Weather or space weather affects GNSS performance by

• A. Weather has no impact on GNSS accuracy.
• B. GNSS is unaffected by solar activity.
• C. Only rain affects GNSS signals but not space weather.
• D. Ionospheric delay and scintillation; solar activity can degrade signal causing higher errors or outages.

Answer: (D)

Space weather affects GNSS primarily through the ionosphere, the layer of charged particles that the signals pass through on their way to Earth. Solar activity drives changes in electron density in this region, and when activity is high, the ionosphere becomes both denser and more irregular. This leads to two main problems.

First is ionospheric delay. The ionosphere is dispersive, so the amount of delay depends on the signal frequency and on the total electron content along the path. A higher electron content slows the signal differently at different frequencies, introducing errors into distance measurements. Dual‑frequency receivers can estimate and compensate for much of this delay, but during disturbed conditions residual errors can remain and still degrade positioning accuracy.

Second is scintillation. In practice, rapid irregularities in the ionosphere cause fluctuations in signal amplitude and phase, which can disrupt the receiver’s tracking loops, cause cycle slips, and even momentarily lose lock on the signal. This can lead to outages or significantly worse errors.

Weather-related delays in the troposphere also exist, but the key point here is that space weather drives ionospheric delay and scintillation, which can degrade GNSS performance or cause outages when solar activity is strong.