2008-01-21 23:45:34.000 – Ryan Knapp, Staff Meteorologist
Problems with our winds…
Back when I was in college, I was required to take a number of general education courses. These courses where usually fun but what made them interesting were their sizes. My meteorology classes only had about five students where as my general education lectures would have upwards of one hundred people or more crammed in a lecture hall. But despite the class size, a handful of phrases were always repeated on the first day of each class in one way or another. One of them was, “Don’t hesitate to ask a question because odds are if you don’t understand something, there is at least one other person in the room that doesn’t understand it with you.”
If you checked out our current weather page on the 21st, you would have noticed something odd with the wind profile. If you did not check it out, I have posted a picture highlighting the issue with two black circles. Someone raised the question in our forums asking “Did you get some icing on the pitot tube?” The short answer is yes.
So to start, we use a pitot-static (that’s pitot not pilot) anemometer. This instrument is usually what is on aircrafts to provide pilots with speeds and altimeter readings. We have adapted this technology to measure winds on the summit. So instead of us flying through the air the air flies through us. In a nut shell, it measures wind based on differences of pressure. For a more in-depth description, you can CLICK HERE for a fairly descriptive wikipedia.org entry or you can always take a tour of the facility via our Edutrips, daytrips or during the summer when the building is open.
Anyhow, hooked up to this instrument are two, quarter inch diameter lines of copper and plastic tubing. One measuring total pressure and the other measures what is called static pressure. The whole unit is heated although it still needs to be de-iced because it does have parts that are vulnerable to icing. We also make use of heat tape to heat the tubes coming into the building since they are in an unheated part of the building. From time to time, some moisture makes it into the line and will either make its way down into the weather room muffling the gusts measured or it will condensate on the inside of the tube. The condensation will then become ice, especially when temperatures are as low as we received last night (around -26, not a record but still cold). Despite the heating elements and heat tape, with temperatures as low as they got, the system is still vulnerable.
As the ice builds, it will either cause an instant jam causing measured winds to die in a matter of minutes or gradually freeze up and reducing winds slowly. The first case was an instantaneous jam while the other was a gradual jam. To remedy this problem, we try to reverse pressurize the system to dislodge the ice or in extreme circumstances (like these two were), we use Methanol. Methanol is a type of alcohol that works as an antifreeze and also quickly evaporates so it works great to deice the lines with. The down side is it is highly flammable (and burns invisibly, or without smoke), can cause blindness, damage to the central nervous system or respiratory failure. So we have to wear latex gloves and a face mask when dealing with this chemical and keep all heat sources away. Despite the risks, we unclogged the lines and all seems well for now and we didn’t miss any of the 100 mph gusts thankfully. So now you know and knowing is half the battle.
Ryan Knapp, Staff Meteorologist