As far as the weather is concerned.

On a certain day, the temperature in Xi 'an is 13 ~25 degrees, and the temperature difference in Xi 'an is 25- 13 = 12 degrees.

Daily temperature range and its influencing factors

I. Concept

The daily temperature difference is also called the daily temperature difference. It is the difference between the highest temperature and the lowest temperature in a day. Its size is related to latitude, season, surface characteristics and weather conditions.

Second, the influencing factors

1. The low latitude area is larger than the high latitude area: the average value of low latitude area is 12℃, the middle latitude area is 7-9℃, and the high latitude area is 3-4℃.

Reason: The higher the latitude, the smaller the daily variation of the sun's height.

2. In mid-latitude area, summer is greater than winter, but in low-latitude and high-latitude areas, it doesn't change much with the seasons.

3. As far as land and sea are concerned, the ocean is smaller than the inland: the average ocean is only 1-2℃, and the inland can reach 15℃, even 25-30℃.

Reason: the difference of thermal properties between land and sea.

As far as the weather is concerned, the daily amplitude of cloudy days is smaller than that of sunny days.

Reason: On cloudy days, the atmosphere has a stronger weakening effect on solar radiation and heat preservation.

5. As far as topography is concerned, the valley is bigger than the peak, and the depression is bigger than the height. Mountains are smaller than plains.

Why is the daily temperature difference in mountainous areas smaller than that in nearby plains? There are three main reasons: first, it is influenced by the heat source in the troposphere. The main heat source of troposphere atmosphere comes directly from the underlying surface, so the temperature changes with the underlying surface temperature. Affected by the temperature change of the underlying surface, the closer the troposphere atmosphere is to the underlying surface, the higher the average temperature and the greater the daily variation range of temperature. The farther away from the underlying surface, the lower the average temperature and the smaller the daily variation of temperature. Secondly, it is influenced by the thermal conditions of mountain clouds. Mount Tai has high altitude, low temperature, many clouds in the atmosphere and high reflectivity to solar radiation during the day. Thirdly, the temperature in mountainous areas is influenced by the adjustment of the surrounding "free atmosphere". Mountainous areas have high altitude and good air mobility, which is beneficial to exchange with the surrounding "free atmosphere". When the temperature rises in mountainous areas during the day, the "free atmosphere" at the same height has a certain cooling effect because of its low temperature and small daily variation. At night, due to the thin atmosphere over the mountain area, weak heat preservation and rapid cooling, the "free atmosphere" at the same height reduces the temperature drop in the mountain area, so the daily temperature difference in the mountain area is smaller than that in the nearby plain.

Then why is it that "the daily temperature difference is proportional to the height, and the higher the altitude, the greater the daily temperature difference" in large-scale topographic areas? Due to the high altitude and low air density, the Qinghai-Tibet Plateau is affected by atmospheric thermal conditions, and the atmosphere has a low weakening effect on solar radiation during the day and a poor heat preservation effect on ground radiation at night, so it heats up quickly during the day and cools down quickly at night. So the daily temperature difference is large.

6. This is also related to the nature of the surface. Turpan basin in northwest China is known as "wearing fur coats in the morning, wearing shirts in the afternoon, and eating watermelons in the stove". In areas with large daily temperature difference above 15℃, there is generally plenty of sunshine in the daytime, strong solar radiation and high temperature, which is beneficial to plant photosynthesis and can produce and accumulate more nutrients. The lower the temperature at night, the weaker the respiration of plants and the less energy they consume, which is beneficial to the storage of sugar. So Xinjiang cantaloupe is big and sweet.