Is it hot or cold?

Cold weather is high pressure, low temperature in winter, air cooling and sinking, forming high pressure, that is, cold high pressure; When the temperature is high in summer, the air is heated and expanded, forming a low pressure, that is, a thermal low pressure.

Cold high pressure mostly occurs in the middle and high latitudes of the mainland and is mainly composed of cold air, so it is customarily called "cold high pressure" or cold anticyclone. Its intensity gradually weakens from the ground to the sky and becomes a ridge of high pressure at a height of three or four kilometers. According to statics, the intensity of cold high pressure decreases with the increase of height, and turns into cold low pressure at high altitude. Therefore, it is a relatively shallow weather system with an average thickness of less than 3km. Cold high pressure often appears behind the high altitude trough. Due to the mass convergence behind the trough, the high pressure below it is maintained and strengthened, and it will move under the guidance of high-altitude airflow. Under the guidance of the northwest airflow behind the trough, the whole high pressure system will go south, or split into several high pressures, in which the strong high pressure can form a cold wave process.

Thermal depression is a kind of low pressure without front, which is a low pressure area formed by a single thermal factor in the lower troposphere. Due to the difference between land and sea, the air in the higher temperature area is heated, resulting in low pressure. Every spring (February to May), due to the weakening or interruption of the winter wind, when the height from India to Myanmar is controlled by the southwest airflow in front of the south branch westerly ridge, the airflow in the mountains and plains keeps getting warmer and the ground pressure decreases, so that a dry-hot low-pressure system (also known as southwest thermal low-pressure) often appears from the northwest of Indo-China Peninsula to the southwest of China. Once it is strengthened eastward, it will often be in southern Sichuan, Yunnan, Guangxi and Leizhou, Guangdong.