The great aurorae of 29 and 30 October 2003

Hanna, E. (2004) The great aurorae of 29 and 30 October 2003. Weather, 59 (6). pp. 143-144. ISSN 0043-1656

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Item Type:Article
Item Status:Live Archive

Abstract

Three massive solar storms erupted during
the second half of October 2003. This was
somewhat surprising because solar activity
was well on a downturn from its previous
peak in May 2000, as part of its 11-year cycle.
There were three simultaneous naked-eye
sunspots – usually individually quite rare
events – and the active (magnetically dis-
turbed) region linked in with one of these
covered an area of 2600 millionths of the
solar hemisphere. These remained visible on
the solar disc for about two weeks (due to
the Sun’s relatively slow rotation). Regions of
opposed and twisted magnetic field were
forced together above the active regions to
form solar flares (rapid releases of magnetic
energy, electromagnetic radiation and ener-
getic particles from active regions in the
solar corona – the outer atmosphere of the
Sun). There were several dozen medium to
strong flares in late October. On 28 October
at 1110
GMT an X17.2 flare (the third largest
in the last 25 years) was associated with a
‘halo’ coronal mass ejection (a vast magnet-
ic bubble of plasma) aimed directly at the
Earth. This hurtled along with a velocity of
about 1000 km s
–1
, creating a bow shock in
the solar wind (a background stream of
charged particles from the Sun, travelling at
typically 400 km s
–1
), and reaching our plan-
et about 20 hours later. The result was huge
numbers of energetic particles cascading
down the Earth’s magnetic field lines and
generating intense geomagnetic storm con-
ditions of strength normally seen only once
per sunspot cycle.

Keywords:aurorae
Subjects:F Physical Sciences > F890 Geographical and Environmental Sciences not elsewhere classified
Divisions:College of Science > School of Geography
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ID Code:26176
Deposited On:03 Feb 2017 19:27

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