Definition

By definition, temperature is a measure of the molecular agitation of a body or system, expressed in degrees Celsius (°C) or Fahrenheit (°F). In meteorology, it is often used to describe how hot or cold the air feels.

Different types of temperatures in meteorology

In meteorology, there are various temperature measurements, each of which has a specific importance for understanding weather phenomena and making forecasts. Here are some of these measurements:

• Ambient air temperature (T, in °C) : this measures the temperature of the air at a certain height above sea level. This measurement is crucial for understanding cloud formation, precipitation and air pressure.
• Dew point temperature (Td) : indicates the temperature at which the air must be cooled at constant pressure for the water vapour it contains to begin condensing. This measurement is useful to evaluate the humidity of the air.
• Feeling temperature : This takes into account wind speed and air humidity to calculate the actual temperature sensation that people experience. It is important for understanding the impact of weather conditions on the human body.
• Sea Surface Temperature (SST) : measures the temperature of the water at the surface of the sea, often measured by satellite or buoys. This measurement is important for predicting the conditions for the formation of tropical storms or cyclones.
• Air temperature as a function of altitude : the temperature decreases with altitude by an average of 0.65°C per 100 meters. The measurement of temperature and pressure by radiosonde is crucial to better understand the behavior of the atmosphere.

How to measure it ?

Temperature is usually measured with a thermometer. In fact, we do not measure the temperature itself, but rather a variation of it. Temperature is a thermodynamic quantity that describes the agitation of molecules in a body (the atmosphere in our case).

Thermometers can use substances that expand or contract with temperature, such as mercury or alcohol. There are also resistance thermometers that measure the variation of resistance in a conductor. This one varies according to the temperature. There are also semiconductor measuring devices: these instruments use the voltage variations to determine the temperature variation.

In meteorology, we measure the temperature under shelters at 2m, but we also place sensors at different heights (near the ground, under the ground, in height and under radio sounding balloons). The WMO has made recommendations on these means of measurement to harmonize the monitoring of temperatures around the world. This is an important work to obtain reliable data to quantify climate change.

How to make a temperature forecast?

In general, the weather forecaster will use the output of a numerical weather prediction model to obtain the forecast of the coming temperatures. Two pieces of information are often given to characterize a day: the minimum temperature (Tn) and the maximum temperature (Tx). In the short and medium term, it is a good method to forecast the temperature.
For more distant time frames, climatology can give a good idea of the temperatures likely to be reached during a period of time.
Finally, future climate trends give an indication of how the global average temperature will change.

Facts

The highest temperature ever recorded was 56.7°C (134°F) at Furnace Creek Ranch, California on July 10, 1913.

On the other hand, the lowest temperature ever recorded is -89.2°C (-128.6°F) at Vostok, Antarctica on July 21, 1983.

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