Click on PROPLAB-PRO Version 2.0 for additional map samples.
These maps are very useful for radio communicators for several reasons. First, they can be used to help determine where the sun is rising or setting (notice on this map that the 90-degree contour line is obscured by the thicker gray-colored sunrise/sunset terminator line). They can also be used to help determine the regions of the world where solar-flare related short-wave fadeouts are strongest.
Solar flares result in the attentuation of radio
signals if the signals are passing through regions of the ionosphere that
are sunlit (indicated by contours that are less than or equal to 90 degrees).
The intensity of the attenuation is approximately proportional to the solar
zenith angle. A signal that passes through the ionosphere where the solar
zenith angle is low (corresponding to the region where the Sun is the highest
in the sky) will experience the greatest signal loss. Signals that pass
through regions where the solar zenith angle is higher will experience
less signal loss (and hence greater signal strength at the receiver). These
maps are therefore useful to help diagnose the potential impacts of solar
flares on communications.
The map shows the radio auroral zones as green bands near the northern and southern poles. The area within the green bands is known as the auroral zone. Radio signals passing through these auroral zones will experience increased signal degradation in the form of fading, multipathing and absorption.
The radio auroral zones are typically displaced equatorward from the optical auroral zones (or the regions where visible auroral activity can be seen with the eye).
The great-circle signal path from the Eastern United States to Tokyo is shown along with the distance of the path (in km) and the bearing from the U.S. to Tokyo (in degrees from north).
If this signal path crosses through the
green lines indicating the position and width of the radio auroral zones,
propagation will be less stable and degraded compared to if the signal
never crossed through the auroral zones. Using your mouse, PROPLAB-PRO
will let you plot the great-circle paths and azimuths between any two points
while this display is continually updated.
The yellow Sun symbol near the equator indicates the location where the Sun is directly overhead.
The regions of the world where the Sun is exactly rising or setting is known as the Grayline and is shown as the solid gray-colored line that is closest to the Sun symbol.
The second solid gray-colored line defines the regions of the world where the Sun is exactly 12 degrees below the horizon. This line defines the end of evening twilight. Everything inside of this second line is experiencing night-time conditions.
The area between the two lines (shaded a lighter shade than the night-time sector) is known as the grayline and has special significance to radio communicators. Signals which travel inside the grayline region often experience significant improvements in propagation because of the loss of ionization in the D-region as the Sun sets. However, because the higher F-regions of the ionosphere remain strongly ionized for longer periods of time, signals with higher frequencies are able to travel to greater distances with less attenuation when they are within the grayline.
The great-circle path from the eastern U.S. to Japan is also shown with the accompanying distance (in kilometers) and bearing (clockwise from north). Notice how this path may occassionally pass into the influential auroral zones if geomagnetic activity increases or during the night-times.
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