What is the difference between squall line and cold front weather, and what is the relationship with frontal cyclone?

"Squall line" refers to the weather phenomenon that the wind direction changes suddenly and the wind speed increases sharply. When it appears, the temperature will drop, accompanied by rainfall. The squall line is a linear mesoscale thunderstorm group, not a cold front weather.

Conditions for the formation of squall line-The collision of two air masses with different characteristics is a necessary condition for the formation of squall line. The most common situation is cold air mass collision, but sometimes dry air collides with wet air. In either case, there will be wind shear in the sky. When the direction and speed of two adjacent winds are different, wind shear will occur. It can be an updraft leaving the cloud top.

Although squall line belongs to mesoscale weather system, its formation and development are related to a certain large-scale weather situation. Squall lines mostly appear behind the high-altitude trough and in the south or southwest of the cold vortex; Sometimes it appears in the low-altitude southwest warm and humid airflow in front of the upper trough and the northwest edge of the subtropical high; Some squall lines are produced in the inverted trough or easterly wave of typhoon front. According to the corresponding ground conditions, most squall lines are related to frontal activities, mainly occurring in the warm area before the ground cold front 100 ~ 500 km.

Squall lines are generated in stratification with strong potential instability (see atmospheric static stability). This unstable stratification is mostly caused by the cold advection in the middle or upper layer superimposed on the warm and humid airflow in the lower layer. Squall lines are also related to high-altitude rapids, which often occur in areas where the vertical shear of rapids or winds is large.