What happens when many swallows suddenly appear in the sky and fly?

The air pressure is low, the heavy rain is coming, insects fly around in the air because of the air pressure, and swallows feed for themselves and swallows in time. Suddenly, many swallows are flying around in the sky because of the change of air pressure. The low pressure causes swallows to fly around, because swallows are most sensitive to the atmospheric pressure field.

Generally speaking, areas with high ground pressure are often sunny, and areas with low ground pressure are often rainy. The air pressure in a certain area is higher than the surrounding air pressure, which is called high pressure area; The air pressure in a certain area is lower than the surrounding air pressure, which is called low pressure area. On the same horizontal plane, if the air pressure distribution is uneven, the air will flow from the high pressure area to the low pressure area. Therefore, the air pressure in a certain area is high, and the air in this area flows out in the horizontal direction. The air above the high pressure area will drop. Because the atmospheric pressure increases with the decrease of altitude, when the air at high altitude falls, the pressure is increased, the volume is decreased, the temperature is increased, and the condensate in the air evaporates and dissipates. Therefore, the high-pressure central area is not conducive to the formation of clouds and rain, and it is often sunny. If the air pressure in a certain area is low, the air in the surrounding area will flow into the area horizontally, causing the air in the area to rise, the rising air will expand due to the pressure drop, the temperature will drop, and the water vapor in the air will condense. Therefore, it often rains in the central area of low pressure. Because the air pressure is closely related to the weather, each meteorological station observes the local air pressure at the same time every day and reports it to the meteorological center as one of the bases for weather forecast.