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70-Mile-Wide Butterfly Migration Detected on Radar in Colorado
Published: October 5, 2017
Meteorologists at the National Weather Service (NWS) in Boulder, Colorado, spotted something unusual Tuesday when checking Doppler radar on what was an otherwise calm weather day.
At first, the NWS meteorologists thought the radar echoes spreading from east to west across the Colorado Front Range, including the Denver metro area, were birds. Observing birds on radar is a fairly common occurrence, especially when they take flight early in the morning.
But after some additional investigation, the mystery of what the radar was sensing pointed to another culprit: migrating butterflies.
You can see the radar echoes in purple (left side) and blue (right side) advancing from right to left in the animation below (originally labeled as birds). The NWS estimated that the swath of butterflies was more than 70 miles wide, extending across all of Arapahoe County.
There was ground truth to prove that butterflies were the cause of the radar echoes based on photo reports from social media. Several tweets described seeing dozens of painted lady butterflies in yards of Denver metro residents Tuesday.
The NWS said that insects rarely produce such a well-defined radar signature as they saw on Tuesday, which led to the initial hunch that they were seeing birds.
This case was different, however, since butterflies have larger wings than a typical insect and the fact that they were highly concentrated as they flew with the wind flow at that time. Those two factors made them a big enough target for the radar to detect in a vivid manner.
Painted lady butterflies migrate 9,000 miles from California to Mexico each year, according to 9news.com. The Denver metro area has been encountering them since at least the middle of September.
This isn't the only non-weather feature radar can detect. Here are 17 other things we've seen in recent years.
1. Flying Ants
In mid-July 2017 the Met Office tweeted out the image below that showed radar detecting something in an area with no clouds over the United Kingdom. After taking a poll of answers, the Met Office revealed that the radar spotted flying ants.
The Met Office said flying ants "disperse in particular conditions dependent on temperature, humidity and wind speed." It's a summertime occurrence when the winged ants take off on a reproduction mission to create a new colony, according to BBC.com.
2. Ski Resort Chairlift
Doppler radar in Montana detected an unusual feature on April 10, 2017 as a small area of orange and red echoes made an appearance southwest of Billings in calm weather conditions.
The small blip of radar activity was investigated by the National Weather Service (NWS) in Billings after a Twitter user asked them what it may have been. It was determined that the radar activity was likely associated with chairlifts at the Red Lodge Mountain ski area.
Zooming in closer on the radar image of the orange and red pixels you can see how they match up with the ski area. Notice how the various ski runs appear through the slightly transparent radar echoes.
3. Interstate Traffic
Traffic moving along Interstate 37 between Corpus Christi and San Antonio was spotted on April 17, 2017, as the National Weather Service pointed out. You can see this in the narrow line of pink and light blue shadings in the animation below well northwest of Corpus Christi between the town labels for Mathis and Edroy.
In cases with a warm layer of air just above the surface, and relatively cool air near the surface, radar can detect traffic, most commonly at night. When this happens, the radar beam is ducted, or bent downward, following the curvature of the Earth, rather than its normal path shooting up higher and higher, reflecting off things such as highway traffic. Another example of this occurred on Interstate 20 near Dallas-Fort Worth during July 2016.
4. Gaggle of Geese
As the International Space Station soared southeastward across the evening sky Feb. 15, 2017 in northeastern Arkansas, the National Weather Service office in Memphis, Tennessee, spotted a large flock of geese on radar, which appeared to be chasing the ISS.
The grayish-colored reflectivity appearing in the two-hour radar loop above, spanning from 6:30 to 8:30 p.m. CST on Feb. 15, indicates the gaggle of geese flying over northeastern Arkansas in hopes of catching up with the ISS. In reality, they can't physically catch it since the ISS is in space and the geese are likely flying just a few thousand feet above the Earth's surface.
A couple hours later, NWS-Memphis checked on the geese again. The determined animals had slipped below the main Memphis radar beam but were spotted by a smaller tower radar near the Mississippi River in Tunica, Mississippi.
5. Birds Inside the Eye of Hurricane Hermine
As Hurricane Hermine made landfall along Florida's Gulf coast in early September 2016, radar detected an interesting phenomenon: birds trapped flying inside the calm eye of Hermine.
The birds were detected using differential reflectivity from NOAA's Dual-Polarization radar. This particular radar feature can be used to detect non-meteorological radar echoes such as birds and insects, in addition to its normal precipitation detection function.
We've seen this occur one other time in recent years during another U.S. hurricane landfall. Birds were detected on radar in the eye of Arthur as it moved near the coast of North Carolina in 2014.
6. Mayfly Hatch
(National Weather Service La Crosse, Wisconsin.)
At some point during the summer every year, the Doppler radar at the NWS in La Crosse, Wisconsin, lights up with echoes, indicating that a mayfly hatch has occurred.
This happened most recently on the evening of July 26, 2016, where it usually does right along the Mississippi River near the Minnesota and Wisconsin border. The mayflies often emerge in enormous numbers, allowing radar to detect them.
You can see the recent hatch in the image above in the green echoes from near the label for the city of La Crosse southward along the river.
7. The Bat Signal
This image was posted by the NWS in San Antonio, Texas, on June 13, 2016 with a caption "The Bat Signal is strong tonight!"
Each circle on the map shows an emerging bat colony detected by radar as they depart for the evening to feast on insects. This is a common summertime occurrence in central Texas.
Sometimes, bats even exit their caves in waves like seen here north of San Antonio as concentric rings.
8. Swarming Termites
We're used to seeing bird flocks on radar at sunrise, but it looks like insect swarms are getting picked up tonight. pic.twitter.com/ohord8G8lJ— NWS New Orleans (@NWSNewOrleans) May 30, 2016
The above image posted by the NWS in New Orleans on the evening of May 29, 2016. In that radar image, termites can be seen swarming near the Big Easy, captured in the shades of dark blue and light green. The image was part of a radar loop that was posted to the NWS office's Twitter account.
9. Birds Along Nebraska's Platte River
This radar image from March 2, 2016, shows birds that were observed by radar along the Platte River in Nebraska. The birds are represented by the green and blue shadings near the red line, which is Interstate 80 along the Platte River in central Nebraska. Video taken the previous day verified the existence of a large number of sandhill cranes in the area, according to a Facebook post by the Rowe Sanctuary.
10. Grasshoppers and Beetles
Grasshoppers and beetles detected by radar near the border between Texas and Oklahoma on July 22, 2015.
The green and yellow radar echoes in this image from July 22, 2015, show grasshoppers and beetles detected by radar near the border between Texas and Oklahoma, according to a tweet sent by the NWS office in Norman, Oklahoma. Since the radar is very sensitive, you would not see a huge swarm at ground level, the NWS said.
11. Monarch Butterfly Migration
(National Weather Service Reno, Nevada)
The NWS office in Reno, Nevada, posted to Twitter on March 27, 2015, the radar image above that shows the spring migration of Monarch butterflies. These butterflies were spotted using a differential reflectivity scan, which is typically used to identify different types of precipitation, hail size and tornadic debris. As shown in the example above, it can also identify non-meteorological echoes such as birds and insects. In this case, the NWS says the differential reflectivity shows objects that are much wider than they are taller, or what you would expect from the body type of a butterfly.
12. Birds Migrating
Tom Niziol, winter weather expert at The Weather Channel, captured this radar image of migrating birds in western New York on the evening of April 12, 2012.
Niziol says, "On the animation above I have penciled in what I describe as 'bird front' to outline the leading edge of the bird migration as it heads from the south shores of both Lakes Erie and Ontario across the water just after sunset."
You can read Tom's full article on this subject here.
13. Departing Train
Watch closely. Now, watch it again. That brief red streak moving to the northwest is actually a train leaving a terminal. The NWS office in El Paso captured it on its radar.
This is similar to how radar detected the interstate traffic earlier in this article.
On April 30, 2013, the NWS office in Flagstaff, Arizona, grabbed this radar image detecting bugs in the green and blue shadings at the top left. The velocity image on the top right shows that the radar is able to track the direction of movement of these bugs.
15. Military Exercises
This image from the NWS office in Jacksonville, Florida, shows chaff in the narrow bands of green and blue radar echoes. Chaff are small pieces of aluminum which are released by military aircraft for self-defense to avoid radar detection.
16. California's Springs Fire
On May 2, 2013, the smoke plume from the Springs fire near Camarillo, California, was picked up on radar. The smoke plume shows up in the green and blue shaded radar echoes south-southwest of Camarillo.
17. Wind Farm Interference
Energy created by wind farms can mess with radar results. The Butler Ridge wind farm west of Milwaukee is one example. According to NWS Milwaukee/Sullivan, turbines stretch about 400 feet into the air, and sit within the line of sight of the NWS doppler radar in Jefferson County, Wisconsin.
"A small part of the electromagnetic energy radar beam sent from the radar is reflected back by the rotating turbines," the NWS said. "The radar processes this 'returned energy' as an area of precipitation and plots it accordingly on the map," which you can see circled in yellow.
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