Identifying icing events in wind data

Here are a few general guidelines regarding icing events:

• Typically, the vanes will freeze first. Both the average and standard deviation of an iced vane channel will read 0 before the average and standard deviation of an iced anemometer channel found at the same level on the tower will read 0. The time can be from a few hours to several hours ahead of the anemometer channel going to 0.
• For an anemometer, the standard deviation will slowly decrease to lower than normal levels over the course of many 10 minute intervals as the ice builds up on the cups. The additional mass of the ice makes the anemometer act more like a flywheel -responding more slowly to changes in wind speed. Hence, the lower standard deviation.
• After many 10 minute intervals of showing a decreasing standard deviation, the anemometer channel will often show a standard deviation "spike" in the 10 minute interval right before the anemometer stops spinning. That is, the standard deviation will rise sharply in one interval within a few 10 minute intervals of the anemometer stopping and then quickly go to 0.
• Check the temperature probe channel. Icing likes to happen in the temperature range right around the freezing point of 0 C (32 F).

Whenever possible, use an IceFree3 sensor.