Complete detailed information on atmospheric circulation

Atmospheric circulation generally refers to a world-scale, large-scale atmospheric operation phenomenon. It includes both average states and instantaneous phenomena. Its horizontal scale is more than thousands of kilometers, its vertical scale is more than 10km, and its time scale is more than several days. It is also a state of large-scale movement of the atmosphere. The atmospheric movement of a certain large-scale region (such as the Eurasian region, the hemisphere, the world), a certain atmospheric layer (such as the troposphere, stratosphere, mesosphere, and the entire atmosphere) over a long period of time (such as months, seasons, years, and years) The average state or the changing process of atmospheric movement in a certain period of time (such as a week, a rainy season) can be called atmospheric circulation. Basic introduction Chinese name: Atmospheric circulation Foreign name: atmospheric circulation Category: Natural phenomenon Characteristics: orbiting the earth along the latitudinal direction Discipline: Atmospheric science Characteristics: global movement, large-scale causes, characteristic description, main methods, average latitude Circulation, mean horizontal circulation, mean radial circulation, manifestation, latitudinal circulation, research significance, the first reason is solar radiation, which is the source of atmospheric motion energy on the earth. Due to the rotation and revolution of the earth, the surface of the earth receives solar radiation energy is uneven. There are many tropical regions and few polar regions, thus forming a thermal circulation in the atmosphere. The second is the rotation of the earth. The atmosphere moving on the surface of the earth will be deflected by the geostrophic deflection force. Third, the distribution of land and sea on the earth's surface is uneven. The fourth is the mutual exchange of heat and momentum between the north and south of the atmosphere. The above factors constitute the average state and complex and changeable forms of the earth's atmospheric circulation. The fundamental reason for the different climates in different places on the earth is the uneven solar radiation energy received by the earth's surface, which results in the flow of the atmosphere. Heat and moisture are transported to another place along with the circulation, causing different places to have different climates. The thermal difference tends to be uniform. In the troposphere, the horizontal temperature gradient is from the equator to the poles. If the ground conditions are basically uniform, the air will flow from the equator to the poles, while on the surface it will flow from the poles to the equator, forming a large radial circulation. Due to the biasing force of the earth's rotation, the airflow above the friction layer is not in the radial direction, but in the latitudinal direction, causing the airflow moving from the equator to the poles to converge at about 30° latitude, causing the air to sink. , forming a subtropical high-pressure area. The airflow in the high-pressure area diverges in the lower layer, causing the air to flow north and south along the surface. In the Northern Hemisphere, air flowing southward creates northeasterly winds, and air flowing northward creates southwesterly winds. This southwesterly wind converges with the cold air from the polar regions at around 60° north latitude, forming a subpolar low pressure area. The air that converges and rises in this low-pressure area diverges when it reaches high altitudes, and flows north and south respectively. The one flowing toward the poles converges at the poles, where it creates a downward flow of air, forming a polar high-pressure area. In this way, three circulations are formed between the equatorial low pressure area, the subtropical high pressure area, the subpolar low pressure area and the polar high pressure area. These three circulations are not combined and can flow from one circulation to another. and change its own characteristics. Characteristic Description From the perspective of the global average zonal circulation, in the troposphere, the most basic characteristics are: the atmosphere generally moves around the earth in the latitudinal direction, and easterly winds often prevail in low latitudes, called easterly belts, also known as trade winds. The northern hemisphere has northeasterly trade winds, while the southern hemisphere has southeasterly trade winds. In the mid-latitudes, westerly winds prevail and are called westerlies. The latitude it spans is wider than that of the easterly wind. The intensity of westerly winds increases with latitude. The maximum wind occurs near 200 hectopascals at 30°-40°, which is called the planetary westerly jet. Near the poles, there are shallow, weak easterly winds at low levels, which are called polar easterlies. Atmospheric circulation From the perspective of global radial circulation, the average movement in the north-south direction and the vertical direction constitutes three meridional circulations: 1. The positive circulation at low latitudes is the Hadley cell. The air in the near-equator area is heated and rises. It runs northward at high levels and gradually turns to westerly winds. There is an airflow sinking around 30°N, and it is divided into two branches at low levels. One flows southward back to near the equator, and the other Move north. 2． A counter circulation or indirect circulation, the Ferrel circulation, is formed at mid-latitudes. . 3． Positive circulation in the polar region, that is, the pole sinks and rises near 60°N, thus forming a positive circulation, but it is weak. There are often polar front activities between mid-latitudes and low-latitudes. Atmospheric circulation usually includes three parts: mean zonal circulation, mean horizontal circulation and mean radial circulation. The main method is the mean zonal circulation, which refers to the prevailing zonal air current centered on and rotating around the pole. This is the most basic state of atmospheric circulation. As far as the tropospheric mean zonal circulation is concerned, the prevailing easterly wind in low latitudes is called East wind belt (due to the rotation of the earth, the northern hemisphere mostly has northeast trade winds, and the southern hemisphere mostly has southeast trade winds, so it is also called the trade wind belt); the westerly wind prevails in mid- and high latitudes, called the westerly belt (its intensity increases with height, It reaches a maximum value near the tropopause, which is called the westerly jet stream); there are also shallow and weak easterly winds in the poles, which are called polar easterlies. The average horizontal circulation of the atmospheric circulation diagram refers to the wavy airflow superimposed on the average zonal circulation (also known as the average trough and ridge) prevailing on the horizontal plane at mid- and high latitudes. Usually there are 3 waves in the northern hemisphere in winter and 4 waves in summer. The three waves are the same as those in the summer. Transitions between four waves characterize seasonal changes. Mean radial circulation refers to the motion state composed of meridional and vertical motion of the atmosphere on the north-south-vertical section.

Usually, there are three circles of radial circulation in the troposphere: the positive circulation or direct circulation at low latitudes (the airflow rises at the equator, heading north at high altitudes, sinks at mid- and low latitudes, and heads south at low altitudes), also known as the Hadley cell; mid-latitudes It is a countercirculation or indirect circulation (the mid- and low-latitude air sinks, moves northward at low altitudes, rises at mid-high latitudes, and moves southward at high altitudes), also known as the Ferrel circulation; the poles are weak positive circulation (the airflow sinks at the poles, moves southward at low altitudes, and moves southward at low altitudes, Rising at high latitudes and heading north at high altitudes). The main manifestations of atmospheric circulation are: global-scale east-west wind belts, three circulations (Hadley cell, Ferrel cell and polar circulation), steadily distributed mean troughs and ridges, high-altitude jet streams and large disturbances in westerly belts, etc. . Atmospheric circulation is not only an important mechanism for the exchange of physical quantities such as heat, moisture, angular momentum, and energy exchange in the earth-atmosphere system, but also an important result of the transportation, balance, and conversion of these physical quantities. The non-uniform distribution of solar radiation on the earth's surface is the driving force behind atmospheric circulation. Atmospheric circulation chart Atmospheric circulation constitutes the basic situation of global atmospheric movement, is the dominant factor in global climate characteristics and large-scale weather conditions, and is also the background of weather system activities at various scales. Latitudinal circulation The latitudinal circulation is also called the planetary wind system or the pressure belt wind belt. The wind belts and surge currents on the earth are driven by three convective circulations (three-circle circulation): Hadley cell (low latitudes), Ferrel cell (middle latitudes). latitude) and polar circulation. Sometimes several circulations of the same type (such as at low latitudes) can exist simultaneously at the same latitude (such as the equator), moving randomly over time, merging and splitting with each other. For simplicity, the same circulation is usually treated as one circulation. Low-latitude circulation The operation of low-latitude circulation is relatively clear. The atmospheric circulation patterns described by George Hadley (1685-1768) to explain the formation of trade winds are consistent with observations. This is a closed circulation that begins with warm, moist air rising from the equatorial low-pressure area, rising to the tropopause, and heading poleward. Until about 30 degrees north and south latitude, this air sinks in the high-pressure area. Part of the air returns to the ground and then returns to the equator, forming trade winds and completing low-latitude circulation. Atmospheric Circulation Chart Low-latitude circulation is basically active in the tropics. Guided by the direct sun point, it travels back and forth between the north and the south in a half-year cycle. The Polar Gyre is also a simple system. Although the air here is cooler and drier than the air at the equator, there is still enough heat and moisture to conduct convection and complete the thermal cycle. The activity range of this circulation is limited to the troposphere, and the highest is only to the tropopause (8 kilometers). Poleward airflow is mainly concentrated in the air, while equatorial airflow is mainly concentrated on the ground. When the air reaches the polar range, its temperature has been greatly reduced. It sinks in this high-pressure, dry and cold area, and is deflected westward by the geostrophic deflection force, forming a polar easterly wind. The outflow of the polar circulation forms a Rossby wave with a simple harmonic waveform. These ultralong waves play an important role in influencing the flow direction of the midlatitude circulation and the tropopause surge. The polar circulation acts like a radiator, balancing the heat surplus in low-latitude circulation areas and balancing the heat budget of the entire Earth. It can be said that in mid-to-high latitudes, the polar circulation is the main cause of the weather here. While Canada and Europe experience occasional storms in the summer, the real cold is felt in the winter when the high pressure in Siberia brings cold. In fact, it was the airflow in the polar high pressure area that caused the East Antarctic Research Station to record the lowest temperature ever recorded on Earth in 1983: minus 89.2 degrees Celsius. The low-latitude circulation has the same characteristics as the polar circulation: both occur due to surface temperature and are directly related to thermal energy. At the same time, its thermal characteristics overwhelm the weather phenomena it produces. The large amount of heat energy transmitted by low-latitude circulation and the heat-absorbing ability of the giant polar circulation prevent short-term meteorological effects from being received by the system and cannot be produced except under special circumstances. In areas other than 30 degrees to 60 degrees latitude, you cannot feel the mid-latitude air pressure center endlessly turning from low to high and then back to low every day. These two circulations are quite stable. Although they strengthen and weaken from time to time, they will not completely disappear. Mid-latitude circulation The mid-latitude circulation proposed by William Ferrel (1817-1891) is a secondary circulation that depends on the other two circulations to appear. For example, a ball bearing in between appears due to the eddy cycle (high and low pressure areas) in mid-latitudes. Therefore, this area is sometimes called the "mixed area". To the south it lies on the low-latitude circulation, and to the north it floats on the polar circulation. The trade winds can be found beneath the low latitude circulation, and likewise the westerlies can be found beneath the mid latitude circulation. Unlike the low-latitude circulation and the polar circulation, the mid-latitude circulation is not a truly closed cycle, but the focus is on the westerly belt. Unlike the trade winds and polar easterly winds, the associated circulations defend their dominance in the region. Prevailing westerly winds are not so lucky and are often at the mercy of passing weather systems. Above, westerly winds usually dominate, but at the surface the wind direction can change suddenly at any time. From the reference frame (perspective) of the northern hemisphere, low pressure to the north or high pressure to the south tend to maintain or even accelerate the flow speed of the westerly wind; however, a cold front passing through the local area may reverse this situation. The high pressure heading north brings easterly-dominated airflow, which often lasts for several days. The movement of air masses is one of the underlying characteristics of midlatitude circulation.

The surge absorbs air rising from the surface low-pressure area, and its location is one of the reasons that affects the position of the air mass (you can see on the weather map that the surface low-pressure area moves with the surge). The overall flow direction of surface wind is from 30 degrees to 60 degrees of latitude. However, the flow direction over the mid-latitude circulation has not yet been fully defined. On the one hand, the circulation itself is between the polar circulation and the low-latitude circulation, and there is no strong heat or cold source to promote convection. On the other hand, surface vortices also have an impact on the upper environment. causing destabilizing effects. Research significance: The state of large-scale movement of the atmosphere. The atmospheric movement of a certain large-scale region (such as the Eurasian region, the hemisphere, the world), a certain atmospheric level (such as the troposphere, stratosphere, mesosphere, and the entire atmosphere) over a long period of time (such as months, seasons, years, and years) The average state or the changing process of atmospheric movement in a certain period of time (such as a week, a rainy season) can be called atmospheric circulation. Atmospheric circulation diagram Atmospheric circulation is an important mechanism for completing the transportation and balance of angular momentum, heat and moisture in the earth-atmosphere system, as well as the mutual conversion between various energies. It is also an important result of the transportation, balance and conversion of these physical quantities. Therefore, studying the characteristics of atmospheric circulation, its formation, maintenance, changes and effects, and mastering its evolution rules are not only an indispensable and important part of human understanding of nature, but will also help improve and increase the accuracy of weather forecasts, and are helpful It is conducive to exploring global climate change and making more efficient use of climate resources. Atmospheric circulation usually includes three parts: mean zonal circulation, mean horizontal circulation and mean radial circulation.