Why does lightning appear when the sky is overcast and windy?

Lightning in atmospheric science refers to the strong discharge phenomenon in the atmosphere. Lightning is more common in thunderstorm weather in summer. Its occurrence is related to the movement intensity of airflow in the cloud. According to some data, lightning may also occur when it snows in winter, that is, it thunders and snows, but the probability of occurrence is quite small. If a serious volcanic eruption occurs, or an atomic bomb explodes to produce haze clouds, lightning may appear in the air due to short circuit.

Lightning discharge usually produces lightning. The cause of lightning is generally thought to be that various particles in the cloud accumulate charges due to collision and friction. When the amount of charge reaches a certain level, which is equivalent to the voltage between clouds or between clouds and ground reaching or exceeding a certain value, the local electric field strength will reach or exceed the electrical breakdown strength of air at that time, thus causing discharge. Electricity in the air rapidly heats the expanding air through discharge, and is compressed into plasma due to expansion, thus generating a special component of lightning (sound of shock wave). At present, the specific process of discharge is not fully understood, and it is generally considered to be similar to the long gap breakdown phenomenon.

The current of lightning is very large, the peak value can generally reach tens of thousands of amperes, but the duration is very short, generally only a few tens of microseconds. Therefore, the energy of lightning current is not as great as expected. However, the power of lightning current is very large, which does great damage to buildings and other equipment, especially electrical equipment. Therefore, it is necessary to install lightning rods or lightning arresters to protect the safety of these buildings and equipment to some extent.

When dark clouds are gathering, when clouds with opposite charges approach each other, a strong discharge phenomenon will occur, forming lightning.