What This Map Shows:
- The global contour map gives the highest frequency that will reflect from the Earth's ionization layer for a 3000 kilometer path length. Read the MUF value at the halfway point of the radio path (1500 kilometers). Higher frequencies will punch through the ionosphere and travel into space.
- Also shown are the current location of the auroral oval. Signals traveling through the auroral oval will most probably be degraded.
- The locaton of the sunrise/sunset terminator are given and the regions where the sun is less than 12 degrees below the horizon (called the gray-line corridor). In the gray-line corridor, the lowest altitude ions (that degrade the signal) are rapidly lost as the sun sets but the high altitude ions (that reflect the signal) are still plentiful. These are particularly good conditions for short-wave radio signal propagation.
Space Weather Impacts:
Click here for information on the basic types of radio wave propagation paths. Radio waves at frequencies higher than the MUF will not reflect but will punch through the ionosphere. During space weather disturbances, the ionospheric density can become depleted in some regions, lowering the MUF, causing a loss of signals to space and severely impacting short wave communications. Operators must lower their selected frequency ranges in response.