Monday, April 4, 2011

More Radar Fun

A check of Nexrad tonight showed a bit of migration along the east coast just ahead of the big storm moving through. Behind the front, little if any movement. A look at the radar in the Florida Keys shows some activity.

In this image the returns over the keys is actually a movement of birds that came out of Cuba and are headed to Florida. In the past there was a radar image in Cuba that was viewable but it was often not functioning and I haven't seen an image from there in a while.

Once this big storm system moves offshore and the winds switch around the movement of birds should resume. The next 2 nights should see birds headed north.

1 comment:

Anonymous said...

I think you have to be very careful when concluding that the returns are a result of migrating birds. The more likely cause for this return is atmospheric and scientific. Anomalous Propagation or false return, is most common late in the evening and especially around dawn when relative humidity's are at their highest. Such returns are typical under an inversion when warm dry air overlaps humid and relatively cooler air near the surface. The most common type of false return is called superrefraction. Superrefraction is where the radar beam is bent greater than normal back toward the earth. If the bending is severe it can actually intersect with the earth's surface. With superrefraction, not only can the radar not see the more distant "real" precipitation, it can also appear the most real.
Furthermore, assuming that most birds will migrate between 1000ft and 2000ft, their signal (and there would almost have to be millions of birds) would most likely not be detected on radar unless they were flying very close to the site. In other words, the radar beam increases in height as the signal travels out from the radar site. Most birds would be flying "under the radar" if you will. Finally, I also checked the winds in the SE part of the country and found that most winds were Southwesterly or even Westerly in direction which is not an ideal tail wind that birds often take advantage of.