How are thunderstorms formed?

Thunderstorm is a local storm formed by strong cumulonimbus clouds, accompanied by lightning, thunder and heavy showers, and also refers to the weather system that produces this weather phenomenon. Lightning and thunder without precipitation become dry thunderstorms. When thunderstorms cross the border, the meteorological elements and weather phenomena will change greatly. Strong thunderstorms can even bring serious disasters such as hail and tornado.

Thunderstorms often occur in warm moisture masses in front of the front.

Warm and humid air is forced to rise, forming high cumulonimbus clouds. The rising air becomes cold, and water vapor gradually condenses into water droplets or ice crystals. As they collide with each other, their volume becomes larger and larger, and finally they penetrate the clouds and land on the surface. They will still collide with each other and get bigger during the landing.

Raindrops will lower the temperature of the surrounding air, while cold air will sink. The interaction between sinking cold air and strong rising warm air will bring strong winds and produce thunderstorms.

The formation process of rainstorm is quite complicated. Generally speaking, sufficient and continuous water vapor, strong and lasting upward movement of airflow and instability of atmospheric structure are the main physical conditions for heavy rain. The favorable combination of various scales of weather system and underlying surface, especially topography, can produce heavy rain.

Cloud Flash, Ground Flash and "Sky Flash" in Thunderstorm Weather

Q: How to understand cloud lightning and ground lightning?

A: Lightning is usually divided into two types: ground lightning and cloud lightning. Ground lightning refers to lightning that hits the ground, and cloud lightning refers to lightning that occurs in or between clouds, that is, all lightning that does not hit the ground. On average, lightning only accounts for less than 1/3 of all lightning, while cloud lightning accounts for more than 2/3. The occurrence of lightning is closely related to the development of strong convective clouds. Almost all the first lightning in the clouds are cloud flashes, and some lightning in thunderstorm clouds may be cloud flashes, so the research and detection of cloud flashes are very important, and the information of cloud flashes is more important for the early warning and indication of severe convection development.

Q: Is there a kind of discharge that flashes from clouds to the sky instead of to the ground?

A: Yes, the discharge between thunderstorm clouds and the ionosphere is called a transient luminous event in the middle and upper atmosphere, or it can be more vividly called "sky flash", which is typically called "red elf". It's hard to observe. First, the occurrence time is short, the location is unpredictable, and it is difficult to capture. Second, the occurrence height is high, and it must be observed dozens of kilometers away, so the instrument has high sensitivity. Because it is optical observation, the field of view near the observation site and on the optical observation path is better, and there can be no strong light pollution, fog, haze and heavy precipitation.

Q: Is positive and negative lightning correct negative charge?

A: Positive lightning refers to lightning that transfers the positive charge in the cloud to the earth. Negative lightning refers to lightning that neutralizes negative charges in clouds and shoots at the earth. Generally speaking, the proportion of positive ground lightning is low, accounting for less than 10% of all ground lightning, but it is strong and harmful. The peak current intensity of negative lightning return stroke is generally tens of thousands of amperes, and the neutralization charge is several coulombs to dozens of coulombs. The current intensity and neutralization charge of positive lightning return stroke are several times, even dozens of times.

Q: Is the probability of generating positive and negative charges in the atmosphere the same? All 50%?

A: If the ground-air system is considered together, the separated positive and negative charges should be equal and the charges should be conserved.

Generally, the atmosphere is negatively charged and positively charged on sunny days, so the atmosphere is weakly conductive. The current flows from the ionosphere to the ground, and the electric field near the ground is about110v/m. The global thunderstorm is a generator to maintain the ionospheric potential (250 kV to 300 kV relative to the ground) and the electric field in sunny days.

Q: What is the relationship between up and down lightning and positive and negative lightning?

A: Up and down lightning refers to ground lightning. According to the polarity, there are upward positive lightning, upward negative lightning, downward positive lightning and downward negative lightning, but the latter two are much more than the former two, and the first one is the least.

Rising lightning develops upward from tall buildings or towers. Usually, lightning is downward lightning that develops from clouds to the ground, while upward lightning is rare. With the increase of high-rise buildings, communication towers and wind turbines in cities, this upward lightning is more and more.

Q: Is ball lightning rare? How is it probably formed?

A: It can be described by how rare spherical lightning is: our team has seen it with the naked eye, and the instrument has observed it for millions of times, but there is no spherical lightning. Its formation mechanism is also difficult to fully explain. Physicists have studied many theories and laboratory simulations, and there are also many theories and hypotheses. So far, the international observation evidence is only a spectral observation by the Physics Department of Northwest Normal University. Spectral characteristics generally support a so-called vaporized silicon hypothesis: when the earth is struck by lightning, the silicon in the soil is vaporized into pure silicon, and when the vaporized silicon combines with oxygen in the air, it generates heat and produces spherical luminous air masses. But the problem is that some spherical lightning does not happen before lightning, so there should be other mechanisms. Spherical lightning is also an atmospheric phenomenon that we can't fully explain, which is too complicated.