April is the season of spring and summer, with rising temperatures, increased water vapor, and frequent weather changes. However, in April this year, there were some unusual phenomena that allowed everyone to see the anomalies of this year's climate - for example, on April 28, the central and eastern parts of the continent were in the same frame with fierce snowstorms, violent rainstorms and strong high temperatures, showing the extreme strength of cold and warm air masses.
First, the midsummer rain belt appeared in the central and eastern regions
On the morning of April 29, a particularly long rain belt appeared on the Qinghai-Tibet Plateau on the mainland, which stretched thousands of kilometers from the two lakes, Sichuan and Chongqing all the way to Jilin. Today's most intense weather is from north and south China to Chongqing and Hunan, this area should pay attention to guard against thunderstorms, strong winds and hail attacks, from the radar map, the shape of the rain belt on April 29, like the subtropical high control of the Huai River and the Yellow River basin in midsummer.
In fact, it can be seen from the 500 hPa level weather map that at 8 o'clock this morning, the subtropical high was located off the coast of South China on the mainland, covering Hainan, Guangdong, Taiwan, and other places.
So why are rainbands like this today? Rainbands are areas where precipitation occurs continuously or intermittently within a certain range. The formation and movement of rain bands are mainly affected by the airflow system at high and low altitudes. The cold air and warm and humid air currents at low altitude are the main conditions for precipitation, and for the northern region, the rain bands that spread today are the cold front systems formed by the cold air moving southward and the warm and humid air currents.
Second, the large-scale rainstorm is confirmed!
The situation is different here as the rain band extends to the south, where satellite images show that the clouds in the southwest have some spiral shapes that appear to be spinning, as a southwest vortex system is developing and intensifying. Recently, the thermal conditions in the southern part of the mainland are strong, and many places in the Sichuan Basin were hot from April 27 to April 28, and the southwest vortex came into being with the eastward spread of the westerly wind belt.
Therefore, with the cold front rain band and the southwest vortex rain band connected, it appears to form a rain band similar to midsummer, but the circulation situation is completely different from that of the midsummer rain band. The southwest vortex is absorbing a lot of water vapor and moving eastward, and there is widespread heavy rain in the south of the continent. The Central Meteorological Observatory continued to issue a yellow warning for heavy rain at 10 o'clock on April 29: It is expected that from 14 o'clock on April 29 to 14 o'clock on the 30th, there will be heavy to heavy rain in parts of central and northern Chongqing, eastern Guizhou, most of Jiangnan, and central and northern South China, among them, there will be heavy rain (100~200 mm) in parts of southern Hunan, central Jiangxi, northwest Fujian, northeast Guangxi, and northern Guangdong.
3. Multi-factor anomalies in April
In fact, the intensity of extreme weather, high temperatures, heavy rains, heavy snowfall, and strong convection has been very alarming recently, indicating that there are anomalies in various elements of the circulation. First of all, there is the anomaly of the westerly wind belt. The westerly wind belt is an important factor affecting precipitation in the central and eastern parts of the continent, and its location and intensity determine the activity range and intensity of cold air and warm and humid airflow. In April this year, the position and intensity of the westerly wind belt were obviously abnormal, and huge amplitudes frequently appeared, resulting in the alternation of continental warm ridges and cold vortices, and the inland hot and dry air masses and cold air were very active in the south, very hot when it was hot and very cold when it was cold.
For example, since the evening of April 27, it has snowed extensively in northern Hebei Province and central and eastern Inner Mongolia, and although it is not uncommon for the grassland to snow at the end of April, it is indeed outrageous that the snow falls so heavily. This morning, Inner Mongolia Duolun snowed 18 centimeters, ranking second in April, Gangzi 15 centimeters broke the record, and the snowfall in various places reached the level of a heavy blizzard.
Secondly, there is the anomaly of the subtropical high, which affects the intensity of warm and humid airflow over the continent. Warm and humid airflow is a necessary condition for precipitation, and its source, intensity, range and path will affect the spatial and temporal distribution of precipitation. Generally speaking, spring is the season with the most frequent activity of warm and humid airflows, and the intensity and extent of warm and humid airflows will also change with the change of the subtropical high. However, in April this year, the activity of the warm and humid airflow was also obviously abnormal, with strong intensity, wide range, and northerly path, resulting in a humid climate state in the south, and the intensity of rainfall in some areas has far exceeded the average of the year.
Recently, including the mainland, the intensity of the warm air mass is extraordinary, and there has been an extremely strong abnormal high temperature in Southeast Asia, Hainan, Yunnan and other places in the mainland, which has also promoted the frequent occurrence of abundant atmospheric energy in many places in the central and eastern regions, with the background of cold air frequently moving southward, stimulating atmospheric energy, and the intensity and frequency of strong convective weather are also quite amazing.
To sum up, we can see that in April this year, there were anomalies of a variety of meteorological elements in the central and eastern parts of the continent, resulting in a series of abnormal precipitation and high temperature processes. These abnormal meteorological elements show the combined effect of global climate change, ocean circulation, El Niño and other factors, and we need to continue to be vigilant about the occurrence of extreme weather in the coming period.