Why is there so much rain in Beijing recently from afternoon to night?
2024-08-20
한어Русский языкEnglishFrançaisIndonesianSanskrit日本語DeutschPortuguêsΕλληνικάespañolItalianoSuomalainenLatina
Original title: Why is there so much rain in Beijing recently from afternoon to night?
According to the National Meteorological Information Center, the most frequent precipitation periods in Beijing in July and August are from 17:00 to 19:00 and from 20:00 to 21:00.
Beijing has recently experienced frequent rainfall, with the afternoon and night being the peak rainfall period. Meteorological data show that precipitation in July and August in North China often occurs in the evening or at night, and plain cities such as Beijing, Tianjin and Tangshan all have the phenomenon of "more night rain in summer".
According to the forecast of the Beijing Meteorological Observatory, it will be cloudy to overcast during the day today (20th), with scattered showers or thunderstorms.
"More night rain" is one of the characteristics of summer precipitation in the North China Plain
After entering the last dog days of summer, Beijing still has active rain. In the past week, "scattered thunderstorms in the afternoon and at night" has been forecast almost every day. Many areas in Beijing often issue thunderstorm and rainstorm warnings, with scattered thunderstorms and heavy rainfall in some areas.
Judging from the recent rainfall characteristics, the rain almost always "gets serious" at night, and in some local areas the hourly rainfall may reach heavy rain levels.
For example, last Saturday afternoon (August 17), the rain was only splashed in some urban areas of Beijing and the southwestern mountainous areas, and most citizens did not feel the rain. As night fell, the rain suddenly became fierce. From 20:00 to 21:00 on the 17th, the rainfall in Qianmu Lake Park in Chaoyang was 58.8 mm; from 22:00 to 23:00, the rainfall in Wulituo, Shijingshan was 53.1 mm; from 23:00 on the 17th to 0:00 on the 18th, the rainfall in Yujiawu, Tongzhou was 60.3 mm, which was also the most intense hour of the entire rainfall process last Saturday. The one-hour rainfall in the above-mentioned areas all reached the level of heavy rain.
From yesterday afternoon to night, scattered thunderstorms occurred again in Beijing. Fangshan, Pinggu and Miyun successively issued blue warnings for thunderstorms. According to the yellow warning for heavy rain issued by the Central Meteorological Observatory, from 14:00 on August 19 to 14:00 on August 20, there will be heavy to torrential rain in some parts of eastern Beijing.
Consistent with people's feelings, meteorological data show that precipitation in North China often occurs in the evening or at night in July and August, and rainfall in summer often occurs at night. According to the analysis of the National Meteorological Information Center, the most precipitation periods in most cities in the Beijing-Tianjin-Hebei region in July and August are concentrated between 19:00 and 22:00. Among them, the most precipitation periods in Beijing are from 17:00 to 19:00 and from 20:00 to 21:00. The night rain phenomenon is more obvious in cities located in plain areas such as Tianjin and Cangzhou, Hebei, and Tangshan. "More night rain" is one of the important characteristics of summer precipitation in the North China Plain.
Frequent night rains are related to high summer temperatures and topographic distribution.
Why is there more night rain in the North China Plain in summer? This is related to the high temperature in summer. In summer, solar radiation is strong, the ground temperature can rise rapidly during the day, the atmospheric turbulence activity in the boundary layer is relatively strong, and the mixing effect with the upper air is strong. This turbulence is equivalent to applying friction resistance to the air, resulting in a weakening of the low-level jet stream; while the boundary layer air is relatively stable at night, the turbulence activity is weak, and the friction is significantly reduced, so the low-level jet stream is strengthened. When the low-level jet stream strengthens at night, the Beijing-Tianjin-Hebei region, which is located at the northwest edge of the subtropical high and in front of the left side of the low-level jet stream, is located in the low-level air convergence area. Due to the lifting of the air, night rain is prone to occur.
In addition, the topographic distribution also has a certain impact. According to the Meteorological Data Center of the China Meteorological Administration, from southern Hebei to Beijing, there are Taihang Mountains in the west and plains in the east, so a thermal circulation similar to valley wind will be formed. At night, the air in the mountains sinks and the air in the plains rises, forming a temperature gradient. Through the effect of atmospheric thermal wind, the low-level jet stream is enhanced, which in turn promotes the occurrence of night rain.
The rainfall in summer is often stronger at night, which makes people feel that "there is more rain at night in summer". Zhu Dingzhen, former chief of public meteorological services of the China Meteorological Administration, explained that the occurrence of heavy rainfall requires unstable atmospheric stratification, continuous water vapor, and strong and persistent upward air movement. The instability of atmospheric stratification and convection are both related to "heat".
"In summer, the daytime is relatively sunny and hot, so the heat storage is more obvious, which is conducive to maintaining the intensity of convection in the evening or at night. During this period, the air in the high altitude begins to cool down. In this case, the convection formed by the heat accumulated during the day and the cold air in the high altitude will converge more obviously, making it more likely for heavy rainfall to occur at night." Zhu Dingzhen said.
The meteorological department reminds people to pay attention to weather forecasts and warning information, prepare rain gear in advance, and pay attention to the impact of nighttime precipitation on transportation. Due to frequent rainfall in recent days, people should try to avoid activities in areas with geological disaster risks such as rivers and mountainous areas.
