What's the difference between dew point temperature and air temperature?

1, the dew point temperature refers to the temperature when the air is cooled to saturation under the condition that the water vapor content and air pressure are constant.

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 air 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. It is a necessary condition for water vapor condensation that the temperature drops below the dew point.

2. In meteorology, the physical quantity representing the degree of air heat and cold is called air temperature, which is referred to as air temperature for short. The international standard unit for temperature measurement is Celsius (℃).

The temperature mentioned in the weather forecast refers to the air temperature measured in the open air without direct sunlight (usually measured by blinds). The highest temperature is the highest temperature in a day, generally appearing in14-15; The lowest temperature is the lowest temperature in a day, usually before sunrise.

Extended data:

1, dew point meter:

An instrument that can directly measure dew point temperature. Let a mirror cool in the humid air of the sample until dew (or ice crystal) appears on the mirror, and measure the average temperature of the mirror, which is the dew (frost) point temperature. It has high humidity measurement accuracy, but it needs a mirror with high smoothness, a temperature control system with high accuracy and an optical detection system with high sensitivity to dew (ice crystals). When in use, the pipeline for inhaling sample gas must be kept clean, otherwise impurities in the pipeline will absorb or release water, resulting in measurement errors.

2. Common instruments for measuring temperature:

(1) glass thermometer:

The sensing part is a glass ball or column filled with liquid, and the indicating part connected with the sensing part is a glass capillary with one end closed and uniform thickness. The temperature measuring liquid is usually mercury, alcohol or toluene. Because the thermal expansion coefficient of liquid in glass ball is much larger than that of glass, the liquid column in capillary tube will fluctuate with the change of temperature. Commonly used glass thermometers include the highest thermometer, the lowest thermometer and the dry and wet bulb thermometer.

(2) Metal thermometer:?

This is an instrument that can automatically record the continuous change of temperature. The sensing element is a bimetal, which is welded by two metals with different expansion coefficients. One end of the metal is fixed, and the other end is displaced with the change of temperature. The displacement is almost linear with the air temperature. A self-recording system consists of a self-recording clock and a self-recording pen. The self-recording pen is connected with the amplification lever and controlled by the sensing element.

(3) Metal resistance thermometer:

It is made by using the principle that the resistance of metal wire is proportional to the temperature change. There are three kinds of commonly used metal wires: platinum wire, copper wire and iron wire, with resistance values ranging from tens to100Ω, among which platinum wire has the best stability and can be used as a standard thermometer. Resistance thermometers are suitable for telemetry.

(4) Thermistor thermometer:

Inductive element is a conductor resistance formed by mixing and sintering several metal oxides, and its resistance value is usually several tens of kiloohms. Its resistance temperature coefficient is large, its sensitivity is higher than that of metal resistance thermometer, but its stability is a little worse, so it is widely used in high-altitude telemetry.

(5) Thermocouple thermometer:

Made of thermoelectric phenomenon, two metal conductors A and B with different physical and chemical properties are connected into a closed loop, which is called thermocouple. When measuring, one contact of the thermocouple is placed at a constant temperature (such as ice water solution), which is called the reference end, and the other contact is placed on the measured object, which is called the working end. When the temperatures of two contacts are different, thermoelectric electromotive force will be generated, which is directly proportional to the temperature difference between the two contacts. The thermoelectric potential of copper-constantan thermocouple commonly used in meteorology is only tens of microvolts, so in order to improve the sensitivity of temperature measurement, dozens of thermocouple pairs are often connected in series to form a thermopile. Thermocouple thermometers can be used for telemetry and are widely used in solar radiation instruments and microclimate observation.

References:

Dew point temperature Baidu encyclopedia temperature Baidu encyclopedia