Scintillation

Scintillation in the ionosphere occurs when small-scale structures (irregularities) modify radio waves as they pass through it. In particular, signals from global navigation satellite systems (GNSS) such as GPS can be severely degraded by strong scintillation, causing receivers to lose the signal and prevent position determination. Even moderate scintillation can impact the accuracy of the position calculations. The S4 index quantifies the amplitude variations; S4 above 0.3 indicates scintillation is present.

effects on GNSS

When little or no scintillation is present (S4<0.3), 8-10 GPS satellites can be available, such as around 1800-2000 UT in this example (left panel). GPS location solutions form a tight locus (center panel). Once scintillation begins, around 2100 UT, multiple satellites are affected (bottom left) and the GPS location solutions can be off by 10s of meters (right panel).