Why does it rain and thunder?

Rain, among common natural phenomena, can be said to be the most touching. On a sultry summer afternoon, large clouds piled up in the sky. The temperature drops suddenly, followed by strong winds, showers, thunder and lightning, and sometimes hail. Irritable weather will soon become cool, refreshing and comfortable. The rain stopped, the wind stopped and the clouds dispersed. The blue sky was washed away by rain, which made it particularly bright. The setting sun shines on the wet earth-what a beautiful night!

In sultry summer, thunderstorm seems to be a kind of adjustment and a meditation endowed by nature. It turns out that in summer, the sun is facing the northern hemisphere, and the direct sunlight makes the water on the ground evaporate faster than in other seasons. As the temperature rises, the air near the ground can contain more water vapor. Even so, if there is no wind, the water vapor in the air near the ground will soon reach saturation, that is to say, it is impossible to contain more water vapor in the air. At this point, the water on the ground no longer continues to evaporate. We are sticky and wet, so you can fan as much as you like, and you can't sweat. We were drowsy and panting from the heat.

There is no wind in this sultry time, but don't think that the air is stagnant, and the air close to the ground is rising sharply. The rise of temperature and the increase of water vapor all reduce the density of air, which is commonly known as "light". Lighter air must rise. However, the sky is not as hot as the ground. The hot air near the ground gradually cools down with the rising, and the temperature drops by 100℃ for every rising100 meters. When the air gets cold, it can't contain as much water vapor as before, and some water vapor has to be broken and condensed into small water droplets. Seen from the ground, there are clouds in the sky.

Why don't these little drops fall into the rain at once? These small water stains are too small. It is the rising air that stops them from falling. In the hot summer afternoon, the air force rising on the ground is very strong, which not only holds the small water point, but also pushes the small water point higher and higher, so the clouds pile up higher and higher. The clouds generated in this way look very special-they can often be seen in hot summer afternoons-their feet are almost flat, and they overlap, like snow-covered peaks and castles made of marble. Under the sunlight, the light and shade are particularly distinct. This kind of cloud has a special term in meteorology, called cumulus. Its feet are about 2000 meters from the ground, that is to say, the hot air rising from the ground rises to that height, and the water vapor contained in it condenses into small drops. Its top may be above the ground 1 10,000 meters. It is very cold at such a high altitude, and the temperature is below the freezing point of water. If cumulus clouds pile up higher and higher, we can see that the top of cumulus clouds sticks out like an anvil used by blacksmiths to strike iron, surrounded by thin clouds like white scarves, which are ice flowers formed by water vapor.

Although cumulus clouds are like high peaks. It looks quiet, but its heart is churning violently. Small water droplets merged into larger water droplets and began to fall. The air rising from the ground is constantly rushing upwards, and the two are violently rubbed, so they are both charged: the rising air is negatively charged and the falling water drops are positively charged. Gradually, at the top of cumulus clouds, negative charges accumulate; At the bottom, positive charges accumulate. The ground is positively charged and negatively charged at the bottom of cumulus clouds.

The thrilling scene began at once: first, a strong wind blew people down, and then tiny raindrops. The big water droplets finally broke through the rising air and fell straight from the clouds. The hot air in the lower layer is drenched by rain, which suddenly cools, contracts and presses down the ground, so strong winds often come before the rain. At this time, there was a flash of dendritic lightning in the sky, followed by rumbling thunder. Lightning occurs between clouds and the ground, from the top to the bottom of cumulus clouds, and between two cumulus clouds. The air penetrated by lightning immediately exploded violently. If lightning is close to us, our eyes will shine, and then we will hear a clear thunderbolt; If you are far away from us, it will be a while before we can hear the thunder after the lightning. This is because the speed of sound is slower than the speed of light. Sometimes, the thunder rumbles for a long time, just like a wheel running over in the clouds. That's because clouds, mountains and the ground reflect thunder back and forth.

Thunderstorms sometimes have hail. Hail occurs when the ground is particularly hot, the air rises strongly, and the altitude is particularly cold. The top of cumulus clouds extends to the sky below freezing point, and some water droplets have condensed into ice beads. These ice beads fell from the sky before they could melt and were pushed up by the fierce rising air. When they reached high altitude, there was a layer of ice outside. In this way, falling and pushing, the ice beads are getting bigger and bigger, and finally they break through the block of updraft and fall from the sky. This is hail. Sometimes hail is bigger than eggs, and it rains heavily, which will damage crops, trees and houses and hurt people and animals. Fortunately, not every thunderstorm will hail.

Thunderstorms are most common in summer, but not necessarily in summer. The violent rise of low-level air containing more water vapor may cause thunderstorms. Sometimes, the sky is too cold, and the air with more water vapor near the ground is much lighter than the air at high altitude, so it rises violently. Thunderstorms in the ocean at night are mostly formed in this way. In winter, a strong cold air mass comes from the north, pushing the air close to the ground with more water vapor into the sky, which may also form thunderstorms. On the windward side of the mountain, the wind with more water vapor is blocked by the mountain, and going straight up and down along the hillside will also cause thunderstorms. In summer, thunderstorms are mostly caused by high temperature and too much water vapor in the air. Thunderstorms caused by this reason are usually called thermal thunderstorms.

Common thermal thunderstorms begin between 3 pm and 5 pm, which is the hottest time of the day. In less than an hour, the rain stopped, the wind stopped, the lightning and thunder disappeared, the clouds pushed away and even dissipated, and a beautiful rainbow might appear in the eastern sky.

Thunderstorm not only lasts for a short time, but also has a small area because it is caused by the updraft on the local ground. A thunderstorm, the rain area is usually only thirty or fifty kilometers long and more than ten kilometers wide. Clear boundaries are also the characteristics of thunderstorms. Sometimes there is only one river, with heavy rain on one side and sunshine on the other, so the saying goes, "Summer rain separates fields." Sometimes, a thunderstorm seems to have just passed and come back. Actually, it's not like this, but another thunderstorm followed.

Although the thunderstorm time is short and the area is not large, the rainfall is heavy. On land, thunderstorms in summer account for almost 1/3 of the annual rainfall. Cultivators attach great importance to thunderstorms. Have you ever thought that when we are suffocating from the heat, the crops in the field have faded. They are hot and thirsty, and their heads are drooping, hoping to have a good bath and drink enough. However, because the rainfall is too concentrated, in mountainous areas and river valleys, thunderstorms will cause flash floods, destroy roads, railways, bridges, farmland and villages, and even drown people and animals. Lightning sometimes kills people and animals and causes fires; But compared with showers, the disaster caused by lightning is much smaller after all.

Seen from the whole surface of the earth, the number of thunderstorms is amazing. It is said that there are more than 44,000 thunderstorms every day. At any time, there are 1800 thunderstorms, mostly in tropical areas. Thunderstorms in China are mostly in Nanling area in northern Guangdong, because the climate there is hot and humid, and Nanling blocks the sea breeze with more water vapor. There are also more coastal areas and southern China, and less north of the Yellow River. Ningxia, Gansu Province has a dry climate with few thunderstorms, but it often carries hail.

In the sultry summer, we all hope for a thunderstorm, but we often meet it. This is not providence. Hot because the temperature is too high, stuffy because the humidity is too high. High temperature and high humidity are two main conditions for the formation of thunderstorms.