What color is autumn? Fill in the blanks.

In autumn, the most obvious change of natural landscape is in trees. The city will begin to clean up a lot of fallen leaves, and many tourists will flock to the mountains to watch the red leaves. Autumn, the third season of the year, is a transitional season from summer to winter. The lunar calendar is from beginning of autumn in July to beginning of winter in September, the solar calendar is from 9: 00 to 1 1, and the astronomical vernal equinox starts from the winter solstice.

The standard for meteorologists to study phenology is: after the intense summer heat, the average temperature for five days is stable below 22 degrees, which means that it is autumn, and it is over when it is below 10 degrees.

The autumnal equinox is a solar term representing seasonal changes. On the day of the autumnal equinox, the sun is located at longitude 180 degrees, and the sunlight is almost direct to the equator, and day and night are almost equal. At this time, the waiting temperature in the southern region has generally dropped below 22℃, and it has entered a cool autumn. "An autumn rain and a cold".

The cold air from the south meets the warm and humid air that gradually decays, resulting in repeated rainfall and the temperature dropping again and again. In the northern part of the northwest plateau, the daily minimum temperature has dropped below 0℃, and you can already see the magnificent snow scene flying all over the sky and the earth wrapped in silver.

After the autumnal equinox, rainfall in most parts of the south decreased significantly, and heavy rain and heavy rain rarely appeared. However, rainy days increase, rainy days are frequent, and the night rain rate is high. Li Shangyin, a famous poet in the Tang Dynasty, famously said, "It rains late in autumn pond", which vividly describes the climate characteristics of autumn rainy nights in the south.