What effect does atmospheric circulation have on climate?

Atmospheric circulation guides the generation and movement of air masses, fronts, cyclones and anticyclones with different properties, which is of great significance to the formation of climate. The equatorial belt is controlled by low pressure all the year round, mainly by updraft, with abundant precipitation and dense forests; On the contrary, under the control of high air pressure, the subtropical zone, which is dominated by subsiding airflow, has little precipitation and forms a desert. Air masses from high latitudes or inland areas are cold and dry, while air masses from low latitudes or oceans are mild and humid. When an area is controlled by two different air masses in a year, the climate has obvious seasonal changes. On a global scale, atmospheric circulation has carried out a lot of heat and water transfer between high latitude and low latitude and between land and ocean. In the meridional heat transfer, the heat transferred by atmospheric circulation accounts for about 80%.

Atmospheric circulation also plays an important role in water transport in the atmosphere. The quantity, direction and speed of moisture transport in the atmosphere are closely related to the circulation situation. In the northern hemisphere, the water vapor is transported to the middle and high latitudes by the westerly airflow around 30 north latitude. It was transported southward by the trade winds to low latitudes. There are two main types of water vapor transport in China: one comes from the Bay of Bengal, the Indian Ocean and the South China Sea and enters China with the southwest airflow; The other comes from the Atlantic Ocean and the Arctic Ocean and enters China with the northwest airflow. The transportation capacity of the south branch is large, while the transportation capacity of the north branch is small. The dividing line between Huanghuai and Qinling is basically equivalent to the dividing line between humid and semi-humid climate.

The formation of precipitation is inseparable from the weather system, the input of clouds and water vapor, and the vertical upward movement of air. All this is closely related to the circulation situation. For example, the amount of precipitation is related to the amount of water vapor entering various weather systems. The inflow of warm and humid equatorial airflow can produce 100 mm precipitation in a few hours or an hour; The precipitation of thunderstorms can be proportional to the amount of water vapor flowing into cumulonimbus clouds.

Atmospheric circulation plays an extremely important role in the formation of climate. Under the control of different circulation, there will be different climates. Even if the intensity of the same circulation system changes, the climate in the area it controls will change. If the circulation is abnormal, the climate will be abnormal.

The change of atmospheric circulation can be expressed by the intensity and transformation of meridional circulation and zonal circulation. There is an average condition for the change of atmospheric circulation in a certain area over a long period of time. When the duration and switching frequency of meridional circulation and zonal circulation in a certain period of a year greatly exceed the average situation in that period, the atmospheric circulation in a certain period of a year is called circulation anomaly. For example, the main circulation characteristics of 1972 show that there are two stable and powerful long-wave troughs in the northern hemisphere, which are blocking high pressure over Europe and the North Pacific Ocean from February to March, a low trough over the western Atlantic Ocean and Asia, blocking high pressure over Europe and western North America from May to September, and a large trough over eastern North America and East Asia. Throughout the year, the North Atlantic, the North Pacific, eastern and northeastern Europe and most parts of western Asia are under the control of strong blocking high, so 1972 is an abnormal circulation year for the northern hemisphere.

Due to the abnormal circulation, the numerical values of meteorological elements such as pressure field, temperature field and humidity field will inevitably be obviously deviated, which will lead to abnormal precipitation, cold and warm, drought and flood, continuous cold and other climate anomalies.

In a word, atmospheric circulation plays an important role in climate formation. It not only affects the zonality of climate through the zonal distribution of circulation, but also expands the influence range of land, ocean and terrain through the transport of heat and moisture, and destroys the zonality of climate. When the circulation situation tends to the long-term average situation, the climate is normal; When the circulation situation is abnormal in individual years or seasons, it will directly affect the weather and climate of that period and make it abnormal.