Geography: Analyze four kinds of special weather from the aspects of definition, occurrence time, influence and occurrence area (preferably from the geography book in the first volume of Grade Two).

First, the cold wave: the cold wave is a disastrous weather in winter, and people are used to calling it the cold wave. The so-called cold wave is a weather process in which cold air from the north invades China on a large scale, resulting in a large-scale sharp cooling and northerly winds. Cold waves generally occur in late autumn, winter and early spring.

2. Meiyu: It rains continuously from the middle and late June to the first half of July every year, which is a climatic phenomenon. This period is the mature period of plums in Jiangnan, so it is called "Meiyu". In the rainy season, the air humidity is high and the temperature is high, so clothes are easy to get moldy, so some people call the rainy season "moldy rain".

3. Typhoon: Typhoon is a kind of tropical cyclone. Tropical cyclones can be divided into six grades according to their intensity: tropical depression, tropical storm, strong tropical storm, typhoon, strong typhoon and super typhoon. The typhoon is in the western part of the North Pacific Ocean, west of the international date, including the South China Sea;

4. Sandstorm: refers to a serious sandstorm weather phenomenon in which strong winds blow up and throw a large amount of sand and dust on the ground into the air, making the air particularly turbid and the horizontal visibility less than one kilometer.

There are two sandstorm-prone areas in China:

The first frequent area is in the northwest, mainly concentrated in three areas, namely, the surrounding area of Tarim Basin, Turpan-Hami Basin passing through Hexi Corridor, Ningxia Plain to northern Shaanxi, Alashan Plateau, Hetao Plain and Ordos Plateau in Inner Mongolia;

The second frequent area is in North China, Chifeng and Zhangjiakou, which directly affects the safety of the capital Beijing.

Occurrence time: 1, cold wave: winter 2, plum rain: from mid-late June to July every year 3, typhoon: summer 4, sandstorm: depending on the climate and weather, there is no outstanding season.

Hazard: 1. Sandstorm:

1, people and animals died, buildings collapsed, and agricultural production was reduced. Sandstorms are as harmful to people, animals and buildings as typhoons and tornadoes. In the past five years, the northwest of China has been hit by sandstorms for more than 20 times, resulting in economic losses of more than 654.38+0.2 billion yuan, and more than 200 people have died and disappeared.

2. Air pollution and topsoil loss. Dust storms contain at least 38 chemical elements, which greatly increase the concentration of atmospheric solid pollutants and cause long-term and potential harm to the atmospheric environment, soil and agricultural production in the origin, surrounding areas and downwind areas. Especially after the meager topsoil on which crops depend is scraped away, the barren land will seriously affect the yield of crops.

In addition to the general wind hazard, it also quickly eroded fertile farmland, blew away and killed seeds and seedlings, and knocked down fruits and flowers of cash crops. It also used sand to bury the lifelines of farmland, pasture and arid areas-canals and karez. After the leaves of the surviving crops are covered with dust, the photosynthesis and respiration are greatly weakened, which seriously affects the growth of crops.

Typhoon: 1, strong wind level 2, rainstorm level 3, storm surge.

Meiyu: 1, insufficient ultraviolet radiation, high air humidity, easy to cause utensils rot.

4. Cold wave: Cold wave is a large-scale weather process, which will cause a wide range of severe cooling, strong winds and snowfall along the way. Disasters caused by cold wave, such as gale, frost, snowstorm, etc., have great influence on agriculture, transportation, electricity, navigation and people's health.