What is the correct explanation for crisp autumn?

What is the correct explanation for crisp autumn? It describes the clear sky and cool weather in Wan Li. Combined type; As a predicate; It is of positive significance to describe the clear sky and refreshing weather in Wan Li.

The reason why autumn is crisp.

1, changes of solar radiation and atmospheric circulation;

Autumn, as the transitional season in Xia Dong, the situation of solar radiation and atmospheric circulation enters seasonal adjustment, and the subtropical high zone entrenched in the mainland retreats southward, and the warm and humid airflow weakens. At the same time, as the source of winter wind, the cold air in Siberia, Mongolia is also "eager to try". When the cold air in the high latitude inland goes south, the area occupied by the cold air not only reduces the temperature, but also greatly reduces the water vapor in the air.

In addition, the formation of cold high pressure prevents the rise of water vapor, so we can feel comfortable and dry in autumn compared with sultry summer. As the direct point of the sun moves southward, the daylight time in the northern hemisphere is shortened, and the solar radiation received by the ground is obviously less than that in summer. More sunny days and less clouds at night directly lead to the reduction of atmospheric inverse radiation, the weakening of thermal insulation, the decrease of near-surface temperature and the decrease of comfortable temperature.

2. High sky:

The sky looks bluer in autumn, and the improvement of atmospheric transparency has a lot to do with cold air. Cold air takes away dust and impurity particles in the atmosphere. The reduction of dust and water droplets makes the proportion of blue-violet light with shorter wavelength in the sky increase obviously, and the blue sky is as clean as water, and the air quality is also improved obviously.

3, the autumn wind is cool:

In early autumn, the Siberian high in Mongolia mainly controlled the northern part of China. At this time, the numerical value of the high pressure center is low, and the pressure gradient force is not great, so the autumn wind always looks mild and pleasant, and the cool breeze blows gently, bringing a "dry" sense of body.

Phenological characteristics of autumn:

It is autumn in beginning of autumn so far, which means that precipitation and humidity are at the turning point of the year, and there is a tendency to decrease or decrease. In nature, everything begins to grow from lush to rich and mature. Autumn is the harvest season, and many plants mature in autumn.

In autumn, in nature, the qi of yin and yang begins to change, the yang is gradually declining, the yin is gradually flourishing, the climate turns from hot to cold, and everything is born with cold and gradually falls. This is the season of alternating hot and cold.

As the temperature gradually drops, the leaves of many deciduous perennial plants will gradually change color, wither and fall off, leaving only branches for winter. Panicum miliaceum will come to the end of his life, wither and die.

Seasonal variation covers many aspects of climate characteristics, and it is not accurate to judge autumn only by temperature. The most obvious change in autumn is that the leaves of vegetation change from lush green to yellow, and the leaves begin to fall and the crops begin to mature.