What is a weather system?

Weather system usually refers to the atmospheric motion system with typical characteristics, such as high pressure, low pressure, high pressure ridge and low pressure trough, which cause the change and distribution of weather.

So, what are high pressure and low pressure? What are high-pressure ridges and low-pressure troughs? The so-called high pressure is "high pressure". It is an area where the atmospheric pressure is higher than the atmospheric pressure at the same height around it. This kind of high pressure is represented by the isobath on the designated isobath plane or the contour lines on the designated isobath on the weather map, which enclose the higher air pressure value or height value in the middle. Low pressure is the antonym of high pressure, which is an area in the atmosphere where the air pressure is lower than the same height.

Here, it is necessary for us to introduce the knowledge of isobar and isobar. The so-called isobar is a closed line formed by connecting places with equal air pressure in a certain time on the plane. Isobaric surface is a surface composed of points with equal pressure, that is, a surface composed of points with equal air pressure in space. Because of the same height, the air pressure in different places is not equal, and the isobaric surface is not flat in space, but fluctuates like a terrain.

A weather system with low air pressure on three sides and high air pressure on one side is called ridge for short. The ridge of high pressure is a long and narrow part of high pressure protruding outward, or a group of unclosed isobars protruding to the low pressure side. In the ocean ridge, the connecting line at the maximum bend of each isobar is called the ridge line. The air pressure is the highest along the ridge line and decreases to both sides. The spatial isobaric surface near the ridge is similar to the ridge. The part of the weather map where the high-voltage line extends in a certain direction and is slightly "U" or "N" shaped is called the high-voltage ridge. Low pressure trough is the antonym of high pressure ridge.

All kinds of weather systems have certain time and space scales, and they are intertwined and influence each other. The combination of many weather systems constitutes a large-scale weather situation and hemispheric and even global atmospheric circulation. The weather system is always in the process of rebirth, development and extinction, and there are corresponding weather phenomena in different development stages. Therefore, the weather and weather changes in a region are related to the weather system and its development stage, and are the comprehensive results of atmospheric dynamic and thermal processes.

All kinds of weather systems are formed, developed and evolved in a certain atmospheric circulation and geographical environment, and all reflect the environmental characteristics of a certain region. For example, the polar regions and their surroundings are covered with ice and snow all year round, and the air is cold and dry. This unique geographical environment has become the background condition for the formation and development of polar low-altitude cold high pressure and high-altitude polar vortex and low trough. It is a necessary condition for the emergence and development of convective weather system that the equatorial and low latitudes are hot and humid all the year round and the atmosphere is unstable. Middle and high latitudes are areas where cold and warm air currents often meet. Cold and warm air masses not only come and go frequently, but also have unstable baroclinic, which is an important basis for the formation and development of frontal and cyclone systems. The formation and activities of weather system will in turn have a profound impact on the structure and evolution of geographical environment.