Cloud Circles on radar.

As you know a great deal of speculation and rumour surrounds the subject of cloud circles.  These have been highlighted by radar across the USA and Canada in the last 18 months or so.
I have made many inquiries within the Meteorological Service in the UK (Dept of MOD-British Government) and here in the USA through a number of Meteorological organisations.  In the USA it has been impossible to reach an actual human being - all attempts are either ignored or referred to machines.

cloudcircle99.jpg (25503 bytes)

I have been successful with detailed and very useful discussion with scientists working for the British Government.  It seems most likely that these strange patterns are a radar artefact.  It has been confirmed by the MOD that the cloud circles are also appearing in the UK but that they have no reason to believe that they are meteorological in nature.
For information here is a reply from an expert at the UK Met. office:


Your email has been passed onto me for reply.

I have looked at the sample image and my guess would be that this and similar patterns do not have a meteorological origin. There can be several causes of geometric ring or spoke patterns:-

a) If there is an unexpected increase in the amount of electrical noise in the radar system. This noise tends to 'break through' at a particular range because the effective  gain is higher at long range to compensate for the inverse square fall off in the signal. Having said that, the smaller 'holes' in your sample image at extreme range dont fit this.

b) when the engineers are checking or calibrating the radar, they may inject artificial signals into the system but forget to turn off the data supply to the outside world. This can result in  ring patterns.

c) Interference from other radars or noise sources can produce spoke patterns. - particularly when two radars which are close together in frequency are pointing at each other.

The UK weather radar network also suffers from similar artefacts to some extent (maybe one or two incidents per month on average)

Malcolm Kitchen,
Meteorological Office

horizontal rule

Return to CPRI Homepage

Mark Fussell & Stuart Dike

Hit Counter