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Re: [CALBIRDS] Bird Migration Radar Images

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  • Al Eisner
    ... Jim: 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
    Message 1 of 4 , May 4 1:37 PM
      On Tue, 4 May 2004, Jim Gain wrote:

      > 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
      > north.

      Jim:
      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
    • Jim Gain
      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
      Message 2 of 4 , May 4 7:18 PM
        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.

        Jim Gain
        Modesto

        -----Original Message-----
        From: Jim Gain [mailto:sta-birder@...]
        Sent: Tuesday, May 04, 2004 5:36 AM
        To: central_valley_birds@yahoogroups.com; 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
        north.



        Jim Gain

        Modesto



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      • SJPeterson@aol.com
        In a message dated 5/5/2004 12:48:18 AM Mountain Standard Time, CALBIRDS@yahoogroups.com writes: These could be caused by one of three things, clouds, birds or
        Message 3 of 4 , May 5 10:40 AM
          In a message dated 5/5/2004 12:48:18 AM Mountain Standard Time,
          CALBIRDS@yahoogroups.com writes:
          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
          bugs.

          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!

          Best,

          --Stacy

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