This phenomenon is caused by a period of increased solar activity that repeats itself every 11 years, a period during which the Sun’s surface shows an increased number of dark areas, the so-called sun spots. This activity generates a stream of particles and radiation towards the earth, creating disturbances in the ionosphere.
The start of the current solar cycle 24 was in 2008, and the maximum is expected to be 2013.
The effects of these disturbances will be most prominent in equatorial (essentially following the geomagnetic equator) and high latitude regions (auroral regions). Mid-latitude areas are less affected.
There are two main effects on GNSS systemsDelay of the signal due to less predictable thickness of the ionosphere causing errors in the range measurements to the satellites.Loss of lock on satellites due to scintillations in the ionosphere creating fading in the amplitude and phase of the satellite signal.
The delay of the signal can de determined by using dual frequency measurement. This is done in the decimeter level phase based Differential GNSS services available today. The scintillation effect typically affect parts of the sky, and is mitigated by using several GNSS systems (GPS, GLONASS etc), thereby increasing the chance of receiving enough unaffected signals for use in the position solution.
The first effects of solar cycle 24 on GNSS systems were seen in 2010. During a magnetic storm in Tromsø in Northern Norway (70 deg latitude) on 4 August 2010 a Fugro G2 receiver tracking both GPS and GLONASS satellites experienced loss of about half of the total number of 18 satellites tracked.
Scintillations in equatorial regions are now starting to appear more frequently. Plasma bubbles (regions with plasma density depletion) around magnetic equator are causing scintillations almost on a daily basis for a few hours after local sunset.
There are also incidents where energy in the L-Band from the sun interferes with GNSS signals, lowering signal tracking margins. This happened 24 Sept 2011 and lasted 10 minutes.
In summary, to prepare for the solar cycle 24, it is important to use dual frequency receiver to remove errors in the range measurements, and to use all available satellites (GPS and GLONASS) to increase the chance of retaining enough satellite signals for a stable position solution.