A weather balloon system is a specialized atmospheric probe used globally to capture a vertical snapshot of the air above the Earth’s surface. This system consists of a large, gas-filled latex or rubber balloon carrying a small, expendable instrument package known as a radiosonde. The assembly gathers upper-air data necessary for modern weather forecasting and atmospheric research. Launched twice daily at globally coordinated times, the balloon ascends rapidly through the troposphere and into the stratosphere, providing a continuous profile of conditions as it rises. This data is then fed immediately into complex computer models to predict weather patterns and track atmospheric changes.
Core Atmospheric Measurements
The radiosonde’s sensor package is designed to take direct, in-situ measurements of three fundamental atmospheric properties. Air temperature is measured using an electronic sensor, often a thermistor, which records the thermal conditions of the surrounding air mass. Temperature is a foundational measurement because it determines air density, which in turn influences atmospheric stability and the potential for cloud formation or precipitation.
Atmospheric pressure is the second direct measurement, recorded by a specialized pressure sensor as the radiosonde ascends through ever-thinner air. This reading defines the vertical structure of the atmosphere, allowing meteorologists to delineate boundaries between different air masses. The third direct measurement is relative humidity, which is sensed by a capacitive or resistive hygrometer that measures the amount of moisture present in the air. High humidity readings in the upper atmosphere can indicate a significant potential for heavy rain or severe weather development.
Calculating Wind Speed and Altitude
Wind speed and direction are not directly measured by a dedicated environmental sensor on the radiosonde. Instead, these wind components are calculated by precisely tracking the balloon’s horizontal movement as it is carried along by the air currents. Modern radiosondes include a Global Positioning System (GPS) receiver that records the instrument’s latitude, longitude, and altitude every second.
By comparing the change in the radiosonde’s three-dimensional position over time, ground-based computers calculate the precise speed and direction of the wind at every altitude. This combined observation of both direct sensor readings and wind data from tracking is sometimes referred to as a rawinsonde observation. Altitude is determined using the GPS data.
The Radiosonde and Data Transmission
The radiosonde is a compact, battery-powered device weighing only a few hundred grams, housing the sensors, a processor, and a radio transmitter. As the instrument package rises, the sensors take measurements and the internal processor digitizes this data. The radiosonde then immediately broadcasts this information back to a ground receiving station via a continuous radio signal.
A typical ascent rate is approximately 300 meters per minute, and the entire flight can last more than two hours. During this time, the radiosonde may reach an altitude exceeding 35 kilometers (about 115,000 feet). The flight terminates when the balloon bursts, having expanded significantly due to decreasing external pressure. A small parachute attached to the radiosonde then slows the instrument’s fall back to Earth.