Global morphology of ionospheric scintillations

Amplitude fluctuations produced by small irregularities in electron density in the F layer of the ionosphere can be a problem to communication and navigation systems in the very-high frequency-ultra-high frequency (VHF-UHF) range. Recent measurements are shown with emphasis on high and equatorial latitude observations. At high latitudes an irregularity region exists whose lower boundary reaches 57° invariant latitude near midnight. During magnetic storms the boundary descends to lower latitudes and the fading becomes deeper. Over the polar cap scintillations are somewhat diminished. Observing synchronous satellites through the irregularity region, deep fading is seen frequently with fade rates to one per second. Irregularities produce deep scintillations in the VHF range ±15° from the geomagnetic equator. In equatorial regions maximum occurrence of high level scintillations takes place between 2100 and 2400 during the equinoxes; a minimum occurrence is observed in the solstices. The data for various latitudes have been placed in statistical form, i.e., distribution of amplitudes for 15-min samples as well as for periods of one year and longer. To minimize the effect of this phenomenon on satellite transmissions, the systems designer can utilize the amplitude distributions, fading rates, and depths in designing his modulation.