WSR-88D DEPICTION OF "FOWL" WEATHER
As you may or may not know, weather RADAR (RAdio Detection And
Ranging) has been in use for decades to detect precipitation in all
forms, from rainfall to snow to hail. These targets are known
as non-biological targets. In addition to precipitation, radar
is used to monitor aircraft on a regular basis. But did you
know that the radar "sees" other objects in the sky as well?
Radar operates by sending out a narrow beam of electromagnetic
energy into the atmosphere as it rotates. Some of that energy
bounces back off precipitation and is captured by the radar dish as
a "return echo". Those echoes are then processed by a computer
and plotted on the radar map which you can access through many
sources including TV and Internet. Although the radar is
"tuned" to see objects about the size of rain drops and snow flakes,
it also receives reflected energy from other sources ranging from
dust particles, smoke and cloud droplets on the small side to
insects and birds on the large side. The FAA has radars that
are tuned to look at even bigger objects such as aircraft.
Fig 1: WSR-88D Mosaic Radar Image
8/16/11 1034z at 0.5 degree elevation showing several bird
rings across the Lower Great Lakes.
|This time of the year some really weird patterns begin
to appear on the weather radar. One of those patterns
is a series of rings that appear right around sunrise for
just a few minutes on certain days. If you look at a
mosaic of weather radars, you may see several of these
"rings" on any given day (Fig.1 ). What are they?
Well, they're actually birds, hence the reference to "Fowl"
weather in the headline.
|Beginning in late June and July, after most birds have
completed the breeding season, they begin to assemble in
large groups at roosting sites. These groups of birds
can sometimes number in the thousands. Each morning,
right around sunrise, the birds begin to leave the roosting
site for the day to feed. As they rise into the sky
and head out in all directions, they pass through the radar
beam and reflect a bit of energy back to the radar.
Since they all leave around the same time and head in all
directions, they form a ring as they move away from the
roosting site, hence the rings that appear on the radar.
|If you click on Figure 2, you will load an animated
gif (warning, it's 3mb in size) that will provide a loop
of the development of several bird rings that occurred
on a recent morning across the Lower Great Lakes Region.
You can follow the development of the rings, beginning in
the east and expanding westward as the sun rises across
the landscape. As noted, when the birds leave their
roost, the bird rings expand. Most of the
rings occur along the shoreline of the Great Lakes where
there are several State, Provincial or National Wildlife
Fig. 2: WSR-88D animation showing the evolution of
the bird rings across the Lower Great lakes Region on
In Figure 3, I have identified
the locations of nearly a dozen of those bird
rings which, not too surprisingly, are
associated with popular bird watching spots
and known locations for roosting sites.
These include but are not limited to:
Fig 3: Locations of several bird rings
detected on the WSR-88D.
- Cape Vincent at the head of the St. Lawrence River
- Montezuma National Wildlife Refuge in The Finger Lakes
Region of New York
- The Iroquois National Wildlife Refuge in Western New
- Presqu'ile Point on the north shore of Lake Ontario,
- Selkirk Provincial Park near Port Dover on the north
shore of Lake Erie Ontario Canada
- Long Point Ontario on the north shore of Lake Erie
- Presque Isle on south shore of Lake Erie near Erie PA
- Near Fairport Harbor on south shore of Lake Erie
- Pt. Mouillee State Game Area MI at west end of Lake Erie
- East shore of Lake St. Clair, Ontario Canada
- East shore of Saginaw Bay on Lake Huron.
|In summary, the weather radar's main
role is to help the meteorologist analyze
and diagnose the atmosphere for
precipitation. That analysis covers
everything from precipitation type to
intensity to severe weather characteristics
for thunderstorms and tornadoes.
However, it also gives us a look at other
features in the atmosphere that you may not
have been aware of. Before leaving, I
will bet some of you were wondering about
those curious "spikes" that occur from each
radar for a scan or two in the animation you
saw. That is the radar detecting the
electromagnetic energy from the sun as it
rise above the horizon. We will talk
more about that in a future article, stay