Temperature Measurements from Earth
Temperature is measured regularly at weather stations around the world. These measurements generally fall into two categories: surface measurements and upper-air measurements.
Surface Temperature Measurements. There are thousands of locations in the world at which ground-level temperature has been measured continuously for hundreds of years.
Surface weather stations in Canada.
For proper temperature measurements, the thermometer should be placed inside some sort of shelter to avoid collecting dew, being heated by the sun, or other things that would result in an inaccurate reading.
Instrument shelters for protecting thermometers from sun, rain, dew and other hazards (like bird droppings). The device on the is a radiation shield. The thermometer is placed inside a series of upside-down plastic plates. The two devices on the right are Stevenson screens, designed to protect several instruments from the elements. All of the shelters are white to reflect away sunlight, and they are not airtight so that wind can provide proper ventilation of the instruments.
Surface measurements reveal air temperatures close to the ground. Temperatures at higher altitudes require upper-air measurements.
Upper-Air Measurements. Temperatures at above-surface altitudes are generally measured by radiosondes. A radiosonde, sometimes called a weather balloon, consists of a small instrument package carried aloft by a balloon. The package contains a radio transmitter to send the measurements to a base station at the ground, and a parachute to allow the package to drift slowly back to the earth when the balloon pops.
Launch of a radiosonde. The photo at right shows a close-up view of the instrument package.
Since the atmosphere is over 100 miles thick, temperatures measured by radiosonde are extremely important in determining weather conditions above the ground, and in assessing how the climate has changed over the years. There are a lot fewer radiosonde stations than there are surface weather stations.
Radiosonde station locations in Canada.
As you might imagine, the pattern of atmospheric temperature changes is different at different altitudes.
Globally-averaged temperature changes measured at different altitudes by radiosonde. According to meteorological custom, altitude is indicated by pressure (millibars, or mb). The figure at the right shows the approximate conversion of pressure to altitude.
