This week we were all thrilled by the jump of Felix Baumgartner from a balloon that ascended to 128,000 ft. At that height he was above the vast majority of the atmosphere (99% of the atmosphere was below him!), the sky was nearly as black as space, and the curvature of the earth was obvious (see picture). Simply amazing.
But what about weather balloons...also know as radiosondes...how high do they fly?
Radiosondes are launched twice a day at 92 locations around the U.S. (see map and picture).
As shown by the picture, these units include a balloon, a parachute, and an instrument package that radios back temperature, humidity, pressure, and sometimes position (for units with GPS). Winds can be computed by tracking the radio signal and some trigonometry. Radiosondes originated in the late 1920s and have been an important part of the weather observing network ever since. The biggest problem with them is that they are mainly limited to land stations.
The pressure near sea level averages around 1013 hPa (hPa is unit of pressure and is the same as a millibar). Most radiosondes rise to 5-15 hPa before the balloons burst (the balloon expands as the pressure decreases around it...finally the balloon gets so large it breaks up). Then the parachute brings the unit back down to earth in an controlled way.
What heights are these balloons reaching? Roughly 100,000 ft or 20 miles. A few of the balloons ascend to 5 hPa, reaching around 115,000 ft---not quite as high as Felix Baumgartner.
Pressure tells you about the amount of atmosphere above you, so if you go from roughly 1000 hPa to 10 hPa, you are rising above 99% of the atmosphere. Felix was virtually in space--without his space suit he would not have survived.
Many people wonder...how many of the radiosonde are recovered and reused? According to the National Weather Service less than 20% of the 75,000 radiosonde launched by the U.S. are recovered. Considering that they cost several hundred dollar each, this is not a trivial cost (plus gas, parachutes, labor costs).
A funny story...several years ago I gave a lecture on radiosondes to my 101 class. The next day a grinning student walks in with one. Where did you get it, I asked? Turns out he was playing basketball with his friends when the sonde drifted down into their game. The radiosonde had been launched at McChord and then drifted north under southerly winds. His friends were mighty impressed with his knowledge of the device!
Here is the plot of the latest radiosonde data from a nearby launch location: Quillayute (or Forks) on the Washington coast. This unit got to 10 hPa. The black line to the right is temperature, left line is dewpoint, and the y axis is pressure. The bottom (x axis) is temperature. Temperatures dropped off with height until the radiosonde reached the stratosphere, after which they increased. The winds were weaker up there too.
One of my favorite type of videos are made by folks launching a camcorder on a weather balloon--essentially doing remotely what Felix did this week. Here is a good one (click on image)