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#958448 - 08/02/2011 19:34 Confusing radar images, seeking explanation
Jax Offline
Weather Freak

Registered: 16/12/2009
Posts: 659
Loc: WA
Hi, I wasn't sure where else to put this and hope starting a new thread here for it is okay. I'm hoping someone with some technical knowledge about radars might be able to help explain a couple of things.

If you stop the radar loop of Yasi crossing at 15:50 UTC and then take it forward one frame to 16:00 (link to loop here) you'll notice an odd circle appears for one frame and is then gone again. Has anyone seen that happen before?

Other interesting places to stop for a frame by frame look are:
06:20 (straight blue line)
11:50 (large part of image disappears, but not completely?)
14:50 (same as 11:50 but different place)


I'm also curious as to why this radar loop, which coincides with Cyclone Yasi crossing, is presenting this way?

Finally, what do you make of this image I took from the tv?
[img:left][/img]


Thanks in advance.

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#958449 - 08/02/2011 19:39 Re: Confusing radar images, seeking explanation [Re: Jax]
!SCHUMMY! Offline
Weatherzone Addict

Registered: 22/04/2008
Posts: 2873
Loc: Jimboomba, SEQ
i quote this from the BoM....

"If you notice any circular patterns or straight lines originating from the centre of the radar location, this is due to occasional interference to the radar data. The Bureau is currently investigating ways to reduce these interferences."

hope this helps you.
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#958555 - 08/02/2011 22:32 Re: Confusing radar images, seeking explanation [Re: !SCHUMMY!]
Jax Offline
Weather Freak

Registered: 16/12/2009
Posts: 659
Loc: WA
Thanks Schummy That message was apparently put there on the BoM site last year after they got queries about the following radar images - around the time of the massive storm over Melbourne and Cyclone Olga.

16/1/2010 -


22/1/2010 - Melbourne


22/1/2010 - Broome


27/1/2010 - Melbourne again?




28/1/2010 Broome



Here's another one from March 15 2010 - when Ului was approaching.

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#959388 - 11/02/2011 09:36 Re: Confusing radar images, seeking explanation [Re: Jax]
Loopy Radar Offline
Weather Freak

Registered: 05/10/2010
Posts: 836
Loc: Nimbin storm hole NSW
I am yet to hear an explanation of what the interference is caused by.
And Jan.2010 seems to be the only time this has happened.
_________________________
One thing is certain with conspiracy theories and global warming. There are just as many idiots on both sides.

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#959417 - 11/02/2011 11:33 Re: Confusing radar images, seeking explanation [Re: Loopy Radar]
Dave-Wx Offline
Weatherzone Addict

Registered: 27/08/2001
Posts: 4945
Loc: Heritage Park, Brisbane, QLD
I have seen these random, silly outputs/interference/radar errors on the images every month since I started looking at the radar a good decade ago.

Notice that they all emanate from a central point, and that point is always the location of the radar itself? Yes, that means that it is something going on with the radar, whether briefly, before going back to normal again, or goes for a longer term in which case the Bureau needs to send some techs out to fix the radar.

If you want to believe that it is HAARP or some other thing then good for you, but I feel that it's worth posting about this myth on this occasion, as this forum is getting a lot of attention lately and its certainly not worth giving anybody ideas (though I doubt the media would be interested in it). People post threads about this very thing on a semi regular basis on here...no doubt not helped by that guy who has put up a website, wondering what on earth these funny looking radar images are.

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#959609 - 11/02/2011 18:13 Re: Confusing radar images, seeking explanation [Re: Dave-Wx]
Jax Offline
Weather Freak

Registered: 16/12/2009
Posts: 659
Loc: WA
LoopyRadar.
The images are not all from Jan 2010. The image I posted first is actually Feb this year - that is Cyclone Yasi you can see to the right of the screen. The eastern side of it I suppose is missing because Willis Is. had dropped out. Why the western side of it is missing I don't know.
The last image in that post is March 2010.

Dave-Wx.
Thanks for your input. I was actually hoping for a technical explanation as to why these radar images might occur. Do you recall if you've noticed these outside of the cyclone season?


Is there anyone here who can explain how these "random, silly outputs/interference/radar errors" might also be influencing the clouds such as the ones visible in this NASA satellite picture?



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#959626 - 11/02/2011 19:10 Re: Confusing radar images, seeking explanation [Re: Jax]
Pucci. Offline
Weather Freak

Registered: 01/02/2011
Posts: 77
Loc: Brisbane.
Maybe they're a new form of crop circles!

(Joking!)
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Rain! Whose soft architectural hands have power to cut stones, and chisel to shapes of grandeur the very mountains. (Henry Ward Beecher)


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#959652 - 11/02/2011 20:10 Re: Confusing radar images, seeking explanation [Re: Pucci.]
ROM Offline
Meteorological Motor Mouth

Registered: 29/01/2007
Posts: 6627
The radar echos that return a number of what are obviously false echos are due to Radar Clutter.

A very good an comprehensive tutorial on radar can be found at Radar Tutorial
There are also a number of papers on "Radar Clutter" and "Angel Echoes" using google search.

To quote from Radar Tutorial;
Quote:
Angel Echo
Dry roll convection in the atmospheric boundary layer in clear-air condition is named as dot angel echo, or Bragg scattering.
Sharp inhomogenities in the refractive index of the athmosphere, such as occur, for example, at air mass boundaries, can result in the backscatter of radar power. This can therefore be defined as a phenomen.

A quote from an abstract in the Quarterly Journal of the Meteorological Society goes a long way to describing the possible reasons for those way out radar echoes and the explanation makes good sense as radar being another form of electromagnetic radiation as is" light" has all of the features that are associated with" light "propagation.
Quote:
Abstract
An exceptional radar echo of long duration which was observed from the zenith of an apparently clear sky is described, and it is shown that the height of origin of the echo was close to that of an anticylonic ‘inversion’ which was present at the time. It is deduced that the echo cannot have been due to a layer of water or dust haze at the inversion, but that it must have been caused by an abrupt discontinuity in the lapse rates of temperature, humidity, or both. If changes in humidity alone are taken into account, then in order to explain the observed intensity of the echo, it is necessary to suppose that the dew point changed by 15°F through a layer not more than 300 ft deep. It is suggested that more use might be made of radar for investigating such tropospheric discontinuities.


That explanation ties in with the presence or approach of cyclones, severe storms and other weather phenomena which seems to be one of the more favoured periods when these echos are received.
And of course in clear skies often at night when the presence of a very sharply marked and very strong inversion and therefore a probability of a very marked difference in refraction layers in the in the lower levels of the atmosphere as described in the quote..

In short, very marked changes in the characteristics of the atmosphere within very narrow bands of height will likely give some Clutter and Angel Echoes in weather radar, apparently extending out to very long ranges.



Edited by ROM (11/02/2011 20:11)

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#959737 - 12/02/2011 01:15 Re: Confusing radar images, seeking explanation [Re: ROM]
Jax Offline
Weather Freak

Registered: 16/12/2009
Posts: 659
Loc: WA
Hey thanks for providing all that info ROM.

This was a bit of an eye-opener.

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#965297 - 23/02/2011 12:47 Re: Confusing radar images, seeking explanation [Re: Jax]
Dustydevil Offline
Weather Freak

Registered: 12/04/2010
Posts: 186
Loc: Darwin
Really interesting sat pic of the clouds. Don't know what caused that but the causes of interference to radar images would almost certainly not be the same reasons for any unusual formations in clouds.

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#965317 - 23/02/2011 13:48 Re: Confusing radar images, seeking explanation [Re: Dustydevil]
Jax Offline
Weather Freak

Registered: 16/12/2009
Posts: 659
Loc: WA
When you compare the sat pic to this one there are close similarities. As to what caused either of them I'm still in the dark.

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#965323 - 23/02/2011 14:02 Re: Confusing radar images, seeking explanation [Re: Jax]
Scud Offline
Weatherzone Addict

Registered: 27/08/2001
Posts: 1205
Loc: Mcleans Ridges
Originally Posted By: Jax
When you compare the sat pic to this one there are close similarities. As to what caused either of them I'm still in the dark.


There aren't any close similarities with your example as the sat pic you have just posted has a radar overlay on it. The circular patterns aren't clouds, it's radar interference. Look towards Adelaide and you can see further radar returns from showers in the region.

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#965327 - 23/02/2011 14:23 Re: Confusing radar images, seeking explanation [Re: Scud]
dlcat1 Offline
Weather Freak

Registered: 31/01/2011
Posts: 765
Loc: Melbourne (NE burbs)
I've noticed that Yarrawonga, which since the Doppler radar was installed several years? ago has had great clarity and resolution, has been fairly 'furry' for several months now. I first noticed this after the area received significant rainfall and flooding late last year.

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#965364 - 23/02/2011 16:25 Re: Confusing radar images, seeking explanation [Re: dlcat1]
Jax Offline
Weather Freak

Registered: 16/12/2009
Posts: 659
Loc: WA
I get that Scud - I'm just saying that the cloud formations in the sat pic I posted earlier do resemble the same pattern in the radar overlay; I'm not suggesting that one is a direct cause of the other. The cloud formations look like they've been affected by a gravity wave to me.

What's interesting is how this "noise-modulated jamming" radar picture from here at the radar tutorial website also resembles some of the other odd radar images I posted earlier.
.

I'm not sure what to make of what you're noticing dlcat1. If it's stayed constantly "furry" my guess is there's a problem with the settings. These other oddities only seem to happen occasionally rather than constantly.

I don't know, I was really just interested to see if other people had noticed anything like them. It was a surprise to see them plastered all over the tv during Yasi so I thought I'd ask, and then found it odd that the website I came across with similar shots had also picked them up around the time of cyclonic weather events.

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#965781 - 24/02/2011 17:10 Re: Confusing radar images, seeking explanation [Re: Jax]
dlcat1 Offline
Weather Freak

Registered: 31/01/2011
Posts: 765
Loc: Melbourne (NE burbs)
I'm seeing it more at night or in the evening. My guess is that the radar is being bounced off a discontinuity (don't know the weather term) in the atmosphere and is then getting a strong return signal off saturated soil and wet vegetation. So rather than going radar-cloud or water droplets-radar, the beam is going radar-atmosperic mirror-ground-mirror-radar.

I've always seen the odd anomaly like the radiating moonbeams or dumbells or halos, but I've noticed them increase in frequency this year and last and not just in relation to cyclones. I'd love someone with expertise in this area to comment but I do suspect it is directly related to 'wet' air.

I did all my remotes sensing and wave physics yonks ago, so I'm sure someone here will know better, but I suspect a lot of what we are seeing is due to the software at the back end struggling to filter out noise, or getting confused by out of phase return signals, or multi path signals. Here's my theory. All radar signals are affected by back scatter, where the signal does not bounce back cleanly but bounces off the target at an angle, and multi-pathing, where the signal bounces off the not just the primary target but other things, like the atmospheric mirrors caused by distinct changes in temperature and pressure. This results in the original clean output pulse returning as a temporally chopped up and partially out of phase signal. Normally, you can filter out the spurious returns by looking for the strongest signal and chopping out what turns up at different times and different phases. I suspect, as air gets saturated, or precipitation gets heavier, the signal is attenuated to such an extent that this method of filtering doesn't work, as the backscatter and multi path signals are nearly as strong as the primary return, and hence the poor computer produces elegantly mathematical but ultimately useless images out of the noise.

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#965783 - 24/02/2011 17:19 Re: Confusing radar images, seeking explanation [Re: dlcat1]
dlcat1 Offline
Weather Freak

Registered: 31/01/2011
Posts: 765
Loc: Melbourne (NE burbs)
As for the clouds in that image, you can achieve much the same sort of pattern by chucking two pebbles in a still pool, or tapping your feet gently in a few millimetres of water on the bottom of the shower. Again, I'm firing off into the unknown, but I think what you are seeing is a pressure wave, with clouds forming at the low pressure part of the wave, rather like the crests of the waves in the pool. Why there seems to be two sources of waves I don't know, and would love to know. One way of achieving two sources of waves in the lab is to pass a single wave through a screen with two slits in it, although I'd have no idea what an atmospheric slit might be made of. Perhaps two areas of low pressure in a ridge of high pressure???

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#965937 - 25/02/2011 08:32 Re: Confusing radar images, seeking explanation [Re: dlcat1]
Dustydevil Offline
Weather Freak

Registered: 12/04/2010
Posts: 186
Loc: Darwin
dlcat1,

sounds like an interesting theory (two areas of low pressure in a ridge of high pressure). I'd really like to know what could cause that cloud formation, if anyone finds out or knows, please post the info. I can't think of anything that might create such a disturbance. The puzzle is going to drive me nuts!!!

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#965942 - 25/02/2011 08:55 Re: Confusing radar images, seeking explanation [Re: Dustydevil]
dlcat1 Offline
Weather Freak

Registered: 31/01/2011
Posts: 765
Loc: Melbourne (NE burbs)
Me too Dustydevil. I'm quite happy with the software/hardware issues to explain any number of weird anomalies with the radar images, but I don't have a clue what might cause those cloud patterns, only what they remind me of.

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#965970 - 25/02/2011 10:39 Re: Confusing radar images, seeking explanation [Re: dlcat1]
ROM Offline
Meteorological Motor Mouth

Registered: 29/01/2007
Posts: 6627
[ EDIT ] OOPS!, Big OOPS! I should read things a bit better.
That is supposed to be a satellite pic but is it?
Or is it a sat radar pic?
I'll leave my post below stand but if that is an actual photo then I'm all wrong.
IIf it is a sat radar pic which I suspect it may be then maybe ??


OK I will have a crack at this one as it is a very interesting puzzle to try and work through.
But I will be wrong no doubt but it might give somebody a different way of looking at this phenomena.

The cloud formations to the right and left of the photo indicate that a trough / front was passing through leaving unstable air with typical cold air speckled cloud cells behind the trough / front which is orientated down the centre of the photo.
Both the orientation of and the layout of the clouds reinforce that this radar photo was somewhere in the southern hemisphere unless the photo has been inverted or doctored.
The radar images are taken almost exactly at the time the trough / front was passing over the radar establishment hence the two images, one from air in front of the change in air mass and the other behind the change in air mass.
When such a frontal system passes through there are very marked changes in the air mass obviously but there are also huge differences in the heights at which things happen in the airmass in front of the change and behind the change.
I have ridden southern cold fronts and trough lines here in western Victoria many times over the last 50 years during my time in my sport of gliding.
Strong lift, turbulent air sometimes extreme so as to frighten the hell out of this old pilot, big temperature differences and etc can all be found anywhere from 5000 to 12000 feet up [ as high as i have gone in a frontal lift zone ] right on the frontal change line.
Move back behind the frontal zone [ into and over the speckled cloud area ] which might be anywhere from a half kilometer or less wide to perhaps 10 kilometers wide and you fly out into dead smooth air.
The inversion behind the front where one will again encounter some light turbulence may be only perhaps 3000 feet or less high which is where and at the height that the speckled cloud cells form some many kilometers behind the front.

The comments from one of my previous posts and the Radar Tutorial suggest that such images as in the photo arise when there is a very sharp marked change in air mass characteristics re temp differences ie; lapse rates, moisture loads and etc within a very narrow height band in the atmosphere of maybe only a few tens of metres deep and such discontinuities do occur in some circumstance both before and behind fronts / trough lines.

I would suggest that as the radar image seems to be taken as above, right as the front / trough passes over the radar establishment that those two overlapping images are actually radar echoes, radar clutter, echo angels from two air masses at two very different heights and at the same time, one from the air mass in front of the front / trough and the other from the much different airmass immediately behind the trough / front.
As the fronts / troughs generally slope back quite a long way with increasing height, the overlap in the different radar echoes can be explained by the difference in heights of the overlapping airmasses from which the radar echoes reflect due to the slope back of the front / trough at the different heights.

As pointed out in previous posts, it often seems that such radar clutter, echoes, call them what you will, occur in the vicinity of significant changes within the airmass in the range of the radar.
This seems to be the case here, unusual because it caught two different systems at the same time by the same radar establishment.

My suggestion so make of it what you will.


Edited by ROM (25/02/2011 10:48)

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#966006 - 25/02/2011 13:28 Re: Confusing radar images, seeking explanation [Re: ROM]
ROM Offline
Meteorological Motor Mouth

Registered: 29/01/2007
Posts: 6627
Just to reinforce my suggestion that this is a satellite radar pic and that those echoes are from two very different height levels within a frontal / trough system, the RH echo from an air mass discontinuity some thousands of feet higher than the much lower LH echoes extends back over the lower echoes due to the slope back of the upper air mass in the front /trough.
The defining item here is the quite sharp cutoff line running parallel to the front/ trough [ and speckled low level cloud ] at the LH edge of the RH, leading radar echo, right where I would from my previous gliding experience, expect to find the rear edge of the upper levels of the frontal air mass.

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