They are the digital-age equivalent of crop circles -- mysterious patterns appearing on the Australian Bureau of Meteorology's national radar system without any explanation. UFOs, perhaps?

And the random images, described as red stars, rings of fire and white doughnuts, are sending online conspiracy Web sites into meltdown. The anomalies first began on January 15 when an "iced doughnut" appeared over Kalgoorlie in Western Australia.

Satellite imagery showed there was no cloud over the area at the time to explain the unusual phenomenon, but farmers' online comments claimed it was "unusually hot" all day. It was followed by a bizarre red star over Broome on January 22 and a sinister spiral burst over Melbourne described by amateur radar buffs as the Ring Of Fire Fault.

The Bureau, which did not respond to repeated requests for comment, has acknowledged the anomalies on its popular Web site. It has posted a disclaimer above the national loop feed putting the images down to "occasional interference to the radar data."

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

Based at a remote research station in Alaska, the HAARP project involves shooting extremely high frequency radar bursts into the upper reaches of the atmosphere to see what happens after particles of the ionosphere are temporarily excited.

For more theories and speculation, visit News.com.au.