China has a vast territory, mainly located in the middle and low latitudes. Low latitude refers to the spatial range between 30 degrees north and south latitude on the earth's surface, that is, the area between 30 degrees north latitude and 30 degrees south latitude, including tropical and subtropical hot zones, which is the area where global solar radiation and heat are concentrated. China's low latitude area (South China) is characterized by abundant precipitation, abundant sunshine, high humidity and small temperature difference between winter and summer.
Climate factors such as sunshine and precipitation change obviously in seasonal changes. Mid-latitude is the latitude zone between 30 and 60 degrees north latitude. The main air masses at high latitude and low latitude overlap each other in this area, and cyclone activities are frequent. Mid-latitude areas (northern areas) are characterized by less precipitation, dryness and large temperature difference between winter and summer. Temperature is the obvious change of climate factors during seasonal changes. The climate varies greatly at different latitudes.
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There are many ways to divide the four seasons. In daily life, people usually regard the arrival of beginning of spring solar terms as beginning of spring, and beginning of spring is defined from the perspective of astronomy. Meteorological departments generally divide the solar calendar into four seasons, and March-May is spring.
However, this division method has a disadvantage for some places. According to this method, March in the south of China belongs to spring. At this time, of course, the Yangtze River valley is pink and green, and it is spring. However, Heilongjiang Province is still freezing cold and snowy. Therefore, meteorologists have formulated a standard to divide the four seasons according to the temperature change, that is, the five-day average temperature.
When the average temperature of five days after winter passes 10℃ stably, it begins to enter spring, and when the temperature is higher than 22℃, it means late spring and early summer.