Re: [CALBIRDS] Bird Migration Radar Images
- On Tue, 4 May 2004, Jim Gain wrote:
> I have been following the TexBirds email last night about a massive birdJim:
> liftoff during the night that they have been following on the NEXRAD
> website. So, naturally curious to see how it looked over the valley, I
> checked it out. WOW
> There is a huge flight of birds over the central valley right now. I started
> checking from the San Diego area and moved north. There is only a little
> movement right now down south, but by the time you look at the Fresno area,
> the radar screen is full.
> Go to http://www.rap.ucar.edu/weather/radar/ and click on an area, then
> click on the image to see the direction of the flocks. They are moving due
These plots look interesting, but forgive some naive questions. First,
how does one tell that these are birds one is seeing? Second, how does one
get a direction (such as "due north") from a one-dimensional color scale?
(Direction somehow needs to be two-dimensional.)
Thanks, Al Eisner
- I am not an expert in this, but I did sleep in a Holiday Inn last night...
Just kidding. I have received several emails asking for more clarification
about the radar images. My school Internet was shut down today because of
the worm going around so I couldn't respond until now. I only know a little
about this phenomenon. If you go to the site below and click on one of the
sites in California, you will get an image with lots of cloud-like
formations. You shouldn't have to change any of the settings. These could be
caused by one of three things, clouds, birds or bats. On a cloudless
evening, you can rule out the clouds. If you click on the image, you get a
second image that shows the relative movement of whatever the radar is
picking up. Blue indicates movement towards the radar and orange indicates
movement away from the radar. The images this morning clearly indicated a
northward movement. So that should indicate that it would be a large
movement of birds, not bats. I just checked the area over Hanford and it
shows a mixed cloud, without much uniform direction. When I then checked the
area over Brownsville TX (in darkness right now) the migration had begun. I
guess the birds start heading northward right before or shortly after
sunset. I would check it out starting around 8 or 8:30 this evening and see
how the clouds of migrants move north during the evening.
Again, I only know a little about this and am mostly passing along what I
followed on TexBirds.
From: Jim Gain [mailto:sta-birder@...]
Sent: Tuesday, May 04, 2004 5:36 AM
To: firstname.lastname@example.org; CALBIRDS@yahoogroups.com
Subject: [CALBIRDS] Bird Migration Radar Images
I have been following the TexBirds email last night about a massive bird
liftoff during the night that they have been following on the NEXRAD
website. So, naturally curious to see how it looked over the valley, I
checked it out. WOW
There is a huge flight of birds over the central valley right now. I started
checking from the San Diego area and moved north. There is only a little
movement right now down south, but by the time you look at the Fresno area,
the radar screen is full.
Go to http://www.rap.ucar.edu/weather/radar/ and click on an area, then
click on the image to see the direction of the flocks. They are moving due
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- In a message dated 5/5/2004 12:48:18 AM Mountain Standard Time,
These could be
caused by one of three things, clouds, birds or bats.
Or bugs. NEXRAD is very sensitive and can even show reflectivity from smoke
(range / forest fires). It's great at picking up evening flights of bugs
(moths, etc.), especially in the Southeast at night. You'll see a nice "bloom"
around the radar sites, usually going in the direction of the prevailing winds.
Check the winds -- if the direction of movement shown on radar (radial
velocity) is against the prevailing winds, then it's probably something mobile
enough to proceed against the breeze (birds) and not most bugs (which generally
flow with the prevaling winds, depending on strength).
During the daytime, flights of birds can be seen on radar as a "donut" shape
around the radar shape -- an orangish circle or crescent, depending on whether
or not the bird "frontal migration" is just approaching the radar or whether
it is all around the site. This is because the birds generally fly at a given
altitude range, and since the radar shoots at an angle from the ground, it
will only start picking up reflectivity from birds a certain distance away from
the radar site (corresponding to the elevation of the birds). At least this
is the case over the Gulf of Mexico and slightly inland. I'm not sure how
birds migrate once far inland...
Evening flights of moths, (or the evening departure of birds from the ground,
gaining altitude) show up as a multi-colored "bloom" instead of a donut,
because of the reflectivity at altitudes from ground-level to much higher. Again,
prevailing breezes can provide a clue as to whether or not these are birds or
It's fun stuff to watch, but can be tricky to interpret correctly. It's
easier to note arrivals off the Gulf of Mexico in spring than it is to observe and
interpret departures in fall!
Stacy Jon Peterson
4442 Sijan St. Apt. A
Mtn Home AFB, ID 83648
USDA zone 6a; Sunset zone 3, AHS Heat zone 7
Race for the Rain Forest!
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