The weather forecast always says "the trough moves eastward". Why did the trough move eastward?

The terms "trough of low pressure" and "ridge of high pressure" often appear in weather forecast broadcasts. They are actually cyclones and anticyclones.

In the westerlies of the northern hemisphere, the atmosphere fluctuates. The low-pressure trough is a low-pressure trough. The airflow rotates counterclockwise, and the air pressure distribution is low in the middle and high around. The air flows from the periphery to the trough, and the air in the trough converges and rises, forming rainy weather. The peak area of the wave is the ridge of high pressure, the airflow rotates clockwise, the air pressure distribution is high in the middle and low around, the air diverges outward from the center, and the downward flow prevails in the ridge, and the weather is generally sunny. A pair of ridges, one low and one high, form waves. The upper trough ridge system in the westerly belt is called westerly storm.

The high-altitude ridge system is closely related to the weather change on the ground. For example, in the westerly belt of the northern hemisphere, southwest winds usually blow in front of the high-altitude trough. This kind of wind energy transports warm and humid air over the Bay of Bengal and the Indian Ocean to the mid-latitude area of China, creating conditions for the formation of clouds and rain. The northwest wind generally blows behind the high-altitude trough (that is, before the high-pressure ridge), and the ground is a high-pressure area, and the weather turns from cloudy to sunny.

After the formation of the high-altitude ridge, it constantly moves and changes, sometimes strengthening and sometimes weakening. With the movement, change and weakening of the high-altitude ridge, the weather on the ground will also change. Therefore, it is an important content of weather forecast to make a good forecast of the activity change of the upper-altitude trough-ridge system.