As with any star, the Sun’s activity is permanent, with regular expulsions of huge bursts of material called solar flares.

The Sun has what is known as a “solar corona“, which is made up of plasma, a completely ionised gas whose temperature is higher than its surface temperature. During solar flares, jets of plasma, magnetic waves and charged particles are expelled into interstellar space at speeds of up to 2 000 kilometres per second.

Solar flares are all different in power and last from minutes to hours. The impact on our planet depends on their intensity. For this reason, space weather services monitor and assess them.

Solar flares are rated according to their intensity (watts/m²) on a scale similar to the Richter scale in seismology.

They are classified into six categories, A, B, C, M and finally X and X10 for the most powerful (the solar flare of 1859, known as the Carrington event). Each category corresponds to an intensity 10 times greater than the previous class. To this alphabetical value is added an identity coefficient ranging from 1 to 9.

Powerful solar flares of the M and X classes can cause coronal mass ejections (CMEs). CMEs have their own magnetic fields. CMEs can then cause magnetic field disturbances. When they head towards Earth, they can have effects on our planetary environment.

Coronal mass ejections (CMEs), also known as “solar storms”. CMEs are bubbles of plasma often caused by a strong solar flare.

These giant bubbles change the atomic characteristics of the solar wind. The solar wind travels through interstellar space in all directions including the Earth.

In general, the vast majority of the particles emitted by the solar wind are blocked by the Earth’s magnetic field and therefore have no effect. This phenomenon is visible on Earth in the areas near the poles and is known as the ‘polar aurora’.

However, since the beginning of the year, the Sun has been experiencing coronal mass ejections (CMEs) on an almost daily basis, according to the National Oceanic and Atmospheric Admistration. And the frequency will continue to increase. Why is this happening?

Like the Earth, the Sun is subject to a rhythm of seasons that follow one another almost constantly. We speak of a Solar Cycle, the average duration of which is 11.2 years (varying between 9 and 25 years). 

One of the criteria for determining the progress of the solar cycle is the number of spots visible on the surface of the Sun. There are few in the Solar Minimum and many in the Solar Maximum.

Sunspots are the result of intense magnetic activity. The activity is so strong that it slows down the convection ( flow ) of matter and reduces the heat inflow to the surface of the Sun. Thus some areas become less hot than others. This is the reason why we can observe a difference in contrast on the surface of our star. When there are many sunspots, there are many flares and solar storms.

Thus, during solar maximum, solar storms are at their peak. There is a high probability of M and X category solar storms.

Currently, we are close to Solar Maximum, which is expected to be reached between 2023 and 2025. Solar storms and ejections will become very active. Only a small part of the solar storms are directed towards Earth. Nonetheless, the impacts on our environment can still be numerous.

Below is a graph highlighting the variations in solar activity over the eleven-year solar activity cycle. The estimated and anticipated values are shown in red, and the actual values measured monthly are shown in black.

 https://www.swpc.noaa.gov/products/solar-cycle-progression

De manière plus générale, une forte tempête solaire peut provoquer :

As mentioned above, the solar wind, ejections of ionised matter, etc. cause magnetic reconnections when they reach the Earth’s magnetosphere. This interaction is at the origin of magnetic storms.

These magnetic storms occur in the ionosphere, the atmospheric layer in which satellites operate and from which telecommunication and geolocation signals are transmitted.

Solar activity therefore causes fluctuations in the ionosphere, which leads to numerous malfunctions in electronic devices, including GNSS equipment. GNSS equipment receives signals through this disturbed atmospheric layer.

In addition to the impact of magnetism on the devices themselves, signal delay due to the ionosphere is one of the main sources of error in GNSS. Sudden disturbances of this atmospheric layer make it a subject of major importance.

Practical consequences in the field

During a CME there will be a significant loss of accuracy at the beginning and end of the magnetic storm event. At the peak of the storm, positioning solutions will probably be lost. All receivers remain impacted by ionospheric disturbances. Dual-frequency receivers retain much better accuracy than single-frequency ones.

In practice, ionospheric fluctuations prevent a GNSS receiver from fixing ambiguities. Even if the receiver uses an accuracy enhancement service, it remains in RTK Float mode and can only achieve decimetre accuracy.

Today, many devices are single frequency in mass market products. They are dual-frequency for entry-level and mid-range professional measurement devices.
As mentioned, ionospheric disturbances will continue to increase over several years with a solar maximum in 2024-2025, so it is important to anticipate this factor in the field and provide a solution.