Many countries use weather balloons to gather high-altitude data on air temperature ... including a balloon that can stay aloft for up to 16 days instead of just a couple of hours.

FILE - A National Weather Service weather balloon sits ready for launch in the Upper Air Inflation Building at the National Weather Service, April 27, 2006, in Sterling, Va. (AP Photo/Chris ...

But what is the purpose of these weather balloons? Chris Mulcahy explains ... reads the atmospheric conditions up to 10 to 20 miles high in the lower troposphere (lowest level of the atmosphere).