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Current Grayline Map of MUFs

The map above can be used by Topband operators to determine the current location of the grayline (sunrise/sunset terminator), and other useful information regarding the state of the Earth's ionosphere and auroral zones. The sunrise/sunset terminator is the thick solid gray line that is located nearest the Sun symbol (the symbol showing where the Sun is positioned directly overhead). The other thick gray line represents regions where the Sun has set on the ionosphere.

The green lines show the locations of the auroral ovals. Topband radio communicators should interpret these green lines as follows: The regions between the green lines show areas where auroral activity is most likely to be observed. They do NOT necessarily represent the location or current latitudinal thickness of the auroral ovals! But the auroral oval should be located somewhere between the green lines. For the precise location of the auroral oval, consult the previous ultraviolet aurora maps shown above.

For convenience only, the great-circle path from the eastern U.S. to Japan is shown on the plot, with the distance between these two points displayed at the mid-point of the path, in kilometers.

The cyan-colored contours represent the estimated maximum usable frequencies for paths of 3,000 kilometers. Consult the Realtime MUF Map section for more details regarding the use of these contours.