What is temperature and how is it measured?

In the case of the atmosphere, which is what meteorology is primarily concerned with, we measure this using a mercury thermometer (in certain situations we use an alcohol thermometer and of course modern times have given us things like dewcells and digital thermometers but we always go back to the mercury thermometer for accuracy). The higher the temperature, the more kinetic energy a particle possesses.

In a mercury thermometer, heat is transferred from the atmosphere into the mercury. This increase in energy in the mercury atoms causes them to vibrate faster, which changes the volume of the mercury. This process is known as thermal expansion. The higher the temperature of a particle, the more energy it transfers when it comes into contact with another particle. This transfer is called heat.

The mercury bulb at the bottom of a thermometer can only expand up the thermometer's tube, so the distance the mercury travels up the tube is an accurate measurement of how much the mercury has expanded. Since the thermal expansion of mercury is known, measuring the expansion of the mercury allows us to measure the increase in temperature.

Temperature is a measure of the average kinetic energy of the particles in a substance. It is commonly measured using various types of thermometers, such as liquid-in-glass thermometers, digital thermometers, infrared thermometers, and thermocouples. These instruments detect changes in physical properties, such as expansion, resistance, or radiation, caused by temperature variations.