NFC-enthusiasts, Jeff pointed out the radar echoes tonight which are pretty impressive, especially along the Carolina and Virginia coasts. Being a meteorologist and a birdwatcher, this is of great interest to me. For those who are interested in sources of information about the weather patterns aside from using the radar to detect objects, you can get some information on my personal website: http://homes.comet.ucar.edu/~guarente/birdweather/index.htm I have compiled the links I often use for my own meteorological exploration, as well as sites that would be useful specifically for bird migration.
I personally am a fan of checking the forecast streamlines for bird migration as this is a good predictor of which nights will be good for migration, but does not necessarily dictate when there will be detectable NFCs, as other meteorological factors play in to this. To see the streamlines you can go here: http://homes.comet.ucar.edu/~guarente/birdweather/stream.htm Streamlines show the direction weightless particles would travel if released in the wind field. All times on this page are plotted on the top of the images, but they are noted in UTC. To see the current UTC time, you can go here: http://www.time.gov/timezone.cgi?UTC/s/0/java Also, the maps differ in height from the surface through 700mb (or hPa). These maps use pressure as the height coordinate, but can be roughly thought of as 900mb = .5km above sea-level, 850mb = 1.0km above sea-level, and 700mb = 1.5km above sea-level. The "Surface" maps plotted here are the surface of the earth following topography. Sorry to all those individuals outside of the US, I only have access to the US model data, so I cannot currently plot other locations aside from North America. Where the current streamlines have a component pointing toward the south the radar echoes are brightest, except for where there is significant topography to block the radar beam (the western 1/3 of the US). Back to the radar: I am hoping someone will be able to point me in the direction of a publication that discusses the radar cross-section or backscattering properties of a bird in flight. Are there any papers out there about this? I have found the papers that mention that birds show up on radar, but none of them seem to mention the backscattering properties of the birds. The current radars in the United States are very sensitive to the size of the object they are reflecting waves off, up to a point. This can mean very different echoes for drizzle drops, rain drops, small hail, very large hail, and birds because of the scattering regime in which it lies (click link to read wikipedia article about scattering). Most particles in the atmosphere that are detected by weather radars are in the Rayleigh scattering regime, but birds don't always fit in this regime, often extending in to the Mie scattering regime which is not ideal for US weather radar detection. However, that is assuming that a bird is a sphere, which is a poor assumption. I am hoping to get my hands on some papers about the scattering properties of birds that show how the radar waves reflect, but have yet to find any. There are some algorithm papers available by Dinevich, but these lack the actual scattering properties. Anyone have a reference for me? Thanks for any references you may have, Bryan Guarente Instructional Designer The COMET Program University Corporation for Atmospheric Research Boulder, CO -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html --
