The Science Behind the Monitors
What is Space Weather?
Some conditions in space have the potential to seriously affect us on Earth. We call
these conditions "space weather". The causes can include radiation storms and ejections
from the Sun as well disturbances in the Earth's magnetic field caused by the Sun.
Besides triggering beautiful auroras, these solar storms can damage satellites, disrupt
power grids and electrical systems, interfer with cell phones and other communications,
and disturb animal movements. They can even threaten astronauts and high-flying
airplanes with their radiation!
What
is a Solar SID?
About
60 km (40 miles) above us lies the Earth's ionosphere, a
desolate place where continual blasts of particles and energy
from the Sun hit our atmosphere so strongly that electrons
are stripped away from their nuclei. This "ionized" region,
where electrons and nuclei run around freely, is a plasma
which we call the ionosphere.
The
free electrons in the ionosphere have a strong influence
on the propagation of radio signals. Radio frequencies
of very long wavelength (very low frequency or "VLF")
"bounce" back off the ionosphere thus, conveniently for
us, allowing radio communication "over the horizon" and
around our curved Earth.
The
ionosphere reacts strongly to the intense x-ray and ultraviolet
radiation released by the Sun during a solar flare, solar
storm, or coronal mass ejection. By monitoring the signal
strength from distant VLF transmitters and noting unusual
changes as the waves bounce off the ionosphere, we can
monitor and track these disturbances.
To
monitor a VLF signal, we need a radio receiver which can
"tune" to very low frequency stations, an antenna to pick
up these VLF signals, and a computer to keep track of
the data. Since most consumer radios cannot pick up the
very low frequence signals, we need to build our own radio
receiver and our own antenna. This combination of receiver
and antenna we call a Sudden Ionospheric Disturbance Monitor
(SID).
Where
Do We Find the VLF Radio Waves?
Again,
conveniently for us, the US Navy uses VLF (very low frequency)
waves to communicate with its submarines. They have a collection
of transmitters scattered around the country and the Earth.
Even though these are many miles away, the VLF signals bounce
off our ionosphere and can be picked up almost anywhere.
When you obtain your SID monitor, you also recieve a frequency
board that is tuned to a particular station, which need
not be the closest to you. You can request frequency boards
for other stations as well. However, to best match up your
experiences with the station, it's wise to choose one at
the same longitude, where your sunrise and sunset phenomena
will occur at roughly the same time. Here is a
VLF station list.
How
Does Solar Activity Affect the Ionosphere, and hence the
VLF Waves?
VLF Waves and Earthquakes
Other Uses of VLF Waves
