Near-Real-Time Map of the F2-Layer Height Maximum

The following image is a recent global map indicating the altitude above the surface of the Earth where the ionospheric electron density reaches a maximum. It is known as the height maximum of the F2 layer (or hmF2) and is given in kilometers above the surface of the Earth. It is also a map showing the current location of the auroral ovals, the sunrise/sunset terminator and the regions of the world where the sun is 12 degrees below the horizon (which estimates the gray-line corridor where HF propagation is usually enhanced). This is one of a plethora of constructable maps that is produced by PROPLAB-PRO Version 2.0, a very powerful radio propagation software package for IBM or compatible computers, ideal for amateur or professional radio communicators. Instructions on how to use this map follow below.
(This map is updated every 5 minutes.)
Near-Real-Time Global hmF2 Map

Click on PROPLAB-PRO Version 2.0 for additional map samples. 

Using this Map

This is a very useful map for radio communicators. In the ionosphere, the density of the electrons dominate in determining whether a signal will be refracted sufficiently to be returned to the Earth. The region of the ionosphere where the electron density is greatest occurs in the F2 region of the ionosphere and is known as the height maximum of the F2 layer (or hmF2).

Just as a rock can be thrown farther in distance if the rock attains a greater altitude when thrown, a radio signal can propagate to greater distances if the level where the signal is reflected occurs at a higher altitude. This hmF2 map shows you the maximum altitude that any and all radio signals can achieve if they are to be reflected back to the Earth. If any signal (regardless of the frequency) passes the hmF2 altitude level, it will never return to the Earth but will penetrate the ionosphere and travel forever into space.

So this map can be used as a guide to help determine the regions of the ionosphere that will permit propagation to the greatest distances. Signals that pass through the equatorial region (where the hmF2 is high) may easily travel much farther than signals that are broadcast elsewhere, specifically because the maximum altitude where signals can be returned to the Earth is higher than elsewhere.

These maps are also very useful to help determine where the ionosphere is tilted. Ionospheric tilts exist wherever the gradient (spacing between the contours on the maps) is greatest (where the contours are closer together). Signals that pass through these tilted regions will experience non-great-circle propagation and may end up being received at locations great distances away from your intended audience. Only sophisticated ray-tracing methods can model ionospheric tilts and show you where your signal is going (PROPLAB-PRO contains such a sophisticated 3-dimensional ray-tracing engine to model these situtations accurately).

Signals that travel PARALLEL to the hmF2 contours will experience non-great-circle propagation that will intensify as the gradient increases. Signals that travel PERPENDICULAR to the hmF2 contours will not suffer much non-great-circle propagation, but may initiate very-long-distance chordal hops or inter-layer ducting (depending on the gradient, the frequency of the signal, angle of incidence of the signal, etc). Again, only ray-tracing software such as PROPLAB-PRO can accurately determine how the signals will behave in these situations.

To ensure the greatest probability of great-circle propagation, paths should be sought where the hmF2 contour gradients are farthest apart and do not curve or turn very much. 

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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