Zero-pressure balloon

{
  "id": "MLC-T-MET-010324",
  "term": "Zero-pressure balloon",
  "field": "Meteorology and atmospheric science",
  "definition": "A large plastic-film balloon with open vent ducts at its base, so that lifting gas escapes and the internal pressure stays equal to the surrounding air. It expands as it rises until the envelope is full, then floats near a fixed altitude, sinking at night as the gas cools unless ballast is dropped. Such balloons carry heavy telescopes and instruments into the stratosphere, and flights last from hours to a few weeks.",
  "url": "https://mlchart.com/terminology/meteorology/zero-pressure-balloon/"
}