What is the relationship between air pressure and temperature?

First, thermal reasons cause hot low pressure and cold high pressure.

Both low pressure and cold high pressure are air pressure relations formed due to thermal reasons. The uneven surface heat and cold is an important reason for the change of air pressure.

1. Thermal low pressure: Thermal low pressure is the dual expression of air temperature and air pressure, and they are related. "Low pressure is caused by heat".

The gas near the ground is heated and expanded, which makes the air density near the ground smaller and forms a low pressure near the ground. This is the "low pressure" caused by thermal reasons. The equatorial low pressure zone is the most typical thermal low pressure zone. In summer in the northern hemisphere, due to the different heat capacities of land and ocean, the temperature of land is higher than that of ocean at the same latitude, resulting in a thermal depression on land, an Asian depression (Indian depression) in Eurasia and a North American depression in North America. In summer afternoon in China (14 o'clock), the weather is "sultry" and there is a lot of convective rainfall, which is caused by high temperature and low pressure.

2. Cold high pressure: Cold high pressure means that the air near the ground is less heated, the temperature is low, the gas contracts and sinks, a large number of air molecules gather near the ground, the air density increases, and the air pressure rises at the same level. For example, point b in the thermal cycle diagram. In the three-circle circulation model map, the polar high pressure area is a typical cold high pressure, the polar temperature is low, and the high-altitude gas sinks. In winter, due to the low temperature in Mongolia and Siberia in the northern hemisphere, the Asian high is formed. Under the influence of this high pressure, the dry air pressure in winter in northern China shows the causal relationship between temperature and airflow. Vertical airflow can be considered as cold airflow and hot airflow. Its formation is different from cyclone and anticyclone (airflow distribution). The central air pressure of cyclone separator is low pressure. Under the action of horizontal pressure gradient force, the atmosphere flows from all directions to the center, and a large number of central gases gather, thus forming an updraft in the vertical direction, which can be called pushing airflow. On the contrary, the center of the anticyclone is high pressure, the central gas flows around, and the airflow in the vertical direction of the center sinks to supplement it, which can be called compensation airflow. Whether it is pushing airflow or compensating airflow, its causes are different from those of cold and hot airflow, and they are all caused by power.

Second, the dynamic reasons caused by hot high pressure and cold low pressure

Subtropical high pressure area (hot high pressure) and subtropical low pressure area (cold low pressure) are pressure areas formed due to dynamic reasons.

1. Thermal high pressure: the subtropical high pressure zone of 30 north and south latitude is a typical thermal high pressure. Heat refers to low latitudes, and high pressure refers to gas accumulation. There is no causal relationship between the two. If there is, it can be said that high pressure has aggravated the "heat". The steady airflow from the equator in the northern hemisphere moves towards the polar region, and gradually turns into the west wind under the action of geostrophic bias current (no friction). The airflow gathers over 30 degrees north and south latitude, and finally sinks near the ground, forming a subtropical high pressure zone. Under the control of subtropical high, some areas in the world have formed a tropical desert climate, which is hot and dry all year round, such as the Sahara desert in Africa and the Australian desert. In July and August in China, when the front rain belt moved to the northeast and north China, the Yangtze River basin was under the control of subtropical high, forming a summer dry weather, and the continuous high temperature did not drop, which can be described as "true heat"!

2. Cold depression: At latitude 60, the climate is very cold because it is located at high latitude. Here, the warm and hot air flow from low latitude meets the cold air flow from the polar region, and the gas converges and rises, forming a high altitude pressure and a near-surface low pressure, that is, a sub-polar low pressure region.

Third, the influence of topography on temperature and pressure. The topography of Asia is high in the middle and low around. Known as the "roof of the world", the Qinghai-Tibet Plateau is located in the middle of China's topography. Because of the high terrain and altitude, the air on the plateau is thin, the temperature is low, and it is cold and oxygen-deficient. Near the ground, the air pressure is low because of the low air density. We know that because the boiling point is directly proportional to the air pressure, the eggs boiled on the plateau are not cooked even if they reach the boiling point. The temperature is low and the air pressure is low, which we call "cold low pressure". Therefore, people in plain areas often have some altitude sickness when they first arrive at the plateau.