Now, while all of this stuff is going on in the geomagnetic field, what's happening in space? Hard radiation, and lots of it, that's what. After all, that's basically what's causing the disturbance in the geomagnetic field.
And of course NOAA has another scale
that relates to that, called the solar storm scale, and represented
by – you guessed it – S.
There's not a direct correlation that
I've ever been able to find between the G scale and the S scale,
because the S scale is determined by the number of protons of a given
energy that passes through, say a square meter in a second. This
number is called the proton flux. (In the case of the S scale, the
energy of the protons must be greater than or equal to 10MeV, where
MeV is mega-electron-volts. An electron volt is very tiny, only
1.6x10-19 joules. So an MeV is an energy of 1.6x10-12
joules. It's not big, but when you're talking about something as
small as a proton, it's big enough.)
So at S1, our proton flux is 10 protons
per second per steradian per square centimeter. (This is not a very
big area. The bigger the number of protons passing through, the
bigger the radiation dose.) An S1 is a minor solar storm. According
to NOAA, the effects are as follows, “Biological: none.
Satellite operations: none. Other systems: minor
impacts on HF radio in the polar regions.” This happens a lot, but
not quite as often as a G1 – an S1 occurs about 50 times per solar
cycle.
An S2 is a moderate solar storm. It
requires a proton flux of 100, and occurs half as often as an S1.
Effects: “Biological: passengers and crew in high-flying
aircraft at high latitudes may be exposed to elevated
radiation risk. Satellite operations: infrequent
single-event upsets possible. [A single-event upset, or SEU, is
when the bit of a computer is accidentally reset to its opposite
condition by a proton or electron impact.] Other systems:
small effects on HF propagation through the polar regions and
navigation at polar cap locations possibly affected.”
S3 is a little stronger still; it's a
“strong” solar storm, with a proton flux of 1000. (Note that the
solar storm scale is a logarithmic scale like the Richter scale, with
each step of the scale having 10x greater proton flux than the
previous.) Only 10 of these typically occur per solar cycle, but they
aren't pleasant. “Biological: radiation hazard avoidance
recommended for astronauts on EVA; passengers and crew in
high-flying aircraft at high latitudes may be exposed to radiation
risk. Satellite operations: single-event upsets,
noise in imaging systems, and slight reduction of efficiency
in solar panel are likely. Other systems: degraded HF
radio propagation through the polar regions and navigation
position errors likely.”
Stepping up to an S4, a severe solar
storm, we have a proton flux of 10,000. They are pretty rare, with
only about 3 per solar cycle occurring. “Biological:
unavoidable radiation hazard to astronauts on EVA; passengers
and crew in high-flying aircraft at high latitudes may be exposed
to radiation risk. Satellite operations: may experience
memory device problems and noise on imaging systems;
star-tracker problems may cause orientation problems, and
solar panel efficiency can be degraded. Other systems:
blackout of HF radio communications through the polar regions
and increased navigation errors over several days are likely.”
And finally the granddaddy of solar
storms, the S5, the extreme storm. It has a proton flux of 100,000
protons per second per steradian per square centimeter. Simply put, a
flood of 100,000 protons is striking every square centimeter (less
than half an inch each way), every second. These are very rare, and
may or may not occur in any given solar cycle. But they can be
devastating. “Biological: unavoidable high radiation
hazard to astronauts on EVA (extra-vehicular activity);
passengers and crew in high-flying aircraft at high latitudes
may be exposed to radiation risk. Satellite operations:
satellites may be rendered useless, memory impacts can cause
loss of control, may cause serious noise in image data, star-trackers
may be unable to locate sources; permanent damage to solar panels
possible. Other systems: complete blackout of HF (high
frequency) communications possible through the polar regions, and
position errors make navigation operations extremely difficult.”
We're fortunate those don't occur very
often at all.
But
even the typical description of a G5 or S5 doesn't match the
strongest geomagnetic storm in history.
-Stephanie
Osborn
