In the weather forecast, "cloudy" weather is strictly defined, which refers to a kind of weather that can be called "between sunny and cloudy". In meteorology, it means that the cloud coverage in the sky accounts for four-tenths to eight-tenths of the sky.

When observing a certain weather phenomenon, meteorological observers should record the corresponding symbols in the "Weather Phenomenon" column of the observation record book of the day, except for a few phenomena, and also record the starting and ending time.

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Be careful of ultraviolet rays when you are active in cloudy weather. Ultraviolet ray is the general name of radiation with the wavelength from 10 nm to 400 nm in the electromagnetic spectrum, which can't be detected by human eyes, but too much ultraviolet ray may harm eyes.

The German Good Vision Association reminds that in cloudy summer, people should not forget to protect sensitive eyes, because some ultraviolet rays can still reach the surface through clouds, and long-term use may cause certain damage to eyes.