Weird National Radar mosaic
- Thread starter gismo
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We been tellin' ya. The country got a lotta rain. 
ScottM
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iBazinga!
EMPs
This is a phenomena known as anomalous propagation (or anaprop) which is caused by temperature inversions bending the radar beam back to the surface. It tends to happen under high pressure conditions at night. Unlike ground clutter, which is stationary in nature it is hard to filter since it is often transient and its characteristics depend on the the nature of the temperature inversion.
Hope this helps!
Cheers,
Gareth.
Hope this helps!
Cheers,
Gareth.
wby0nder
Cleared for Takeoff
You will also sometimes see lines or induvidual rays projecting from each radar site all pointed in the same direction either east-ish or west-ish. They appear around sunrise or sunset and are apparently the result of the radar somehow interacting with the sun.
Teller1900
En-Route
That's not just the radars being put into clear-air mode for the night?
wsuffa
Touchdown! Greaser!
It's the birds.... birds everywhere.... (calling Alfred Hitchcock...)
I think maybe you're right about that one - I've checked a few archived radar images ( http://www.rap.ucar.edu/weather/radar/ ) from different sites and they seem to swith to clear air mode at the same time for a few frames.
When I've been in NWS offices I've found that the individual offices change the mode depending on what they are interested in. Looks like the data source at NWS headquarters got curfuddled - some sort of odd computer glitch from the looks of it.
Gareth.
gismo
Touchdown! Greaser!
That's my guess, but I thought the national mosaic generator was supposed to suppress the clutter.
BTW I'm pretty sure this is NOT anomalous propagation. The chances for a nice symmetrical circular refraction around one site are extremely low, to get this many in that condition is less likely than the sun exploding this year.
Joe B
Pre-takeoff checklist
Measles.
azure
Final Approach
I'm glad someone else noticed this! I hadn't looked at the mosaic, but the dtx and apx short range images have been like that since after Ike blew through here on Sunday. I've wondered what was going on...
I noticed the ground clutter was there last night on the Nexrad radar image from weatherunderground on the Tribune's page, and I was soooooo cocky that now I knew why!
gismo
Touchdown! Greaser!
Lance,
You need to look at the radar more often my friend...look what you've been missing!
I've probably looked at nearly as much radar as you have Scott, having actually designed weather radar displays back in the WSR57 days <g>. I even knew that antenna side lobes are responsible for the close in ground clutter and what the appearance of AP looks like and what generally causes it (that stuff is right up my EE alley).
But I'm definitely not current on what methods are employed to create a national mosaic these days from the national network of WSR-88s which is where my question came from. And I'm not sure your answer to my specific question, is complete (not sure it isn't either). I thought that in addition to NEXRADs site based ground clutter filtering there was more done in the process of combining several site's data that normally removed virtually all of the "ground clutter" (but not necessarily the distant AP). And it does seem somewhat improbable that the atmospheric conditions needed to produce AP in such a symmetrical and consistent pattern on a large number of radar sites would exist over more than half the country at the same time. Can you explain further?
My money is on a computer/data problem. If you look at the radar imagery on the RAP site it tells you if the display is in precip or clear air. At time of typing the archive is still available - you'll see only about a third of them are in clear air mode. If I remember correctly the night of the 16th Sept saw and extratropical Ike moving into Ontario with a cold front trailing back towards Texas (someone correct me if I'm wrong!), basically splitting the are of interest. There isn't going to be similar temperature profiles across the region, so large scale AP is not probably.
I work with these sorts of datasets on a daily basis (Grad student/slave in Atmos. Science) and it's not unusual to see a glitch like this in a real time feed.
Gareth.
I work with these sorts of datasets on a daily basis (Grad student/slave in Atmos. Science) and it's not unusual to see a glitch like this in a real time feed.
Gareth.
gismo
Touchdown! Greaser!
So I guess you are suggesting that this actually was the result of atmospheric conditions that covered a large portion of the continental US, right?
ScottM
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iBazinga!
Are the US WX Radars in the 5GHz frequency band?
One of the committees I sit on has been looking at 5.8GHz interference from 802.11a hot spots interfering with European WX radars. Not really my area of concern so I am usually stepping into the hallway to catch up on phone calls when that agenda topic shows up. But the Europeans are really worked up about and are trying to get the 802.11 guy to change the DFS detection algorithm to help prevent the interference.
Oh and this problem that is being talked about here is NOT the 802.11 interference. I have seen the resulting pattern and this looks nothing like it and tends to only affect one radar site.