ERAU Prescott Observatory

Sudden Ionospheric Disturbance (SID) Monitoring

The ionosphere is a layer of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km to more than 1000 km.   It is created by the Sun, primarily due to ultraviolet and X-Ray radiation from the Sun.  This radiation contains sufficient energy to dislodge electrons from gases in the atmosphere (ionization).   The density of these free electrons can greatly affect radio propagation and therefore the ability to receive radio waves over long distances. 

The ionosphere is comprised of layers that behave differently to the the various types of radiation received from the Sun, location relative to the Sun, altitude, time of day, day of year, sunspots and geomagnetic activity.

Ionospheric Layers

Ionospheric Layers
A sudden ionospheric disturbance (SID) is an abnormally high density of free electrons in the ionosphere caused by an occasional sudden solar flare, which often interrupts or interferes with telecommunications systems.

When a solar flare occurs on the Sun a blast of ultraviolet and x-ray radiation hits the dayside of the Earth after 8 minutes. This high energy radiation produces intense increase in the “D" layer ionization. The effects of this sudden increase in the "D" layer ionization on High Frequency (HF) radio waves is that they are absorbed by the increased particles in the low altitude ionosphere causing a complete black out of HF radio communications. This is called a Short Wave Fadeout. These fadeouts last for a few minutes to a few hours and are most severe in the equatorial regions where the Sun is most directly overhead. However, the ionospheric disturbance enhances Very Low Frequency (VLF) radio propagation.

SIDs can be observed and recorded by monitoring the signal strength of a distant VLF transmitter.

In conjunction with the Stanford University Space Weather Program and the Society of A. Radio Astronomers we have obtained a Super-SID detector. The students constructed and multi-turn VLF loop antenna and completed construction of a console to house the Super SID detector. This equipment is currently active and capturing data on a 24/7 basis. The data is stored on the computer for future analysis by the students.

 SID Receiver Assembly  SID Antenna Under Construction  Completed SID Antenna
Space Physics students assembling the
Super SID monitor
Space Physics students making the SID antenna Completed SID antenna

The Super SID system uses the loop antenna to collect signals from VLF radio stations that are reflected off the ionosphere. When the ionosphere is excited by solar storms the signals are detectable. With the sun in a very active state collection and analysis of this data will be provided to Stanford Solar Center to add to their data base of solar activity.
 Coronal Mass Ejection  SID Screen  SID Activity
Coronal Mass Ejection (CME) - Responsible for Sudden Ionospheric Disturbances ERAU Super SID activity Sample of SID data. Labels added for clarity.