1. Formation process of thermal cycle
Uneven heat and cold near the ground → vertical movement (rising or sinking) of air → pressure difference on the same horizontal plane → horizontal movement of air → formation of thermal cycle. As shown in the figure below:
2. The formation of thermodynamic cycle-one key, two movements and three differences.
"A key" (uneven heat and cold is the key to forming a thermal cycle)
(1) The same underlying surface, considering the latitude difference.
(2) Considering the difference of heat capacity for different underlying surfaces.
"two kinds of sports"
Caused by uneven cold and heat near the ground → caused by vertical motion of the atmosphere → caused by pressure difference on the same horizontal plane → caused by horizontal motion of the atmosphere.
"Three differences"
(1) The air rises and falls differently: hot air rises near the ground and cold air sinks near the ground.
(2) The air pressure on the same plane is different: hot low pressure and cold high pressure-high pressure is formed near the cold ground and low pressure is formed near the hot ground.
(3) The air pressure in space is different: the air pressure near the ground is opposite to that at the high altitude-high pressure near the ground and low pressure at the high altitude; Low pressure near the ground and high pressure at high altitude.
3. Three common forms of thermal cycle
(1) urban wind
Due to the release of a large amount of man-made heat from people's production and life in the city, the urban temperature and air are rising continuously, which forms urban thermal circulation with the downward flow from the suburbs, and the downward flow brings pollutants from the suburbs from the near surface to the city center, seriously polluting the urban environment. Therefore, in order to reduce urban pollution, how to reduce the use of fossil fuels and how to arrange suburban industries and satellite cities has become a common concern.
Green belts are generally arranged at the sinking place, within the sinking distance of airflow, and satellite cities or heavily polluted factories are arranged outside the sinking distance.
(2) Land and sea breeze
During the day, under the irradiation of the sun, the temperature on the land rises rapidly, the temperature is higher than that on the sea, the air expands and rises, the air pressure at high altitude is higher than the original air pressure, and the air flows into the sea from the mainland; The low pressure is formed on the land near the surface, while the high pressure is formed on the ocean. Because of the low temperature, the low-level air flows from the ocean into the mainland, forming a sea breeze. At night, the thermal effect of the atmosphere is opposite to that during the day, forming a land wind.
(3) Mountain breeze
During the day, due to the intense warming of the air on the hillside, warm air rises along the hillside, forming a valley wind (as shown in Figure A). At night, the air on the hillside cools rapidly and the density increases, so it slides down the hillside and flows into the valley, forming a mountain wind (as shown in Figure B).
The direction of urban wind circulation does not change with time, because the temperature in urban areas is always higher than that in suburbs. However, the flow directions of sea-land wind circulation and mountain-valley wind circulation change in opposite directions with the change of day and night, because the air pressure between land and sea and valley changes with the change of day and night.
Difficult point analysis
1. Distinguish isobars from isobars.
The distribution of air pressure is represented by the distribution of isobars on the contour plane. Isobars are many intersecting lines formed on the isobar plane when an isobar with the same height cuts several different isobars in the air (because the air pressure decreases from the ground up, there are many isobars with decreasing values from bottom to top). Similar to the contour principle in terrain distribution;
The raised area on the isobaric surface corresponds to the high value area of isobaric line, indicating high pressure, and vice versa, as shown in the following figure. If the local air pressure is equal, the isobar surface is a contour surface, and there is no isobar on the contour surface. It can be simply understood that the isobaric surface is the pressure change in the vertical direction, and the isobar is the pressure change in the horizontal direction.
2. Reading skills of isobaric surface (line) diagram
Use the following figure to illustrate the basic skills and problems that should be paid attention to when reading isobaric surfaces:
(1) from the definition of isobaric surface, pa ′ = Pb ′ =1000 hectopascals, and PD ′ = PC ′ = 500 hectopascals.
(2) From the concept of air pressure, in the air columns L 1 and L2, the closer to the ground, the longer the upper air column and the higher the air pressure value, so the air pressure value decreases with the elevation, and then PA ′ >: PA, PD & gtPD' ′, PB & gtPB' ′, PC ′ >; Personal computer. From this, we can draw that the relationship between air pressure and altitude is that air pressure decreases with the elevation.
(3) Point A is a low-pressure area relative to Point B, and Point C is a low-pressure area relative to Point D, and the isobaric surface near it is depressed downwards; Point b and point d are high pressure areas, and the isobaric surface protrudes upward. From this, we come to the conclusion that the pressure level in the same horizontal plane is "convex high and concave low" with the shape of isobaric surface.
(4) Based on the above analysis, the order of pressure values at four points A, B, C and D should be PB & gtPA & gtPD & gtPC, and then we can know that the direction of atmospheric circulation in the illustrated area is B → A → D → C.
(5) The convexity and concavity of the isobaric surface are mainly related to the heat and cold of the underlying surface. The air pressure difference between A and B is due to the rising and sinking movement of air caused by the difference of ground thermal conditions. When the ground temperature is high, the air expands and rises when heated, and the ground pressure is low; When the ground temperature is low, the air cools, contracts and sinks, and the ground pressure is high. So we can infer the cold and hot situation of the ground according to the air pressure on the ground. The low air pressure near the ground at A indicates that the air is heated, and it is concluded that the ground temperature is high.
3. Judge the air pressure according to the air pressure distribution law.
(1) On the same horizontal plane, the air pressure is low where the temperature near the ground is high, and high where the temperature is low, which mainly depends on the air density. Where the temperature is high, the air expands and rises, and the air density near the ground is low and the air pressure is low; Where the temperature is low, the situation is just the opposite.
(2) In the vertical direction, with the increase of altitude, the air pressure decreases, which depends on the length of air column at different altitudes. As shown in the following figure: the air column height on the plane where point A is located is h2, and point B is h 1, h2>H 1, so the air pressure at point A is higher than that at point B..
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