Graphic by John Idzikowski News from the Night Sky Radar and Songbird Migration by Kevin Kearns, Neenah, Wisconsin
Watching the Radar for "Donuts" When I read the National Weather Service maps, I watch for "donuts" to form. The donuts that I am referring to are what appear on the radar at liftoff. If you look at a site before sunset, the image should be mostly clear. But when the birds pick up, the radar will pick them up in all 360 degrees. This forms a large circle. The center directly above the radar will be empty because there is no signal bouncing back due to the radar beam going out at a .5 degree angle. Where the beam encounters the highest density of birds, there will be the highest reading. As the beam continues outward, it will encounter fewer birds due to higher elevation until it encounters nothing. The entire image then looks like a donut. I am looking for an increase in "clutter" being detected on the radar at a certain time at night - sunset - and lasting for anywhere from 4 hours to all night. As the night progresses, the colors in the "Donut" go from light blue to darker blue to Green. Medium Blue: 10 decibels (DBZ) or 71 birds per cubic km Dark Blue: 15 DBZ or 109 birds per cubic km Light Green: 20 DBZ or 229 birds per cubic km Medium Green: 25 DBZ or 602 birds per cubic km Dark Green is 30 DBZ or 1,788 birds per cubic km. Yellow: above 35 DBZ, or over 3,000 birds per cubic km Wisconsin occasionally reaches yellow. These peak night usually happen in mid-May along the Mississippi river	A "donut" where migration is strong
	Graphic by John Idzikowski
	Radar beam and height of birds
	Graphic by John Idzikowski
	Radar sites in the United States
What do the colors mean? The colors are the different values of energy that are reflected back toward the radar. What do the colors mean? Copyright 1996-2006 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form