo of snow and ice. Although the warmer equatorial temperature regions emit more heat than the polar regions, the thermal balance is such that the polar regions lose more energy than they gain, and the equatorial regions gain more energy than they lose. Since there is neither warming of the equatorial regions nor cooling of the polar regions, it is obvious that in order to maintain the Earth's thermal balance, excess heat must move from the tropics to the poles. This movement is the main driving force of atmospheric circulation. The air in the tropics warms up, rising and expanding, and flows towards the poles at an altitude of approx. 19 km. Near the poles it cools, becomes denser and sinks to the earth's surface, from where it spreads towards the equator.
Main features of circulation.
Air rising near the equator and heading towards the poles is deflected by the Coriolis force. Let's consider this process using the Northern Hemisphere as an example (the same thing happens in the Southern Hemisphere). When moving towards the pole, the air is deflected to the east, and it turns out that it comes from the west. This is how westerly winds are formed. Some of this air cools as it expands and radiates heat, sinks and flows back toward the equator, deflecting to the right and forming the northeast trade wind. Part of the air that moves poleward forms a westerly transport in temperate latitudes. The air descending in the polar region moves towards the equator and, deviating to the west, forms an eastern transport in the polar regions. This is just a basic diagram of atmospheric circulation, the constant component of which is the trade winds.
Wind belts.
Under the influence of the Earth's rotation, several main wind belts are formed in the lower layers of the atmosphere ( see pic.).
Equatorial calm zone,
located near the equator, is characterized by weak winds associated with the convergence zone (i.e., convergence of air flows) of stable southeast trade winds of the Southern Hemisphere and northeast trade winds of the Northern Hemisphere, which created no favorable conditions for the movement of sailing ships. With converging air currents in this area, the air must either rise or fall. Since the surface of the land or ocean prevents its descent, intense upward movements of air inevitably occur in the lower layers of the atmosphere, which is also facilitated by the strong heating of the air from below. The rising air cools and its moisture capacity decreases. Therefore, this zone is characterized by dense clouds and frequent precipitation.
Horse latitudes
– areas with very weak winds, located between 30 and 35° N. latitude. and S. The name probably dates back to the age of sail, when ships crossing the Atlantic were often becalmed or delayed en route by weak, variable winds. Meanwhile, water supplies were depleted, and the crews of ships transporting horses to the West Indies were forced to throw them overboard.
Horse latitudes are located between the areas of trade winds and the prevailing westerly transport (located closer to the poles) and are zones of divergence (i.e., divergence) of winds in the surface layer of air. In general, downward air movements predominate within their boundaries. Lowering air masses is accompanied by warming of the air and an increase in its moisture capacity, so these zones are characterized by slight clouds and insignificant amounts of precipitation.
Subpolar cyclone zone
located between 50 and 55° N. latitude. It is characterized by stormy winds of variable directions associated with the passage of cyclones. This is a convergence zone of the westerly winds prevailing in temperate latitudes and the eastern winds characteristic of the polar regions. As in the equatorial convergence zone, ascending air movements, dense clouds and precipitation over large areas predominate here.
INFLUENCE OF LAND AND SEA DISTRIBUTION
Solar radiation.
Under the influence of changes in solar radiation, land heats and cools much more and faster than the ocean. This is explained by the different properties of soil and water. Water is more transparent to radiation than soil, so the energy is distributed in a larger volume of water and leads to less heating per unit volume. Turbulent mixing distributes heat in the upper layer of the ocean to a depth of approximately 100 m. Water has a greater heat capacity than soil, therefore, with the same amount of heat absorbed by equal masses of water and soil, the water temperature rises less. Almost half of the heat that reaches the water surface is spent on evaporation rather than heating, and on land the soil dries out. Therefore, the ocean surface temperature changes significantly less per day and per year than the land surface temperature. Since the atmosphere heats and cools primarily due to thermal radiation from the underlying surface, these differences are manifested in air temperatures over land and oceans.
Air temperature.
Depending on whether the climate is formed mainly under the influence of the ocean or land, it is called marine or continental. Marine climates are characterized by significantly lower average annual temperature amplitudes (more than warm winter and cooler summers) compared to continental ones.
Islands in open ocean(for example, Hawaiian, Bermuda, Ascension) have a well-defined maritime climate. On the outskirts of continents, climates of one type or another can form depending on the nature of the prevailing winds. For example, in the zone of predominance of western transport, the marine climate dominates on the western coasts, and the continental climate dominates on the eastern coasts. This is shown in table. 3, which compares temperatures at three US weather stations located at approximately the same latitude in the zone of predominant westerly transport.
On the west coast, in San Francisco, the climate is maritime, with warm winter, cool summers and low temperature ranges. In Chicago, in the interior of the continent, the climate is sharply continental, with cold winters, warm summers and a significant temperature range. The climate on the east coast, in Boston, is not very different from the climate in Chicago, although Atlantic Ocean has a softening effect on it thanks to the winds that sometimes blow from the sea (sea breezes).
Monsoons.
The term "monsoon", derived from the Arabic "mawsim" (season), means "seasonal wind". The name was first applied to the winds in the Arabian Sea, blowing for six months from the northeast and for the next six months from the southwest. Monsoons reach greatest strength in South and East Asia, as well as on tropical coasts, when the influence of the general atmospheric circulation is weak and does not suppress them. The Gulf Coast experiences weaker monsoons.
Monsoons are the large-scale seasonal equivalent of a breeze, a wind with a diurnal cycle that blows alternately from land to sea and from sea to land in many coastal areas. During the summer monsoon, the land is warmer than the ocean, and warm air, rising above it, spreads outward in the upper layers of the atmosphere. As a result, low pressure is created near the surface, which promotes the influx of moist air from the ocean. During the winter monsoon, the land is colder than the ocean, so cold air sinks over the land and flows toward the ocean. In areas of monsoon climate, breezes can also develop, but they cover only the surface layer of the atmosphere and appear only in the coastal strip.
The monsoon climate is characterized by a pronounced seasonal change in the areas from which air masses come - continental in winter and sea in summer; the predominance of winds blowing from the sea in summer and from land in winter; summer maximum precipitation, cloudiness and humidity.
The area around Bombay on the west coast of India (approx. 20° N) is a classic example of an area with a monsoon climate. In February, the winds blow from the north-east about 90% of the time, and in July - approx. 92% of the time - southwestern directions. The average precipitation in February is 2.5 mm, and in July - 693 mm. The average number of days with precipitation in February is 0.1, and in July - 21. The average cloudiness in February is 13%, in July - 88%. The average relative humidity is 71% in February and 87% in July.
INFLUENCE OF RELIEF
The largest orographic obstacles (mountains) have a significant impact on the climate of the land.
Thermal mode.
In the lower layers of the atmosphere, the temperature decreases by about 0.65 ° C with a rise for every 100 m; in areas with long winters the temperature occurs a little slower, especially in the lower 300-meter layer, and in areas with long summers it occurs somewhat faster. The closest relationship between average temperatures and altitude is observed in the mountains. Therefore, average temperature isotherms for areas such as Colorado, for example, generally follow the contour patterns of topographic maps.
Cloudiness and precipitation.
When the air encounters a mountain range on its way, it is forced to rise. At the same time, the air cools, which leads to a decrease in its moisture capacity and condensation of water vapor (the formation of clouds and precipitation) on the windward side of the mountains. When moisture condenses, the air heats up and, upon reaching the leeward side of the mountains, becomes dry and warm. This is how the Chinook wind arises in the Rocky Mountains.
| Table 4. EXTREME TEMPERATURES OF THE CONTINENTS AND ISLANDS OF OCEANIA | ||||
| Region | Maximum temperature, °C |
Place | Minimum temperature °C |
Place |
| North America | 57 | Death Valley, California, USA | –66 | Northis, Greenland 1 |
| South America | 49 | Rivadavia, Argentina | –33 | Sarmiento, Argentina |
| Europe | 50 | Seville, Spain | –55 | Ust-Shchugor, Russia |
| Asia | 54 | Tirat Zevi, Israel | –68 | Oymyakon, Russia |
| Africa | 58 | Al Azizia, Libya | –24 | Ifrane, Morocco |
| Australia | 53 | Cloncurry, Australia | –22 | Charlotte Pass, Australia |
| Antarctica | 14 | Esperanza, Antarctic Peninsula | –89 | Vostok Station, Antarctica |
| Oceania | 42 | Tuguegarao, Philippines | –10 | Haleakala, Hawaiian Islands, USA |
| 1 In mainland North America, the minimum temperature recorded was –63° C (Snag, Yukon, Canada) |
||||
| Table 5. EXTREME VALUES OF AVERAGE ANNUAL PRECIPITATION ON THE CONTINUES AND ISLANDS OF OCEANIA | ||||
| Region | Maximum, mm | Place | Minimum, mm | Place |
| North America | 6657 | Henderson Lake, British Columbia, Canada | 30 | Batages, Mexico |
| South America | 8989 | Quibdo, Colombia | Arica, Chile | |
| Europe | 4643 | Crkvice, Yugoslavia | 163 | Astrakhan, Russia |
| Asia | 11430 | Cherrapunji, India | 46 | Aden, Yemen |
| Africa | 10277 | Debunja, Cameroon | Wadi Halfa, Sudan | |
| Australia | 4554 | Tully, Australia | 104 | Malka, Australia |
| Oceania | 11684 | Waialeale, Hawaii, USA | 226 | Puako, Hawaii, USA |
SYNOPTIC OBJECTS
Air masses.
An air mass is a huge volume of air, the properties of which (mainly temperature and humidity) were formed under the influence of the underlying surface in a certain region and gradually change as it moves from the source of formation in the horizontal direction.
Air masses are distinguished primarily by the thermal characteristics of the areas of formation, for example, tropical and polar. The movement from one area to another of air masses that retain many of the original characteristics can be traced using synoptic maps. For example, cold, dry air from the Canadian Arctic moves over the United States and slowly warms up but remains dry. Similarly, warm, moist tropical air masses that form over the Gulf of Mexico remain moist but can warm or cool depending on the properties of the underlying surface. Of course, such a transformation of air masses intensifies as the conditions encountered along their path change.
When air masses with different properties from distant sources of formation come into contact, they retain their characteristics. For most of their existence, they are separated by more or less clearly defined transition zones, where temperature, humidity and wind speed change sharply. Then the air masses mix, disperse and, ultimately, cease to exist as separate bodies. Transition zones between moving air masses are called "fronts".
Fronts
pass along the troughs of the pressure field, i.e. along low pressure contours. When a front crosses, the wind direction usually changes dramatically. In polar air masses the wind can be northwest, while in tropical air masses it can be southerly. The most bad weather established along fronts and in the colder region near the front where warm air slides up a wedge of dense cold air and cools. As a result, clouds form and precipitation falls. Sometimes extratropical cyclones form along the front. Fronts also form when cold northern and warm southern air masses located in the central part of the cyclone (an area of low atmospheric pressure) come into contact.
There are four types of fronts. A stationary front forms at a more or less stable boundary between polar and tropical air masses. If cold air retreats in the surface layer and warm air advances, a warm front forms. Typically, before an approaching warm front, the sky is overcast, there is rain or snow, and the temperature gradually rises. As the front passes, the rain stops and temperatures remain high. When a cold front passes, cold air moves in and warm air retreats. Rainy, windy weather occurs in a narrow band along the cold front. On the contrary, a warm front is preceded by a wide area of clouds and rain. An occluded front combines features of both warm and cold fronts and is usually associated with an old cyclone.
Cyclones and anticyclones.
Cyclones are large-scale atmospheric disturbances in an area of low pressure. In the Northern Hemisphere, winds blow from an area of high pressure to an area of low pressure counterclockwise, and in the Southern Hemisphere - clockwise. In temperate latitude cyclones, called extratropical, it is usually expressed cold front, and a warm one, if it exists, is not always clearly visible. Extratropical cyclones often form downwind of mountain ranges, such as over the eastern slopes of the Rocky Mountains and along the eastern coasts of North America and Asia. In temperate latitudes, most precipitation is associated with cyclones.
An anticyclone is an area of high air pressure. It is usually associated with good weather with clear or partly cloudy skies. In the Northern Hemisphere, winds blowing from the center of the anticyclone are deflected clockwise, and in the Southern Hemisphere - counterclockwise. Anticyclones are usually larger in size than cyclones and move more slowly.
Since air spreads from the center to the periphery in an anticyclone, higher layers of air descend, compensating for its outflow. In a cyclone, on the contrary, the air displaced by converging winds rises. Since it is the ascending air movements that lead to the formation of clouds, cloudiness and precipitation are mostly confined to cyclones, while clear or partly cloudy weather predominates in anticyclones.
Tropical cyclones (hurricanes, typhoons)
Tropical cyclones (hurricanes, typhoons) are the general name for cyclones that form over the oceans in the tropics (excluding the cold waters of the South Atlantic and southeastern Pacific Ocean) and do not contain contrasting air masses. Tropical cyclones occur in different parts of the world, usually striking the eastern and equatorial regions of continents. They are found in the southern and southwestern North Atlantic (including the Caribbean Sea and Gulf of Mexico), the northern Pacific Ocean (west of the Mexican coast, the Philippine Islands and the China Sea), the Bay of Bengal and the Arabian Sea , in the southern part Indian Ocean off the coast of Madagascar, off the northwestern coast of Australia and in the South Pacific Ocean - from the coast of Australia to 140° W.
By international agreement, tropical cyclones are classified depending on the strength of the wind. There are tropical depressions with wind speeds of up to 63 km/h, tropical storms (wind speeds from 64 to 119 km/h) and tropical hurricanes or typhoons (wind speeds of more than 120 km/h).
In some areas of the globe, tropical cyclones have local names: in the North Atlantic and Gulf of Mexico - hurricanes (on the island of Haiti - secretly); in the Pacific Ocean off the western coast of Mexico - cordonazo, in the western and most southern regions - typhoons, in the Philippines - baguyo, or baruyo; in Australia - willy-willy.
A tropical cyclone is a huge atmospheric vortex with a diameter of 100 to 1600 km, accompanied by strong destructive winds, heavy rainfall and high surges (a rise in sea level under the influence of wind). Incipient tropical cyclones usually move to the west, slightly deviating to the north, with increasing speed and increasing in size. After moving towards the pole, a tropical cyclone can “turn around”, join the westerly transport of temperate latitudes and begin to move east (however, such a change in the direction of movement does not always occur).
The counterclockwise rotating cyclonic winds of the Northern Hemisphere have their maximum strength in a belt with a diameter of 30–45 km or more, starting from the “eye of the storm.” Wind speeds near the earth's surface can reach 240 km/h. At the center of a tropical cyclone there is usually a cloud-free area with a diameter of 8 to 30 km, which is called the “eye of the storm”, since the sky here is often clear (or partly cloudy) and the wind is usually very light. The zone of destructive winds along the typhoon's path is 40–800 km wide. Developing and moving, cyclones cover distances of several thousand kilometers, for example, from the source of formation in the Caribbean Sea or in the tropical Atlantic to inland areas or the North Atlantic.
Although hurricane-force winds at the center of a cyclone reach enormous speeds, the hurricane itself can move very slowly and even stop for a while, which is especially true for tropical cyclones, which usually move at a speed of no more than 24 km/h. As the cyclone moves away from the tropics, its speed usually increases and in some cases reaches 80 km/h or more.
Hurricane-force winds can cause a lot of damage. Although they are weaker than in a tornado, they are nevertheless capable of felling trees, overturning houses, breaking power lines and even derailing trains. But the greatest loss of life is caused by floods associated with hurricanes. As the storm progresses, huge waves are often formed, and sea levels can rise by more than 2 m in a few minutes. Small vessels are washed ashore. Giant waves destroy houses, roads, bridges and other buildings located on the shore and can wash away even long-existing sand islands. Most hurricanes are accompanied by torrential rains, which flood fields and spoil crops, wash out roads and demolish bridges, and flood low-lying settlements.
Improved forecasts, accompanied by rapid storm warnings, have led to a significant reduction in the number of casualties. When a tropical cyclone forms, the frequency of forecast broadcasts increases. The most important source of information is reports from aircraft specially equipped to observe cyclones. Such aircraft patrol hundreds of kilometers from the coast, often penetrating the center of a cyclone to obtain accurate information about its position and movement.
The areas of the coast most susceptible to hurricanes are equipped with radar systems to detect them. As a result, the storm can be detected and tracked at a distance of up to 400 km from the radar station.
Tornado (tornado)
A tornado is a rotating funnel-shaped cloud that extends toward the ground from the base of the thundercloud. Its color changes from gray to black. In approximately 80% of tornadoes in the United States, maximum wind speeds reach 65–120 km/h, and only 1% reach 320 km/h or higher. An approaching tornado usually makes a noise similar to a moving freight train. Despite their relatively small size, tornadoes are among the most dangerous storm phenomena.
From 1961 to 1999, tornadoes killed an average of 82 people per year in the United States. However, the probability that a tornado will pass through this location is extremely low, since the average length of its path is quite short (about 25 km) and the coverage area is small (less than 400 m wide).
A tornado originates at altitudes up to 1000 m above the surface. Some of them never reach the ground, others may touch it and rise again. Tornadoes are usually associated with thunderclouds that drop hail onto the ground, and can occur in groups of two or more. In this case, a more powerful tornado is formed first, and then one or more weaker vortices.
For a tornado to form in air masses, a sharp contrast in temperature, humidity, density and air flow parameters is necessary. Cool, dry air from the west or northwest moves toward the warm, moist air at the surface. This is accompanied by strong winds in a narrow transition zone, where complex energy transformations occur that can cause the formation of a vortex. Probably, a tornado is formed only with a strictly defined combination of several rather usual factors, varying over a wide range.
Tornadoes occur all over the globe, but the most favorable conditions for their formation are found in the central regions of the United States. The frequency of tornadoes generally increases in February in all eastern states adjacent to the Gulf of Mexico and peaks in March. In Iowa and Kansas, their highest frequency occurs in May–June. From July to December, the number of tornadoes declines rapidly across the country. The average number of tornadoes in the United States is approx. 800 per year, with half of them occurring in April, May and June. This indicator reaches the highest values in Texas (120 per year), and the lowest in the northeastern and western states (1 per year).
The destruction caused by tornadoes is terrible. They occur both due to winds of enormous force and due to large pressure differences over a limited area. A tornado is capable of tearing a building to pieces and scattering it through the air. Walls may collapse. A sharp decrease in pressure leads to the fact that heavy objects, even those located inside buildings, rise into the air, as if sucked in by a giant pump, and are sometimes transported over considerable distances.
It is impossible to predict exactly where a tornado will form. However, it is possible to define an area of approx. 50 thousand sq. km, within which the probability of tornadoes is quite high.
Thunderstorms
Thunderstorms, or lightning storms, are local atmospheric disturbances associated with the development of cumulonimbus clouds. Such storms are always accompanied by thunder and lightning and usually strong gusts of wind and heavy rainfall. Sometimes hail falls. Most thunderstorms end quickly, and even the longest ones rarely last more than one or two hours.
Thunderstorms arise due to atmospheric instability and are associated mainly with the mixing of layers of air, which tend to achieve a more stable density distribution. Powerful upward air currents are distinctive feature the initial stage of a thunderstorm. Strong downward air movements in areas of heavy precipitation are characteristic of its final phase. Thunderclouds often reach heights of 12–15 km in temperate latitudes and even higher in the tropics. Their vertical growth is limited by the stable state of the lower stratosphere.
A unique property of thunderstorms is their electrical activity. Lightning can occur within a developing cumulus cloud, between two clouds, or between a cloud and the ground. In reality, a lightning discharge almost always consists of several discharges passing through the same channel, and they pass so quickly that they are perceived by the naked eye as the same discharge.
It is not yet entirely clear how the separation of large charges of the opposite sign occurs in the atmosphere. Most researchers believe that this process is associated with differences in the sizes of liquid and frozen water droplets, as well as with vertical air currents. Electric charge A thundercloud induces a charge on the earth's surface beneath it and charges of the opposite sign around the base of the cloud. A huge potential difference arises between the oppositely charged areas of the cloud and the earth's surface. When it reaches a sufficient value, an electrical discharge occurs - a flash of lightning.
The thunder that accompanies a lightning discharge is caused by the instantaneous expansion of air along the path of the discharge, which occurs when it is suddenly heated by lightning. Thunder is more often heard as long peals, rather than as a single strike, since it occurs along the entire channel of the lightning discharge, and therefore the sound travels the distance from its source to the observer in several stages.
Jet air currents
– winding “rivers” of strong winds in temperate latitudes at altitudes of 9–12 km (at which long-distance flights of jet aircraft are usually confined), blowing at speeds sometimes up to 320 km/h. An airplane flying in the direction of the jet stream saves a lot of fuel and time. Therefore, forecasting the spread and strength of jet streams is essential for flight planning and air navigation in general.
Synoptic maps (Weather maps)
To characterize and study many atmospheric phenomena, as well as for weather forecasts, it is necessary to simultaneously carry out various observations at many points and record the obtained data on maps. In meteorology, the so-called synoptic method.
Surface synoptic maps.
Throughout the United States, weather observations are made every hour (less often in some countries). Cloudiness is characterized (density, height and type); barometer readings are taken, to which corrections are introduced to bring the obtained values to sea level; wind direction and speed are recorded; the amount of liquid or solid precipitation and air and soil temperatures are measured (during the observation period, maximum and minimum); air humidity is determined; visibility conditions and all other atmospheric phenomena (for example, thunderstorm, fog, haze, etc.) are carefully recorded.
Each observer then encodes and transmits the information using the International Meteorological Code. Since this procedure is standardized by the World Meteorological Organization, such data can be easily deciphered in any area of the world. Coding takes approx. 20 minutes, after which messages are transmitted to information collection centers and international exchange data. Then the observation results (in the form of numbers and symbols) are plotted on contour map, on which meteorological stations are indicated by dots. This gives the forecaster an idea of the weather conditions within a large geographic region. The overall picture becomes even more clear after connecting the points at which the same pressure is recorded with smooth solid lines - isobars and drawing boundaries between different air masses (atmospheric fronts). Areas with high or low pressure are also identified. The map will become even more expressive if you paint or shade the areas over which precipitation occurred at the time of observation.
Synoptic maps of the surface layer of the atmosphere are one of the main tools for weather forecasting. The specialist developing the forecast compares a series of synoptic maps for different periods of observation and studies the dynamics of pressure systems, noting changes in temperature and humidity within air masses as they move over different types of underlying surface.
Altitude synoptic maps.
Clouds move with air currents, usually at significant heights above the earth's surface. It is therefore important for the meteorologist to have reliable data for many levels of the atmosphere. Based on data obtained from weather balloons, aircraft and satellites, weather maps are compiled for five altitude levels. These maps are transmitted to weather centers.
WEATHER FORECAST
The weather forecast is made based on human knowledge and computer capabilities. A traditional part of creating a forecast is the analysis of maps showing the horizontal and vertical structure of the atmosphere. Based on them, a forecast specialist can assess the development and movement of synoptic objects. The use of computers in a meteorological network greatly facilitates the forecast of temperature, pressure and other meteorological elements.
To forecast the weather, in addition to a powerful computer, you need a wide network of weather observations and a reliable mathematical apparatus. Direct observations provide mathematical models with the data necessary for their calibration.
An ideal forecast should be justified in all respects. It is difficult to determine the cause of forecast errors. Meteorologists consider a forecast to be correct if its error is less than weather prediction using one of two methods that do not require special knowledge of meteorology. The first of them, called inertial, assumes that the weather pattern will not change. The second method assumes that the weather characteristics will correspond to the monthly average for a given date.
The length of time during which the forecast is justified (i.e., gives a better result than one of the two named approaches) depends not only on the quality of observations, mathematical apparatus, computer technology, but also on the scale of the forecast meteorological phenomenon. Generally speaking, the larger the weather event, the longer it can be forecast. For example, often the degree of development and path of cyclones can be predicted several days in advance, but the behavior of a particular cumulus cloud can be predicted no more than the next hour. These limitations appear to be due to the characteristics of the atmosphere and cannot yet be overcome by more careful observations or more accurate equations.
Atmospheric processes develop chaotically. This means that different approaches are needed to predict different phenomena at different spatiotemporal scales, in particular for predicting the behavior of large mid-latitude cyclones and local severe thunderstorms, as well as long-term forecasts. For example, a daily forecast of air pressure in the surface layer is almost as accurate as the measurements from the weather balloons against which it was verified. Conversely, it is difficult to give a detailed three-hour forecast of the movement of a squall line - a strip of intense precipitation ahead of a cold front and generally parallel to it, within which tornadoes can arise. Meteorologists can only tentatively identify large areas of possible occurrence of squall lines. Once captured on satellite imagery or radar, their progress can only be extrapolated by one to two hours, making it important to communicate weather reports to the public in a timely manner. Prediction of adverse short-term meteorological phenomena(squalls, hail, tornadoes, etc.) is called an urgent forecast. Computer methods are being developed to predict these hazardous phenomena weather.
On the other hand, there is the problem of long-term forecasts, i.e. more than a few days in advance, for which weather observations over the entire globe are absolutely necessary, but even this is not enough. Because the turbulent nature of the atmosphere limits the ability to predict weather over a large area to approximately two weeks, a forecast for longer periods must be based on factors that affect the atmosphere in a predictable manner and will themselves be known more than two weeks in advance. One such factor is ocean surface temperature, which changes slowly over weeks and months, influences synoptic processes and can be used to identify areas of abnormal temperatures and precipitation.
PROBLEMS OF THE CURRENT STATE OF WEATHER AND CLIMATE
Air pollution.
Global warming.
Content carbon dioxide in the Earth's atmosphere has increased by about 15% since 1850 and is projected to increase by almost the same amount by 2015, most likely due to the burning of fossil fuels: coal, oil and gas. It is assumed that as a result of this process the average annual temperature on the globe will rise by approximately 0.5 ° C, and later, in the 21st century, it will become even higher. The consequences of global warming are difficult to predict, but they are unlikely to be favorable.
Ozone,
the molecule of which consists of three oxygen atoms, is found mainly in the atmosphere. Observations carried out from the mid-1970s to the mid-1990s showed that ozone concentration over Antarctica changed significantly: it decreased in the spring (October), when the so-called ozone formed. “ozone hole”, and then increased again to normal levels in the summer (in January). Over the period under review, there is a clear downward trend in the spring minimum ozone content in this region. Global satellite observations indicate a slightly smaller but noticeable decrease in ozone concentrations occurring everywhere, with the exception of the equatorial zone. It is assumed that this happened due to the widespread use of fluorochlorine-containing refrigerants (freons) in refrigeration units and for other purposes.
El Niño.
Once every few years, extremely strong warming occurs in the eastern equatorial Pacific Ocean. It usually starts in December and lasts for several months. Due to the proximity in time to Christmas, this phenomenon was called " El Niño", which means "baby (Christ)" in Spanish. The atmospheric phenomena accompanying it were called the Southern Oscillation, since they were first observed in the Southern Hemisphere. Due to the warm water surface, convective rise of air is observed in the eastern part of the Pacific Ocean, and not in the western part, as usual. As a result, the area heavy rains shifts from the western regions of the Pacific Ocean to the eastern ones.
Droughts in Africa.
References to drought in Africa go back to biblical history. More recently, in the late 1960s and early 1970s, drought in the Sahel, on the southern edge of the Sahara, led to the death of 100 thousand people. The drought of the 1980s caused similar damage in East Africa. Unfavorable climatic conditions these regions were exacerbated by overgrazing, deforestation and military action (as, for example, in Somalia in the 1990s).
METEOROLOGICAL INSTRUMENTS
Meteorological instruments are designed both for immediate immediate measurements (thermometer or barometer for measuring temperature or pressure) and for continuous recording of the same elements over time, usually in the form of a graph or curve (thermograph, barograph). Only instruments for urgent measurements are described below, but almost all of them also exist in the form of recorders. Essentially, these are the same measuring instruments, but with a pen that draws a line on a moving paper tape.
Thermometers.
Liquid glass thermometers.
Meteorological thermometers most often use the ability of a liquid enclosed in a glass bulb to expand and contract. Typically, a glass capillary tube ends in a spherical extension that serves as a reservoir for liquid. The sensitivity of such a thermometer is inversely dependent on the cross-sectional area of the capillary and directly dependent on the volume of the reservoir and on the difference in the expansion coefficients of a given liquid and glass. Therefore, sensitive meteorological thermometers have large reservoirs and thin tubes, and the liquids used in them expand much faster with increasing temperature than glass.
The choice of liquid for a thermometer depends mainly on the range of temperatures being measured. Mercury is used to measure temperatures above –39° C – its freezing point. For lower temperatures, liquid organic compounds, such as ethyl alcohol, are used.
The accuracy of the tested standard meteorological glass thermometer is ± 0.05 ° C. The main reason for the error of the mercury thermometer is associated with gradual irreversible changes in the elastic properties of the glass. They lead to a decrease in glass volume and an increase in the reference point. In addition, errors can occur as a result of incorrect readings or due to placing the thermometer in an area where the temperature does not correspond to the true air temperature in the vicinity of the weather station.
The errors of alcohol and mercury thermometers are similar. Additional errors can occur due to the adhesive forces between the alcohol and the glass walls of the tube, so that when the temperature drops quickly, some of the liquid is retained on the walls. In addition, alcohol reduces its volume in the light.
Minimum thermometer
designed to determine the lowest temperature for a given day. A glass alcohol thermometer is usually used for these purposes. A glass pointer pin with thickenings at the ends is immersed in alcohol. The thermometer works in a horizontal position. When the temperature drops, the column of alcohol retreats, dragging the pin along with it, and when the temperature rises, the alcohol flows around it without moving it, and therefore the pin fixes minimum temperature. Return the thermometer to working condition by tilting the reservoir upward so that the pin comes into contact with the alcohol again.
Maximum thermometer
used to determine the highest temperature for a given day. Usually it's glass mercury thermometer, similar to medical. There is a narrowing in the glass tube near the reservoir. Mercury is squeezed out through this constriction when the temperature rises, and when the temperature decreases, the constriction prevents its outflow into the reservoir. Such a thermometer is again prepared for work on a special rotating installation.
Bimetal thermometer
consists of two thin strips of metal, such as copper and iron, which expand into to varying degrees. Their flat surfaces fit tightly against one another. This bimetallic tape is twisted into a spiral, one end of which is rigidly fixed. As the coil heats or cools, the two metals expand or contract differently, and the coil either unwinds or curls tighter. The magnitude of these changes is judged by a pointer attached to the free end of the spiral. Examples of bimetallic thermometers are room thermometers with a round dial.
Electric thermometers.
Such thermometers include a device with a semiconductor thermoelement - a thermistor, or thermistor. The thermocouple is characterized by a large negative resistance coefficient (i.e. its resistance decreases rapidly with increasing temperature). The advantages of a thermistor are high sensitivity and speed of response to temperature changes. Thermistor calibration changes over time. Thermistors are used on weather satellites, sounding balloons, and most indoor digital thermometers.
Barometers.
Mercury barometer
- This is a glass tube approx. 90 cm, filled with mercury, sealed at one end and tipped into a cup with mercury. Under the influence of gravity, some of the mercury pours out of the tube into the cup, and due to the air pressure on the surface of the cup, the mercury rises through the tube. When equilibrium is established between these two opposing forces, the height of the mercury in the tube above the surface of the liquid in the reservoir corresponds to atmospheric pressure. If the air pressure increases, the mercury level in the tube rises. The average height of the mercury column in the barometer at sea level is approx. 760 mm.
Aneroid barometer
consists of a sealed box from which the air has been partially evacuated. One of its surfaces is an elastic membrane. If atmospheric pressure increases, the membrane bends inward; if it decreases, it bends outward. A pointer attached to it records these changes. Aneroid barometers are compact and relatively inexpensive and are used both indoors and on standard weather radiosondes.
Instruments for measuring humidity.
Psychrometer
consists of two thermometers located next to each other: a dry thermometer, which measures air temperature, and a wet thermometer, the reservoir of which is wrapped in a cloth (cambric) moistened with distilled water. Air flows around both thermometers. Due to the evaporation of water from the fabric, a wet-bulb thermometer will typically read a lower temperature than a dry-bulb thermometer. The lower the relative humidity, the greater the difference in thermometer readings. Based on these readings, relative humidity is determined using special tables.
Hair hygrometer
measures relative humidity based on changes in human hair length. To remove natural oils, hair is first soaked in ethyl alcohol and then washed in distilled water. The length of hair prepared in this way has an almost logarithmic dependence on relative humidity in the range from 20 to 100%. The time required for the hair to react to changes in humidity depends on the air temperature (the lower the temperature, the longer it is). In a hair hygrometer, as the hair length increases or decreases, a special mechanism moves the pointer along the scale. Such hygrometers are usually used to measure relative humidity in rooms.
Electrolytic hygrometers.
The sensing element of these hygrometers is a glass or plastic plate coated with carbon or lithium chloride, the resistance of which varies depending on the relative humidity. Such elements are commonly used in instrument packages for weather balloons. When the probe passes through the cloud, the device becomes moistened, and its readings are distorted for quite a long time (until the probe is outside the cloud and the sensitive element dries out).
Instruments for measuring wind speed.
Cup anemometers.
Wind speed is usually measured using a cup anemometer. This device consists of three or more cone-shaped cups vertically attached to the ends of metal rods that extend radially symmetrically from a vertical axis. The wind acts with the greatest force on the concave surfaces of the cups and causes the axis to rotate. In some types of cup anemometers, the free rotation of the cups is prevented by a system of springs, the magnitude of the deformation of which determines the wind speed.
In free-rotating cup anemometers, the speed of rotation, roughly proportional to the wind speed, is measured by an electrical meter, which signals when a certain volume of air flows past the anemometer. The electrical signal turns on the light signal and the recording device at the weather station. Often a cup anemometer is mechanically coupled to a magneto, and the voltage or frequency of the electrical current generated is related to the wind speed.
Anemometer
with a mill turntable consists of a three-four-bladed plastic screw mounted on the magneto axis. The propeller, with the help of a weather vane, inside of which a magneto is located, is constantly directed against the wind. Information about the wind direction is received via telemetry channels to the observation station. Electricity, produced by the magneto, varies in direct proportion to the wind speed.
Beaufort scale.
Wind speed is assessed visually by its effect on objects surrounding the observer. In 1805, Francis Beaufort, a sailor in the British Navy, developed a 12-point scale to characterize the strength of wind at sea. In 1926, estimates of wind speed on land were added to it. In 1955, to distinguish between hurricane winds different strengths, the scale was expanded to 17 points. The modern version of the Beaufort scale (Table 6) allows you to estimate wind speed without using any instruments.
| Table 6. Beaufort SCALE FOR DETERMINING WIND STRENGTH | |||
| Points | Visual signs on land | Wind speed, km/h | Wind power terms |
| 0 | Calmly; smoke rises vertically | Less than 1.6 | Calm |
| 1 | The direction of the wind is noticeable by the deflection of the smoke, but not by the weather vane. | 1,6–4,8 | Quiet |
| 2 | The wind is felt by the skin of the face; leaves rustle; regular weather vanes turn | 6,4–11,2 | Easy |
| 3 | Leaves and small twigs are in constant motion; light flags flutter | 12,8–19,2 | Weak |
| 4 | The wind raises dust and pieces of paper; thin branches sway | 20,8–28,8 | Moderate |
| 5 | The leafy trees sway; ripples appear on land bodies of water | 30,4–38,4 | Fresh |
| 6 | Thick branches sway; you can hear the wind whistling in the electrical wires; difficult to hold umbrella | 40,0–49,6 | Strong |
| 7 | Tree trunks sway; it's hard to go against the wind | 51,2–60,8 | Strong |
| 8 | Tree branches break; It's almost impossible to go against the wind | 62,4–73,6 | Very strong |
| 9 | Minor damage; the wind tears smoke hoods and tiles from roofs | 75,2–86,4 | Storm |
| 10 | Rarely happens on land. Trees are uprooted. Significant damage to buildings | 88,0–100,8 | Heavy storm |
| 11 | It happens very rarely on land. Accompanied by destruction over a large area | 102,4–115,2 | Fierce Storm |
| 12 | Severe destruction (Scores 13–17 were added by the US Weather Bureau in 1955 and are used in the US and UK scales) |
116,8–131,2 | Hurricane |
| 13 | 132,8–147,2 | ||
| 14 | 148,8–164,8 | ||
| 15 | 166,4–182,4 | ||
| 16 | 184,0–200,0 | ||
| 17 | 201,6–217,6 | ||
Instruments for measuring precipitation.
Atmospheric precipitation consists of water particles, both liquid and solid, that come from the atmosphere to the earth's surface. In standard non-recording rain gauges, the receiving funnel is inserted into the measuring cylinder. The ratio of the area of the top of the funnel and the cross-section of the graduated cylinder is 10:1, i.e. 25 mm of precipitation will correspond to the 250 mm mark in the cylinder.
Recording rain gauges - pluviographs - automatically weigh the collected water or count how many times a small measuring vessel fills with rainwater and automatically empties.
If precipitation in the form of snow is expected, the funnel and measuring cup are removed and the snow is collected in a precipitation bucket. When snow is accompanied by moderate to strong winds, the amount of snow falling into the container does not correspond to the actual amount of precipitation. Snow depth is determined by measuring the thickness of the snow layer within a typical area for a given area, taking the average of at least three measurements. To establish the water equivalent in areas where the impact of blowing snow is minimal, a cylinder is immersed in the snow and a column of snow is cut out, which is melted or weighed. The amount of precipitation measured by a rain gauge depends on its location. Turbulence in the air flow, caused by the device itself or obstacles surrounding it, leads to an underestimation of the amount of precipitation entering the measuring cup. Therefore, the rain gauge is installed on a flat surface as far as possible from trees and other obstacles. To reduce the impact of vortices created by the device itself, a protective screen is used.
AIR OBSERVATIONS
Instruments for measuring cloud heights.
The simplest way to determine the height of a cloud is to measure the time it takes a small balloon released from the surface of the earth to reach the base of the cloud. Its height is equal to the product average speed lifting the balloon during the flight.
Another method is to observe a spot of light formed at the base of the cloud with a spotlight directed vertically upward. From a distance of approx. 300 m from the spotlight, the angle between the direction towards this spot and the spotlight beam is measured. Cloud height is calculated by triangulation, similar to how distances are measured in topographic surveys. The proposed system can operate automatically day and night. A photocell is used to observe a spot of light at the bases of clouds.
Cloud height is also measured using radio waves - 0.86 cm long pulses sent by a radar. Cloud height is determined by the time it takes for a radio pulse to reach the cloud and return. Since clouds are partially transparent to radio waves, this method is used to determine the height of layers in multi-layer clouds.
Meteorological balloons.
The simplest type of meteorological balloon is the so-called. A balloon is a small rubber balloon filled with hydrogen or helium. By optically observing changes in the azimuth and altitude of the balloon, and assuming that its rate of rise is constant, wind speed and direction can be calculated as a function of height above the earth's surface. For night observations, a small battery-powered flashlight is attached to the ball.
A weather radiosonde is a rubber ball carrying a radio transmitter, an RTD thermometer, an aneroid barometer and an electrolytic hygrometer. The radiosonde rises at a speed of approx. 300 m/min up to a height of approx. 30 km. As it ascends, measurement data is continuously transmitted to the launch station. A directional receiving antenna on Earth tracks the azimuth and altitude of the radiosonde, from which wind speed and direction at various altitudes are calculated in the same way as in balloon observations. Radiosondes and pilot balloons are launched from hundreds of locations around the world twice a day - at noon and midnight Greenwich Mean Time.
Satellites.
For daytime cloud cover surveys, lighting is provided sunlight, while the infrared radiation emitted by all bodies allows shooting day and night with a special infrared camera. Using photographs in different ranges of infrared radiation, it is even possible to calculate the temperature of individual layers of the atmosphere. Satellite observations have a high horizontal resolution, but their vertical resolution is much lower than that provided by radiosondes.
Some satellites, such as the American TIROS, are placed in a circular polar orbit at an altitude of approx. 1000 km. Since the Earth rotates around its axis, from such a satellite every point on the earth's surface is usually visible twice a day.
The so-called are even more important. geostationary satellites that orbit over the equator at an altitude of approx. 36 thousand km. Such a satellite requires 24 hours to complete a revolution. Since this time is equal to the length of the day, the satellite remains above the same point on the equator and has a constant view of the earth's surface. In this way, a geostationary satellite can repeatedly photograph the same area, recording changes in weather. In addition, wind speeds can be calculated from the movement of clouds.
Weather radars.
The signal sent by the radar is reflected by rain, snow or temperature inversion, and this reflected signal is sent to the receiving device. Clouds are usually not visible on radar because the droplets that form them are too small to effectively reflect the radio signal.
By the mid-1990s, the US National Weather Service was re-equipped with Doppler radars. In installations of this type, the so-called principle is used to measure the speed at which reflecting particles approach or move away from the radar. Doppler shift. Therefore, these radars can be used to measure wind speed. They are especially useful for detecting tornadoes, since the wind on one side of the tornado quickly rushes towards the radar, and on the other, it quickly moves away from it. Modern radars can detect weather objects at a distance of up to 225 km.
meteoblue weather charts are based on 30 years of weather models available for every point on Earth. They provide useful indicators of typical climatic features and expected weather conditions (temperature, precipitation, sunshine or wind). Weather data models have a spatial resolution of about 30 km in diameter and may not reproduce all local weather events such as thunderstorms, local winds or tornadoes.
You can study the climate of any location, such as the Amazon rainforest, West African savannas, Sahara Desert, Siberian tundra or Himalayas.
30 years of hourly historical data for Bombay can be purchased with history+. You will be able to download CSV files for weather parameters such as temperature, wind, cloudiness and precipitation relative to any point on the globe. The last 2 weeks of data for the city of Bombay are available for free evaluation of the package.
Average temperature and precipitation
The "mean daily maximum" (solid red line) shows the maximum average temperature for every month for Bombay. Likewise, the "Minimum Average Daily Temperature" (solid blue line) indicates the minimum average temperature. Hot Days and Cold Nights (the dotted red and blue lines indicate the average temperature of the hottest day and coldest night of each month for 30 years. When planning your vacation, you'll be aware of the average temperature and prepared for both the hottest and coldest on cold days. The default settings do not include wind speed indicators, but you can enable this option using the button on the graph.
The rainfall schedule is useful for seasonal variations, such as the monsoon climate in India or the humid period in Africa.
Cloudy, sunny and precipitation days
The graph indicates the number of sunny, partly cloudy, foggy, and precipitation days. Days when the cloud layer does not exceed 20% are considered sunny; 20-80% cover is considered partly cloudy, and more than 80% is considered completely cloudy. While the weather in Reykjavik, the capital of Iceland, is mostly cloudy, Sossusvlei in the Namib Desert is one of the most sunny places on the ground.
Attention: In countries with a tropical climate, such as Malaysia or Indonesia, the forecast for the number of days of precipitation may be overestimated by a factor of two.
Maximum temperatures
The maximum temperature diagram for Bombay displays how many days per month reach certain temperatures. In Dubai, one of the hottest cities on earth, the temperature almost never drops below 40°C in July. You can also see a chart of cold winters in Moscow, which shows that only a few days a month the maximum temperature barely reaches -10°C.
Precipitation
The precipitation diagram for Bombay shows how many days per month reach certain precipitation amounts. In areas with tropical or monsoon climates, rainfall forecasts may be underestimated.
Wind speed
The diagram for Bombay shows the days per month, during which the wind reaches a certain speed. An interesting example is the Tibetan Plateau, where the monsoons produce prolonged strong winds from December to April and calm air flows from June to October.
Wind speed units can be changed in the preferences section (top right corner).
Wind speed rose
The wind rose for Bombay shows how many hours per year the wind blows from the indicated direction. Example - southwest wind: The wind blows from southwest (SW) to northeast (NE). Cape Horn, the most southern point in South America, it is characterized by a characteristic powerful westerly wind, which significantly impedes passage from east to west, especially for sailing ships.
general information
Since 2007, meteoblue has been collecting model meteorological data in its archive. In 2014, we began comparing weather models with historical data going back to 1985, creating a global archive of 30 years of hourly weather data. Weather charts are the first simulated weather data sets available on the Internet. Our weather data history includes data from all parts of the world covering any time period, regardless of the availability of weather stations.
The data is obtained from our global weather model NEMS over a diameter of approximately 30 km. Consequently, they cannot reproduce minor local weather events such as heat domes, cold blasts, thunderstorms and tornadoes. For locations and events that require a high level of accuracy (such as energy allocation, insurance, etc.), we offer high-resolution models with hourly weather data.
License
This data may be used under the Creative Community "Attribution + Non-commercial (BY-NC)" license. Any form is illegal.
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