large balloons filled with helium or hydrogen and carry radiosondes (weather instruments) aloft to measure temperature pressure and humidity as the balloon rises through the air. The whole contraption is attached to a small parachute so that when the balloon inevitably breaks, the radiosone doesn't hurtle back to earth dangerously quickly.
WEATHER BALLOON
Meaning of WEATHER BALLOON in English
Weather and meteorology English vocabulary. Английский словарь погоды и метеорологии . 2012