What can be used to indicate the degree of hot and cold weather, and what should be used to measure it?

The degree of hot and cold weather is usually expressed by temperature and measured by thermometer. The working principle of this temperature measuring tool is that liquid expands when heated and contracts when cooled. It specifies the reading starting point (zero point) of temperature and the basic unit for measuring temperature. The international unit is the thermodynamic temperature scale (K). Other temperature scales widely used in the world are Fahrenheit scale (F), centigrade scale scale (C) and international practical temperature scale.

moisture measurement

Humidity indicates the content of water vapor in the air or the degree of dryness and wetness, and it is commonly expressed by three physical quantities: water vapor pressure, relative humidity and dew point temperature in meteorological observation.

Water vapor pressure (e) is the partial pressure of water vapor in the total atmospheric pressure. It represents the absolute content of water vapor in the air in millibar. There is a limit to the absorption of water vapor by air. When it reaches its limit, it is no longer absorbed. This limit is called "saturation point".

The water vapor pressure when the water vapor in the air reaches the saturation point is called saturated water vapor pressure (or maximum water vapor tension). The saturated vapor pressure is a function of temperature and increases with the increase of temperature. At the same temperature, the saturated vapor pressure on pure ice is less than that on pure water.

Relative humidity can directly indicate the relative degree of air distance saturation. When the air is completely dry, the relative humidity is zero. The smaller the relative humidity, the drier the air. When the relative humidity is close to 100%, it means that the air is humid, and the closer it is to saturation.

Dew point (or frost point) temperature: refers to the temperature at which air is cooled to saturation without changing the water vapor content and air pressure. Figuratively speaking, the temperature at which water vapor in the air becomes dew is called dew point temperature.

Dew point temperature is a temperature value, but why use it to represent humidity? This is because when the water vapor in the air reaches saturation, the temperature is the same as the dew point temperature. When water vapor is unsaturated, the temperature must be higher than the dew point temperature. So the difference between dew point and air temperature can indicate the saturation of water vapor in the air.