From the Sun to Earth: What Are Solar Flares?

If geomagnetic storms are the “echo” we feel on Earth, then solar flares are the “thunder” itself. They are among the most powerful releases of energy in the Solar System and occur in the Sun’s atmosphere. Their radiation reaches Earth in around eight minutes. Solar flares are sometimes accompanied by a coronal mass ejection - a cloud of plasma and magnetic field that travels much more slowly.

But how do scientists measure the strength of these solar events, and where can we follow them in real time? Let’s find out.

How is the strength of solar flares measured?

Solar flares are classified according to the peak flow of X-rays measured by specialised GOES satellites.

Scientists use a scale consisting of five main classes:

• Classes A and B: Low background activity.
• Class C: Small flares, usually with limited effects on Earth.
• Class M: Moderately strong flares that can cause short-term disruptions to radio communications.
• Class X: The strongest class, associated with more significant disruptions to the ionosphere and radio communications.

Each main class is ten times stronger than the one before it.

What do the numbers after the letter mean?

A number is added to the letter to indicate the strength within that particular class, e.g. M1, M5 or X2.

Class X has no fixed upper limit. On 4 November 2003, an exceptionally powerful flare was recorded and estimated at approximately X28. It exceeded the measurement range of the sensor on the GOES satellite, which means that its exact strength could not be fully determined.

Where can we follow solar flares in real time?

The most reliable information about solar flares and space weather comes from specialised ground-based and space-based monitoring systems.

Here are several useful sources:

1. SpaceWeatherLive - a good choice for enthusiasts spaceweatherlive.com

Suitable for people looking for easy-to-understand charts and up-to-date information about solar flares, geomagnetic activity and the aurora.

2. NOAA Space Weather Prediction Center - the official source swpc.noaa.gov

An official source of space weather data, alerts and forecasts.

3. Solar and Heliospheric Centre at the Space Research and Technology Institute, Bulgarian Academy of Sciences space.bas.bg

The Bulgarian portal can be used to monitor current Sun–Earth conditions. It provides information about present geomagnetic activity, indices such as Kp and Kpm, and short-term forecasts of disturbances in Earth’s magnetic field. These data do not directly show the strength of every solar flare, but they help us follow how solar activity affects the environment around Earth.

Why does a solar flare not always lead to a geomagnetic storm?

Solar flares and geomagnetic storms are related, but they are different phenomena. The two terms are often confused. Here is a simple way to distinguish between them.

We can loosely compare the radiation from a solar flare to lightning. It reaches Earth in around eight minutes - almost immediately on a cosmic timescale. This radiation can affect the ionosphere and certain radio communications, but it is not the direct cause of a geomagnetic storm.

A coronal mass ejection is a separate phenomenon that sometimes accompanies a solar flare. It is a cloud of plasma and magnetic field that travels much more slowly.

When a geomagnetic storm is associated with a solar flare, it is usually caused not by the radiation itself, but by a coronal mass ejection directed towards Earth. Depending on its speed, it may reach us in one to several days.

If the coronal mass ejection is not directed towards Earth, it may pass us by or affect Earth’s magnetic field only with its outer edge. The strength of the solar flare alone is therefore not enough to predict whether a geomagnetic storm will occur.

When you see news about a powerful X-class flare, check reliable space weather sources. What matters is not only the strength of the flare, but also whether it was accompanied by a coronal mass ejection directed towards Earth.

Do solar flares have anything in common with EMFs in the home?

Solar flares and the electromagnetic fields produced by household devices are different phenomena.

Solar activity is part of space weather and can affect the ionosphere, radio communications, satellites and electricity networks.

Mobile phones, Wi-Fi routers and electrical appliances produce local electromagnetic fields with different characteristics and sources. The two types of effects should therefore not be confused.