When is the sun hottest - when is it higher overhead or lower?
The sun heats up more when it is higher. The sun's rays in this case fall at a right, or close to a right angle.
What kinds of rotation of the Earth do you know?
The earth rotates on its axis and around the sun.
Why does the day and night cycle occur on Earth?
The change of day and night is the result of the axial rotation of the Earth.
Determine how the angle of incidence of the sun's rays differs on June 22 and December 22 at the parallels of 23.5 ° N. sh. and yu. sh.; at the parallels of 66.5° N. sh. and yu. sh.
On June 22, the angle of incidence of the sun's rays at the parallel of 23.50 N.L. 900 S - 430. At the parallel 66.50 N.S. – 470, 66.50 S - sliding angle.
On December 22, the angle of incidence of the sun's rays at the parallel 23.50 N.L. 430 S - 900. At the parallel 66.50 N.S. - sliding angle, 66.50 S - 470.
Think about why the warmest and coldest months are not June and December, when the sun's rays have the greatest and smallest angles of incidence on earth's surface.
Atmospheric air is heated from the earth's surface. Therefore, in June, the earth's surface warms up, and the temperature reaches a maximum in July. It also happens in winter. In December, the earth's surface cools down. The air cools down in January.
Define:
average daily temperature according to four measurements per day: -8°C, -4°C, +3°C, +1°C.
The average daily temperature is -20C.
the average annual temperature of Moscow using the table data.
The average annual temperature is 50C.
Determine the daily temperature range for thermometer readings in Figure 110, c.
The temperature amplitude in the figure is 180C.
Determine how many degrees the annual amplitude in Krasnoyarsk is greater than in St. Petersburg, if average temperature July in Krasnoyarsk +19°С, and January -17°С; in St. Petersburg +18°C and -8°C respectively.
The temperature range in Krasnoyarsk is 360С.
The temperature amplitude in St. Petersburg is 260C.
The temperature amplitude in Krasnoyarsk is 100C higher.
Questions and tasks
1. How does the air in the atmosphere heat up?
When the sun's rays pass through, the atmosphere from them almost does not heat up. As the earth's surface heats up, it becomes a heat source itself. It is from it that the atmospheric air is heated.
2. How many degrees does the temperature in the troposphere decrease for every 100 m ascent?
As you climb up, every kilometer the air temperature drops by 6 0C. So, 0.60 for every 100 m.
3. Calculate the air temperature outside the aircraft, if the flight altitude is 7 km, and the temperature at the Earth's surface is +200C.
The temperature when climbing 7 km will drop by 420. This means that the temperature outside the aircraft will be -220.
4. Is it possible to meet a glacier in the mountains at an altitude of 2500 m in summer if the temperature at the foot of the mountains is + 250C.
The temperature at an altitude of 2500 m will be +100C. The glacier at an altitude of 2500 m will not meet.
5. How and why does the air temperature change during the day?
During the day, the sun's rays illuminate the earth's surface and warm it up, and the air heats up from it. At night, the flow of solar energy stops, and the surface, along with the air, gradually cools. The sun is highest above the horizon at noon. This is the time when the most solar energy comes in. However, the highest temperature is observed after 2-3 hours after noon, since it takes time for heat to transfer from the Earth's surface to the troposphere. The lowest temperature is before sunrise.
6. What determines the difference in the heating of the Earth's surface during the year?
During the year, in the same area, the sun's rays fall on the surface in different ways. When the angle of incidence of the rays is steeper, the surface receives more solar energy, the air temperature rises and summer comes. When the sun's rays are more tilted, the surface heats up slightly. The air temperature at this time drops, and winter comes. Most warm month in the Northern Hemisphere - July, and the coldest - January. In the Southern Hemisphere, on the contrary: the most cold month year - July, and the warmest - January.
- devices used for heating air in supply ventilation systems, air conditioning systems, air heating as well as in dryers.
According to the type of coolant, heaters can be fire, water, steam and electric. .
The most widespread at present are water and steam heaters, which are divided into smooth-tube and ribbed ones; the latter, in turn, are divided into lamellar and spiral-wound.
Distinguish between single-pass and multi-pass heaters. In single-pass, the coolant moves through the tubes in one direction, and in multi-pass, it changes the direction of movement several times due to the presence of partitions in the collector covers (Fig. XII.1).
Heaters perform two models: medium (C) and large (B).
The heat consumption for heating the air is determined by the formulas:
 |
where Q"— heat consumption for air heating, kJ/h (kcal/h); Q- the same, W; 0.278 is the conversion factor from kJ/h to W; G- mass amount of heated air, kg / h, equal to Lp [here L- volumetric amount of heated air, m 3 / h; p is the air density (at a temperature tK), kg / m 3]; with- specific heat capacity of air, equal to 1 kJ / (kg-K); t k - air temperature after the heater, ° С; t n— air temperature before the air heater, °C.
For heaters of the first stage of heating, the temperature tn is equal to the temperature of the outside air.
The outdoor air temperature is assumed to be equal to the calculated ventilation temperature (category A climate parameters) when designing general ventilation designed to combat excess moisture, heat and gases, the MPC of which is more than 100 mg / m3. When designing general ventilation designed to combat gases whose MPC is less than 100 mg / m3, as well as when designing supply ventilation to compensate for air removed through local exhausts, process hoods or pneumatic transport systems, the outside air temperature is assumed to be equal to the calculated outside temperature tn for heating design (climate parameters category B).
In a room without heat surpluses, supply air with a temperature equal to the indoor air temperature tВ for this room should be supplied. In the presence of excess heat, the supply air is supplied at a reduced temperature (by 5-8 ° C). Supply air with a temperature below 10°C is not recommended to be supplied to the room even in the presence of significant heat emissions due to the possibility of colds. The exception is the use of special anemostats.
The required surface area for heating heaters Fк m2, is determined by the formula:
where Q— heat consumption for air heating, W (kcal/h); To- heat transfer coefficient of the heater, W / (m 2 -K) [kcal / (h-m 2 - ° C)]; t cf.T.— average coolant temperature, 0 С; t r.v. is the average temperature of the heated air passing through the heater, °C, equal to (t n + t c)/2.
If the coolant is steam, then the average temperature of the coolant tav.T. is equal to the saturation temperature at the corresponding vapor pressure.
For water temperature tav.T. is defined as the arithmetic mean of the hot and return water temperatures:
The safety factor 1.1-1.2 takes into account the heat loss for air cooling in the air ducts.
The heat transfer coefficient of heaters K depends on the type of coolant, the mass velocity of air movement vp through the heater, the geometric dimensions and design features of the heaters, the speed of water movement through the tubes of the heater.
The mass velocity is understood as the mass of air, kg, passing through 1 m2 of the living section of the air heater in 1 s. Mass velocity vp, kg/(cm2), is determined by the formula
According to the area of the open section fЖ and the heating surface FK, the model, brand and number of heaters are selected. After choosing the heaters, the mass air velocity is specified according to the actual area of the open section of the heater fD of this model:
where A, A 1 , n, n 1 and t- coefficients and exponents, depending on the design of the heater
The speed of water movement in the heater tubes ω, m/s, is determined by the formula:
where Q "is the heat consumption for heating air, kJ / h (kcal / h); rp is the density of water, equal to 1000 kg / m3, sv is the specific heat of water, equal to 4.19 kJ / (kg-K); fTP - open area for coolant passage, m2, tg — temperature hot water in the supply line, ° С; t 0 - return water temperature, 0С.
The heat transfer of heaters is affected by the scheme of tying them with pipelines. With a parallel scheme for connecting pipelines, only part of the coolant passes through a separate heater, and with a sequential scheme, the entire flow of the coolant passes through each heater.
The resistance of heaters to the passage of air p, Pa, is expressed by the following formula:
where B and z are the coefficient and exponent, which depend on the design of the heater.
The resistance of the heaters located in series is equal to:
where m is the number of successively located heaters. The calculation ends with a check of the heat output (heat transfer) of the heaters according to the formula
where QK - heat transfer of heaters, W (kcal / h); QK - the same, kJ/h, 3.6 - conversion factor W to kJ/h FK - heating surface area of heaters, m2, taken as a result of calculation of heaters of this type; K - heat transfer coefficient of heaters, W/(m2-K) [kcal/(h-m2-°C)]; tav.v - the average temperature of the heated air passing through the heater, °C; tav. T is the average temperature of the coolant, °С.
When selecting heaters, the margin for the estimated heating surface area is taken in the range of 15 - 20%, for the resistance to air passage - 10% and for the resistance to water movement - 20%.
Research carried out at the turn of the 1940s-1950s made it possible to develop a number of aerodynamic and technological solutions that ensure the safe overcoming of the sound barrier even by production aircraft. Then it seemed that the conquest of the sound barrier creates unlimited possibilities for a further increase in flight speed. In just a few years, about 30 types of supersonic aircraft were flown, of which a significant number were put into mass production.
The variety of solutions used has led to the fact that many of the problems associated with flying at high supersonic speeds have been comprehensively studied and solved. However, new problems were encountered, much more complex than the sound barrier. They are caused by the heating of the structure. aircraft when flying at high speed in dense layers of the atmosphere. This new obstacle was once called the thermal barrier. Unlike the sound barrier, the new barrier cannot be characterized by a constant similar to the speed of sound, since it depends both on the flight parameters (speed and altitude) and the design of the airframe (constructive solutions and materials used), and on the equipment of the aircraft (air conditioning, cooling systems, etc.). P.). Thus, the concept of "thermal barrier" includes not only the problem of dangerous heating of the structure, but also issues such as heat transfer, strength properties of materials, design principles, air conditioning, etc.
The heating of the aircraft in flight occurs mainly for two reasons: from the aerodynamic braking of the air flow and from the heat release of the propulsion system. Both of these phenomena constitute the process of interaction between the medium (air, exhaust gases) and a streamlined solid body (aircraft, engine). The second phenomenon is typical for all aircraft, and it is associated with an increase in the temperature of engine structural elements that receive heat from the air compressed in the compressor, as well as from combustion products in the chamber and exhaust pipe. When flying at high speeds, the internal heating of the aircraft also occurs from the air decelerating in the air channel in front of the compressor. When flying at low speeds, the air passing through the engine has a relatively low temperature, as a result of which dangerous heating of the airframe structural elements does not occur. At high flight speeds, the heating of the airframe structure from hot engine elements is limited by additional cooling with low-temperature air. Typically, air is used that is removed from the air intake using a guide separating the boundary layer, as well as air captured from the atmosphere using additional intakes located on the surface of the engine nacelle. In two-circuit engines, air from the external (cold) circuit is also used for cooling.
Thus, the level of the thermal barrier for supersonic aircraft is determined by external aerodynamic heating. The intensity of heating of the surface flowed around by the air flow depends on the flight speed. At low speeds, this heating is so insignificant that the increase in temperature can be ignored. At high speed, the air flow has a high kinetic energy, and therefore the temperature increase can be significant. This also applies to the temperature inside the aircraft, since the high-speed flow, stagnant in the air intake and compressed in the engine compressor, becomes so high that it is unable to remove heat from the hot parts of the engine.
The increase in the temperature of the aircraft skin as a result of aerodynamic heating is caused by the viscosity of the air flowing around the aircraft, as well as its compression on the frontal surfaces. Due to the loss of speed by air particles in the boundary layer as a result of viscous friction, the temperature of the entire streamlined surface of the aircraft increases. As a result of air compression, the temperature rises, however, only locally (mainly the nose of the fuselage, the windshield of the cockpit, and especially the leading edges of the wing and plumage), but more often reaches values that are unsafe for the structure. In this case, in some places there is an almost direct collision of the air flow with the surface and full dynamic braking. In accordance with the principle of conservation of energy, all the kinetic energy of the flow is converted into heat and pressure energy. The corresponding temperature rise is directly proportional to the square of the flow velocity before braking (or, without wind, to the square of the aircraft speed) and inversely proportional to the flight altitude.
Theoretically, if the flow around is steady, the weather is calm and cloudless, and there is no heat transfer by radiation, then heat does not penetrate into the structure, and the skin temperature is close to the so-called adiabatic stagnation temperature. Its dependence on the Mach number (speed and flight altitude) is given in Table. 4.
Under actual conditions, the increase in the temperature of the aircraft skin from aerodynamic heating, i.e., the difference between the stagnation temperature and the ambient temperature, turns out to be somewhat smaller due to heat exchange with the environment (by means of radiation), neighboring structural elements, etc. In addition, complete deceleration of the flow occurs only at the so-called critical points located on the protruding parts of the aircraft, and the heat influx to the skin also depends on the nature of the boundary layer of air (it is more intense for a turbulent boundary layer). A significant decrease in temperature also occurs when flying through clouds, especially when they contain supercooled water drops and ice crystals. For such flight conditions, it is assumed that the decrease in the skin temperature at the critical point compared to the theoretical stagnation temperature can reach even 20-40%.
Table 4. Dependence of the skin temperature on the Mach number
Nevertheless, the overall heating of the aircraft in flight at supersonic speeds (especially at low altitude) is sometimes so high that an increase in the temperature of individual elements of the airframe and equipment leads either to their destruction, or, at least, to the need to change the flight mode. For example, during studies of the XB-70A aircraft in flights at altitudes of more than 21,000 m at a speed of M = 3, the temperature of the leading edges of the air intake and the leading edges of the wing was 580-605 K, and the rest of the skin was 470-500 K. Consequences of increasing the temperature of aircraft structural elements Such high values can be fully estimated if we take into account the fact that already at temperatures of about 370 K, organic glass, which is widely used for glazing cabins, softens, fuel boils, and ordinary glue loses its strength. At 400 K, the strength of duralumin is significantly reduced, at 500 K, the chemical decomposition of the working fluid in the hydraulic system and the destruction of seals occur, at 800 K, titanium alloys lose the necessary mechanical properties, at temperatures above 900 K, aluminum and magnesium melt, and steel softens. An increase in temperature also leads to the destruction of coatings, of which anodizing and chromium plating can be used up to 570 K, nickel plating up to 650 K, and silver plating up to 720 K.
After the appearance of this new obstacle in increasing the speed of flight, research began to eliminate or mitigate its consequences. Ways to protect the aircraft from the effects of aerodynamic heating are determined by factors that prevent the temperature rise. In addition to the flight altitude and atmospheric conditions, the degree of heating of the aircraft is significantly affected by:
is the coefficient of thermal conductivity of the sheathing material;
- the size of the surface (especially the frontal) of the aircraft; -flight time.
It follows that the simplest ways to reduce the heating of the structure are to increase the flight altitude and limit its duration to a minimum. These methods were used in the first supersonic aircraft (especially experimental ones). Due to the rather high thermal conductivity and heat capacity of the materials used for the manufacture of heat-stressed structural elements of the aircraft, from the moment the aircraft reaches high speed until the moment the individual structural elements are heated to the design temperature of the critical point, it usually takes quite a long time. big time. In flights lasting several minutes (even at low altitudes), destructive temperatures are not reached. Flight at high altitudes takes place under conditions of low temperature (about 250 K) and low air density. As a result, the amount of heat given off by the flow to the surfaces of the aircraft is small, and the heat exchange takes longer, which greatly alleviates the severity of the problem. A similar result is obtained by limiting the speed of the aircraft at low altitudes. For example, during a flight over the ground at a speed of 1600 km/h, the strength of duralumin decreases by only 2%, and an increase in speed to 2400 km/h leads to a decrease in its strength by up to 75% compared to the initial value.
Rice. 1.14. Temperature distribution in the air duct and in the engine of the Concord aircraft during flight with M = 2.2 (a) and the temperature of the skin of the XB-70A aircraft during flight at a constant speed of 3200 km/h (b).
However, the need to ensure safe operating conditions over the entire range of used speeds and flight altitudes forces designers to look for appropriate technical means. Since the heating of aircraft structural elements causes a decrease in the mechanical properties of materials, the occurrence of thermal stresses on the structure, as well as deterioration in the working conditions of the crew and equipment, such technical means used in current practice can be divided into three groups. They respectively include the use of 1) heat-resistant materials, 2) design solutions that provide the necessary thermal insulation and allowable deformation of parts, and 3) cooling systems for the cockpit and equipment compartments.
In aircraft with a maximum speed of M = 2.0-1-2.2, aluminum alloys (duralumin) are widely used, which are characterized by relatively high strength, low density and retention of strength properties with a slight increase in temperature. Durals are usually supplemented with steel or titanium alloys, from which the parts of the airframe that are subjected to the greatest mechanical or thermal loads are made. Titanium alloys were used already in the first half of the 50s, at first on a very small scale (now details from them can be up to 30% of the weight of the airframe). In experimental aircraft with M ~ 3, it becomes necessary to use heat-resistant steel alloys as the main structural material. Such steels retain good mechanical properties at high temperatures, typical for flights with hypersonic speeds, but their disadvantages are high cost and high density. These shortcomings in a certain sense limit the development of high-speed aircraft, so other materials are also being researched.
In the 1970s, the first experiments were made on the use of beryllium in aircraft construction, as well as composite materials based on boron or carbon fibers. These materials still have a high cost, but at the same time they are characterized by low density, high strength and rigidity, as well as significant heat resistance. Examples of specific applications of these materials in the construction of the airframe are given in the descriptions of individual aircraft.
Another factor that significantly affects the performance of a heated aircraft structure is the effect of so-called thermal stresses. They arise as a result of temperature differences between the outer and inner surfaces of the elements, and especially between the skin and the internal structural elements of the aircraft. Surface heating of the airframe leads to deformation of its elements. For example, warping of the wing skin can occur in such a way that it leads to a change in aerodynamic characteristics. Therefore, many aircraft use brazed (sometimes glued) multilayer skin, which is characterized by high rigidity and good insulating properties, or internal structural elements with appropriate expansion joints are used (for example, in the F-105 aircraft, the spar walls are made of corrugated sheet). Experiments are also known for cooling the wing with fuel (for example, in the X-15 aircraft) flowing under the skin on the way from the tank to the combustion chamber nozzles. However, at high temperatures, the fuel usually undergoes coking, so such experiments can be considered unsuccessful.
Currently, various methods are being investigated, among which is the application of an insulating layer of refractory materials by plasma spraying. Other methods considered promising have not found application. Among other things, it was proposed to use a "protective layer" created by blowing gas onto the skin, "sweating" cooling by supplying a liquid with a high evaporation temperature to the surface through the porous skin, as well as cooling created by melting and entraining part of the skin (ablative materials).
A rather specific and at the same time very important task is to maintain the appropriate temperature in the cockpit and in the equipment compartments (especially electronic), as well as the temperature of the fuel and hydraulic systems. At present, this problem is solved by using high-performance air conditioning, cooling and refrigeration systems, effective thermal insulation, the use of hydraulic fluids with a high evaporation temperature, etc.
The problems associated with the thermal barrier must be addressed comprehensively. Any progress in this area pushes the barrier for this type of aircraft towards higher flight speeds, without excluding it as such. However, the desire for even greater speeds leads to the creation of even more complex structures and equipment requiring the use of higher quality materials. This has a noticeable effect on the weight, purchase price, and the cost of operating and maintaining the aircraft.
From the table. 2 of these fighter aircraft shows that in most cases the maximum speed of 2200-2600 km / h was considered rational. Only in some cases is it believed that the speed of the aircraft should exceed M ~ 3. Aircraft capable of developing such speeds include the experimental X-2, XB-70A and T. 188 machines, the reconnaissance SR-71, and the E-266 aircraft.
1* Refrigeration is the forced transfer of heat from a cold source to a high-temperature environment with artificial opposition to the natural direction of heat movement (from a warm body to a cold one when the cooling process takes place). The simplest refrigerator is a household refrigerator.
They pass through the transparent atmosphere without heating it, they reach the earth's surface, heat it, and the air subsequently heats up from it.
The degree of surface heating, and hence the air, depends primarily on the latitude of the area.
But at each specific point, it (t o) will also be determined by a number of factors, among which the main ones are:
A: height above sea level;
B: underlying surface;
B: distance from the coasts of oceans and seas.
A - Since the air is heated from the earth's surface, the lower the absolute heights of the area, the higher the air temperature (at the same latitude). In conditions of air unsaturated with water vapor, a pattern is observed: for every 100 meters of altitude, the temperature (t o) decreases by 0.6 o C.
B - Qualitative characteristics of the surface.
B 1 - surfaces different in color and structure absorb and reflect the sun's rays in different ways. The maximum reflectivity is typical for snow and ice, the minimum for dark-colored soils and rocks.
Illumination of the Earth by the sun's rays on the days of the solstices and equinoxes.
B 2 - different surfaces have different heat capacity and heat transfer. So the water mass of the World Ocean, which occupies 2/3 of the Earth's surface, due to the high heat capacity, heats up very slowly and cools very slowly. The land quickly heats up and quickly cools, i.e., in order to heat up to the same t about 1 m 2 of land and 1 m 2 of water surface, it is necessary to spend a different amount of energy.
B - from the coasts to the interior of the continents, the amount of water vapor in the air decreases. The more transparent the atmosphere, the less sunlight is scattered in it, and all the sun's rays reach the Earth's surface. In the presence of a large amount of water vapor in the air, water droplets reflect, scatter, absorb the sun's rays, and not all of them reach the surface of the planet, while heating it decreases.
Most high temperatures air recorded in areas of tropical deserts. In the central regions of the Sahara, for almost 4 months, t about air in the shade is more than 40 ° C. At the same time, at the equator, where the angle of incidence of the sun's rays is the largest, the temperature does not exceed +26 ° C.
On the other hand, the Earth, as a heated body, radiates energy into space mainly in the long-wave infrared spectrum. If the earth's surface is wrapped in a "blanket" of clouds, then not all infrared rays leave the planet, since the clouds delay them, reflecting back to the earth's surface.
With a clear sky, when there is little water vapor in the atmosphere, the infrared rays emitted by the planet freely go into space, while the earth's surface cools down, which cools down and thereby reduces the air temperature.
Literature
- Zubashchenko E.M. Regional physical geography. Climates of the Earth: teaching aid. Part 1. / E.M. Zubashchenko, V.I. Shmykov, A.Ya. Nemykin, N.V. Polyakov. - Voronezh: VGPU, 2007. - 183 p.
All life processes on Earth are caused by thermal energy. The main source from which the Earth receives thermal energy is the Sun. It radiates energy in the form of various beams - electromagnetic waves. The radiation of the Sun in the form of electromagnetic waves propagating at a speed of 300,000 km / s is called, which consists of rays of various lengths that carry light and heat to the Earth.
Radiation can be direct or diffuse. If there were no atmosphere, the earth's surface would receive only direct radiation. Therefore, radiation that comes directly from the Sun in the form of direct sunlight and with a cloudless sky is called direct. It carries the greatest amount of heat and light. But, passing through the atmosphere, the sun's rays are partially scattered, deviate from the direct path as a result of reflection from air molecules, water droplets, dust particles and turn into rays going in all directions. Such radiation is called diffuse. Therefore, it is also light in those places where direct sunlight (direct radiation) does not penetrate (forest canopy, shady side of rocks, mountains, buildings, etc.). Scattered radiation also determines the color of the sky. All solar radiation coming to the earth's surface, i.e. direct and scattered, called the total. The earth's surface, absorbing solar radiation, heats up and itself becomes a source of heat radiation into the atmosphere. It is called terrestrial radiation, or terrestrial radiation, and is largely delayed by the lower layers of the atmosphere. The solar radiation absorbed by the earth's surface is spent on heating water, soil, air, evaporation and radiation into the atmosphere. Earthy, not defining temperature regime troposphere, i.e. the sun's rays passing through everything do not heat it. Most a large number of heat is received and heated to the highest temperatures by the lower layers of the atmosphere, directly adjacent to the heat source - the earth's surface. As you move away from the earth's surface, the heating weakens. That is why in the troposphere, with height, an average of 0.6 ° C decreases for every 100 m of ascent. This is general pattern for the troposphere. There are times when the overlying layers of air are warmer than the underlying ones. This phenomenon is called temperature inversion.
The heating of the earth's surface differs significantly not only in height. The amount of total solar radiation directly depends on the angle of incidence of the sun's rays. The closer this value is to 90°, the more solar energy the earth's surface receives.
In turn, the angle of incidence of the sun's rays on a certain point on the earth's surface is determined by its geographical latitude. The strength of direct solar radiation depends on the length of the path that the sun's rays travel through the atmosphere. When the Sun is at its zenith (near the equator), its rays fall vertically on the earth's surface, i.e. overcome the atmosphere in the shortest way (at 90 °) and intensively give up their energy to a small area. As you move away from the equatorial zone to the south or north, the length of the path of the sun's rays increases, i.e. the angle of their incidence on the earth's surface decreases. More and more, the rays begin to slide along the Earth, as it were, and approach the tangent line in the region of the poles. In this case, the same beam of energy is scattered over a larger area, and the amount of reflected energy increases. Thus, where the sun's rays fall on the earth's surface at an angle of 90 °, they are constantly high, and as they move towards the poles, it becomes progressively colder. It is at the poles, where the sun's rays fall at an angle of 180 ° (i.e., tangentially), that there is the least amount of heat.
Such an uneven distribution of heat on the Earth, depending on the latitude of the place, makes it possible to distinguish five thermal zones: one hot, two and two cold.
The conditions for heating water and land by solar radiation are very different. The heat capacity of water is twice that of land. This means that with the same amount of heat, land heats up twice as fast as water, and when it cools, the opposite happens. In addition, water evaporates when heated, which consumes a considerable amount of heat. On land, heat is concentrated only in its upper layer, only a small part of it is transferred to the depth. In water, the rays immediately heat up a significant thickness, which is also facilitated by the vertical mixing of water. As a result, water accumulates heat much more than land, retains it longer and spends it more evenly than land. It heats up slower and cools down slower.
The surface of the land is not uniform. Its heating depends to a large extent on physical properties soils and, ice, exposure (the angle of inclination of land areas in relation to the incident sun's rays) slopes. Features of the underlying surface determine the different nature of the change in air temperatures during the day and year. The lowest air temperatures during the day on land are observed shortly before sunrise (no influx of solar radiation and strong terrestrial radiation at night). The highest - in the afternoon (14-15 hours). During the year in the Northern Hemisphere, the highest air temperatures on land are observed in July, and the lowest in January. Above the water surface, the daily maximum air temperature is shifted and is observed at 15-16 hours, and the minimum is 2-3 hours after sunrise. The annual maximum (in the Northern Hemisphere) is in August, and the minimum is in February.
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