thumb|A weather balloon in preparation for launch
thumb|Picture taken at approximately 30 km above [[Oregon using a 1,500 gram weather balloon]]
thumb|upright|[[Rawinsonde weather balloon just after launch. Notice a parachute in the center of the string and a small instrument box at the end. After release it measures many parameters. These include temperature, relative humidity, pressure, and wind speed and wind direction. This information is transmitted back to surface observers.]]
A weather balloon, also known as a sounding balloon, is a high-altitude balloon (HAB) that carries instruments into the stratosphere for measuring atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde. First invented in the late 19th century, weather balloons have overgone several remodels and are still used by researchers across Europe, North America, and Asia to this day. Other uses for weather balloons consist of supplements for satellite readings, support for rocket launches, and other miscellaneous recordings.
These early weather balloons carried self-recording instruments that would be recovered upon landing, allowing researchers to atmospheric profiles from higher than ever before.
During the early 20th century, weather balloons expanded to broader upper-atmosphere research, investigating ozone, cosmic rays, and stratospheric circulation. Weather balloon observatories were established worldwide across Europe, North America, and Asia. The technology advanced even further in the 1920s through the invention of radiosondes, instruments which could relay real-time measurements of temperature, pressure, and humidity through radio signals.
The drone technology boom has led to the development of weather drones since the late 1990s.
These drones offered the potential for precise, targeted measurements in areas and weather that would be impossible for balloons.
Materials and equipment
The balloon itself produces the lift, and is usually made of a highly flexible latex material, though chloroprene may also be used. Weather balloons may reach altitudes of or more, limited by diminishing pressures causing the balloon to expand to such a degree (typically by a 100:1 factor) that it disintegrates.
Aerospace and rocket launch support
Weather balloons are also used as atmospheric sounding systems to assist with rocket launches. In a test performed by the Lukasiewicz Research Network - Institute of Aviation a balloon sounding system was used to assist the ILR-33 Amber sub-orbital rocket. In a series of test launches in 2019, the system acquired atmospheric data such as information on vertical wind profile in real time that was used in pre-launch procedures for the rocket. Weather balloons have also been adapted as drifting platforms in chemistry and air quality research. Instead of ascending rapidly through the air, these systems are designed to drift with air masses, measuring trace gases, aerosols, and other chemical constituents in the lower troposphere. These balloons are useful in pollution research to examine transport, mixing, and chemical transformation of pollutants along moving air parcels. In a recent study, researchers launched a weather balloon carrying live microorganisms to investigate how exposure to these conditions affected cell survivability. These missions provide a cheaper alternative to orbital spaceflight experiments. a United Airlines flight collided with a weather balloon at cruising altitude over Utah, fracturing its windshield, releasing shards of glass into the cockpit that injured the captain's right arm, and causing an emergency descent and diversion. The NTSB has begun an investigation, and the company behind the weather balloon has taken measures to reduce future risk.
Coverage and observational gaps
Regions such as Africa, South America, the Southern Ocean, and the Antarctic are particularly underrepresented for weather balloon observations. This means if a balloon bursts prematurely or insufficient ascent height is reached the upwards extent of temperature and humidity measurements will be limited, which is a big issue for climate networks like GRUAN that rely on this information.
thumb|Weather balloon bursting after reaching stratosphere, dispersing shards of latex debris across earth
Weather balloons, after reaching an altitude of approximately 35 kilometers, burst, releasing their instruments and the latex material they are made of. While the instruments are often recovered, the latex remains in the environment, posing a significant threat to marine ecosystems. Studies have shown that a substantial portion of weather balloons eventually end up in the ocean. For instance, one Australian researcher collected over 2,460 pieces of weather balloon debris from the Great Barrier Reef, estimating that up to 300 balloons per week may be released into the marine environment. This environmental impact underscores the need for sustainable alternatives in weather data collection.