We are at that time of year when there are a large number of migratory water fowl transiting the area. With the change of seasons, a wide variety of avian species are heading south. Many nest in area lakes, taking off around sunrise.
When the atmospheric conditions are correct, these flocks of birds are 'visible' on the Mayville Doppler RADAR as they lift off of area lakes. As they take flight, near concentric rings become visible, expanding outward, quickly "dissipating" as the flocks disperse. Below are a few images from the Mayville Doppler captured around sunrise, Tuesday September 13 2011.
This phenomena is relatively common, especially in the spring, fall and other times when the Flyways are especially busy. Atmospheric conditions have to be just right, with an inversion near the surface of the Earth. This inversion bends the RADAR beam in such a way that it is closer to the surface than it is under normal conditions. This "ducting" of the RADAR beam allows for objects close to the actual surface - such as birds taking off - to be readily visible.
Although weather RADAR's main role is to help the meteorologist analyze and diagnose the atmosphere for precipitation, that analysis covers everything from precipitation type to intensity to severe weather characteristics for thunderstorms and tornadoes. However, it also gives us a look at other features in the atmosphere that you may not have been aware of. Birds taking flight is one of the less common, but very interesting phenomena we see from time to time.
Mayville Doppler RADAR image of Bird Rings at 709am CDT September 13 2011. Click for a larger version. The line extending to the east from the Mayville RADAR is the "sunrise effect".
A negative image of the Mayville Doppler from 659 am September 13 2011. Click for a larger version.