A Tour of the Balloon Launching Process
The National Weather Service in Lincoln launches weather balloons twice a day, collecting valuable information on the temperature, humidity, pressure, and winds aloft. We took some pictures of the process during the evening launch of July 31st. (Click images to enlarge.)
This is the building that we use to inflate the balloons. The small dome on top contains the tracking antenna.
As we begin, the balloon is hooked up to a nozzle connected to a tank of hydrogen.
The amount of hydrogen gas that is used depends on the weather conditions. Windy conditions require additional gas, in order to provide enough lift to prevent the instrument package (which is connected to the balloon by a long string) from hitting the ground. Precipitation also requires additional gas, so that the balloon can overcome any ice that forms from the wet balloon flying through sub-freezing temperatures. Typically, we will fill the balloon with about 1400 grams of hydrogen.
Here, the balloon is shown completely inflated. Attached to the balloon is the "train", which consists of a parachute and the instrument package (called a radiosonde). Typically there is about a 100 foot distance between the balloon and the radiosonde.
This is a closer view of the parachute that is attached to the balloon. Once the balloon bursts (typically at a height around 95,000 or 100,000 feet depending on season), the parachute will slow the descent of the radiosonde.
The parachute has this warning tag attached. Usually by the time the balloon reaches the ground again, it will be in shreds with no inflation possible. But, one may still be partially inflated if it develops a hole early in the flight, forcing it to the ground.
This is the instrument package attached to the balloon, called a radiosonde. The angled wire measures temperature, while the horizontal probe measures the relative humidity. Inside the radiosonde, there is a pressure sensor. A GPS sensor within the radiosonde sends back the exact position of the instrument; this data is used to calculate the winds. Attached to the handle is a postage-paid mailing bag. If you find one of these instruments, you can place it inside the bag and mail it back to our reconditioning center, for recycling into future radiosondes.
Before we launch the balloon, we need to test the radiosonde to make sure it works. The control screen on the computer processes the data from the radiosonde. It also shows the positioning of the tracking antenna, and contacts with GPS satellites.
Now we launch the balloon:
This picture shows the balloon about 1 minute after launch. In this particular example, it was going straight up, due to calm winds. Normally there is some horizontal drift, depending on the wind speed.
Once we return to the office, we need to perform quality control of the data. If bad data is transmitted, this adversely affects the computer models. This process will go on for about 90 minutes, until the balloon finally bursts.
Once we transmit the observation, it is plotted on a special chart called a Skew-T. The trace on the right shows the temperature, and the one on the left is the relative humidity. The winds are shown as well. Such charts are analyzed to determine severe weather potential, ice/snow potential, location of clouds, and more.