Ionospheric scintillation is the rapid modification of radio waves
caused by small scale structures in theionosphere.
Severe scintillation conditions can prevent a GPS receiver from locking on
to the signal and can make it impossible to calculate a position. Less
severe scintillation conditions can reduce the accuracy and the confidence
of positioning results.
Scintillation of radio waves impacts the power and phase of the radio
signal. Scintillation is caused by small-scale (tens of meters to tens of
km) structure in the ionospheric electron density along the signal path
and is the result of interference of refracted and/or diffracted
(scattered) waves. Scintillation is usually quantified by two indexes: S4
for amplitude scintillation and σφ (sigma-phi) for phase scintillation.
The indexes reflect the variability of the signal over a period of time,
usually one minute. Scintillation is more prevalent at low and high
latitudes, but mid-latitudes, such as the United States, experience
scintillation much less frequently. Scintillation is a strong function of
local time, season, geomagnetic activity, and solar cycle but it also
influenced by waves propagating from the lower atmosphere.