Our Earth is a large magnet. The magnetic field lines extend out in space in great arches form the North to the South pole. The magnetic poles of the earth don’t quite coincide with the North and South geographic poles, in fact they tend to drift around a bit. As of 2005 the North Magnetic Pole lay near Ellesmere Island in northern Canada at 82.7° N 114.4° W.
The Earth’s magnetic field protects us from cosmic rays and the Solar Wind by deflecting particles around the Earth. This magnetic field is also important in creating many of the Natural Radio sounds that we are able to hear.
The magnetosphere is the area around the Earth where the Earth’s magnetic field is dominant. Outside the magnetosphere the interplanetary magnetic field is dominant.
Above the breathable part of the atmosphere lies the ionosphere. From about 60 or 70 miles up the air thins out and the UV radiation from the Sun strips electrons away form the atoms and forms an ionized plasma. The reflective properties of the ionosphere bend radio waves of certain frequences that would otherwise travel in straight lines out into space, and sends them back to earth, thus allowing global shortwave communications.
Above the Ionosphere is a region of the magnetosphere that contains plasma, a highly ionized state of matter. The plasmasphere contains the Van Allen radiation belts.
Whistler Mode Waves
Radio waves propagate through free space at 186,000 miles per second. In the conductive plasmasphere, another type of propagation is possible. Whistler mode wave propagate through plasma along magnetic field lines. These waves are circularly polarized as they spiral along the Earth’s magnetic field lines. Propagation is much slower than through free space.
Coronal mass ejections and sometimes the solar wind carry magnetic fields that can couple with the Earth’s field and disrupt it causing a geomagnetic storm. A severe geomagnetic storm may induce currents in long power lines that will destroy equipment and cause power outages. Compasses become useless and auroral displays may be seen in much lower latitudes than normal. Geomagnetic storms also tend to generate VLF Emissions, Chorus and other signals that are very interesting to Natural Radio listeners.
Page created by Mark Karney