Basic information of squall line

squall line

Definition: Squall line is a strong convective cloud belt formed by many thunderstorm cell (including several supercells) arranged horizontally. Its horizontal scale is about tens to hundreds of kilometers long and lasts for several hours to more than ten hours. When the squall line appears, it is usually accompanied by thunderstorms, strong winds (or tornadoes), hail and so on. , great energy, strong destructive power. 1. Meaning: thunderstorm cell (including several supercells) is horizontally arranged to form many strong convective cloud belts.

2. Horizontal scale: tens to hundreds of kilometers long and tens to 200 kilometers wide.

3. Life history: a few hours to more than ten hours.

4. Weather phenomena: thunderstorms, strong winds, hail and tornadoes. Squall lines are thunderstorms arranged in bands. Discontinuous lines with small range, short life history, air pressure and wind. Its width ranges from less than one kilometer to several kilometers, the widest to tens of kilometers, the length generally ranges from tens of kilometers to hundreds of kilometers, and the maintenance time ranges from several hours to more than ten hours. The squall line appeared unexpectedly. When the squall line crosses the border, the wind direction changes suddenly, the air pressure rises and the temperature drops sharply. At the same time, the combination of strong wind, heavy rain and hail will cause serious disasters. In the temperate zone of the northern hemisphere, there is a southerly wind before the squall line, and then it turns into a westerly wind or a northerly wind. The wind speed after the squall line is generally more than ten meters per second, and it can exceed 40 meters per second when it is strong. The weather is better before the squall line, and the precipitation area is mostly behind the squall line. The temperature difference between the two sides of the squall line can reach above 65438 00℃.

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 strongly unstable airflow, and are also related to high-altitude rapids, which mostly occur in areas with large vertical shear of rapids or winds. The squall line is located in the cold front of thunderstorm cloud sinking, and its spatial structure is similar to that of cold front. It is the interface between cold and warm air. When crossing the border, with the sudden change of wind direction, the wind force increases sharply, the temperature drops and the air pressure rises. In addition, it often appears near the cold front and is easily confused with the cold front. Although there are many similarities between squall line and cold front, there are also great differences, so squall line is often called "false cold front" or "false cold front"

The main differences between them are as follows: 1. The cold front is the interface of two air masses with different properties, which is a large-scale system, while the squall line is a mesoscale system formed and spread in the same air mass.

2. The weather phenomenon near the squall line is much more serious than that near the cold front, and the variability of meteorological elements is much greater than that near the cold front;

3. The squall line generally moves faster than the cold front, sometimes even 2-3 times faster than the cold front;

4. The squall line intensity has obvious diurnal variation, but the cold front does not.