Causes, characteristics and preventive measures of plum rain

Since every spring, the power of warm and humid air in the ocean has been gradually strengthened. After entering the mainland, it meets the cold air from north to south. Because the warm and humid air from the ocean contains a lot of water vapor, it forms a long rain belt. From June to July every year, the rain belt moves northward to the middle and lower reaches of the Yangtze River. Because the cold and warm air are equal, these two different forces confront each other in this area, launching a more lasting "tug-of-war", thus forming a stable rain belt, resulting in a long-lasting rainy weather, so it is just the time when plums are ripe, so it is called "plum rain".

Characteristics of Meiyu:

In June and July every year, there is usually a period of continuous rainy weather or concentrated precipitation in the middle and lower reaches of the Yangtze River and Huaihe River. During this period, due to the monsoon adjustment of atmospheric circulation, the warm and humid airflow from the ocean and the cold air from north to south continued to meet in the Jianghuai Basin, forming an east-west quasi-static front, commonly known as Meiyu Front, which caused continuous rain and concentrated heavy rain. At this time, it is the yellow ripening period of plums in the south of the Yangtze River, so it is called "Meiyu" or "Huangmei weather". Because of the high temperature and humidity at this time, clothes are prone to mildew, also known as "mildew rain". During the meiyu period, a stable and lasting rain belt was maintained from Jianghuai Valley to southern Japan. The distribution of rainstorm in rain belt is uneven, and there are often multiple rainstorm centers. The rainstorm intensity of Meiyu front is generally much smaller than that of typhoon, but because Meiyu front lasts for a long time and the rainstorm area is wide, the scope of flood disaster is generally larger than that of typhoon. For example, 199 1 year, the meiyu period in the Jianghuai basin lasts about 56 days, and there are heavy rains and severe floods in the lower reaches of the Yangtze River, Taihu Lake and Huaihe River basins. The scale, duration and severity of the disaster are rare in history. Taihu Lake, Lixia River, Chuhe River and Qinhuai River all have the highest water levels in history.

The atmospheric circulation conditions that form the Meiyu front rainstorm generally include: ① blocking high pressure or stable high pressure ridge exists in the middle troposphere in high latitudes of Asia, and the atmospheric circulation is relatively stable and rarely changes; ② The westerly circulation in mid-latitude area is flat, and frequent short-wave activities provide cold air conditions for Jianghuai area; ③ The western Pacific subtropical high has an obvious process of extending westward and jumping northward. The ridge line of the 500 HPA subtropical high is stable between 20 and 25 degrees north latitude, and the warm and humid air flow is transported from the edge of the subtropical high to the Jianghuai basin. Under this circulation condition, Meiyu front lingers in the Jianghuai basin, often accompanied by southwest vortex and shear line, and the mesoscale system on Meiyu front is active. It not only maintains the continuous precipitation during the Meiyu period, but also provides abundant water for the rainstorm. Meiyu front rainstorm is a special weather in a specific area formed by the interaction of circulation systems of different scales. The variability of atmospheric circulation leads to the late start and short duration of meiyu period every year. In some years, the Meiyu front is particularly active, with frequent rainstorms, leading to flooding. In some years, the meiyu front is not obvious, and there are "empty plums", which leads to dry weather. In some years, the Meiyu belt will move northward and then return to the Jianghuai basin to maintain relative stability, which is customarily called "inverted Huangmei". After the meiyu in Jianghuai basin ended, the rain belt moved to North China, and the Jianghuai basin entered high temperature and little rain.

Preventive measures for plum rains:

In the rainy season in previous years, many housewives had this experience: in a few days, the dry goods at home quietly grew a layer of "green hair", and the rice noodles and peanuts in Kaifeng, Lian Gang became wet and sticky. These are all caused by mold. Mold is easy to grow in the environment with temperature of 20℃ ~ 28℃ and relative humidity of 80% ~ 90%, and the climatic conditions in rainy season just meet these requirements. Dry foods such as grain, rice, noodles, dried mushrooms, nuts, dried peppers, dried radishes, fungus, dried bamboo shoots, dried salted fish and dried seaweed are easy to get wet and breed molds. Once contaminated by mold, food will change color and taste, and the nutritional components will be destroyed, which not only reduces the edible value, but also causes poisoning, deformity and cancer after mycotoxin enters the human body. Four factors of water affecting the growth of mold: refers to the water needed for the growth and reproduction of mold. The drier the food, the less likely it is for mold to grow. Temperature: refers to the temperature. Temperature has an important influence on the reproduction and toxin production of mold. The optimum growth temperature of different kinds of molds is different, mostly 25℃ ~ 30℃, and the toxin production ability is weakened below 0℃ or above 30℃. Fat: refers to the nature of food. Generally speaking, the more nutritious the food, the greater the possibility of mold growth. Therefore, under the same culture conditions, the aflatoxin yield of wheat and rice rich in sugar is higher than that of oil crops. Wind: refers to ventilation. If the air is not ventilated or poorly ventilated, mold will easily breed and produce poison. Anti-mildew measures 1, dry preservation Dry mushrooms, fungus, dried bamboo shoots, nuts, dried peppers, dried radishes and other dry goods should be kept in sealed containers, and desiccant should be placed in conditional containers; Grain products such as rice and flour should be stored in ventilated and dry places, which can greatly reduce the production of mold. 2. Cryopreservation at low temperature will slow down the propagation of mold. Meat food can be stored for 20 days at 0℃ ~ 4℃. Soak the rice cake completely in a porcelain jar filled with cold water and it can be kept for about a week. 3. Most molds preserved in hypoxia belong to aerobic microorganisms, and oxygen is needed for their growth and reproduction. Sterilized food in bottles (cans) can be filled with nitrogen or carbon dioxide, compacted, degassed or sealed with oil, which can create an anoxic environment and prevent most molds from multiplying. For example, dropping a layer of cooked soybean oil or sesame oil in a bottle filled with soy sauce and vinegar can isolate the soy sauce and vinegar from contact with the air and prevent the growth of mold. Warm reminder, food should be discarded in time after it is moldy and should not be eaten. Some people think it is a pity, so it is extremely inappropriate to remove the moldy part and keep the rest. Although the mold on the surface of food has been removed, mycotoxins often remain in food, which may cause food poisoning after eating. It is particularly important to note that moldy peanuts and corn should never be eaten, because they are the foods where aflatoxin is most likely to grow and produce, and general cleaning, cooking and other methods can not remove aflatoxin.