These data are relayed back to earth and input into the computer programs that produce our daily weather forecasts. Included in each balloon's instrument package is a sensor to measure temperature, and a completely different one to measure atmospheric pressure. The weather balloon global temperature record has been around for years. The temperatures it has recorded in the lower and middle atmosphere are almost exactly the same as those recorded by satellites orbiting the earth. What Pielke and colleagues did was derive a new temperature data set from the record of atmospheric pressure readings.
Warm air fills more volume than an equal amount of cold air.
The temperatures derived this way are largely independent from those recorded by the balloons' thermometers, and thus represent a new measure of temperatures in the lower and middle atmosphere. But when we examined the seasonal behavior of the new data set for each hemisphere, we found some unusual activity. The new data showed that the summer months were warming relative to the winter months. So we wondered why it appeared only in the pressure-based temperatures and not in any of the other temperature histories. Now we know.