by Jeff Fleischer(Sydney Morning Herald, October 20, 2003)
Don’t hold your breath about seeing a spectacular aurora in tonight’s sky Sydneysiders. The geomagnetic storm fallout is only likely to be visible in pollution-free country areas.
The storm has been unusual not only in its size – the largest since 1989 – but in its timing.
“It is an exceptionally intense storm, and has come rather late in the solar cycle, which makes it so unusual,” Dr Nick Lomb, curator of astronomy at Sydney Observatory, said today. “Under normal conditions, we’d be in downtime.”
The last major storm took place in 2000, at the peak of the solar cycle, which usually lasts about 11 years. Normally, another storm would not come until the peak of the next cycle, but flares like Tuesday night’s can happen sporadically, said Dr Richard Thompson, service manager for the Government agency IPS Radio and Space Services.
“It all comes back to the sun,” Dr Thompson said. “The sun in the last few years has been going through a quiet phase. Sometimes the sun wakes up and you see a generation of sunspot regions where those regions produce solar flares.”
The sun currently features the biggest sunspot region of this cycle, Dr Thompson said. The region has been visible for the past seven to eight days, and scientists can continue to view it for about six more days. “Then it will disappear from our view over the western side of the sun,” he said. “What happens when it comes back around is anybody’s guess. It can be a rather sporadic phenomenon.”
Sunspot activity created a large, powerful solar flare Tuesday night, which “triggered a coronal mass ejection, a whole cloud of charged particles toward the earth,” Dr Lomb said.
The planet’s atmosphere breaks up much of the debris, while the rest is drawn toward the poles where it interacts with the earth’s magnetic field. This interaction usually creates the aurora effect known as the “Northern Lights” and “Southern Lights,” but the size of the recent storm created effects further from the poles.
Dr Thompson said IPS has heard reports of aurora sightings last night from around Australia, including Perth, Hobart, Wollongong and Goulbourn.
“I would imagine that aurora were visible over much of southern Australia,” he said. “You just needed to be under a dark sky.”
Aurora effects might be visible tonight as well, depending on how long the space weather continues. But light pollution in the Sydney area will likely prevent residents from seeing them.
“From a lot of the inner cities, you’re lucky to see stars, let alone aurora,” Dr Thompson said.