MHAS is involved in a solar flare search program sponsored by Stanford University and The Society of Amateur Radio Astronomers (SARA) SuperSID Program. This program monitors for the effects of solar flares on the ionosphere of the earth. A number of Very Low Frequency (VLF) stations operated by various navies of the world are transmitting continuous streams of data to submarines and surface ships. These signals are in the 15-45 kHz frequency range and have wavelengths of 7 to 20 km (By way of comparison, AM radio uses wavelengths of 200-500 m and FM wavelengths are on the order of 3 m).
The main advantage of VLF for navies is that it penetrates seawater much better than shorter wavelengths. Thus submarines can receive these signals while submerged at moderate depths. When a solar flare occurs, the sun emits a huge amount of X-rays and earth’s ionosphere is strongly ionized. When this happens, the signals from the VLF stations jump in amplitude and then slowly decrease back to the ambient level. Such spikes in signal strength may last from 1-3 hours.
Receiving equipment is simple, a computer sound card that can detect frequencies as high as 48 kHz is used. In addition, a 40×40 cm square receiving loop of around 100 turns feeds a preamp whose output supplies the signal for the sound card. The preamp and wire for the loop is supplied by the SuperSID program. Software running on the computer from SuperSID logs data from multiple stations simultaneously and records signal strengths every 5 seconds. At midnight GMT the data from all the active monitor stations are uploaded to a central database and may be viewed at: http://sid.stanford.edu/database-browser/