杏吧原创

THE shaking of the Sun by solar flares powers 鈥渟unquakes鈥� that dwarf their
terrestrial counterparts. Researchers report seeing a single flare release as
much energy in seismic waves as the US consumes in 20 years.

During solar flares, energy stored in magnetic fields in the Sun鈥檚 outer
layers is discharged in an outburst lasting a few seconds. This creates strong
electric fields, which accelerate electrons and protons. The blast shakes the
Sun, creating giant ripples in the hot opaque gas we see as the solar
surface.

Now Alexander Kosovichev of Stanford University in California and Valentina
Zharkova of the University of Glasgow have analysed data collected by the Solar
and Heliospheric Space Observatory on 9 July 1996, when a single flare appeared
with a moderate X-ray brightness. 鈥淲e knew roughly what the impact should be
from the theory of solar flares,鈥� says Kosovichev.

However, the effect was far more dramatic that they expected. The flare
raised a 3-kilometre seismic wave鈥攖en times larger than
expected鈥攚ith ripples that spread up to 120 000 kilometres from the flare
site. Kosovichev calculates it released 2 脳 10²¹ joules鈥攔oughly the
energy consumption of the US over two decades, and 40 000 times more seismic
energy than the 1906 earthquake that flattened San Francisco.

Kosovichev and Zharkova described the results this week at a meeting of the
American Geophysical Union in Boston, and in a paper in this week鈥檚
Nature (vol 393, p 317).