According to scientists the Sun is gearing up for its most active phase (solar maximum) of its 11-year solar cycle this year.

Experts predict that the peak of the current maximum could happen anytime from May this year which will impact on the availability and performance of GNSS, with performance degradation likely until 2014, due to increased ionospheric scintillation and signal propagation delays.

What happens during a solar maximum?

During the solar maximum sections of the solar system intensify, making our ionosphere denser and thicker.

Higher solar activity; sunspots and solar flares increase ionizing solar radiation creating more free electrons in the ionosphere and cause sudden variations in the density of the ionosphere, causing the GPS signals to scintillate (as a twinkling star).

Impact on marine navigation

The impact of the ionosphere on GNSS performance can be significant due to the propagation effects on the GNSS signals as they pass through the ionized ionosphere at altitudes above 50km from the earth's surface.

The most significant errors experienced by GNSS are due to the effect of solar activity on the ionosphere.

The magnitude of the effect of the ionosphere varies in both time and spatial extent.

The effect is much greater during the day than during the night and will vary with latitude, season and time of day (the hours soon after sunset being most affected).

The effects of the ionosphere can introduce measurement errors of greater than 10 m (even for DGPS users) and in severe conditions, the receiver can lose lock on the signal. Users of dual and multiple frequency GNSS receivers may be less affected. Adverse conditions can persist for several hours, thereby presenting a significant issue for navigation.

Skippers should be able to maintain the vessel's estimated position through periods of GPS outage provided a decent log is kept, but the accuracy we now expect from GPS derived positions will degrade gradually the longer the outage continues.

Skippers should be aware that at the end of the outage, when a GPS position is restored, some onboard systems may require manual intervention to reinitialise.

It is also worth noting that during the last solar maximum the level of dependence on GNSS was much lower than it is now.

Marine navigation warnings

The Space Weather Prediction Center (SWPC) in the United States of America provides alerts and warnings on their website which show GNSS users where problems may occur and the potential effects on their operations.

The UK Hydrographic Office (UKHO) will issue navigation warnings on the basis of information provided to them by the SWPC or the UK Met Office.

An example of the type of warning if as follows;

NAVAREA XX XX/13
SPACE WEATHER
1. STRONG SOLAR RADIATION STORM IN PROGRESS UNTIL 081000 UTC JAN. RADIO AND SATELLITE NAVIGATION SERVICES may be affected.
2. CANCEL THIS MSG 081100 UTC JAN