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Space Weather Basics

Similar to terrestrial weather occurring on Earth, the Sun has its own continuous occurrence of weather. We, therefore, see activities happening on the Sun all the time. However, sometimes these activities reach a certain level of intensity, consequently causing them to interact with the rest of the Solar System. Yet, it is the phenomena created through the interaction between the Sun and other planets and moons that we call ‘space weather’. It is a condition and can be defined as a natural hazard comprising a wide range of phenomena caused by solar activities (i.e. activities happening on the Sun). 

The 11-year Solar Cycle

The Sun has an 11-year Solar Cycle that goes from solar minimum to solar maximum. During solar minimum we see the least number of activities causing space weather, whereas we see the opposite happening during solar maximum. However, this does not mean that we cannot experience space weather during solar minimum or a time between two solar cycles. Current predictions suggest that the next solar maximum will take place in 2025, hence the name ‘Solar Cycle 25’. This means that we should be able to gradual see a change in solar activity the closer we get to 2025. In fact, we already witnessed a slight change in solar activities at the end of 2023.

Image Credit: NASA/GODDARD

Types of solar activities and space weather

There are different types of solar activities that can cause space weather: Solar flares, High-Speed Solar Wind Streams (HSS), Solar Energetic Particles (SEPs) and Coronal Mass Ejections (CMEs). These can cause different types of space weather impact known as Geomagnetic Storms, Solar Radiation Storms and Radio Blackouts. In the following section we will, therefore, look closer at these different solar activities and space weather phenomena.

Solar Flares:

Solar Flares are described as huge impulsive eruptions causing rapid release of plasma (UV and X-ray radiation) into the Solar System. They originate from sunspots which are dark spots on the surface of the Sun but below the corona (i.e. the Sun’s outer atmosphere which is colder than other parts of the Sun’s surface). Their travelling time is less than 10 minutes and can last from 1 minute to several hours. The intensity level of solar flares can be classified in a scale as followed: A, B, C, M, and X-class solar flares, wherefrom A-class solar flares are the weakest and X-class solar flares are the strongest. The key impact from this type of solar activity is radio blackouts. Similar to the classification scale for solar flare intensity levels, a classification scale can also be found for the radio blackouts going from R1-R5 indicating whether it is a minor, moderate, strong, severe or extreme radio blackout.

Image Credit: ESA: Solar Flare.

High-Speed Solar Wind Streams (HSS):

The Sun is the source of a continual but highly variable outflow of plasma called the ‘Solar Wind’. The speed, pressure and magnetic field of the solar wind can change rapidly depending on solar activity. The ‘wind’ is created by the outward expansion of plasma from the Sun's corona (i.e. its outermost atmosphere) which is continually heated to a point where the Sun's gravity no longer can hold it down and eventually realeases it, creating the constant stream of ‘wind’ into the Solar System. Sometimes the speed of the wind reaches higher levels, consequently creating High-Speed Solar Wind Streams (HSS). High-Speed Solar Wind Streams are constant streams of plasma flowing out of regions on the Sun comprising of magnetic field that connects out to interplanetary space. They are formed by higher speed solar wind and - in contrast to the solar wind - originates from coronal holes. Coronal holes appear as dark regions on the surface of the Sun in extreme ultraviolet (EUV) and soft x-ray solar images. This is due to the region’s lower temperature and density level compared to the rest of the plasma on the Sun. The traveling time of High-Speed Solar Wind Streams is less than 10 minutes and can last from 5 minutes to several hours. The key impact from this solar activity is geomagnetic storms and their intensity level can be classified in a scale going from G1-G5 indicating whether it is a minor, moderate, strong, severe or extreme storm.

Video Credit: Data from Craig DeForest, SwRI: Solar Wind.

Solar Energetic Particles (SEPs):

SEPs are large-scale magnetic eruptions on the Sun causing intense inflow of radiation from the Sun carried out into space. They originate from shocks formed at the front of coronal mass ejections and solar flares. Their travelling time is less than 12-15 minutes and can last up to several days. The key impact from Solar Particle Events is solar radiation storms and can cause intense increase in radiation levels. Their intensity level can be classified in a scale going from S1-S5 indicating whether it is a minor, moderate, strong, severe or extreme storm.

Video Credit: ESA: Solar Energetic Particles (SEPs).

Coronal Mass Ejection (CME):

Lastly, we have CMEs which are large explosions of plasma and magnetic field from the Sun thrown into space. They originate from the Sun’s corona which is the outer part of the Sun’s atmosphere. Their travelling time is 1-4 days and can last from 5 minutes to several hours. The key impact from Coronal Mass Ejections are geomagnetic storms and their intensity level can be classified in a scale going from G1-G5 indicating whether it is a minor, moderate, strong, severe or extreme storm.

Image Credit: NASA: Coronal Mass Ejection (CME).

Much more can be said about the four solar activities and their impact presented above. However, something that is important to be aware of is that there is a difference between their magnitude. The physics behind for example a Solar Flare and a Coronal Mass Ejection is the same, yet their magnitude differs. Solar Flares are for example much smaller and more localized, whereas Coronal Mass Ejections happen on a much larger scale and can cause a release of highly energetic particles, consequently increasing the risk of much more damage. Furthermore, as a Coronal Mass Ejection is a much larger phenomenon, the logic often used on Earth suggesting that ‘the faster something is the greater the impact’ does not necessarily apply to space weather, as the travelling time of a Coronal Mass Ejection is more than that of a Solar Flare.

Sources

National Oceanic Atmospheric Administration (NOAA) (US): https://www.swpc.noaa.gov/phenomena

Met Office (UK): https://www.metoffice.gov.uk/weather/learn-about/space-weather/what-is-space-weather