In the world of weather monitoring and forecasting, atmospheric soundings and weather balloon launches are a very important source of data. The concept seems like a simple one -- attach a package of weather sensors (known as a radiosonde) to a balloon, and collect the information it transmits as it ascends through the atmosphere. However, there are certainly many steps that need to be followed in order to ensure the flight is successful!
All across the planet, weather balloons are launched twice each day -- to provide observations at midnight and noon Zulu time (the time in Greenwich, England). Balloon launches are conducted one hour prior to the required observation time. In Wilmington, this corresponds to launch times of 7 AM and 7 PM during daylight savings time, and 6 AM and 6 PM during standard time. Since all upper air sites around the globe launch their balloons at the same time, the data collected creates a "snapshot" of the current state of the atmosphere. This data is used in many ways, such as being the primary input for numerical weather models, and as real-time data to aid forecasters in short-term duties.
This is an in-depth look at the process a meteorologist must go through to successfully launch a radiosonde and collect the data it transmits. It is certainly one of the more fascinating aspects of the day-to-day operations at a National Weather Service office.
The virtual tour will begin at the upper air inflation shelter. This building is located just outside of the office here in Wilmington.
The dome at the top of this building houses the tracking dish and the hardware that helps it operate. This is known technically as the Telemetry Receiving System (TRS). The dish is used to collect the signal transmitted by the radiosonde, and forward it to the computer system for processing. This system is called the Signal Processing System (SPS).
The main section of the building, below the dome, is the balloon inflation shelter. Here, the balloon is prepared for launch. A table in the center of the building is equipped with a nozzle. The nozzle is connected to helium tanks in an adjacent room.
The balloon itself is taken out of its packaging, and attached to the nozzle. Each balloon is made out of latex, which feels similar to the rubber gloves at a doctor's office.
The helium room is adjacent to the main room in the inflation shelter. Generally, around sixteen helium tanks are kept on hand. Each tank contains enough helium to fill three to four balloons.
It is now time to turn on the gas, so that the balloon inflation can begin.
After the valve on the tank is opened, the dials shown here will indicate the pressure of the gas flowing to the balloon.
In the main room, the balloon begins to fill with helium. In time, the helium will support the weight of the balloon and it will lift off the table.
As the balloon fills up, it is usually a good time to construct the rest of the flight train. About 100 feet of twine is used to construct the train, and the radiosonde itself will be attached to the very bottom. For now, a tripod stand is placed on the blacktop near the shelter, in preparation for the radiosonde itself. The end of the twine is taken out to the stand and left there until launch time.
The balloon is finished inflating once it has attained enough of an upward force to properly lift the radiosonde into the atmosphere. The switching column the nozzle is attached to will automatically shut off the flow of helium when the proper upward force is achieved. The balloon is then tied off securely -- in order to make sure there are no leaks on its way up.
The balloon is then attached to an orange parachute, which comprises the middle portion of the flight train.
As the balloon rises, the decreasing atmospheric pressure causes it to expand. While the balloon has a diameter of about 6 feet at the earth's surface, it will approach 30 feet in diameter at the end of the flight! The balloon has a very thin skin, and once it is stretched as thin as possible, the balloon will burst. When this occurs, the parachute will ensure the radiosonde falls back to the earth gently.