Rising to a sunspot peak.

Rising to a sunspot peak

This could be the big one. Last month's jump in the number of sunspots and the accompanying increase in radio emissions put the present solar cycle on track toward matching or surpassing the most active solar cycle on record. The present cycle officially began in September 1986, when the number of sunspots reached an 11-year minimum. The record cycle, based on 250 years of data, peaked in 1957.

"From the nature of the increase and the location of the spot groups, it looks like there is no chance that this [activity] will subside very soon," says Patrick McIntosh of the National Oceanic and Atmospheric Administration in Boulder, Colo. The December observations clearly indicate the sun's shift into its most active phase, which usually lasts about four years. "The activity will not subside much below the present level until 1992," McIntosh says. "We can safely say we are in for an interesting ride for the next four years."

Although the sunspot number is the best-known method for tracking solar cycles, measuring intensity changes in radiowave emissions is proving a more precise way to compare one solar cycle with another. McIntosh's data show an impressive fit between the present solar cycle and the record cycle of the late 1950s. Even last summer's plateau--when the rapid rise in the number of sunspots leveled off for a few months -- was predictable because similar plateaus have shown up at the same point in the radio signatures of the last three solar cycles. Physicists need to look into what may be causing such distinctive, reproducible patterns, McIntosh says.

So far, scientists have not recorded any particularly intense solar flares. "We've had some respectable flares during this episode of increased sunspot activity, but nothing that would cause anybody concern," McIntosh says. "The big fireworks may be yet to come." The radiation from intense solar disturbances could disrupt radio and telephone communications, damage electronic systems in satellites, present radiation hazards to astronauts and aircraft passengers at high altitudes, and alter satellite orbits (SN: 7/2/88, p.8).