Doppler weather radar has become ubiquitous in today’s American culture as people seek to stay updated on weather conditions from home, from their cell phone, and while on the road.Â But on calm weather days, meteorologists have time to examine some of their tools and instruments with a different eye.
While doppler weather radar is traditionally used to detect water and ice droplets in the sky – otherwise known as clouds and precipitation – weather radar has also been shown to detect birds, buildings, vehicular traffic, airplanes, and even the smoke from the collapsing World Trade Center towers and the disintegration of the Space Shuttle following the 2003 Shuttle Columbia disaster.
Take, for instance, the case of the National Weather Service doppler radar located just outside of Chicago, Illinois.Â On August 12, 2008 the local doppler radar was able to detect traffic flowing on Interstates 55 and 57.Â When a low-altitude layer of warm air developed over the region, the radar beam was refracted lower to the ground than normal.Â The result was the radar beam being bounced off of vehicles along the area interstates.Â (Click each image for a larger view).
What sets doppler radar apart from first-generation traditional radar tools is that doppler radar can detect velocities; that is, it can detect the speed at which droplets are moving toward or away from the radar site. Not only does the radar detect the presence of the vehicles, but also their velocities.Â When the radar is switched into velocity mode, the display shows red and green shades – green representing movement toward the radar and red representing movement away from the radar site:
When keyed to the green and red shades represented in the image above, the radar indicates some traffic was flowing as fast as 115 knots (130mph).Â The National Weather Service, however, states that this may simply be “noise” – false radar returns – rather than someone actually driving that fast.
When bats congregate in large swarms, their volume can reflect the radar signal in sufficient strength to be detected by the radar tower, as shown in this image (which also displays a supercell thunderstorm) from the Storm Prediction Center, taken over Texas in 2006:
The National Weather Service has archived a loop of radar images of the above even displaying a supercell thunderstorm swallowing a swarm of bats.
Birds and Migrations
The National Weather Service out of Green Bay, Wisconsin captured an amazing set of images displaying a large group of birds leaving from Green Island on the morning of August 10th, 2006:
Research is being done on how radar may actually be useful in tracking certain migratory species over large distances:Â Radar technology – A tool for detecting migratory aerofauna.
Space Shuttle Columbia Disintegration
In February of 2003, the Space Shuttle Columbia disintegrated on re-entry as it attempted to land in Cape Canaveral, Florida.Â As the shuttle broke apart in the upper atmosphere, weather radar towers in the southern states detected the debris streaming through the atmosphere late that morning, as shown in this image from the Shreveport, LA National Weather Service office on the morning of February 1st, 2003:
The National Weather Service has compiled an in-depth archive of the Shuttle Columbia Diaster.
September 11th Attacks
Following the collapse of the World Trade Center towers in New York City as a result of the terrorist attacks of September 11th, 2001, the New York City radar detected the plume of smoke slowly rising over New York City that morning (click image for larger view):
Sunrises and Sunsets
Whenever the sun gets low in the sky – at sunrise or sunset – its electromagnetic energy can wreck havoc with a doppler radar receiver.Â When the energy is received by the radar site, the algorithms often display this energy as a “spike” on radar.Â The images below are from the Twin cities radar site in Chanhassen, Minnesota.Â Interestingly, the spike changes position with the seasons.Â Click each image for a larger view:
Winter:Â When the sun sets South of due West in the winter, the “sunset spike” indicates as much:
Summer:Â When the sun sets North of due West:
Finally, when the sun rises and sets due East and West, respectively, the radar spike reflects that direction as well – an event that occurs twice each year – the first day of spring and the first day of fall:
Spring and Fall: