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Solar flare could cause interference

David Perlman, Chronicle Staff and News Services Tuesday, September 25, 2001

A powerful flare erupted on the surface of the sun early yesterday, and government forecasters said gusts of charged sub-nuclear particles sweeping past Earth from the explosion could disrupt radio communications and increase radiation levels by late today or tomorrow.

The event will create a magnetic storm across the Earth's northern hemisphere. It is unlikely to interfere seriously with signals between radiation-hardened military communication units, although it may cause brief episodes of noise in images transmitted by satellites, the forecasters predicted.

The burst of solar particles speeding at nearly a million miles an hour is called a coronal mass ejection. X-ray emissions from the event could cause temporary blackouts of high-frequency radio transmissions on the sunlit side of the earth, says Ronald D. Zwickl, assistant director of the National Oceanic and Atmospheric Administration's Space Environment Center in Boulder, Colo.

Navigators aboard ships and planes who rely on America's satellite network called the Global Positioning System may find the system's accuracy degraded for the next two days. Because radiation is greatly increased over the north polar region, commercial aircraft flying the polar route from continent to continent may be diverted along more southerly courses, Zwickl said.

Electric power grids may experience brief current surges during the next few days. Though utilities generally fine-tune their systems in advance to prevent damage, the surges may trigger false alarms on their protective devices, he said.

-- Martin Thompson (, September 26, 2001


Space Weather News for Sept. 25, 2001

AURORA ALERT: An interplanetary shock wave spawned by Monday's powerful solar explosion swept past our planet at approximately 2100 UT (2:00 p.m. PDT) on Tuesday, Sept. 25th. The solar wind velocity soared from 400 km/s to more than 800 km/s in a matter of minutes as the shock wave sped by.

Earth is still inside the resulting high-speed solar stream and auroras are possible tonight even at low latitudes where such displays rarely happen. Sky watchers are advised to look for Northern Lights after local sunset. Local midnight is usually the best time for aurora spotting but if a powerful geomagnetic storm develops bright auroras might be visible at any time of the night.

For details and updates please visit

[Personal note: here at my dark-sky site in mountains of southcentral Pennsylvania, latitude 40 N, I saw no aurora last night before bedtime shortly before local midnight. Clear skies but moon was partly interfering. Will check again tonight.]

-- Andre Weltman (, September 26, 2001.

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