Assuming that the earth's rotation is uniform and the sun shines directly on the equator, the factors that cause atmospheric motion are uneven heating at high and low latitudes and geostrophic deflection.
Seen from the northern hemisphere, the warm air rising in the equatorial region moves northward from above the equator to above the North Pole (southerly wind) under the action of pressure gradient force, and gradually changes from southerly wind to southwest wind under the influence of geostrophic deflection force, and accumulates above 30 N, thus generating a downward airflow, raising the near-surface pressure and forming a subtropical high area.
Near the ground, under the pressure gradient force, the atmosphere flows from the subtropical high to the north and south. Under the influence of geostrophic deflection, the south tributary gradually changes from north wind to northeast wind, which is called northeast trade wind. Similarly, the southeast trade winds will also form in the southern hemisphere, and the northeast trade winds and southeast trade winds in the southern hemisphere will meet and rise near the equator, forming a low-latitude circulation circle between the equator and the subtropical region.
Near the ground, an airflow from the subtropical high to the north gradually turns to the southwest wind under the action of geostrophic bias, that is, the prevailing west wind. Under the influence of geostrophic bias, the airflow (north wind) flowing south from the polar high pressure zone gradually shifts to the right to form the northeast wind, that is, the polar east wind.
The warm prevailing westerly winds collide with the cold polar easterly winds near 60 N, forming a warm front (polar front) near the ground. The warm and light airflow climbs above the cold and heavy airflow, forming a subtropical updraft.
Under the influence of geostrophic bias, the updraft gradually changed from the north wind to the northeast wind, and collided with the southwest wind from the equator around 30 N to form a cold front, which strengthened the downdraft in the subtropical high area and further increased the pressure in the subtropical high area.
Therefore, a mid-latitude circulation circle is formed between the subtropical region and the sub-polar region; A northbound air current sinks in the Arctic, forming a high latitude circulation circle between the sub-polar region and the polar region. Because the sub-polar updraft reduces the air pressure near the ground, a sub-polar low pressure area is formed.
Similarly, there are three circulation circles in the southern hemisphere: low latitude, middle latitude and high latitude. Therefore, near the ground, * * * formed seven pressure zones and six wind zones.
Extended data:
The three cycles are divided into the first cycle, the second cycle and the third cycle:
1, the first circulation circle is Hadley circulation, also known as trade wind circulation circle or tropical circulation circle;
2. The second circulation circle is Ferrer circulation, also called mid-latitude circulation circle;
The third circulation circle refers to the polar circulation circle.
The triple circulation circle is an ideal model of atmospheric circulation, and the main models of atmospheric circulation are as follows:
1, mean zonal circulation
Refers to the prevailing zonal airflow in the atmosphere, centering on the polar regions and rotating around them. This is the most basic state of atmospheric circulation. As far as the average zonal circulation in the troposphere is concerned, easterly winds prevail in low latitudes, which is called easterly belts (due to the rotation of the earth, most of the northern hemisphere is northeast trade winds, and most of the southern hemisphere is southeast trade winds, so it is also called trade winds).
The westerly winds prevail in the middle and high latitudes, which are called westerly belts (its intensity increases with height and reaches the maximum near the tropopause, which is called westerly jet); There is also a shallow weak easterly wind in the polar region, which is called polar easterly wind.
2. Average horizontal circulation
Refers to the wavy airflow prevailing on the horizontal plane in the middle and high latitudes (also known as the average trough ridge). Usually there are three waves in winter and four waves in summer in the northern hemisphere. The transition between the three waves and the four waves represents the seasonal change.
3, the average diameter cycle
Refers to the motion state composed of meridional motion and vertical motion of the atmosphere on the north-south vertical section. Generally, the radial circulation in the troposphere has three circles:
Low latitude is positive circulation or direct circulation (air flow rises at the equator, goes north at high latitude, sinks at middle and low latitude, and goes south at low latitude), also known as Hadley circulation; Mid-latitude is anti-circulation or indirect circulation (low latitude airflow sinks, low altitude goes north, high latitude rises, high altitude goes south), also called Ferrer circulation; The polar region is a weak positive circulation (polar sinking, low altitude to the south, high latitude rising, high altitude to the north).
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