When heavy rainfall occurs, the water vapor in the 500hPa layer diverges, and the water vapor in the 850hPa layer converges to form a suction effect, which allows the water vapor to be maintained and transported upwards
When heavy precipitation occurs, the water vapor in 500hPa layer disperses and the water vapor in 850hPa layer converges to form a suction effect, which makes the water vapor maintain and transport upward
When heavy precipitation occurs, the water vapor diverges at 500hPa layer, and the water vapor converges at 850hPa layer to form a pumping action, so that the water vapor can be maintained and transported upward.