At the upper air shelter, one last check is made of the radiosonde's performance. The control unit on the right allows the user to move the tracking dish, check the strength of the radiosonde's signal, and do plenty of other tasks. The call box on the left is used to talk to a staff member inside the office. They will check the radiosonde workstation computer to ensure that the radiosonde's GPS signal is also coming through properly.
With the final "thumbs up" from the office, it's time to launch the balloon. Up, up, and away!
The radiosonde is released, and the flight has begun!
The computer software will immediately detect when the radiosonde is released, due to the changes measured in atmospheric pressure as it begins to ascend. With the computer properly receiving data, it may be time for one last look at the balloon as it heads up into the sky. The dish must be manually pointed in the general direction of the radiosonde at the beginning of the flight, but once a strong and consistent signal is detected, the dish will track the motion of the radiosonde automatically.
After one minute has elapsed, the entire flight train is still easily visible.
After a few more minutes, the flight train itself will begin to fade from view, but the balloon can remain in sight for quite some time. The balloon will rise at a rate of about 1000 feet per minute -- or about one mile for every five minutes.
On some occasions, calm atmospheric winds may allow the flight train to rise almost directly overhead. On a clear day, the balloon can remain visible for a long period of time. Very rarely, the balloon may remain visible for the entire two hour flight -- right up until it bursts!
In the office, the radiosonde workstation computer will begin processing the incoming data. The data can be monitored throughout the flight, and must be checked to ensure it is of good quality. Below are examples of plots of temperature/humidity, pressure, winds, and trajectory. The trajectory plot follows the physical location of the radiosonde from its starting point at the launch site.
This data was collected from the evening balloon launch on November 16, 2007.
When the radiosonde reaches a pressure level of 70 millibars -- an altitude of around 60,000 feet -- the data is processed for transmission to the National Centers for Environmental Prediction (NCEP). After transmission, the data is made available to the National Weather Service, the private sector, the research community, and anyone else who may be interested. Since there are hundreds of soundings processed across the entire planet at the exact same time, the data can be thought of as creating a "snapshot" of the weather on a global scale. This large data set is one ingredient used in defining the initial atmospheric conditions for processing by numerical weather prediction models.
Below is an example of a fully-processed atmospheric sounding, as viewed on the computers in an National Weather Service office.
Click image for full-size version.
The line on the right represents the actual temperature, and the line on the left represents the dewpoint temperature. Pressure is plotted on a horizontal axis, with pressure decreasing (and therefore, height increasing) as one moves up the diagram. Temperature is plotted on a skewed, diagonal axis. The skewed axis of temperature (or T) gives this particular diagram its name: the Skew-T chart. Plotted on the right edge of the diagram are wind barbs, which depict the direction and speed of the wind throughout the vertical depth of the atmosphere.
As mentioned previously, when the balloon expands beyond the limits of its skin, it will burst, and the flight is terminated. This usually occurs about two hours after the launch, at elevations of above 100,000 feet -- and at atmospheric pressures of less than one percent of that found on the surface of the earth!
After the flight has terminated, the radiosonde will descend back to earth on the attached parachute. This can occur just a few miles from the launch point, or well over 100 miles away, depending on the strength of the winds in the atmosphere! Each radiosonde is equipped with a mailer and instructions for return shipment. About 20 percent of the radiosondes are located and returned for reconditioning and reuse. As for the other 80 percent? They may never be found, and it's such a shame to see them go...
...but there are plenty more where they came from!
12 hours later, the cycle will begin again, and a new set of data will be collected for the world to see.