Northwest Research Associates, Inc.

Introduction to Ionospheric Scintillation

Example of Intensity Scintillation

Ionospheric intensity scintillation at VHF as observed at Poker Flat, Alaska, on 05 May 1976.

Ionospheric scintillation is the rapid fluctuation of the phase and intensity of a radio signal that has passed through the earth's ionosphere, typically on a satellite-to-ground propagation channel. This phenomenon is similar to the twinkling of stars in the night sky, except in this case the fluctuations are caused by small-scale variations (irregularities) in the ionospheric plasma density along the propagation path followed by the signal. Our goal in these pages is to provide the community-at-large with a short tutorial on ionospheric scintillation and its effects on various systems, and with predictions of scintillation parameters both for the upcoming day and for conditions expected at the peak of the next solar cycle (when scintillation levels also reach their peak).

The tutorial (still under construction) is designed to give the casual visitor to these pages a general description of the phenomenon, including a discussion of its climatology, effects on systems, and a reference list for those who are interested in a deeper look.

The two prediction pages, one for the upcoming day and one for solar-maximum conditions, each have predictions for three equatorial sectors (Far East, Middle East, and South America) and two high-latitude sectors (American and European). In the equatorial sectors, the parameter plotted is the standard-deviation of signal intensity normalized by the average intensity, denoted the S4 intensity-scintillation index, calculated on a VHF propagation channel from the ground to a geostationary satellite. In the high-latitude sectors, the parameter plotted is the log of the height-integrated irregularity strength, denoted CkL, calculated on line-of-sight paths from the ground to an overhead satellite. The GMT times for each region are selected to show the time of most severe scintillation in that particular sector (post-sunset in the equatorial cases, midnight sector for the high-latitude cases). The seasons selected for display in the solar-maximum predictions are those in which the most severe scintillation is expected for that particular sector.

These predictions are generated using a tool (SCINTMOD) based on the WBMOD ionospheric scintillation model, a state-of-the-art model developed over the past two decades by scientists at NWRA on contract to various US Government agencies. The WBMOD model is a scintillation climatology, and the predictions shown on these pages reflect the climatology for the various areas given the local time, day of the year, solar epoch (as specified by the sunspot number, SSN), and the state of the geomagnetic field (as specified by the Kp index). The source of the SSN and Kp values used in these predictions is the Space Environment Center (SEC) operated by the National Oceanographic and Atmospheric Administration (NOAA).

For more information on scintillation or SCINTMOD, send e-mail to: scint@nwra.com

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