Something other than the weather showed up in the radar data over St. Louis, Missouri, the other day. Meteorologists at the local branch of the National Weather Service detected an odd-looking cloud moving southwest over the city that was not behaving like any normal weather pattern they were used to observing. What’s more, the skies were clear and there were no clouds in sight. So what was the butterfly-shaped cloud flickering on the radar display? It turns out, real butterflies.
The word “radar” originally comes from the U.S. Navy acronym: RAdio Detection And Ranging. The technology was developed in the late 1930’s and uses radio waves to detect the presence, shape, motion, etc. of objects. A radar dish or antenna sends out radio waves out that hit objects in their path and bounce back. The change between the signal sent out and the signal received provides information on both the type of object the signal encountered and how it’s moving.
Radar systems tailor their wavelengths to match the phenomena they are interested in observing. For weather, that means water in the atmosphere. Weather radar systems use wavelengths comparable to the size of water molecules in order to detect water vapor, raindrops, snowflakes, etc. (roughly 1-10 cm which corresponds to a frequency range of 2-18 GHz).
Sometimes though, their signals pick up other things, like dust or bats or birds. Last month over St. Louis, it was butterflies.
In the radar data are parameters that indicate shape and how that shape is changing. Both of these pointed to something oblate that was morphing with some periodicity, something like a pulse. From experience, meteorologists were able to rule out swarms of bats or birds since they’ve seen those before. But it took a little sleuthing (with Google of all things) to realize migrating monarch butterflies were the likely answer. Truthfully, there’s no way to know for sure, but I like to think the butterfly-shaped cloud was the monarchs’ way of flying south in style. Here’s some other geek that may have flown over your head lately: Keep on geeking! @Summer_Ash
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