Wednesday, October 17, 2012

How high do weather balloons rise?

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 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 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)


Ron said...

But we could get a LOT more of the radiosondes back. Around 2006 the equipment was upgraded with GPS. So now we know the exact latitude/longitude of every radiosonde as it ascends. Unfortunately, the software stops processing this data as soon as the balloon bursts and the parachute deploys. But we could know the exact location of the landing site if the software would just continue processing the data on the descent. Then the locations could be posted on a geo-cache website for folks to retrieve the instruments.

Karen said...

this is my favorite weather balloon video...

dad launching his son's favorite toy up into space and filming the whole thing for him. Hope to do something so cool with my kids one day.

Brian Longworth said...

Dr. Mass,
I think you will enjoy this video then.
Some folks launched a beer can on a weather balloon to test Coors Light's "Super Cold" can.
The great thing about it is that they attached a thermometer to the camera. You can see exactly when the experiment crosses the cryosphere boundary by the dramatic temperature rise.

Snoqualman said...

So 80% of these things are out there littering the landscape? Not good.

anna olive said...

Hi Cliff, I couldn't find another spot to contact you so I"m just leaving this in the comments. Woke up about 7:35am to a beautiful day on Maury Island. I looked to the west and above the Olympics was, what appeared to be a fully formed funnel cloud. It was very thin but very "tight" and tall. By the time I got my camera from the car it was gone.

Ansel said...

Does anyone know- is there some way that planes can avoid these things? Or is there a finite risk that the instrument box of a radiosonde could hit the cockpit window of a jetliner or get sucked through the engine?