WASHINGTON — Space weather forecasters remain divided in their projections about when the next 11-year cycle of sunspot activity will peak and how intense it will be.

A 12-member panel of scientists convened by the U.S. National Oceanic and Atmospheric Administration (NOAA) to predict the upcoming solar cycle announced April 25 that they were divided on whether solar maximum would occur in October 2011 with a peak of 140 sunspots or in August 2012 with a peak of 90 sunspots.

“There is definitely a split on the panel,” said Douglas Biesecker, the NOAA Space Environment Center scientist who chaired the forecast panel.

In the past 100 years, scientists have observed as many as 200 sunspots at solar maximum and as few as 40, with a peak of 115 spots considered average.

So depending on which scientists on the panel are correct, the upcoming solar cycle will either be a little more intense than usual, or a little tamer.

Biesecker said one reason scientists are split on when the next solar cycle will peak is because the current cycle is still 11 months from ending. “We are a long way from solar minimum,” he said “A lot of the information we would like to have is not available yet.”

If solar minimum occurs in March 2008 as some scientists predict, that will mean that the current solar cycle will have lasted 12 years, about a year longer than usual.

Solar cycle predictions are of interest to anyone that has to be concerned about space weather, a growing list that not only includes spacecraft operators worried about the havoc particle storms can play on sensitive electronics, but even commercial airlines that depend on high-frequency radio communication systems to stay in contact with aircraft increasingly flying fuel-saving polar routes.

Biesecker said the panel expects to achieve consensus in the next six to 12 months on when the upcoming solar cycle will peak. But even the current forecast, released during the Space Environment Center’s annual Space Weather Week in Boulder, Colo., is still useful to space agencies and other long term planners if only because it indicates that the coming cycle will not be unusually harsh.

“We’ve removed some of the wild speculation that’s been out there,” he said, noting that some forecasters have predicted that the coming solar cycle would see sunspot peaks as high as 185. “We’ve narrowed the range. We’ve brought it down to something customers can at least begin to take a little more seriously.”

Dean Pesnell, a member of the prediction panel who also serves as project scientist for NASA’s upcoming Solar Dynamics Observatory mission, said long term forecasts are especially important to agencies like NASA that have not only spacecraft in Earth orbit but also astronauts.

Besides the threat that solar storms pose to sensitive electronics both in space and on Earth, space weather also impacts how often spacecraft have to be reboosted to maintain their altitudes and influences how long space debris remains in orbit.

Pesnell said that the Solar Dynamics Observatory, which is slated to launch mid-2008, will help improve solar cycle forecasts by reading sound waves from the sun to see flow patterns forming before they reach the surface in the form of solar flares and other disturbances.