Why does it rain? Why is there light rain, moderate rain and heavy rain?

1: 1. Rain is a natural sight. When the water on the earth is irradiated by sunlight, it turns into steam and is evaporated into the air.

2. Water vapor condenses into water droplets when it meets cold air at high altitude.

3. These water droplets are very small, with a diameter of only .1 ~ .2 mm, and the largest is only .2 mm..

4. They are small and light, and are held in the air by the updraft in the air.

5. It is these small water droplets that gather into clouds in the air.

6. These small water droplets will become raindrops and fall to the ground, and their volume will increase by more than 1 million times.

2. When we listen to or watch the weather forecast broadcast, we often hear terms such as "light rain", "moderate rain" and "moderate to heavy rain", which are the grades of rainfall. Rainfall refers to the depth of accumulation of rainwater falling on the ground without evaporation, infiltration and loss. China stipulates that the unit of depth is millimeters. The grades of rainfall are divided into light rain, moderate rain and moderate rain according to the magnitude of rainfall within 24 hours. Usually, it takes two minutes to completely wet the slate and roof tiles, and the puddle is formed slowly. Moderate rain: the rainfall is between 1 and 25mm, and the rustling sound can be heard. The rain falls like a line, and the raindrops are difficult to distinguish. They splash slightly on the roof holes and hard ground, and the puddle is formed quickly. Heavy rain: the rainfall is between 25mm and 5mm. When it rains heavily, the rain falls like a downpour, and the raindrops splash on the roof tiles and hard ground for several inches. Rainstorms with rainfall of more than 2mm are called torrential rains, and the low-lying areas are flooded. Showers: refer to array precipitation. Raindrops are heavy, and the intensity changes sharply. When it rains, the sky is dark, sometimes it suddenly becomes sunny, and sometimes it is accompanied by thunder.

According to the regulations of China Meteorological Bureau, the rainfall within 24 hours is called daily rainfall, and when the daily rainfall is less than 1mm, it is called light rain, which is 1.24.9mm. The rainstorm is 5. 99.9mm, and the rainstorm is 1. 25.mm. Those exceeding 25.mm are called torrential rains.

Due to China's vast territory, there is a great difference in precipitation between the east, the west and the south. A few areas have formulated local standards for rainstorm according to the specific conditions of this province. For example, in rainy Guangdong Province, the daily rainfall of more than 8mm is called rainstorm. In Yan 'an, Shaanxi province, where there is little rain, it is called rainstorm when the daily rainfall reaches more than 3 mm; The climate in Xinjiang is dry, and there is less precipitation. The Xinjiang Meteorological Bureau specially named rainy days with daily rainfall greater than or equal to 1mm as "heavy precipitation".

The meteorological department called both rain and snow as precipitation, and the amount of precipitation was called precipitation. The unit of precipitation usually used is millimeter. 1mm precipitation, which means how much precipitation fell into fields with a water depth of 1mm. 1mm per unit area? As we know, the area per mu is 666.7 square meters. Therefore, 1 mm of precipitation is equivalent to an increase of .667 cubic meters of water per mu. Each cubic meter of water is 1, kilograms. In this way, 1 mm of precipitation is equivalent to pouring about 65 kilograms of water into each mu. According to the measurement, a rainfall of 5 mm can make the dry land soak 3 cm to 6 cm. In the weather forecast issued by the meteorological department, we often hear light rain and rain. Light rain refers to rain with precipitation less than 1 mm within 24 hours, ranging from small moderate rain to 5 mm ~ 18 mm, moderate rain to 1 mm ~ 25 mm, moderate to heavy rain to 18 mm ~ 38 mm, heavy rain to 25 mm, and heavy rain to 38 mm ~ 75 mm. Rainstorms with rainfall exceeding 5 mm within 24 hours, heavy rains with rainfall exceeding 1 mm, and heavy rains with rainfall exceeding 2 mm. Different sayings have different meanings. For example, "sporadic light rain" means that the precipitation time is very short, and the precipitation does not exceed .1 mm. "Sometimes there is light rain" means that the weather is gloomy, and sometimes there is short-term precipitation. "Rainfall" means that in summer, the beginning and end of precipitation are all sudden, with a big one and a small one, and the rainfall is heavy. "Thundershower" means that it is accompanied by thunder and lightning in some areas.