Weather Radars Reveal an 80 Percent Chance of … Dragonflies?

If it seems that bugs are buzzing around more often and in greater numbers lately — whether swarms of ladybugs over California or hoverflies streaming in and out of England by the billions — it may simply be that radar technology is getting more efficient.

On Monday, Doug Kahn, a meteorologist at the National Weather Service in Cleveland, saw several bluish masses shifting and swelling over Ohio. The undulating blobs on the radar were not storm clouds or a weather system, but a swarm of dragonflies.

“There are millions of them,” he said. “That is why you can see so many of them on the radar.”

According to Mr. Kahn, 24, the Weather Service uses a dual-polarization radar capable of providing an almost 3-D image of whatever may be in the atmosphere.

The technology scans horizontally and vertically to take the dimensions of what is in the air, allowing meteorologists to figure out what is in the atmosphere even before they can see it in person, Mr. Kahn explained.

“We can confirm that it is biological matter because of the dual-polarization radar,” he said.

Radars like the ones used by the Weather Service are often used to track the seasonal movements of bees, birds, flies and other airborne creatures. Migration is common in insects and birds, according to Sara Kross, director of the master’s program in ecology, evolution and conservation biology at Columbia University.

“There are species that will migrate and those that will move due to the weather patterns,” Dr. Kross said.

“We now can predict when we will see waves of birds all through radar and knowledge,” she continued. “Right now, because of radar, we can see it happening in real time.”

It is the same science used to detect precipitation. Meteorologists usually can tell the size of the insect when the activity is picked up on the radar, according to Mr. Kahn. They then compare that with various precipitation to begin to deduce what the objects in the air could be.

“Insects are usually kind of longer” than a raindrop or a snowflake, Mr. Kahn explained. That results in a higher ratio of length to the height.

“If we see a thunderstorm, the radar sends up a beam and it hits clouds in the sky and it returns that imaging to us,” Mr. Kahn said. The only difference with insects is that the radar bounces off the millions of tiny bodies in the swarm.

It appears none of the swarm occurrences are rare.

“Picking up on the sheer scale of migration is something you can deduce from data,” Dr. Kross said. “But having radar really shows the intricacies of those movements.”

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