Sunshine hours in Gansu, Xinjiang and Qinghai

The number of sunshine hours in Gansu decreases from the southeast to the northwest, ranging from 1,500 hours in the southeast to 3,300 hours in the northwest; the number of days and hours in Xinjiang is mostly between 2,700 and 3,300 hours; in Qinghai The sunshine hours decrease from southeast to northwest, mostly between 2400 and 3300 hours.

Sunshine hours refer to the number of hours the sun actually shines on a place. In a given period of time, the number of sunshine hours is defined as the sum of the periods during which the direct solar irradiance reaches or exceeds 120 watts/square meter, measured in hours and rounded to one decimal place. Sunshine hours can also be called actual sunshine hours.

The number of illuminated hours (the number of astronomical illuminated hours) refers to the time it takes for the sun's center to reach the ground from the eastern horizon to the western horizon without any obstruction. The number of hours can be calculated by a formula, or it can be found from an astronomical almanac or a common meteorological table.

Percentage of sunshine = (number of sunshine hours/number of sunshine hours) × 100%, rounded to an integer. Sunshine hours are mainly used to characterize local climate and describe past weather conditions.

There are more sunshine hours in northern China than in the south in summer. In addition, the higher the latitude, the greater the change in day and night length. The farther north you go in summer, the longer the day length becomes. The Qinghai-Tibet Plateau has high altitude, thin air, and many sunny days, so it has more sunshine hours. Opposite to the Tibetan Plateau is the Sichuan Basin, which has a similar latitude, but has a lot of water vapor and is restricted by the terrain, so it is cloudy and has less sunshine.